FR3130888A1 - METHOD FOR DETERMINING ONE OR MORE FUEL CHARACTERISTICS OF AN AVIATION FUEL - Google Patents

Abstract

The invention relates to a method (1040) for determining one or more fuel characteristics of an aviation fuel (F) suitable for supplying a gas turbine engine (10) of an aircraft (1). The method includes: determining (1041), during use of the gas turbine engine (10), one or more contrail parameters related to the formation of contrail by the gas turbine engine ( 10), wherein determining (1041) the one or more contrail parameters includes performing (1042) a sensor measurement on a region behind the gas turbine engine in which contrail is or may to be trained; and determining (1043) one or more fuel characteristics of the fuel (F) based on the one or more contrail parameters. The invention also relates to a system for determining fuel characteristics (140), a method (1065) of operating an aircraft and an aircraft (1). Picture 23

Description

DETERMINATION OF FUEL CHARACTERISTICS

This disclosure relates to methods of determining one or more fuel characteristics of an aviation fuel for powering a gas turbine engine of an aircraft, and associated fuel characteristic determining systems. The present disclosure further relates to methods of operating an aircraft, for example according to the determined fuel characteristics, and to an aircraft having a fuel characteristic determining system and a control system. The present disclosure further relates to a method for generating a maintenance program for an aircraft, to a system for generating a maintenance program and to a method for maintaining an aircraft.

The aviation industry expects the trend to be towards the use of different fuels from the traditional kerosene-based jet fuels typically used today. These fuels may have different fuel characteristics, for example having either or both of lower aromatics content and lower sulfur content, compared to petroleum-based hydrocarbon fuels.

In order to take advantage of the different properties of these fuels, methods for determining fuel characteristics, either on board an aircraft during its operation, or during its refueling are necessary. Based on this determination, the aircraft, and more specifically a gas turbine engine used to propel it, can be operated or maintained accordingly. This can provide performance benefits and/or environmental benefits through better utilization of the characteristics of the fuel on board the aircraft.

According to a first aspect, a method for determining one or more fuel characteristics of an aviation fuel suitable for supplying a gas turbine engine of an aircraft is provided, the method comprising:

exposing the surface of a piezoelectric crystal to fuel;

the measurement of a vibration parameter of the piezoelectric crystal; And

determining one or more fuel characteristics of the fuel based on the vibration parameter.

The inventors have determined that the vibrational properties of a piezoelectric crystal vary depending on the characteristics of the fuel to which it has been exposed. By measuring a vibrational parameter of the crystal, the characteristics of the fuel to which it has been exposed can therefore be determined. For example, deposits can form on the crystal surface from exposure to fuel. By measuring a vibrational parameter of the crystal (eg, a resonant frequency), the amount of surface deposit on the crystal surface can be determined, and the characteristics of the fuel that caused these deposits can be determined.

The vibration parameter may be indicative of a surface deposit formed on the surface of the piezoelectric crystal, which has been exposed to fuel.

Measuring the vibration parameter may include measuring a change in a vibrational mode of the piezoelectric crystal.

The one or more determined fuel characteristics may include a hydrocarbon distribution of the fuel.

The one or more fuel characteristics determined may include any one or more of: (i) the percentage of sustainable aviation fuel in the fuel; and/or (ii) the aromatic hydrocarbon content of the fuel.

The one or more fuel characteristics may include any one or more of: (i) an oxygen content of the fuel; (ii) thermal stability of the fuel; and/or (iii) a fuel coking level.

Fuel may be exposed on the surface of the piezoelectric crystal during operation of the gas turbine engine.

The method may include exposing fuel in a fuel system of the gas turbine engine to the surface of the piezoelectric crystal. Preferably, the fuel may be exposed to the piezoelectric crystal after the fuel has been heated by a heat exchanger of the gas turbine engine.

Fuel within, sampled from, or dispensed to an aircraft fuel tank can be exposed on the surface of the piezoelectric crystal.

The measurement of the vibration parameter may include exposing the piezoelectric crystal to fuel outside the aircraft during a fueling process in which fuel tank(s) of the aircraft is/are being charged (s) of fuel.

According to a second aspect, the present application provides a fuel characteristic determination system for determining a fuel characteristic of an aviation fuel suitable for supplying a gas turbine engine of an aircraft, the system comprising:

a sensor comprising a piezoelectric crystal, a surface of the piezoelectric crystal being adapted to be exposed to fuel, the sensor being arranged to measure a vibration parameter of the piezoelectric crystal; And

a fuel characteristics determining module arranged to determine one or more fuel characteristics of the fuel based on the vibration parameter.

The vibration parameter may be indicative of a surface deposit formed on the surface of the piezoelectric crystal (which has been exposed to fuel).

The sensor can be arranged to measure a change in a vibrational mode of the piezoelectric crystal in order to measure the vibrational parameter.

The determined one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; (iv) an oxygen content of the fuel; (v) fuel thermal stability; and/or (vi) a fuel coking level.

Fuel may be exposed on the surface of the piezoelectric crystal during operation of the gas turbine engine.

The piezoelectric crystal may be adapted to be exposed to fuel in a fuel system of the gas turbine engine. Preferably, the piezoelectric crystal may be adapted to be located at a position downstream (in the direction of fuel flow) of a heat exchanger of the gas turbine engine.

The piezoelectric crystal can be adapted to be exposed to fuel that is within, sampled from, or dispensed to an aircraft fuel tank. The piezoelectric crystal can be adapted to be exposed to fuel outside of the aircraft, with the fuel being loaded onto the aircraft during a fueling process. The piezoelectric crystal may be provided in a fuel charging line or a fuel storage container of a refueling system.

According to a third aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining one or more fuel characteristics using the method of the first aspect; And

the operation of the aircraft according to the fuel characteristic(s).

Aircraft operation under one or more fuel characteristics may include:

a) changing an aircraft control parameter, preferably a gas turbine engine control parameter, in response to the one or more fuel characteristics; and or

b) the provision of fuel with different fuel characteristics (from those of the fuel for which the fuel characteristics have been determined) when refueling the aircraft.

According to a fourth aspect, the present application provides an aircraft comprising the system for determining fuel characteristics of the second aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the one or more characteristics of fuel determined by the fuel characteristic determination system.

According to a fifth aspect, the present application provides a method for determining one or more fuel characteristics of an aviation fuel for supplying a gas turbine engine of an aircraft, the method comprising:

exposing the surface of a sensor component formed from a nitrile fuel sealant;

the measurement of a swelling parameter of the sealing material; And

determining one or more fuel characteristics of the fuel based on the swelling parameter.

The inventors have determined that a swelling parameter of a sealant, such as a nitrile gasket, can be used to determine the characteristics of a fuel to which the sealant has been exposed. The inventors have determined that the degree to which the nitrile material swells upon exposure to fuel depends on the characteristics of the fuel, and can be used as a sensor to determine these characteristics.

The measurement of the swelling parameter may include measuring the expansion or contraction of the sensor component as a result of exposure to fuel.

Measuring the expansion or contraction of the sensor component may include measuring a change in the physical size of the sensor component, or measuring a force applied to a gauge by the sensor component.

The one or more determined fuel characteristics may include a hydrocarbon distribution of the fuel.

The one or more fuel characteristics determined may include any one or more of: (i) a percentage of sustainable aviation fuel in the fuel; (ii) an aromatic hydrocarbon content of the fuel; and/or (iii) a cycloparaffin content of the fuel.

The method may further include generating an alert signal if the swelling parameter is outside an alert threshold. The alert signal can be generated if the inflation parameter is outside of a safe operating range.

Fuel may be exposed on the surface of the sensor component during gas turbine engine operation.

Fuel may be exposed on the surface of the sensor component in a gas turbine engine fuel system. Fuel may be exposed on the surface of the sensor component in a gas turbine engine fuel system purge line.

Fuel within, sampled from, or dispensed to an aircraft fuel tank may be exposed on the surface of the sensor component. The measurement of the swelling parameter may include exposing the sensor component to fuel outside of the aircraft during a fueling process in which fuel tank(s) of the aircraft is/are charged with fuel. The sensor component may be provided in a fuel loading line or a fuel storage container of a fueling system for the aircraft.

According to a sixth aspect, the present application provides a fuel characteristic determination system for determining one or more fuel characteristics of an aviation fuel for supplying a gas turbine engine of an aircraft, the system comprising:

a sensor component formed from a nitrile sealing material, a surface of the sensor component being adapted to be exposed to fuel;

a sensor arranged to measure a swelling parameter of the sealing material; And

a fuel characteristics determining module arranged to determine one or more fuel characteristics of the fuel based on the inflation parameter.

The sensor component formed from the sealing material may be arranged to be fixedly mounted relative to a gauge. The gauge may be arranged to detect movement of the sensor component resulting from expansion or contraction.

The gauge may be arranged to detect a change in the physical size of the sensor component.

The gauge may be arranged to detect a pressure exerted by the sensor component resulting from its expansion or contraction.

The one or more fuel characteristics determined by the fuel characteristic determination module may include a hydrocarbon distribution of the fuel.

The one or more fuel characteristics determined by the fuel characteristic determination module may include any one or more of: (i) a percentage of sustainable aviation fuel in the fuel; (ii) an aromatic hydrocarbon content of the fuel (F); and/or (iii) a cycloparaffin content of the fuel.

The fuel characteristics determination system can also be arranged to generate an alert signal if the inflation parameter is beyond an alert threshold.

The sensor component may be adapted to be located on board the aircraft. The sensor component may be arranged such that fuel is exposed on its surface during operation of the gas turbine engine.

The sensor component may be adapted to be exposed to fuel within, sampled from, or dispensed to an aircraft fuel tank. The sensor component may be adapted to be exposed to fuel outside of the aircraft, with fuel being loaded onto the aircraft during a fueling process. The sensor component may be provided in a fuel loading line or a fuel storage container of a fueling system for the aircraft.

According to a seventh aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining one or more fuel characteristics using the method of the fifth aspect; And

the operation of the aircraft according to the fuel characteristic(s).

Operation of the gas turbine engine or aircraft under the one or more fuel characteristics may include:

a) changing an aircraft control parameter, preferably a gas turbine engine control parameter, in response to the one or more fuel characteristics; and or

b) the provision of fuel with different fuel characteristics when refueling the aircraft.

Changing a control parameter of the aircraft may include changing a control parameter that controls a selection of fuel to be supplied to the gas turbine engine from different fuel sources on board the aircraft to provide a fuel having a different fuel characteristic (from that of the determined fuel).

Providing a fuel with a different fuel characteristic may include any one or more of: i) providing a fuel with a relatively higher aromatics content; (ii) provision of fuel with relatively lower SAF content; and/or iii) the supply of fossil kerosene fuel.

According to an eighth aspect, the present application provides an aircraft, comprising:

a gas turbine engine;

a fuel circuit comprising one or more fuel tanks arranged to contain fuel for supplying the gas turbine engine, the fuel circuit comprising one or more seals, the seals being exposed at least partially fuel;

a detection device located in the fuel circuit and comprising a sensor component made of the same material as the or more seals, the detection device being arranged to measure a swelling parameter of the sealing material.

By measuring the level of swelling of a sensor component made of the same material as one or more seals provided in the aircraft fuel system, the behavior of these seals following exposure to fuel can be indirectly determined. This may provide an indication that gasket swelling of an inadequate amount (e.g. too little) has occurred or is occurring to provide sufficient sealing performance.

The sensing device may be arranged to measure expansion or contraction of the sensor component following exposure to fuel.

The sensing device may be arranged to measure a change in the physical size of the sensor component. The sensing device may be arranged to measure a force applied to a gauge by the sensor component.

The aircraft may further comprise a fuel characteristic determination module arranged to determine one or more fuel characteristics of the fuel based on the inflation parameter.

The one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) a cycloparaffin content of the fuel.

The detection device can be arranged to generate an alert signal if the inflation parameter is beyond an alert threshold.

According to a ninth aspect, the present application provides a method comprising:

exposing one or more seals of a fuel system of an aircraft to fuel in the fuel system, the aircraft having a gas turbine engine supplied with fuel by the fuel system exposing a sensor component, made of the same material as the one or more seals, to the fuel, the component being located in the fuel circuit; And

the measurement of a swelling parameter of the sealing material.

The method may further include determining one or more fuel characteristics of the fuel based on the swelling parameter.

The method may further include generating an alert signal if the swelling parameter is beyond an alert threshold.

According to a tenth aspect, the present application provides a method of operating an aircraft having one or more gas turbine engines, comprising:

measuring a swelling parameter of a sealant using the method of the ninth aspect; And

the operation of the aircraft according to the inflation parameter.

Operating the aircraft according to the swell parameter may include supplying the one or more gas turbine engines with a fuel having a different characteristic than the fuel for which the seal swell was determined. This can be done either by refueling the aircraft or by drawing fuel from a different source on board the aircraft.

Providing a fuel with a different characteristic may include any one or more of: i) providing a fuel with a relatively higher aromatics content; (ii) provision of fuel with relatively low SAF content; and/or iii) the supply of kerosene.

According to an eleventh aspect, the present application provides an aircraft comprising the fuel determination system of the sixth aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the one or more fuel characteristics determined by the fuel determination system.

According to a twelfth aspect, the present application provides an aircraft according to the eighth aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the inflation parameter measured by the detection device.

According to a thirteenth aspect, the present application provides a method for determining one or more fuel characteristics of an aviation fuel for supplying a gas turbine engine of an aircraft, the method comprising:

measuring one or more trace substance parameters of the fuel, the one or more trace substance parameters each being associated with a respective trace substance in the fuel; And

determining one or more fuel characteristics of the fuel based on the one or more trace substance parameters.

The inventors have determined that by measuring the trace substance parameters of a fuel, certain characteristics of that fuel can be determined. Such trace substances may be present only in a trace amount and may indicate an associated characteristic of the fuel by their presence, concentration or absence in the fuel.

At least one of the one or more trace substance parameters may indicate the presence or concentration of the associated trace substance in the fuel.

At least one of the one or more trace substance parameters may indicate the absence of the associated trace substance in the fuel.

The one or more determined fuel characteristics may include:

a) a percentage of sustainable aviation fuel in the fuel; Or

b) an indication that the fuel is a fossil fuel, for example a fossil kerosene fuel.

The trace substance associated with at least one of the substance parameters may be inherently present in the fuel. For example, it can be present naturally in the fuel following its manufacture.

Trace substance parameters may include:

i) a concentration or amount of sulfur in the fuel; and or

(ii) a concentration or amount of aromatic hydrocarbons in the fuel.

The trace substance associated with at least one of the trace substance parameters can be added to the fuel to act as a tracer for detection. For example, the trace substance may be added to fuel for the purpose of acting as a tracer to indicate a certain characteristic or characteristics of the fuel.

The measurement of the one or more trace substance parameters may include performing spectroscopy on the fuel. Performing fuel spectroscopy may include performing Fourier Transform Infrared (FT-IR) or Ultraviolet-Visible (UV-Vis) spectroscopy.

Measuring the one or more trace substance parameters may include performing fluorescence detection.

The measurement of the one or more trace substance parameters may include performing a fuel measurement on board the aircraft.

The measurement of the one or more trace substance parameters may include performing a measurement on fuel within, sampled from, or dispensed to a fuel tank of the aircraft.

The measurement of the one or more trace substance parameters may include performing a measurement on the fuel during operation of the gas turbine engine. This may include performing a measurement on the fuel while it is in a gas turbine engine fuel system.

The measurement of the one or more trace substance parameters may include performing a measurement on fuel external to the aircraft during a fueling process in which the fuel tank(s) of the the aircraft is/are loaded with fuel. A sensor for measuring trace substance parameters may therefore be located in a fuel loading system for the aircraft.

According to a fourteenth aspect, the present application provides a fuel characteristic determination system for determining one or more fuel characteristics of an aviation fuel for supplying a gas turbine engine of an aircraft, the system comprising:

a sensor configured to measure one or more trace substance parameters of the fuel, the one or more trace substance parameters each being associated with a respective trace substance in the fuel; And

a determination module configured to determine one or more fuel characteristics of the fuel based on the one or more trace substance parameters.

At least one of the one or more trace substance parameters may indicate the presence or concentration of the associated trace substance in the fuel.

At least one of the one or more trace substance parameters may indicate the absence of the associated trace substance in the fuel.

The one or more determined fuel characteristics may include:

a) a percentage of sustainable aviation fuel in the fuel; or

b) an indication that the fuel is a fossil fuel, for example, fossil kerosene fuel.

The trace substance associated with at least one of the trace substance parameters may be inherently present in the fuel.

The trace substance parameter can be:

a) a concentration or quantity of sulfur in the fuel (F); and or

(b) a concentration or quantity of aromatic hydrocarbons in the fuel (F).

The trace substance associated with at least one of the trace substance parameters can be added to the fuel to act as a tracer for detection.

The sensor may include a spectroscopy device. The spectroscopy device can preferably be a Fourier Transform Infrared (FT-IR) or Ultraviolet-Visible (UV-Vis) spectroscopy device.

The sensor may include a fluorescence detection device.

The sensor can be configured to perform a measurement on the fuel on board the aircraft.

The sensor may be arranged to make a measurement on the fuel within, sampled from, or delivered to a fuel tank of the aircraft.

The sensor can be arranged to perform a measurement on the fuel during use of the gas turbine engine. The sensor may be located in a fuel circuit of the gas turbine engine.

The sensor may be arranged to perform a measurement on fuel outside the aircraft that is loaded onto the aircraft during a fueling process. For example, the sensor may be located in the aircraft fueling system.

According to a fifteenth aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining one or more fuel characteristics using the method of the thirteenth aspect; And

the operation of the aircraft according to the fuel characteristic(s).

Aircraft operation under one or more fuel characteristics may include:

a) changing an aircraft control parameter, preferably a gas turbine engine control parameter, in response to the one or more fuel characteristics; and or

b) the provision of fuel with different fuel characteristics when refueling the aircraft.

According to a sixteenth aspect, the present application provides an aircraft comprising the fuel characteristic determination system of the fourteenth aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the one or more fuel characteristics. fuel determined by the fuel characteristic determination system.

According to a seventeenth aspect, a method of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft is provided, the method comprising:

passage of UV-visible spectrum light through the fuel;

measuring a transmittance parameter indicating the transmittance of light through the fuel;

determining one or more fuel characteristics of the fuel based on the transmittance parameter; And

communicating the one or more fuel characteristics to a gas turbine engine or aircraft control system.

The inventors have determined that by measuring the UV-Vis spectrum light transmittance properties of an aviation fuel, the characteristics of that fuel can be determined and communicated to a control module of the aircraft so that the aircraft can operate on this basis.

The transmittance parameter can indicate the transmittance of UV-visible spectrum light as a function of wavelength.

The one or more fuel characteristics determined based on the transmittance parameter may include a hydrocarbon distribution of the fuel.

The one or more fuel characteristics may include any one or more of: (i) an aromatic hydrocarbon content of the fuel; ii) a percentage of sustainable aviation fuel in the fuel; and/or iii) an indication whether the fuel is a fossil fuel, for example fossil kerosene.

UV-visible spectrum light can pass through fuel within, sampled from, or delivered to an aircraft fuel tank.

UV-visible spectrum light can pass through fuel during gas turbine engine operation. UV-visible spectrum light can pass through fuel in a gas turbine engine fuel system.

UV-visible spectrum light can pass through fuel outside the aircraft during a fueling process in which the aircraft's fuel tank(s) is/are being charged fuel. A UV-vis transmittance sensor can therefore be provided in an aircraft refueling system.

According to an eighteenth aspect, the present application provides a fuel characteristic determination system for determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft, the system including:

a UV-Vis sensor comprising a UV-Vis spectrum light source arranged to pass the UV-Vis spectrum light through the fuel, the UV-Vis sensor further comprising a transmittance detector arranged to measure a transmittance parameter indicative of the transmittance of UV-visible spectrum light through the fuel; And

a determining module arranged to determine one or more fuel characteristics of the fuel based on the transmittance parameter, wherein the determining module is arranged to communicate the one or more fuel characteristics to a control module of the turbine engine gas or aircraft.

The transmittance parameter can indicate the transmittance of UV-visible spectrum light as a function of wavelength.

The one or more fuel characteristics determined based on the transmittance parameter may include a hydrocarbon distribution of the fuel.

The one or more fuel characteristics may include any one or more of:

(i) an aromatic hydrocarbon content of the fuel (F);

ii) a percentage of sustainable aviation fuel in the fuel (F); and or

(iii) an indication whether the fuel is a fossil fuel, eg fossil kerosene.

The light source may be arranged to pass light through fuel that is within, sampled from, or delivered to a fuel tank of the aircraft.

The light source may be arranged to pass light through the fuel during use of the gas turbine engine. The light source may be arranged to pass light through fuel while in a fuel circuit of the gas turbine engine.

The light source may be arranged to pass light through the fuel, which is outside the aircraft during a fueling process in which the fuel tank(s) of the aircraft is/are loaded with fuel. The light source can therefore be provided in a refueling system of the aircraft.

According to a nineteenth aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining one or more fuel characteristics using the method of the seventeenth aspect; And

the operation of the aircraft according to the fuel characteristic(s).

Aircraft operation under one or more fuel characteristics may include:

a) changing an aircraft control parameter, preferably a gas turbine engine control parameter, in response to the one or more fuel characteristics; and or

b) the provision of fuel with different fuel characteristics when refueling the aircraft.

According to a twentieth aspect, the present application provides an aircraft comprising the fuel determination system of the eighteenth aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the one or more characteristics of fuel determined by the fuel characteristic determination system.

According to a twenty-first aspect, a method of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft is provided, the method comprising:

determining, during use of the gas turbine engine, one or more contrail parameters related to the formation of contrail by the gas turbine engine, wherein determining the one or more contrail parameters contrail includes performing a sensor measurement on a region behind the gas turbine engine in which contrail is or may be formed; And

determining one or more fuel characteristics of the fuel based on the one or more contrail parameters.

The inventors have determined that by performing a sensor measurement sensitive to the formation of contrails on the exhaust smoke of a gas turbine engine, the characteristics of the fuel burned by the gas turbine engine can be determined .

The one or more contrail parameters may include a parameter indicative of the degree of contrail formation taking place. The one or more control parameters may include a parameter indicative of the presence or absence of a contrail produced by the gas turbine engine.

Determining the one or more contrail parameters may include measuring electromagnetic radiation reflected and/or re-emitted by a contrail.

Determining the one or more contrail parameters may include detecting the presence or absence of a contrail, or the degree to which a contrail is formed, in an image of the region behind the engine gas turbine.

The one or more fuel characteristics may further be determined based on one or more ambient atmospheric conditions parameters, each indicative of the ambient atmospheric conditions in which the gas turbine engine is currently operating.

The method may further include obtaining the one or more ambient atmospheric conditions from a weather data source providing real-time or expected information about the ambient atmospheric conditions.

The method may further comprise obtaining the one or more ambient atmospheric conditions from a sensor arranged to measure the ambient conditions in the vicinity of the aircraft.

The one or more fuel characteristics may further be determined based on one or more engine or aircraft operating parameters.

The one or more fuel characteristics may be determined based on measuring the value of a variable parameter at which contrail formation begins. The variable parameter may be a variable engine operating parameter and/or a variable ambient condition parameter.

The determined one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) an indication that the fuel is a fossil fuel, for example kerosene.

According to a twenty-second aspect, a fuel characteristic determination system for determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft is provided, the system comprising:

a contrail sensor arranged to determine one or more contrail parameters related to the formation of contrail by the gas turbine engine, the contrail sensor being arranged to perform a sensor measurement over a region behind the gas turbine engine in which a contrail is or may be formed; And

a fuel characteristics determining module arranged to determine one or more fuel characteristics of the fuel based on the one or more contrail parameters.

The one or more contrail parameters may include a parameter indicative of the degree of contrail formation taking place. The one or more control parameters may preferably indicate a presence or absence of a contrail produced by the gas turbine engine.

The contrail sensor can be arranged to measure electromagnetic radiation reflected and/or re-emitted by a contrail.

The contrail sensor may be arranged to detect the presence or absence of a contrail, or the degree to which a contrail is formed, in an image of the region behind the gas turbine engine.

The fuel characteristic determination module may further be arranged to determine the one or more fuel characteristics based on one or more ambient atmospheric conditions parameters, each indicative of the ambient atmospheric conditions in which the turbine engine gas is currently working.

The fuel characteristics determination module can further be arranged to obtain the one or more ambient atmospheric conditions from a meteorological data source providing real-time or expected information on the ambient atmospheric conditions.

The fuel characteristics determination module can also be arranged to obtain the or several ambient atmospheric conditions from a sensor arranged to measure the ambient conditions in the vicinity of the aircraft.

The fuel characteristics module can further be arranged to determine the one or more fuel characteristics on the basis of one or more operating parameters of the engine or of the aircraft. The one or more engine and aircraft parameters may include a temperature of fuel entering a combustion chamber of the gas turbine engine.

The one or more fuel characteristics may be determined based on a measurement of the value of a variable engine or aircraft operating parameter at which contrail formation begins.

The determined one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) an indication that the fuel is a fossil fuel, for example kerosene.

According to a twenty-third aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining one or more fuel characteristics using the method of the twenty-first aspect; And

the operation of the gas turbine engine or aircraft according to the one or more fuel characteristics.

Operation of the aircraft under the one or more fuel characteristics may include any one or more of:

(i) a change in an operating parameter of a gas turbine engine thermal management system;

ii) change in a fuel temperature of the fuel in the gas turbine engine; and or

iii) the change of a flight characteristic of the aircraft, preferably an altitude of the aircraft, more preferably a cruising altitude.

According to a twenty-fourth aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining, during use of the gas turbine engine, one or more contrail parameters related to the formation of contrail by the gas turbine engine, wherein determining the one or more contrail parameters contrail includes performing a sensor measurement on a region behind the gas turbine engine in which a contrail is or may be formed, and in which the one or more control parameters are determined during variable operation of the aircraft and correspond to a value of a variable parameter at which the formation of a contrail begins; And

controlling the operating parameter of the aircraft or gas turbine engine according to the one or more contrail parameters.

The variable operation of the aircraft can be a phase of climb operation of the aircraft.

According to a twenty-fifth aspect, the present application provides an aircraft comprising the fuel determination system of the twenty-second aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the one or more fuel characteristics determined by the fuel determination system.

According to a twenty-sixth aspect, the present application provides a method for determining one or more fuel characteristics of an aviation fuel suitable for supplying a gas turbine engine of an aircraft, the method comprising:

determining, during use of the gas turbine engine, one or more exhaust gas content parameters by performing a sensor measurement on an exhaust gas from the gas turbine engine; And

determining one or more fuel characteristics of the fuel based on the one or more exhaust gas parameters.

The inventors have determined that the characteristics of a fuel used by a gas turbine engine can be determined by carrying out a measurement on the exhaust gases produced by the engine during its use.

The one or more exhaust gas content parameters may include a parameter indicative of the nvPM content of the exhaust gas.

Performing the sensor measurement may include performing a laser-induced glow measurement to determine the volume concentration of nvPM in the exhaust gas.

Performing the sensor measurement may include performing a condensation particle count measurement to determine an nvPM number in the exhaust gas.

The one or more exhaust gas content parameters may include a parameter indicative of the SO ₂ , CO ₂ or CO content of the exhaust gas.

Performing the sensor measurement may include performing a non-dispersive infrared absorption measurement.

The one or more exhaust gas content parameters may include a sulfate aerosol content of the exhaust gas. Performing the sensor measurement may include performing an aerosol mass spectrometer measurement to determine the presence of sulfates in the exhaust gas.

The one or more fuel characteristics may further be determined based on one or more ambient atmospheric conditions parameters, each indicative of the ambient atmospheric conditions in which the gas turbine engine is currently operating.

The one or more fuel characteristics may further be determined based on one or more engine operating parameters. The operating parameters may include a motor power setting.

The one or more fuel characteristics may be determined based on an exhaust gas content parameter measured in a first engine operating condition in which the emission of the respective measured substance is higher than in a second engine operating condition.

The one or more fuel characteristics may be determined based on a comparison of exhaust gas content parameters determined under different engine operating conditions.

The one or more fuel characteristics may include any one or more of: (i) a hydrogen to carbon ratio of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; (iv) a naphthalene content of the fuel; and/or (v) sulfur content of the fuel.

According to the twenty-seventh aspect, the present application provides a fuel characteristic determination system for determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft, the system including:

an exhaust sensor arranged to determine one or more exhaust gas content parameters, the exhaust sensor being arranged to perform a measurement on an exhaust gas from the gas turbine engine; And

a fuel characteristic determination module arranged to determine one or more fuel characteristics of the fuel based on the one or more exhaust gas content parameters.

The exhaust sensor may be arranged to determine one or more exhaust gas content parameters which include a parameter indicative of the nvPM content of the exhaust gas.

The exhaust sensor may include a laser-induced glow meter arranged to determine the volume concentration of nvPM in the exhaust gas.

The exhaust sensor may include a condensation particle counting device arranged to determine a number of nvPM in the exhaust gas.

The exhaust sensor can be arranged to determine one or more exhaust gas content parameters which include a parameter indicative of the SO ₂ , CO ₂ or CO content of the exhaust gas. The exhaust sensor may include a device for measuring non-dispersive infrared absorption.

The exhaust sensor may be arranged to determine one or more exhaust gas content parameters which include a sulfate aerosol content of the exhaust gas. The exhaust sensor may include an aerosol mass spectrometer measuring device arranged to measure a mass of sulfate in the exhaust gas.

The one or more fuel characteristics may further be determined by the fuel characteristic determination module based on:

i) one or more ambient atmospheric conditions parameters, each indicative of the ambient atmospheric conditions in which the gas turbine engine is currently operating; and or

ii) one or more engine operating parameters, preferably including an engine power setting.

The one or more fuel characteristics may include any one or more of: (i) a hydrogen to carbon ratio of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; (iv) a naphthalene content of the fuel; and/or (v) sulfur content of the fuel.

According to a twenty-eighth aspect, the present application provides a method of operating an aircraft having a gas turbine engine, the method comprising:

determining one or more fuel characteristics using the method of the twenty-sixth aspect; And

the operation of the aircraft according to the fuel characteristic(s).

According to a twenty-ninth aspect, the present application provides an aircraft comprising a gas turbine engine and the fuel characteristic determination system of the twenty-seventh aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the one or more fuel characteristics determined by the fuel characteristic determination system.

According to a thirtieth aspect, the present application provides a method for determining one or more fuel characteristics of an aviation fuel used to power a gas turbine engine of an aircraft, the method comprising:

determining one or more performance parameters of the gas turbine engine during a first period of time of operation of the gas turbine engine;

determining one or more fuel characteristics of the fuel based on the one or more performance parameters.

The inventors have determined that the characteristics of a fuel used by a gas turbine engine can be determined during the use of this engine on the basis of an observation of the performance parameters of the engine. By determining one or more engine performance parameters, fuel characteristics can be determined based on those performance parameters for a different subsequent period of engine operation.

The fuel characteristics may be determined during a second subsequent operating period.

The first operating period may be a first flight phase, and the second operating period may be a second flight phase, different from the first.

The first flight phase can be a take-off and/or climb phase, and the second flight phase can be a cruise phase or a descent phase.

The one or more performance parameters may include one or more of:

a) a rotational speed of a fan of the gas turbine engine;

b) a turbine inlet temperature of the gas turbine engine; and or

c) a gas turbine engine combustion chamber fuel-to-air ratio (this can be defined as the ratio of the mass of fuel flow to the combustion chamber relative to the core airflow).

Determining the one or more fuel characteristics may include comparing each of the one or more determined performance parameters with a reference performance parameter corresponding to operation of the gas turbine engine on a fuel having a known fuel characteristic.

Determining the one or more performance parameters may include determining a plurality of different performance parameters. The one or more fuel characteristics may be determined based on the plurality of performance parameters. The plurality of performance parameters may include at least two different performance parameters, and preferably at least three different performance parameters.

The determined one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) an indication that the fuel is a fossil fuel, for example kerosene.

According to a thirty-first aspect, a method of operating an aircraft having a gas turbine engine is provided, the method comprising:

determining one or more fuel characteristics using the method of the thirtieth aspect;

the operation of the aircraft according to the one or more fuel characteristics during one or the second subsequent period of operation of the gas turbine engine.

The aircraft may include a plurality of fuel tanks. The aircraft may only operate to the one or more fuel characteristics during the second operating period if the fuel is used from the same fuel tank, or is a fuel known to have the same fuel characteristics, as during the first period of operation.

Operating the aircraft according to the one or more fuel characteristics may include modifying a control parameter of the aircraft, preferably a control parameter of the gas turbine engine, in response to the one or more characteristics fuel.

Operation of the aircraft according to the one or more fuel characteristics may include any one or more of: i) changing a fuel consumption parameter of the gas turbine engine; (ii) a change in an operating parameter of the gas turbine engine thermal management system; iii) adjusting a fuel temperature of the fuel in the gas turbine engine; iv) adjusting a flight characteristic of the aircraft, preferably an altitude of the aircraft, more preferably a cruising altitude.

According to a thirty-second aspect, the present application provides a fuel characteristic determination system for determining one or more fuel characteristics of an aviation fuel for powering a gas turbine engine of an aircraft, the system comprising :

a performance parameter sensor configured to determine one or more gas turbine engine performance parameters during a first period of gas turbine engine operating time; And

a fuel characteristic determination module configured to determine one or more fuel characteristics of the fuel based on the one or more performance parameters.

The fuel characteristic determination module may be configured to determine the one or more fuel characteristics during a second subsequent operating period.

The first operating period may be a first flight phase, and the second operating period may be a second flight phase, different from the first.

The first flight phase can be a take-off and/or climb phase, and the second flight phase can be a cruise phase or a descent phase.

The one or more performance parameters may include any one or more of:

a) a rotational speed of a fan of the gas turbine engine;

b) a turbine inlet temperature of the gas turbine engine; and or

c) a gas turbine engine combustion chamber fuel-to-air ratio (this can be defined as the mass ratio of the fuel flow to the combustion chamber relative to the core airflow).

The fuel characteristics determination module can be arranged to determine the one or more fuel characteristics by comparing each of the one or more performance parameters determined with a reference performance parameter corresponding to the operation of the gas turbine engine with a fuel having a known fuel characteristic.

The fuel characteristic determining module may be arranged to determine the one or more fuel characteristics by obtaining a plurality of different performance parameters from the sensor or additional sensors. The one or more fuel characteristics may be determined based on the plurality of performance parameters. The plurality of performance parameters may include at least two different performance parameters, and preferably at least three different performance parameters.

The determined one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) an indication that the fuel is a fossil fuel, for example kerosene.

According to a thirty-third aspect, the present application provides an aircraft comprising the system for determining fuel characteristics of the thirty-second aspect, the aircraft further comprising a control system arranged to control the operation of the aircraft according to the the plurality of fuel characteristics determined by the fuel determination system.

According to a thirty-fourth aspect, the present application provides a method of generating a maintenance program for an aircraft having one or more gas turbine engines powered by aviation fuel, comprising:

determining one or more fuel characteristics of the fuel; And

the generation of a maintenance program according to the one or more fuel characteristics.

The inventors have determined that the characteristics of the fuel that has been used to power the gas turbine have an effect on the operation of the gas turbine engine and the aircraft in general and may therefore require a change in the maintenance program for this aircraft. A maintenance program for the aircraft can therefore advantageously be generated on the basis of the characteristics of the fuel with which it has been operated. This can make it possible to take into account the fuel that was actually used to power the aircraft when carrying out the maintenance.

Generating the maintenance program may include modifying an existing maintenance program for the aircraft according to the determined one or more fuel characteristics.

Generating the maintenance schedule may include comparing the one or more determined fuel characteristics with an expected fuel characteristic.

The existing maintenance program can be associated with the expected fuel characteristic. Modification of the existing maintenance program may be made in response to the determination of a deviation from the expected fuel characteristic.

Determining the one or more fuel characteristics may include making periodic determinations of a fuel characteristic or characteristics.

The one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) an indication that the fuel is a fossil fuel, for example kerosene.

Determining the one or more fuel characteristics may include measuring a change in properties of a sensor component exposed to the fuel used to power the one or more gas turbine engines.

The one or more fuel characteristics may indicate that a threshold level of fuel coking or surface deposit formation is reached.

The sensor component may be a piezoelectric crystal. Determining the one or more fuel characteristics may include measuring a vibration parameter of the piezoelectric crystal.

The sensor component may include a sealant and the one or more fuel characteristics may indicate whether a threshold level of swelling of the sealant exposed to fuel is reached. The sealing material may be the same as that of at least one seal provided in a fuel circuit of the one or more gas turbine engines. The sealing material may be a nitrile sealing material.

According to a thirty-fifth aspect, the present application provides a method for maintaining an aircraft, comprising:

generating a maintenance program using the method of the thirty-fourth aspect; And

carrying out maintenance on the aircraft according to the maintenance program generated.

According to a thirty-sixth aspect, the present application provides a maintenance program generation system for generating a maintenance program for an aircraft having one or more gas turbine engines, comprising:

a fuel characteristic determination module configured to determine one or more fuel characteristics of a fuel supplied to the one or more gas turbine engines of the aircraft; And

a maintenance program generation module configured to generate a maintenance program according to the one or more fuel characteristics.

The generation module can be configured to modify an existing maintenance program for the aircraft according to the one or more determined fuel characteristics.

The maintenance schedule generation module may be configured to compare the one or more determined fuel characteristics to an expected fuel characteristic.

The existing maintenance program can be associated with the expected fuel characteristic. The maintenance schedule generation module may be configured to modify the existing maintenance schedule in response to determining a deviation from the expected fuel characteristic.

The fuel characteristic determination module may be configured to perform periodic determinations of the one or more fuel characteristics.

The one or more fuel characteristics may include any one or more of: (i) a hydrocarbon distribution of the fuel; (ii) a percentage of sustainable aviation fuel in the fuel; (iii) an aromatic hydrocarbon content of the fuel; and/or (iv) an indication that the fuel is a fossil fuel, for example kerosene.

The fuel characteristic determination module may be arranged to receive a sensor parameter indicative of a measured change in properties of a sensor component exposed to the fuel used to power the one or more gas turbine engines, and base the determining the one or more fuel characteristics on the received sensor parameter.

The one or more fuel characteristics may indicate that a threshold level of fuel coking or surface deposit formation is reached. The sensor component may be a piezoelectric crystal, and determining the one or more fuel characteristics may include measuring a vibration parameter of the piezoelectric crystal.

The sensor component may include a sealing material. The one or more fuel characteristics may indicate whether a threshold level of swelling of the fuel-exposed sealant is reached. The sealing material may be the same as that of at least one seal provided in a fuel circuit of one or more gas turbine engines. The sealing material may be a nitrile sealing material.

According to a thirty-seventh aspect, the present application provides an aircraft having one or more gas turbine engines, the aircraft comprising the maintenance program generation system of the thirty-sixth aspect.

As used herein, the term "fuel characteristics" refers to intrinsic fuel properties such as fuel composition, not variable properties such as volume or temperature. Examples of fuel characteristics of a fuel include:

(i) the percentage of sustainable aviation fuel in the fuel;

(ii) the aromatic hydrocarbon content of the fuel;

(iii) the multi-aromatic hydrocarbon content of the fuel;

(iv) the percentage of nitrogen-containing species in the fuel;

(v) the presence or percentage of a trace species or trace element in the fuel (for example, a trace substance inherently present in the fuel, or a substance deliberately added to act as a tracer) ;

(vi) the hydrogen to carbon ratio of the fuel;

(vii) distribution of hydrocarbon fuel;

(viii) the level of non-volatile particulate matter (nvPM) emissions during combustion (e.g. during combustion for a given combustion chamber design, under given operating conditions (FAR, T30, chamber mode combustion, etc.));

(ix) the naphthalene content of the fuel;

(x) fuel sulfur content;

(xi) the cycloparaffin content of the fuel;

(xii) the oxygen content of the fuel;

(xiii) thermal stability of the fuel (eg thermal degradation temperature);

(xiv) fuel coking level;

(xv) an indication that the fuel is a fossil fuel, for example fossil kerosene; And

(xvi) one or more properties such as density, viscosity, calorific value and/or heat capacity.

In any aspect or statement above involving the operation of an aircraft according to one or more determined fuel characteristics, the operation of the aircraft may include the modification of a control parameter of the aircraft, and specifically of a control parameter of the gas turbine engine, in response to the one or more fuel characteristics as described herein. The operation of the aircraft may additionally or alternatively include the supply of fuel having different fuel characteristics, for example during refueling as described elsewhere herein.

As indicated elsewhere herein, this disclosure may relate to a gas turbine engine. Such a gas turbine engine may include an engine core comprising a turbine, a combustor, a compressor and a core shaft connecting the turbine to the compressor. Such a gas turbine engine may include a fan (having fan blades) located upstream of the engine core. Alternatively, in some examples, the gas turbine engine may include a fan located downstream of the engine core. Thus, the gas turbine engine can be an unducted rotor engine or a turboprop.

In the event that the gas turbine engine is an unducted rotor engine or a turboprop, the gas turbine engine may comprise two stages of counter-rotating propellers attached to and driven by a free turbine through a shaft. The propellers can spin in opposite directions so that one spins clockwise and the other counter-clockwise around the motor's axis of rotation. Alternatively, the gas turbine engine may include a propeller stage and a guide vane stage configured downstream of the propeller stage. The guide vane stage may have a variable pitch. Accordingly, high-pressure, intermediate-pressure, and free-running turbines can drive high- and medium-pressure compressors and propellers, respectively, through appropriate interconnecting shafts. Thus, the propellers can provide the majority of the propulsive thrust.

In the event that the gas turbine engine is an unducted rotor engine or a turboprop, one or more of the propeller stages may be driven by a gearbox of the type described.

The arrangements of the present disclosure may be particularly, but not exclusively, advantageous for blowers which are gear box driven. Accordingly, the gas turbine engine may include a gearbox which receives input from the core shaft and outputs a drive to the fan so as to drive the fan at a rotational speed lower than that of the kernel tree. Input to the gearbox can be directly from the core shaft, or indirectly from the core shaft, for example via a gear and/or spur shaft(s). The core shaft can rigidly connect the turbine and the compressor, so that the turbine and the compressor rotate at the same speed (the fan rotates at a lower speed).

The gas turbine engine as described and/or claimed herein may have any suitable general architecture. For example, the gas turbine engine can have any desired number of shafts that connect the turbines and the compressors, such as one, two or three shafts. Purely by way of example, the turbine connected to the core shaft may be a first turbine, the compressor connected to the core shaft may be a first compressor, and the core shaft may be a first core shaft. The engine core may further include a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor. The second turbine, the second compressor and the second core shaft can be arranged to rotate at a higher rotational speed than the first core shaft.

In such an arrangement, the second compressor can be positioned axially downstream of the first compressor. The second compressor can be arranged to receive (for example receive directly, for example via a generally annular duct) a flow coming from the first compressor.

The gearbox may be arranged to be driven by the core shaft which is configured to rotate (e.g. in use) at the lowest rotational speed (e.g. the first core shaft in the example above). For example, the gearbox can be arranged to be driven only by the core shaft which is configured to rotate (e.g. in use) at the lowest rotational speed (e.g. only be first kernel tree, not the second kernel tree, in the example above). Alternatively, the gearbox may be arranged to be driven by any one or more shafts, for example the first and/or the second shaft(s) in the example above.

The gearbox may be a reducer (in the sense that the output to the fan is a lower rotational speed than the input to the core shaft). Any type of gearbox can be used. For example, the gearbox may be a "planetary" or "star" gearbox, as described in more detail elsewhere herein. The gearbox may have any desired gear ratio (defined as input shaft RPM divided by output shaft RPM), e.g. greater than 2.5, by example in the range from 3 to 4.2, or from 3.2 to 3.8, for example of the order of or at least 3, 3.1, 3.2, 3.3, 3, 4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1 or 4.2. The gear ratio can be, for example, between any two values of the values in the previous sentence. Purely by way of example, the gearbox may be a "star" gearbox having a ratio in the range of 3.1 or 3.2 to 3.8. In some arrangements, the gear ratio may be outside these ranges.

In any gas turbine engine as described and/or claimed herein, a fuel of a given composition or mixture is supplied to a combustion chamber, which may be provided axially downstream of the fan and of the compressor(s). For example, the combustion chamber may be directly downstream (eg at the outlet) of the second compressor, where a second compressor is provided. As a further example, the flow at the exit to the combustion chamber can be provided at the inlet of the second turbine, where a second turbine is provided. The combustion chamber can be provided upstream of the turbine(s).

The or each compressor (e.g. the first compressor and the second compressor as described above) may comprise any number of stages, e.g. multiple stages. Each stage may include a row of rotor blades and a row of stator vanes, which may be variable stator vanes (in the sense that their angle of incidence may be variable). The row of rotor blades and the row of stator vanes can be axially offset from each other.

The or each turbine (e.g. the first turbine and the second turbine as described above) may comprise any number of stages, e.g. multiple stages. Each stage may include a row of rotor blades and a row of stator vanes. The row of rotor blades and the row of stator vanes can be axially offset from each other.

Each fan blade can be defined as having a radial span extending from a root (or hub) at a gas-washed radially inboard location, or a 0% span position, to a tip at a 100% span position. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip can be less than (or around) one of the following values: 0.4, 0 .39, 0.38, 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.3, 0.29, 0.28, 0.27 , 0.26 or 0.25. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be within an inclusive range bounded by any two values of the values in the preceding sentence (i.e. say that the values can form upper or lower limits), for example in the range from 0.28 to 0.32. These ratios can be commonly referred to as the hub-to-point ratio. The radius at the hub and the radius at the tip can both be measured at the leading edge (or axially most forward) portion of the blade. The hub-to-tip ratio refers, of course, to the gas-washed portion of the fan blade, that is, the portion radially outboard of any deck.

The fan radius can be measured from the engine axis to the tip of a fan blade at its leading edge. The fan diameter (which can simply be twice the fan radius) can be greater than (or around) one of the following values: 220 cm, 230 cm, 240 cm, 250 cm (about 100 inches), 260 cm, 270 cm (about 105 inches), 280 cm (about 110 inches), 290 cm (about 115 inches), 300 cm (about 120 inches), 310 cm, 320 cm (about 125 inches), 330 cm (about 130 inches), 340 cm (about 135 inches), 350 cm, 360 cm (about 140 inches), 370 cm (about 145 inches), 380 cm (about 150 inches), 390 cm (about 155 inches), 400 cm, 410 cm (about 160 inches) or 420 cm (about 165 inches). The fan diameter can be in an inclusive range limited by any two values of the values in the previous sentence (i.e. the values can form upper or lower limits), for example in the range from 240 cm to 280 cm or from 330 cm to 380 cm.

Blower rotation speed may vary during use. In general, the rotational speed is lower for blowers having a larger diameter. Purely by way of non-limiting example, the rotational speed of the fan under cruising conditions may be less than 2500 rpm, for example less than 2300 rpm. Purely by way of further non-limiting example, the fan rotational speed under cruising conditions for an engine having a fan diameter in the range of 220 cm to 300 cm (e.g. 240 cm to 280 cm or from 250 cm to 270 cm) can be in the range from 1700 rpm to 2500 rpm, for example in the range from 1800 rpm to 2300 rpm, for example in the range from 1900 rpm /min at 2100 rpm. Purely by way of further non-limiting example, the fan rotational speed under cruising conditions for an engine having a fan diameter in the range of 330 cm to 380 cm may be in the range of 1200 rpm min to 2000 rpm, for example in the range from 1300 rpm to 1800 rpm, for example in the range from 1400 rpm to 1800 rpm.

In use of the gas turbine engine, the fan (with associated fan blades) rotates around an axis of rotation. This rotation causes the tip of the fan blade to move with a speed U _tip . The work done by the fan blades 13 on the flow leads to an increase in enthalpy dH of the flow. A fan peak load can be defined as dH/U _tip ² , where dH is the enthalpy rise (e.g. 1-D average enthalpy rise) across the fan and U _tip is the speed ( of translation) of the fan tip, for example at the leading edge of the tip (which can be defined as the radius of the fan tip at the leading edge multiplied by the angular velocity). Peak fan load under cruise conditions may be greater than (or in the range of) any of the following values: 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39 or 0.4 (all values being dimensionless). The fan peak load can be within an inclusive range limited by any two values of the values in the previous sentence (i.e. the values can form upper or lower limits), for example in the range from 0.28 to 0.31, or 0.29 to 0.3.

Gas turbine engines according to the present disclosure may have any desired bypass ratio, where the bypass ratio is defined as the ratio of the mass flow rate of the stream through the bypass conduit to the mass flow rate of the stream at through the core under cruising conditions. In some arrangements, the dilution ratio may be greater than (or around) one of the following values: 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5 , 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5 or 20. The dilution ratio can be within a limited inclusive range by any two values of the values in the previous sentence (i.e. the values can form upper or lower bounds), e.g. in the range 12 to 16, 13 to 15, or 13 to 14. The branch conduit may be substantially annular. The bypass duct may be radially outside the base motor. The radially outer surface of the bypass duct may be defined by a nacelle and/or a fan casing.

The overall pressure ratio of a gas turbine engine as described and/or claimed herein may be defined as the ratio of the stagnation pressure upstream of the fan to the stagnation pressure at the compressor outlet at the higher pressure (before entering the combustion chamber). By way of non-limiting example, the overall pressure ratio of a gas turbine engine as described and/or claimed herein at cruise may be greater than (or on the order of) one of the following values: 35, 40, 45, 50, 55, 60, 65, 70, 75. The overall pressure ratio can be within an inclusive range bounded by any two of the values in the previous sentence (i.e. the values can form upper or lower limits), for example in the range from 50 to 70.

The specific thrust of an engine can be defined as the net thrust of the engine divided by the total mass flow through the engine. In some examples, the specific thrust may depend, for a given thrust condition, on the specific composition of the fuel supplied to the combustion chamber. Under cruising conditions, the specific thrust of an engine described and/or claimed herein may be less than (or in the order of) one of the following values: 110 Nkg ^-1 s, 105 Nkg ^-1 s, 100 Nkg ^-1 s, 95 Nkg ^-1 s, 90 Nkg ^-1 s, 85 Nkg ^-1 s or 80 Nkg ^-1 s. The specific thrust can be in an inclusive range limited by any two values of the values in the previous sentence (i.e. the values can form upper or lower limits), for example in the range from 80 Nkg ^{- 1} s to 100 Nkg ^-1 s, or from 85 Nkg ^-1 s to 95 Nkg ^-1 s. Such engines can be particularly efficient compared to conventional gas turbine engines.

A gas turbine engine as described and/or claimed herein can have any maximum thrust desired. Purely by way of non-limiting example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust of at least (or on the order of) one of the following values: 160 kN , 170 kN, 180 kN, 190 kN, 200 kN, 250 kN, 300 kN, 350 kN, 400 kN, 450 kN, 500 kN or 550 kN. The maximum thrust can be within an inclusive range limited by any two values of the values in the previous sentence (i.e. the values can form upper or lower limits). Purely by way of example, a gas turbine as described and/or claimed herein may be capable of producing maximum thrust in the range of 330 kN to 420 kN, for example 350 kN to 400 kN. The thrust mentioned above may be the maximum net thrust under normal atmospheric conditions at sea level plus 15 degrees C (ambient pressure 101.3 kPa, temperature 30 degrees C) with the engine static.

During use, the temperature of the flow at the inlet to the high pressure turbine can be particularly high. This temperature, which can be called TET, can be measured at the exit to the combustion chamber, for example immediately upstream of the first turbine blade, which can itself be called a turbine nozzle blade. In some examples, the TET temperature may depend, for a given thrust condition, on the specific composition of the fuel supplied to the combustion chamber. In cruise, the TET temperature can be at least (or around) one of the following values: 1400K, 1450K, 1500K, 1550K, 1600K or 1650K. The cruise TET temperature can be within an inclusive range limited by any two values of the values in the previous sentence (i.e. the values can form upper or lower limits). The maximum TET temperature when using the engine can be, for example, at least (or around) one of the following values: 1700K, 1750K, 1800K, 1850K, 1900K, 1950K or 2000K. The maximum TET temperature can be within an inclusive range limited by any two values of the values in the previous sentence (i.e. the values can form upper or lower limits), for example in the range from 1800K to 1950K. The maximum TET temperature can be reached, for example, in a high thrust condition, for example in a maximum takeoff (MTO) condition.

A fan blade and/or an airfoil portion of a fan blade described and/or claimed herein may be fabricated from a material or a combination of any suitable materials. For example at least a portion of the fan blade and/or airfoil may be fabricated at least in part from a composite, for example a metal matrix composite and/or an organic matrix composite, such as a carbon fiber. By way of further example, at least a portion of the fan blade and/or airfoil may be fabricated at least in part from a metal, such as a titanium-based metal or a titanium-based material. aluminum (such as an aluminum-lithium alloy) or a steel-based material. The fan blade may include at least two regions fabricated using different materials. For example, the fan blade may have a protective leading edge, which may be made using a material that is more capable of withstanding impact (e.g. birds, ice, or other material) than the rest of the blade. Such a leading edge can, for example, be manufactured using titanium or a titanium-based alloy. So, purely by way of example, the fan blade may have a body made from carbon fiber or aluminum (such as an aluminum-lithium alloy) with a titanium leading edge.

A fan as described and/or claimed herein may comprise a central part, from which the fan blades may extend, for example in a radial direction. The fan blades can be attached to the central part in any desired way. For example, each fan blade may include a fastener that may engage a corresponding slot in the hub (or disc). Purely by way of example, such a fastener may be in the form of a dovetail which may fit into and/or engage a corresponding slot in the hub/disc to secure the fan blade to hub/disc. As a further example, fan blades can be integrally formed with a central portion. Such an arrangement may be referred to as a bladed disc or a bladed ring. Any suitable method can be used to manufacture such a bladed disc or such a bladed ring. For example, at least a portion of the fan blades may be machined from a block and/or at least a portion of the fan blades may be attached to the hub/disc by welding, such as linear friction welding.

The gas turbine engines described and/or claimed herein may or may not have a variable area nozzle (VAN). Such a variable-section nozzle can make it possible to vary the outlet surface of the bypass duct during use. The general principles of this disclosure can be applied to engines with or without NPV.

The fan of a gas turbine as described and/or claimed herein can have any desired number of fan blades, for example 14, 16, 18, 20, 22, 24 or 26 fan blades.

As used herein, the terms idle, taxi, takeoff, climb, cruise, descent, approach and landing have the conventional meaning and would be readily understood by those skilled in the art. Thus, for a given gas turbine engine for an aircraft, a person skilled in the art would immediately recognize each term to refer to an operating phase of the engine within the framework of a given mission of an aircraft to which the turbine engine gas valve is designed to be attached.

In this regard, ground idle can refer to a phase of engine operation where the aircraft is stationary and in contact with the ground, but it is necessary for the engine to be running. At idle, the engine can produce between 3% and 9% of the engine's available thrust. In other examples, the engine can produce between 5% and 8% available thrust. In yet other examples, the engine can produce between 6% and 7% available thrust. Rolling can refer to a phase of engine operation where the aircraft is propelled along the ground by the thrust produced by the engine. While taxiing, the engine can produce between 5% and 15% of available thrust. In other examples, the engine can produce between 6% and 12% of available thrust. In yet other examples, the engine can produce between 7% and 10% available thrust. Take-off can refer to a phase of engine operation where the aircraft is propelled by the thrust produced by the engine. At an early stage in the takeoff phase, the aircraft may be propelled while the aircraft is in contact with the ground. At a later stage in the takeoff phase, the aircraft may be propelled while the aircraft is not in contact with the ground. During takeoff, the engine can produce between 90% and 100% available thrust. In other examples, the engine can produce between 95% and 100% available thrust. In yet other examples, the engine may produce 100% available thrust.

Climb can refer to a phase of engine operation where the aircraft is propelled by the thrust produced by the engine. During climb, the engine can produce between 75% and 100% available thrust. In other examples, the engine can produce between 80% and 95% available thrust. In yet other examples, the engine can produce between 85% and 90% available thrust. In this regard, climb can refer to an operating phase in an aircraft flight cycle between take-off and arrival in cruise conditions. Additionally or alternatively, climb may refer to a nominal point in an aircraft's flight cycle between takeoff and landing, where a relative increase in altitude is required, which may necessitate a request for additional engine thrust.

As used herein, cruising conditions have the conventional meaning and would be readily understood by those skilled in the art. Thus, for a given gas turbine engine for an aircraft, one skilled in the art would immediately recognize cruise conditions to refer to the mid-cruise engine operating point of a given mission (which may be called in the "economic mission" industry) of an aircraft to which the gas turbine engine is designed to be attached. In this regard, mid-cruise is the point in an aircraft's flight cycle where 50% of the total fuel burned between the end of the climb and the start of the descent has been burned (which can be approximated by the midpoint - in terms of time and/or distance - between the end of the climb and the start of the descent). Cruise conditions thus define an operating point for the gas turbine engine that provides thrust that would ensure steady-state operation (i.e. maintaining constant altitude and constant Mach Number) at mid-range. cruise of an aircraft to which it is designed to be attached, taking into account the number of engines provided for this aircraft. For example, when an engine is designed to be attached to an aircraft equipped with two engines of the same type, under cruise conditions the engine provides half the total thrust that would be required for steady-state operation of that aircraft at mid-cruise.

In other words, for a given gas turbine engine for an aircraft, cruising conditions are defined as the operating point of the engine that provides a specified thrust (required to ensure - in combination with any other engine on the aircraft - the steady-state operation of the aircraft to which it is designed to be attached at a given mid-cruise Mach Number) under mid-cruise atmospheric conditions (defined by the International Standard Atmosphere in accordance with the standard ISO 2533 at mid-cruise altitude). For any given gas turbine engine for an aircraft, the mid-cruise thrust, atmospheric conditions and Mach Number are known, and thus the operating point of the engine in cruise conditions is clearly defined.

Purely by way of example, the forward speed at cruise conditions may be any point in the range of Mach 0.7 to 0.9, for example 0.75 to 0.85, for example 0.76 to 0.84, for example 0.77 to 0.83, for example 0.78 to 0.82, for example 0.79 to 0.81, for example of the order of Mach 0.8, of the order of Mach 0.85 or in the range from 0.8 to 0.85. Any single speed within these ranges can be part of cruising conditions. For some aircraft, cruising conditions may be outside these ranges, for example below Mach 0.7 or above Mach 0.9.

Purely by way of example, cruising conditions may correspond to normal atmospheric conditions (according to the International Standard Atmosphere, ISA) at an altitude which is in the range from 10000 m to 15000 m, for example in the range ranging from 10000 m to 12000 m, for example in the range from 10400 m to 11600 m (about 38000 feet), for example in the range from 10500 m to 11500 m, for example in the range from 10600 m to 11400 m, for example in the range from 10700 m (about 35000 feet) to 11300 m, for example in the range from 10800 m to 11200 m, for example in the range from 10900 m to 11100 m, for example from l order of 11000 m. Cruise conditions may be normal atmospheric conditions at any given altitude within these ranges.

Purely by way of example, cruise conditions may correspond to an engine operating point that provides a known required level of thrust (e.g. a value in the range 30 kN to 35 kN) at a Mach number d advancement of 0.8 and normal atmospheric conditions (according to the International Standard Atmosphere) at an altitude of 38,000 feet (11,582 m). Purely by way of further example, cruise conditions may correspond to an engine operating point that provides a known required level of thrust (e.g. a value in the range of 50 kN to 65 kN) at a Mach number advancement of 0.85 and normal atmospheric conditions (according to the International Standard Atmosphere) at an altitude of 35,000 feet (10,668 m).

In use, a gas turbine engine described and/or claimed herein may operate under cruise conditions defined elsewhere herein. Such cruise conditions may be determined by the cruise conditions (e.g. mid-cruise conditions) of an aircraft on which at least one gas turbine engine (e.g. 2 or 4) may be fitted in order to provide a propelling thrust.

Furthermore, the person skilled in the art would immediately recognize the descent and/or the approach to refer to an operating phase in a flight cycle of an aircraft between the cruise and the landing of the aircraft. During descent and/or approach, the engine can produce between 20% and 50% of available thrust. In other examples, the engine can produce between 25% and 40% available thrust. In yet other examples, the engine can produce between 30% and 35% available thrust. Additionally or alternatively, descent may refer to a nominal point in an aircraft's flight cycle between takeoff and landing, where a relative decrease in altitude is required, and which may necessitate a request for reduced engine thrust.

In one aspect, an aircraft including a gas turbine engine as described and/or claimed herein is provided. The aircraft in this aspect is the aircraft to which the gas turbine engine was designed to be attached. Consequently, the cruise conditions according to this aspect correspond to the mid-cruise of the aircraft, as defined elsewhere here.

In one aspect, a method of operating a gas turbine engine as described and/or claimed herein is provided. Operation may be under cruise conditions as defined elsewhere herein (eg in terms of thrust, atmospheric conditions and Mach number).

In one aspect, a method of operating an aircraft including a gas turbine engine as described and/or claimed herein is provided. Operation under this aspect may include (or may be) mid-cruise operation of the aircraft, as defined elsewhere herein.

Those skilled in the art will understand that, unless mutually exclusive, a characteristic or parameter described in relation to any of the above aspects can be applied to any other aspect. Further, unless mutually exclusive, any feature or parameter described herein may be applied to any aspect and/or combined with any other feature or parameter described herein.

Embodiments will now be described by way of examples only, with reference to the Figures, in which:

[ is a sectional side view of a gas turbine engine;

is a close-up sectional side view of an upstream portion of a gas turbine engine;

is a partially cut-away view of a gearbox for a gas turbine engine;

is a schematic view of an aircraft including a fuel supply system;

is a schematic view of an aircraft comprising a system for determining fuel characteristics;

is a schematic close-up view of the fuel characteristics determination system of the ;

is a schematic view of a system for determining fuel characteristics provided in a fuel circuit of a gas turbine engine;

is a schematic representation of a method for determining fuel characteristics of aviation fuel;

is a schematic view of an aircraft including another example of a fuel characteristic determination system;

is a schematic close-up view of the fuel characteristics determination system of the ;

is a schematic view of a system for determining fuel characteristics provided in a fuel circuit of a gas turbine engine;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic view of a fuel characteristic determining system having a sensor component fabricated from the same material as one or more seals provided in an aircraft fuel system;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic view of an aircraft including another example of a fuel characteristic determination system;

is a schematic close-up view of the fuel characteristics determination system of the ;

is a schematic view of another example of a fuel characteristic determination system provided in a fuel circuit of a gas turbine engine;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic view of an aircraft including another example of a fuel characteristic determination system;

is a schematic close-up view of the fuel characteristics determination system of the ;

is a schematic view of another example of a fuel characteristic determination system provided in a fuel circuit of a gas turbine engine;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic view of an aircraft including another example of a fuel characteristic determination system;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic view of an aircraft including another example of a fuel characteristic determination system;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic view of an aircraft including another example of a fuel characteristic determination system;

is a schematic representation of another example of a method for determining fuel characteristics of aviation fuel;

is a schematic representation of a method of operating an aircraft;

is a schematic representation of another method of operating an aircraft;

is a schematic representation of yet another method of operating an aircraft;

is a schematic representation of a method for generating a maintenance program for an aircraft;

is a schematic representation of an aircraft maintenance process; And

is a schematic view of an aircraft having a maintenance program generation system.

There illustrates a gas turbine engine 10 having a main axis of rotation 9. The engine 10 includes an air intake 12 and a propulsion fan 23 which generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 includes a core 11 which receives core airflow A. The engine core 11 includes, in axial flow series, a low pressure compressor 14, a high pressure compressor 15, combustion equipment 16, high pressure turbine 17, low pressure turbine 19 and core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. Bypass airflow B flows through bypass duct 22. Fan 23 is attached to and driven by low pressure turbine 19 via shaft 26 and gearbox with epicyclic gears 30.

In use, core A airflow is accelerated and compressed by low pressure compressor 14 and directed into high pressure compressor 15 where further compression takes place. The compressed air discharged from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel F and the mixture is subjected to combustion. The resulting hot combustion products then expand through, and so drive, the high pressure and low pressure turbines 17, 19 before being vented through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 through a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reducer.

An exemplary arrangement for a reductant fan gas turbine engine 10 is shown in the . The low pressure turbine 19 (see ) drives shaft 26, which is coupled to sun gear, or sun gear, 28 of epicyclic gear arrangement 30. radially outward from sun gear 28 and meshing therewith. Carrier 34 forces planetary gears 32 to precess around sun gear 28 in synchronism while allowing each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via connecting rods 36 to the fan 23 in order to drive its rotation around the motor shaft 9. A ring or crown 38 which is coupled, via connecting rods 40, to a stationary support structure 24 lies radially outward from and meshing with planetary gears 32.

It should be noted that the terms "low pressure turbine" and "low pressure compressor" as used herein can be interpreted as referring to the lowest pressure turbine stages and the lowest pressure compressor stages respectively (this is i.e. not including the fan 23) and/or the turbine and compressor stages which are interconnected by the interconnecting shaft 26 with the lowest rotational speed in the engine (this is i.e. not including the gearbox output shaft which drives the fan 23). In some publications, the terms "low pressure turbine" and "low pressure compressor" referred to herein may also be referred to as "intermediate pressure turbine" and "intermediate pressure compressor". When such alternative nomenclature is used, fan 23 may be referred to as first stage compression or lowest pressure compression stage.

The planetary gear box 30 is shown by way of example in more detail in the . Each of sun gear 28, planet gears 32 and ring gear 38 includes teeth around its periphery to mesh with the other gears. However, for clarity, only exemplary parts of the teeth are shown in the . There are four planetary gears 32 illustrated, although it will be apparent to those skilled in the art that more or fewer planetary gears 32 may be provided within the scope of the claimed invention. Practical applications of a 30 planetary epicyclic gearbox typically include at least three 32 planetary gears.

The epicyclic gearbox 30 illustrated by way of example in Figures 2 and 3 is of the planetary type, in the sense that the planet carrier 34 is coupled to an output shaft via connecting rods 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 can be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held stationary, with the crown (or ring) 38 allowed to rotate. In such an arrangement, fan 23 is driven by ring gear 38. As a further alternative example, gearbox 30 may be a differential gearbox in which both ring gear 38 and planet carrier 34 are permitted. to turn.

It will be understood that the arrangement shown in Figures 2 and 3 is provided by way of example only, and various variations are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used to locate gearbox 30 within motor 10 and/or to connect gearbox 30 to motor 10. By way of further example, linkages (such as the connecting rods 36, 40 in the example of the ) between gearbox 30 and other parts of motor 10 (such as input shaft 26, output shaft and stationary structure 24) can have any desired degree of rigidity or flexibility . By way of further example, any suitable arrangement of bearings between rotating and stationary parts of the engine (e.g. between input and output shafts from the gearbox and fixed structures, such as the gearbox housing gears) may be used, and the disclosure is not limited to the exemplary arrangement of the . For example, where the gearbox 30 has a star arrangement (described above), those skilled in the art will readily appreciate that the arrangement of the output and support rods and the bearing locations would typically be different from those shown. for example in the .

Accordingly, this disclosure extends to a gas turbine engine having any arrangement of gearbox styles (e.g., star or planetary), support structures, input shaft arrangement and exit and landing locations.

Optionally, the gearbox can drive additional and/or alternative components (eg the intermediate pressure compressor and/or a precompressor).

Other gas turbine engines to which this disclosure can be applied can have alternative configurations. For example, such engines may have an alternating number of compressors and/or turbines and/or an alternating number of interconnecting shafts. As a further example, the gas turbine engine shown in the has a split-flow nozzle 18, 20, i.e. the flow through the bypass duct 22 has its own nozzle 18 which is separate and radially outside of the motor core nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flux through the bypass duct 22 and the flux through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be called a mixed-flow nozzle. One or both nozzles (whether mixed or split nozzle) can have a fixed or variable surface area.

Although the example described relates to a turbofan engine, the disclosure can apply, for example, to any type of gas turbine engine, such as, for example, an unducted rotor engine (of which the fan stage is not surrounded by a nacelle) or a turboprop. In some arrangements, the gas turbine engine 10 may not include a gearbox 30.

The geometry of the gas turbine engine 10, and its components, is defined by a conventional axis system, comprising an axial direction (which is aligned with the axis of rotation 9), a radial direction (in the direction of bottom up on the ) and a circumferential direction (perpendicular to the page in the view of the ). The axial, radial and circumferential directions are mutually perpendicular.

The fuel F supplied to the combustion equipment 16 may comprise a fuel based on fossil hydrocarbons, such as kerosene. Thus, the fuel F can comprise molecules of one or more of the chemical families of n-alkanes, iso-alkanes, cycloalkanes and aromatic compounds. Additionally or alternatively, Fuel F may include renewable hydrocarbons produced from biological or non-biological resources, otherwise known as Sustainable Aviation Fuel (SAF). In each of the examples provided, the fuel F may comprise one or more trace elements including, for example, sulfur, nitrogen, oxygen, inorganic materials and metals.

The functional performance of a given composition, or of a mixture of fuels to be used in the context of a given mission, can be defined, at least in part, by the capacity of the fuel to ensure the Brayton cycle of the engine at gas turbine engine 10. Parameters defining functional performance may include, for example, specific energy; energy density; thermal stability; and emissions, including particulate matter. A relatively higher specific energy (i.e. energy per unit mass), expressed in MJ/kg, can at least partially reduce the take-off weight, thus potentially providing a relative improvement in fuel efficiency. A relatively higher energy density (i.e. energy per unit volume), expressed in MJ/L, can at least partially reduce the take-off fuel volume, which can be particularly important for limited volume missions or military operations involving resupply. Relatively higher thermal stability (i.e. inhibition of fuel degradation or coking under thermal stress) can allow the fuel to withstand high temperatures in the engine and fuel injectors, thus ensuring potentially relative improvements in combustion efficiency. Reduced emissions, including particulate matter, can help reduce contrail formation, while reducing the environmental impact of a given mission. Other fuel properties may also be critical to functional performance. For example, a relatively lower freezing point (°C) can allow long range missions to optimize flight profiles; minimum aromatics concentrations (%) may ensure sufficient swelling of certain materials used in the construction of O-rings and gaskets that have been previously exposed to fuels high in aromatics; and, maximum surface tension (mN/m) can ensure sufficient spray break and fuel atomization.

The ratio of the number of hydrogen atoms to the number of carbon atoms in a molecule can influence the specific energy of a given composition or fuel mixture. Fuels with higher ratios of hydrogen atoms to carbon atoms can have higher specific energies in the absence of bond stress. For example, fossil hydrocarbon fuels may include molecules with approximately 7 to 18 carbons, with a significant portion of a given composition coming from molecules with 9 to 15 carbons, with an average of 12 carbons.

ASTM International (ASTM) D7566, Standard Specification for Jet Fuels Containing Synthesized Hydrocarbons (ASTM 2019c), approves a number of sustainable aviation fuel blends comprising between 10% and 50% aviation fuel sustainable (the remainder comprising one or more fossil hydrocarbon fuels, such as kerosene), with additional compositions pending approval. However, the aviation industry anticipates that sustainable aviation fuel blends comprising up to (including) 100% sustainable aviation fuel (SAF) will eventually be approved for use.

Sustainable aviation fuels can include one or more of n-alkanes, iso-alkanes, cyclo-alkanes and aromatics, and can be produced, for example, from one or more of a synthesis (syngas); lipids (eg fats, oils and fats); sugars; and alcohols. Thus, sustainable aviation fuels may include lower aromatics and/or sulfur content, compared to fossil hydrocarbon fuels. Additionally or alternatively, sustainable aviation fuels may include a higher content of iso-alkanes and/or cyclo-alkanes, compared to fossil hydrocarbon fuels. Thus, in some examples, sustainable aviation fuels may include a density between 90% and 98% that of kerosene and/or a calorific value between 101% and 105% that of kerosene.

Due, at least in part, to the molecular structure of sustainable aviation fuels, sustainable aviation fuels can provide benefits including, for example, one or more of higher energy density; higher specific energy; higher specific heat capacity; higher thermal stability; higher lubricity; lower viscosity; lower surface tension; a lower freezing point; lower soot emissions; and lower CO ₂ emissions, compared to fossil hydrocarbon fuels (eg, when burning in combustion equipment 16). Therefore, compared to fossil hydrocarbon based fuels, such as kerosene, sustainable aviation fuels can result in a relative decrease in specific fuel consumption and/or a relative decrease in maintenance costs.

An aircraft 1 comprising two gas turbine engines 10 according to one of the examples described here is illustrated in the . In this example, the aircraft 1 comprises two gas turbine engines 10, but in other examples it may comprise one or more gas turbine engines. The aircraft 1 further comprises an aircraft fuel supply circuit located on board the aircraft, which is suitable for supplying fuel F to each of the gas turbine engines 10 to be burned in the equipment of combustion engine 16 as described above. The aircraft fuel system is arranged to supply fuel to an engine fuel system provided on each of the gas turbine engines 10. The engine fuel system and the aircraft fuel system aircraft together form the (global) fuel circuit of the aircraft 1 in which the fuel is stored, distributed to the engine and subjected to combustion. The aircraft fuel system includes any component that can store fuel, or through which fuel flows when in use or when refueling.

The aircraft fuel supply system includes an aircraft fuel source arranged to contain fuel F to be supplied to the gas turbine engines. Within the meaning of the present application, the term "fuel source" means either 1) a single fuel tank or 2) a plurality of fuel tanks, which may or may not be fluidly interconnected. In the present example, the fuel source comprises a plurality of wing fuel tanks 53, where at least one wing fuel tank is located in the left wing and at least one wing fuel tank is located in the right wing, and a central fuel tank 55 located mainly in the fuselage of the aircraft 1. Each of the central fuel tank 55 and the wing fuel tanks 53 may comprise a plurality of fluidly interconnected fuel tanks not shown in the figures.

For balancing purposes, one or more fuel tanks 53 in the left wing may be fluidly connected to one or more fuel tanks 53 in the right wing, as shown by the dotted lines on the . This can be done via the central fuel tank 55, or by bypassing the central/central fuel tank(s), or both (for maximum flexibility and safety). In still other examples, the fuel source may include a separate trim fuel tank to balance the aircraft in flight (not shown in the figures).

There illustrates the loading of fuel onto the aircraft 1 from a fuel storage container 60. The fuel storage container 60 may be transported by a fuel supply vehicle (e.g., tank truck) or can be a fixed storage container from which the aircraft 1 can be refueled. The aircraft fuel system includes a fuel line connection port 62, which is coupled to a fuel loading line 61 during refueling. The fuel loading line 61 may comprise a fuel pipe of known design. The fuel line connection port 62 is fluidly coupled to the fuel tanks 53, 55 of the aircraft 1 by a fuel transmission line or lines 63 on board the aircraft so that fuel received via the fuel charging line 61 is transferred and stored in the fuel tanks 53, 55. The fuel charging line 61 and the fuel transmission line 63 may together form a fuel supply line used to supply fuel to the fuel tanks 53, 55 on board the aircraft 1 from the fuel storage container 60. In some examples, the fuel transmission line(s) 63 may/may not be present , with fuel instead being delivered directly from a fuel line connection port for each fuel tank (or set of interconnected fuel tanks). The fuel loading line 61 and storage container (and any associated control or pump components) can form a fueling system for the aircraft.

Fuel characteristics

As used herein, the term "fuel characteristics" refers to intrinsic fuel properties such as fuel composition, not variable properties such as volume or temperature. Examples of fuel characteristics of a fuel include:

(i) the percentage of sustainable aviation fuel in the fuel;

(ii) the aromatic hydrocarbon content of the fuel;

(iii) the multi-aromatic hydrocarbon content of the fuel;

(iv) the percentage of nitrogen-containing species in the fuel;

(v) the presence or percentage of a trace species or trace element in the fuel (for example, a trace substance inherently present in the fuel, or deliberately added to act as a tracer);

(vi) the hydrogen to carbon ratio of the fuel;

(vii) distribution of hydrocarbon fuel;

(viii) the level of non-volatile particulate matter (nvPM) emissions during combustion (e.g. during combustion for a given combustion chamber design, under given operating conditions (FAR, T30, chamber mode combustion, etc.));

(ix) the naphthalene content of the fuel;

(x) fuel sulfur content;

(xi) the cycloparaffin content of the fuel;

(xii) the oxygen content of the fuel;

(xiii) thermal stability of the fuel (eg thermal degradation temperature);

(xiv) fuel coking level;

(xv) an indication that the fuel is a fossil fuel, for example fossil kerosene; And

(xvi) one or more properties such as density, viscosity, calorific value and/or heat capacity.

As used herein, T30, T40, and T41, and all other numbered pressures and temperatures, are defined using position numbering listed in SAE AS755, specifically:

• T30 = Total Temperature at the Outlet of the High Pressure Compressor (HPC);

• T40 = Total Temperature at the Combustion Chamber Outlet;

• T41 = Total Temperature at the Inlet of the High Pressure Turbine (HPT) Rotor.

Piezoelectric sensor

Determination of fuel characteristics during refueling using a piezoelectric sensor:

With reference to the , an example of a fuel characteristic determining system 114 is illustrated, located on board aircraft 1. The fuel characteristic determining system 114 in this example is arranged to determine one or more fuel characteristics of the fuel F loaded on the aircraft 1, these characteristics being one of those described or claimed here.

Further details of the fuel characteristic determining system 114 are illustrated in . The fuel characteristic determining system 114 generally includes a sensor 115, which includes a piezoelectric crystal 116. The piezoelectric crystal 116 is arranged so that it is exposed to fuel F, which flows through the sensor 115. In In the present example, fuel loaded onto aircraft 1 passes through sensor 115 so that piezoelectric crystal 116 is exposed to the fuel. Sensor 115 includes a fuel inlet 115a and a fuel outlet 115b, and a fuel conduit 115c arranged in fluid communication therebetween. In the present example, the sensor 115 is located on board the aircraft 1 and is arranged to receive the fuel F flowing through the fuel transmission line 63, that is to say the fuel flowing from the fuel line connection port 62 to the fuel tanks 53, 55. In the present example, the sensor 115 is arranged so that all fuel flowing through the transmission line 63 is introduced into the sensor inlet 115a, flows through fuel line 115c and exits via fuel outlet 115b to continue to the fuel tanks (i.e. the sensor is connected in series between the fuel line connection 62 and fuel tanks). In other examples, sensor 115 may be connected in parallel so that only a portion of the fuel is redirected from transmission line 63, flows through the sensor, and then returned to fuel transmission line 63. or to the fuel tanks.

The sensor 115 is arranged to measure a vibration parameter of the piezoelectric crystal 116. The vibration parameter can be a vibrational mode of the piezoelectric crystal such as a resonant frequency at which the crystal oscillates. In the present example, the sensor comprises a resonant frequency measurement module 116a arranged to measure a resonant frequency of the crystal by applying a voltage to an electrode near or on the crystal 116. This causes the distortion of the crystal 116 in a electric field created by the voltage. Once the field is removed, the piezoelectric crystal 116 generates an electric field when it returns to its previous shape, generating a voltage. This results in the crystal behaving like an RLC circuit, consisting of an inductor, a capacitor and a resistor with a corresponding resonant frequency as would be known in the art.

The inventors have determined that the resonant frequency of crystal 116 varies according to deposits formed on its surface by the fuel to which it is exposed. By measuring the resonant frequency or other vibrational parameter (or its change over time), the amount of surface deposition on the crystal surface can be determined. In the present example, the fuel characteristic determining system 114 further comprises a fuel characteristic determining module 117 arranged to determine one or more fuel characteristics of the fuel based on the vibration parameter. The fuel characteristics determining module 117 receives the vibration parameter from the sensor 115 so that one or more fuel characteristics can be calculated.

In some examples, the surface deposits can be removed between different uses of the fuel characterizing system, for example, by exposing the crystal to a different type of fuel which removes any deposits from the surface of the crystal. In other examples, the sensor may comprise means for cleaning the surface of the piezoelectric crystal, or means for allowing replacement of the crystal, between uses (for example between flights of the aircraft). This can help determine the fuel characteristics for each use of the aircraft. In yet other examples, surface deposits may not be removed between uses, in which case the sensor 115 is arranged to determine a maximum change in vibrational parameter since the piezoelectric crystal was last cleaned, reset or replaced. time. This can help determine an accumulation of surface deposits over multiple uses of the aircraft (e.g., multiple flights).

For example, a fuel characteristic determined based on the vibration parameter may include fuel oxygen content, fuel thermal stability, and/or fuel coking level. The amount of surface deposit formed and detected on the piezoelectric crystal will depend on these characteristics/properties of the fuel allowing them to be determined based on the measurement of the vibration parameter. In other examples, other fuel characteristics may be determined or inferred based on the measured vibration parameters or other fuel characteristics determined from the vibration parameters. For example, the hydrocarbon distribution of the fuel, the percentage of SAF in the fuel or the aromatic hydrocarbon content in the fuel (e.g. mass or volume percentage) can be determined.

The fuel characteristics determination module 117 is arranged to transmit the determined fuel characteristic(s) to the electronic engine controller EEC 42 (or to another control system of the aircraft). In some examples, determination module 117 may be part of EEC 42 of one or more of the aircraft's gas turbine engines. Once received at the EEC, the fuel characteristics can be used to provide information about the fuel that is supplied from the fuel tanks to the engine so that the operation of the gas turbine engine(s) can be adapted accordingly. In yet other examples, determination module 117 may be part of sensor unit 115, which is in communication with the EEC.

In order to determine the one or more fuel characteristics, the determination module 117 may be arranged to compare a measured vibration parameter to a look-up table of expected vibration parameter values of fuels with known fuel characteristics to determine the corresponding characteristics of the fuel. fuel to which the crystal was exposed. This can allow a range of fuel characteristics to be determined based on a measurement of the surface deposit formed on the piezoelectric crystal. In yet other examples, the determination module may determine a surface deposit level formed on the crystal using the measured resonant frequency of the crystal, then compare the determined surface deposit level to values in a look-up table . Those skilled in the art will understand that this amounts to comparing the resonant frequency.

In some examples, an absolute value of the vibration parameters may be measured and used by determination module 117 to determine the one or more fuel characteristics. In other examples, a change in the vibrational parameter may be used. For example, a deviation from an expected value if no surface deposits are present can be measured, or a change in the vibration parameter over time can be measured. This can allow a slow buildup of surface deposits on the crystal to be measured and used to infer the fuel characteristic(s). Using this method, the characteristics of the fuel used by the aircraft over a long period of time can be determined.

The determination module 117 can also base the determination of the fuel characteristics on one or more performance parameters of the engine or of the aircraft. This may include a fuel temperature to which the surface of the piezoelectric crystal has been exposed. This can allow expected vibration parameters formed by fuels of known characteristics at known temperatures to be compared to measured data to determine fuel characteristics. In other examples, other operating parameters may be used by the determination module 117 so that a relevant fuel characteristic can be reliably determined.

In the examples described above, the fuel characteristic determining system 114 is located on board the aircraft 1 so that the fuel in the fuel transmission line 63 flows therethrough before reach the fuel tanks 53, 55. In other examples, the fuel characteristic determining system 114 may be arranged to use fuel within, or sampled from, one of the fuel tanks 53, 55. In such an example, the sensor 115 may be located in the fuel tank so that the fuel may be exposed to the piezoelectric crystal 116. The sensor may therefore include a piezoelectric crystal mounted on an interior wall of the fuel tank so that it is exposed to the fuel inside the tank. In other examples, fuel may be sampled from a fuel tank on board the aircraft and pass through sensor 115.

In other examples, the fuel characteristic determining system 114, or at least a portion thereof, may be located separately from the aircraft 1. For example, it may be included in the fuel loading line 61 so that it can detect the properties of the fuel before it reaches the aircraft. In certain examples, the sensor 115 can be located in the fuel loading line, or elsewhere separately from the aircraft 1, and arranged to transmit a vibration parameter to a determination module 117 located on board the aircraft 1, where it can be communicated to a control module of the engine (for example the EEC) or of the aircraft. In yet other examples, the fuel characteristic determining system 114 may be located entirely external to the aircraft. In such an example, the fuel characteristics determining module 117 can determine a fuel characteristic which is then communicated to the aircraft 1 (for example to an engine control module or to the engines 10). In this example, a data transfer link may be provided (eg, wireless or wired data connection) and may be used to communicate fuel characteristics to the aircraft from the fuel characteristic determination system 114. In some examples, the data transfer may be performed manually by a user, for example, a technician or other system operator may obtain the fuel characteristics from the determination system 114 and provide them manually to a fueling module. order on board the aircraft.

Determination of fuel characteristics in the engine using a piezoelectric sensor

There illustrates another example of the fuel characteristic determination system 114 described above. The fuel characteristics determination system of the similarly comprises a sensor 115 and a fuel characteristics determining module 117 arranged to measure one or more fuel characteristics based on a vibrational parameter (eg, resonant frequency) of a piezoelectric crystal exposed to the fuel inside the sensor. In this example, the fuel characteristic determining system 114 is arranged to measure the effects of exposure of the piezoelectric crystal 116 to fuel during operation of the gas turbine engine 10.

There depicts a schematic view of a portion of the aircraft fuel system and combustion equipment 16 of gas turbine engine 10. Combustion equipment 16 includes a plurality of fuel injectors (not shown in there ) arranged to inject fuel into a tubular combustion chamber. Fuel is supplied to the combustion equipment 16 by a fuel delivery controller 107 under the control of the EEC 42. Fuel is delivered to the fuel delivery controller 107 by a fuel pump 108 from a fuel source 109 on board the aircraft 1 (for example one or more fuel tanks 53, 55 as described above). The fuel delivery regulator 107 and combustion equipment 16 may be of known design, and may be arranged for staged (lean burn) combustion or rich burn.

In this example, a vibration parameter is measured for fuel when used by the engine. The sensor 115 in this example is arranged to measure the effect of the fuel exposed to the piezoelectric crystal 116 at any point in the fuel system on board the aircraft which is upstream of the combustion equipment 16 (for upstream of the combustion equipment fuel injectors 16) and downstream of the fuel source 109 from which fuel is supplied (e.g. downstream of the one or more fuel tanks 53, 55 forming the source fuel). In some examples, sensor 115 is located at a point within the engine fuel system, such as in a fuel line within or forming part of gas turbine engine 10 (rather than being on the aircraft 1 on which the gas turbine engine 10 is mounted). In some examples, it is located at a point immediately before the fuel enters the combustion chamber 16. In still other examples, the sensor 115 is located at a point within the fuel supply circuit. aircraft fuel, for example, before it enters part of the gas turbine engine 10.

In the example described herein, the engine fuel system further includes a heat management system having a heat exchanger 118. The heat exchanger is arranged to transfer heat between the fuel and an oil system of the engine, for example, transferring heat from the oil system into the fuel in order to cool the oil and warm the fuel. As illustrated on the , sensor 115 is located in the engine fuel system at a point at which fuel has been heated by heat exchanger 118 during operation of gas turbine engine 10. The inventors have observed that during engine operation 10 fuel heating can cause thermal degradation of the fuel which causes deposits to form on the surface of the piezoelectric crystal 116. For example, fuel coking can occur when fuel is heated by the engine heat exchanger to provide cooling. The inventors have determined that the quantity of deposit formed, and therefore the vibrational parameters of the crystal, depend on the susceptibility of the fuel to thermal degradation. As the susceptibility of fuel to thermal degradation varies between different fuels, a sensitive measure of thermal degradation can be used to determine the characteristics of the fuel used by the engine. For example, the SAF content of the fuel can be determined, since a fuel rich in SAF may be associated with a lower degree of thermal degradation. In the present example, the fuel characteristics determining system is therefore arranged to determine the characteristics of the fuel based on the measured level of thermal degradation of the fuel.

In the example of the , the fuel characteristics determination module 117 is arranged to compare the measured vibration parameter (for example the resonance frequency) or the level of surface deposit with a look-up table of values corresponding to those expected for fuels of known characteristics . The fuel characteristics determining module 117 may further base the comparison with the look-up table on a fuel temperature to which the piezoelectric crystal is exposed with temperature values in the look-up table at which changes in vibration parameters are exposed. expected for known fuel characteristics. Thus, the measured surface deposition occurring at a certain temperature can be referenced in the look-up table against that of a known fuel at the same or similar temperature.

In the examples currently described, the fuel characteristics determining module 117 is arranged to determine the one or more fuel characteristics based solely on the determined vibration parameter of the piezoelectric crystal 116. In other examples, the determining module 117 may be arranged to combine the vibration parameter information with inputs from other sensors or other methods of determining fuel characteristics disclosed herein. This may allow a wider range of fuel characteristic types to be inferred or improve the accuracy of fuel characteristic determination.

There illustrates a method 1014 of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft which may be performed by the fuel characteristic determination systems 114 shown in Figures 5, 6 and 7. Method 1014 includes exposing 1015 the surface of a piezoelectric crystal to fuel; the measurement 1016 of a vibration parameter of the piezoelectric crystal; and determining 1017 one or more fuel characteristics of the fuel based on the vibration parameter. Any of the features described above in connection with Figures 5, 6 and 7 may be incorporated into the method of , and will therefore not be repeated here.

Seal inflation sensor

Determination of fuel characteristics during refueling using an inflation sensor

With reference to the , another example of a fuel characteristic determining system 119 is illustrated, located on board the aircraft 1. The fuel characteristic determining system 119 in this example is arranged to determine one or more fuel characteristics of the fuel F loaded on the aircraft 1, these characteristics being one of those described or claimed here.

Further details of the fuel characteristic determining system 119 are illustrated in the . The fuel characteristics determining system 119 generally comprises a detection device 120 which is located in the fuel system of the aircraft. The sensing device 120 includes a sensor component 121 formed from a sealing material. In some examples as described later, the sealing material is formed from the same material as one or more seals provided in the fuel supply circuit. The one or more seals are exposed to fuel during use of the aircraft fuel system, and are configured to swell upon contact with fuel. In other examples, the sealing material may be different from those used elsewhere in the aircraft or engine fuel system. The sealant may be a nitrile sealant (eg, nitrile rubber or Buna-N). Gaskets can be any gaskets that are exposed to fuel in the aircraft fuel system.

In the present example, fuel loaded onto the aircraft passes through sensing device 120 and is exposed to sensor component 121. Sensing device 120 includes a fuel inlet 120a and a fuel outlet 120b, and a conduit 120c fuel arranged in fluid communication therebetween. In the present example, the detection device 120 is located on board the aircraft and is arranged to receive the fuel flowing through the fuel transmission line 63, that is to say the fuel flowing from the fuel line connection port 62 to the fuel tanks 53, 55. The sensor is arranged such that all fuel flowing through the transmission line 63 is introduced into the inlet 120a, flows through the fuel line 120c, and exits via the fuel outlet 120b to continue to the fuel tanks (i.e., the sensing device is connected in series between the fuel line connection port fuel 62 and fuel tanks). In other examples, sensing device 120 may be connected in parallel so that only a portion of the fuel is redirected from transmission line 63, flows through sensing device 120, and then returned to line. fuel transmission 63 or to the fuel tanks.

The fuel characteristics determining system further comprises a sensor 122 arranged to measure a swelling parameter of the sealant from which the sensor component 121 is made. The swelling parameter indicates the degree to which the sealant has changed in shape and/or size in response to exposure of fuel F to its surface. The inventors have determined that the degree of swelling of the sensor component 121 varies depending on the properties of the fuel F to which it is exposed. For example, the gasket material from which the sensor component 121 is made can expand or contract depending on the characteristics of the fuel. By measuring the expansion or contraction of the sealant (or its change over time), various properties of the fuel F can be determined based on the corresponding swelling parameter.

Referring again to the , the sensor component 121 of the present example is fixedly mounted in the sensing device 120 via a fixing structure 123a. As can be seen schematically in the , a portion of sensor component 121 is fixedly coupled to sensing device 120 such that it is free to expand or contract in response to exposure to fuel. Sensor 122 further includes a gauge 123b to which the sealant is fixedly mounted. In the present example, gauge 123b is fixedly mounted in sensing device 120 via gauge attachment structure 123c. Gauge 123b is arranged to detect movement of part of sensor component 121 resulting from its expansion or contraction. Gauge 123b may be a pressure sensing device arranged to sense pressure exerted thereon by sensor component 121. As can be seen in Fig. , the sensor component is constrained between the attachment structure 123a and the gauge 123b so that any change in its size will result in a change in the pressure applied to the gauge 123b.

In other examples, other methods of detecting expansion or contraction of sensor component 121 may be used. For example, the gauge can be arranged to detect a change in the physical shape of the sensor component. The gauge may, for example, be arranged to detect a change in the physical position of an unconstrained surface of the sensor component to determine the level of expansion or contraction.

The fuel characteristic determining system 119 of the present example further comprises a fuel characteristic determining module 124 arranged to determine one or more fuel characteristics of the fuel F based on the inflation parameter. The fuel characteristics determining module 124 receives the inflation parameter from the sensor 122 so that the one or more fuel characteristics can be calculated.

The fuel characteristic determining system 119 of the present example may be arranged to determine one or more of the fuel characteristics defined or claimed herein based on the inflation parameter. For example, the fuel characteristic determining system 119 may be arranged to determine a hydrocarbon distribution of the fuel, for example a property related to the aromatic hydrocarbon content of the fuel. The one or more fuel characteristics determined may therefore include the mass or volume percentage of aromatic hydrocarbon compounds in the fuel. The inventors have determined that the aromatics content of the fuel is related to the swelling of the sealing material, with different levels of aromatics resulting in different levels of swelling. The measurement of the swelling parameter can therefore be used to determine the content of aromatic compounds in the fuel. Other fuel characteristics can, however, be determined based on the inflation parameter. For example, other fuel characteristics such as the percentage of sustainable aviation fuel present in the fuel can be determined (e.g. by being inferred from aromatics content, or due to change in fuel material size). resulting tightness compared to a fuel of known characteristics). In other examples, the fuel characteristic may be the cycloparaffin content of the fuel.

The fuel characteristics determination module 124 is arranged to transmit the determined fuel characteristic(s) to the electronic engine controller EEC 42 (or to another control module of the aircraft). In some examples, the determination module 124 may be part of the EEC 42 of any one or more of the gas turbine engines of the aircraft. Once received at the EEC, the fuel characteristics can be used to provide information about the fuel that is supplied from the fuel tanks to the engine so that the operation of the gas turbine engine(s) can be adapted accordingly. In still other examples, the determination module 124 may be part of the detection device 120, which is in communication with the EEC.

In order to determine the one or more fuel characteristics, the determination module 124 may be arranged to compare a swell parameter to a look-up table of expected swell parameter values of fuels with known fuel characteristics to determine the corresponding characteristics. fuel to which the sensor component has been exposed. This can help determine a variety of fuel characteristics.

In some examples, an absolute value of the inflation parameters may be measured and used by the determination module 124 to determine the one or more fuel characteristics. In other examples, a change in the swelling parameter can be used. For example, a deviation from an expected value can be measured, or a change in the swelling parameter over time can be measured. This can allow a slow change in expansion or contraction of the sealing material to be measured and used to determine the fuel characteristic(s). Using this method, the characteristics of the fuel used by the aircraft over a long period of time can be determined.

In the examples described above, the fuel characteristic determining system 119 is located on board the aircraft 1 so that the fuel in the fuel transmission line 63 flows therethrough before reach the fuel tanks 53, 55. In other examples, the fuel characteristic determining system 119 may be arranged to use fuel within, or sampled from, one of the fuel tanks 53, 55. In such an example, the sensing device 120 may be located in the fuel tank so that the fuel may be exposed to the sensor component 121. The sensing device may therefore include the sensor component mounted on a inner wall of the fuel tank so that it is exposed to the fuel inside the tank. In such an example, the inlet 120a, outlet 120b and conduit 120c structure may not be necessary. Attachment structure 123a, gauge attachment structure 123c, and gauge 123b may still be provided, however. In other examples, fuel may be sampled from the tank and passed through the sensing device 120.

In other examples, the fuel characteristic determining system 119, or at least a portion thereof, may be located separately from the aircraft 1. For example, it may be included in the fuel loading line 61 so that it can detect the properties of the fuel before it reaches the aircraft. In certain examples, the detection device 120 can be located in the fuel loading line, or elsewhere separately from the aircraft 1, and arranged to transmit an inflation parameter to a fuel characteristics determination module 124 located on board of the aircraft 1, where it can be in communication with a control module of the engine (for example the EEC) or of the aircraft. In yet other examples, the fuel characteristic determining system 119 may be located entirely external to the aircraft. In such an example, the fuel characteristics determining module 124 can determine a fuel characteristic which is then communicated to the aircraft 1 (for example to an engine control module or to the engines 10). In this example, a data transfer link may be provided (eg, wireless or wired data connection) and may be used to communicate fuel characteristics to the aircraft from the fuel characteristic determination system 119. In some examples, the data transfer may be done manually by a user, for example, a technician or other system operator may obtain the fuel characteristics from the fuel characteristic determination system 119 and provide them manually. to a control module on board the aircraft.

Determination of fuel characteristics during engine operation using an inflation sensor

There illustrates another example of the fuel characteristic determination system 119 described above. The fuel characteristics determination system of the similarly comprises a sensing device 120 and a determination module 124 arranged to measure one or more fuel characteristics based on an inflation parameter. The swelling parameter is determined by measuring the expansion or contraction of a sensor component exposed to fuel in the sensing device 120. In this example, the fuel characteristics determining system 119 is arranged to measure the effects of exposure of fuel to sensor component 121 during operation of gas turbine engine 10.

There depicts a schematic view of a portion of the aircraft fuel system and combustion equipment 16 of gas turbine engine 10. Combustion equipment 16 includes a plurality of fuel injectors (not shown in there ) arranged to inject fuel into a tubular combustion chamber. Fuel is supplied to the combustion equipment 16 by a fuel delivery controller 107 under the control of the EEC 42. Fuel is delivered to the fuel delivery controller 107 by a fuel pump 108 from a fuel source 109 on board the aircraft 1 (for example one or more fuel tanks as described above). The fuel delivery regulator 107 and combustion equipment 16 may be of known design, and may be arranged for staged (lean burn) combustion or rich burn.

In this example, an inflation parameter is measured for the fuel when it is used by the engine. The sensing device 120 in this example is arranged to measure the effect of fuel exposed to the sensor component 121 at any point in the aircraft fuel system that is upstream of the combustion equipment 16 (e.g. in upstream of the combustion equipment fuel injectors 16) and downstream of the fuel source 109 from which fuel is supplied (e.g., downstream of the one or more fuel tanks 53, 55 forming the fuel source ). In some examples, sensing device 120 is located at a point within the engine fuel system such as in a fuel line within or forming part of gas turbine engine 10 (rather than be on the aircraft 1 on which the gas turbine engine 10 is mounted). In some examples, it is located at a point immediately before the combustion of the fuel (for example, immediately before entering the combustion chamber). In yet other examples, the sensing device 120 is located at a point within the aircraft fuel system, such as before it enters a portion of the gas turbine engine. 10.

In the example shown in the , the sensing device 120 is arranged such that all fuel flowing to the combustion chamber passes through it (eg, it is arranged in series). In other examples, only a portion of the fuel may pass through sensing device 120. For example, the sensing device may be located in the fuel system bleed line where fuel is sampled from the fuel system. fuel supply to the combustion chamber (e.g. before or after fuel mixing).

In the examples currently described (for example, as shown in Figures 9, 10 and 11), the fuel characteristic determination module 124 is arranged to determine the one or more fuel characteristics based solely on the determined inflation parameter of the sealant component 121. In other examples, the determination module 124 may be arranged to combine the inflation parameter information with inputs from other sensors or other methods of determining fuel characteristics disclosed here. This may allow a wider range of fuel characteristic types to be inferred, or improve the accuracy of fuel characteristic determination.

In one of the examples described above, the fuel characteristics determination system is arranged to generate an alert signal if the inflation parameter is beyond an alert threshold or outside a acceptable range, i.e. above a first upper threshold or below a second lower threshold. The alert signal may be generated by the fuel characteristics determination module 124, or may be generated at the sensor 122. The alert signal may be generated based on a comparison with an alert threshold , for example, if the swelling parameter exceeds or falls below the alert threshold. For example, if the swelling parameter indicates that the swelling of the material has fallen below a safe threshold, the alert signal can be generated to indicate that the seals made of the same material or of a material similar on board the aircraft may contract to a degree that would affect their sealing capability. This can be used to provide an indication that there is a risk of insufficient sealing by gaskets that rely on swelling in size when exposed to fuel during use.

There illustrates a method 1021 of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft. Method 1021 may be performed by the fuel characteristic determining systems 119 shown in Figures 9, 10 and 11. Method 1021 includes exposing 1022 the surface of a component formed from a material of nitrile seal (for example, sensor component 121); measuring 1023 a swelling parameter of the sealing material; and determining 1024 one or more fuel characteristics of the fuel based on the swelling parameter. The method may further comprise generating 1024a an alert signal if the swelling parameter is outside an alert threshold (eg above or below the threshold). Any of the features described above in connection with Figures 9, 10 and 11 can be used in method 1021, and will therefore not be repeated here.

As discussed more generally below, the method 1021 of determining one or more fuel characteristics may be part of an aircraft operating method 1065. In such a method, the aircraft, or more specifically an engine gas turbine engine mounted on the aircraft, operates according to the one or more fuel characteristics determined using method 1021. In some examples, operating the aircraft according to the fuel characteristics may include providing a fuel having at least one characteristic different from those measured at the combustion chamber of the gas turbine engine. This may be accomplished by refueling using fuel with different characteristics the next time the aircraft is refueled, or may include controlling the fuel supply from different fuel sources on board the aircraft. For example, fuel from an alternate fuel tank containing fuel of a different characteristic may be used, or a different blend of fuels may be used from two or more different sources.

Supplying a fuel having a different characteristic may include: supplying a fuel having a relatively higher aromatics content against which the fuel characteristics have been determined; (ii) the supply of a fuel with a lower SAF content against which the fuel characteristics have been determined; and/or iii) the supply of fossil kerosene fuel. This may allow the use of fuel causing greater expansion of the seal material, which may improve the performance of other seals provided in the aircraft fuel system by increasing their inflation response to fuel. In other examples, other operating parameters of the aircraft or gas turbine engine may be changed in response to the determined fuel characteristics.

Determination of fuel characteristics using a sensor component made of a material matching that of other seals on board the aircraft:

In the examples described above, the sealing material of sensor component 121 is a nitrile sealing material. The specific material chosen to be used as the sensor can be independent of any other type of sealing material used on board the aircraft. The material can therefore be chosen according to a desired response to certain fuel characteristics to be determined. In other examples, however, the gasket material is not limited to a specific type of material, but is chosen so that it is the same as the material of one or more gaskets which are used on board the aircraft.

An example where the sealing material matches that of the aircraft is shown in the . Features common to Figures 9, 10 and 11 are labeled accordingly. A propulsion system 10a for an aircraft is illustrated, having gas turbine engines 10 and a fuel system 10b comprising fuel tanks 53, 55 arranged to contain fuel to supply the gas turbine engine. In other examples, any number of gas turbine engines and fuel tanks may be provided. The fuel circuit 10b may correspond to the “aircraft fuel circuit” presented above, comprising the engine fuel circuit and the aircraft fuel supply circuit.

The fuel circuit 10b further includes seals 125 (only one of which is labelled). The seals in the present examples are arranged to seal the fuel lines extending between the center (fuselage) fuel tank 55 and the wing fuel tanks 53 and the gas turbine engines 10 The seals 125 are exposed to fuel from the fuel tanks 53, 55 during aircraft operation. In other examples, the seals may be provided for any other use in the aircraft fuel system that are exposed to fuel during use. They can, for example, be part of a fuel pump. Seals 125 are of a type arranged to swell in response to exposure to fuel during use to provide a seal, and may be formed from a nitrile seal material.

The propulsion system further comprises a detection device 120 located in the fuel circuit of the aircraft 1. The detection device may comprise the same components as those described above in relation to FIGS. 10 and 11, and comprises a sensor component 121 which is exposed to fuel in the fuel system. The sensor component is formed from the same material as the 125 gaskets provided in the aircraft fuel system. The sensing device 120 is arranged to sense or determine a swelling parameter of the sealant component as described above.

The inventors have determined that by detecting the swelling of a sensor component made of the same material as the seals otherwise provided in the aircraft fuel system, the degree of swelling of the seals themselves can be determined. This allows indirect monitoring of the degree of seal swelling, without having to dismantle the components for inspection. Since the seals 125 are intended to swell to provide a sufficient seal, measuring the swelling of the sensor component 121 can provide an indirect measure of their performance. For example, a reduction in the swelling of sensor component 121 below a threshold may indicate that the other seals in the aircraft fuel system would not have a sufficient degree of swelling to provide a seal. . The detection device can be arranged to generate an alert signal if the inflation parameter falls below an alert threshold to indicate that insufficient inflation of the seals 125 may occur.

The sensing device 120 may be arranged to receive fuel during use of the gas turbine engine. It may, for example, be located as described in connection with the .

In the present example, the propulsion system further includes a fuel characteristics determination module 124 as described above to allow fuel characteristics to be determined based on the inflation parameter. This can be done as described above in relation to Figures 9, 10 and 11. Any feature described above in relation to these figures can be used in combination with the example shown in Figure 9, 10 and 11. .

In other examples, the fuel characteristics determination module 124 may not be provided. In such instances, the fuel swell parameter may be used to indicate the swell of the seals 125, rather than helping to determine the fuel characteristics.

There illustrates a method 1025 that can be performed using the example of . The method 1025 includes: exposing 1026 one or more fuel system seals of the aircraft to fuel in the fuel system; the exposure 1027 of the sensor component 121 made of the same material as the one or more fuel seals, the component being located in the fuel circuit of the aircraft; and measuring 1028 a swelling parameter of the sealant. The method 1025 may further include determining 1029a one or more fuel characteristics of the fuel based on the swell parameter and/or generating 1029b an alert signal if the swell parameter exceeds a threshold of alert. Any of the features described above in connection with Figures 9 through 13 may be incorporated into the method of .

Trace substance sensor

Determination of fuel characteristics during refueling using a trace substance sensor:

With reference to the , another example of a fuel characteristic determining system 126 is illustrated, located on board the aircraft 1. The fuel characteristic determining system 126 in this example is arranged to determine one or more fuel characteristics of the fuel loaded on the aircraft 1, these characteristics being one of those described or claimed here. In this example, the fuel characteristic is determined based on the detection of trace substances in the fuel F.

Further details of the fuel characteristic determining system 126 are illustrated in . The fuel characteristics determining system 126 generally includes a trace sensor 127 which is arranged to measure one or more trace substance parameters of the fuel supplied to the aircraft fuel tanks 53, 55.

The trace substance parameters measured by sensor 127 are each associated with a respective trace substance in the fuel. By trace substance, we mean a substance in the fuel that has a very low concentration (or other measure of quantity), i.e. it is present in trace form. A trace substance can include any type of substance that is present in a trace state, such as chemical elements, compounds, trace molecules, etc. The trace substance can be a substance which, depending on its presence, absence or amount in the fuel, one or more characteristics of the fuel can be directly determined or inferred. The trace substance parameter(s) may, in some instances, indicate the presence of a concentration of the associated trace substance in the fuel. It can therefore be a concentration measured as the mass fraction of a trace substance in the fuel (e.g. a concentration in parts per million). In other examples, the trace substance parameter(s) may indicate the absence or presence (e.g. within measurement limits) of an associated trace substance in the fuel.

The fuel characteristic determination system 126 further comprises a determination module 128 arranged to determine one or more fuel characteristics of the fuel based on the trace substance parameters. The determination module 128 is arranged to receive the trace substance parameter from the trace sensor 127 so that one or more fuel characteristics can be calculated.

The inventors have determined that by measuring trace substances present or absent in a fuel, the characteristics of this fuel can be determined directly or indirectly.

In one example, the trace substance parameter measured by trace sensor 127 is associated with a fuel sulfur content. The trace substance parameter may in this example be a concentration (or other quantity measure) of sulfur molecules in the fuel. The inventors have observed that for all the SAF production routes, the resulting fuel is characterized by an almost total absence of sulfur molecules. The inventors have determined that this can be used as an indicator of the SAF content of the fuel by measuring the concentration of sulfur molecules by the trace sensor 127. The fuel characteristics determining system 126 can in this example compare the content of sulfur measured in the fuel to that corresponding to the fuel of fossil origin. This may allow system 126 to determine a percentage of SAF in the fuel F supplied to the aircraft. As an SAF contains almost no sulfur molecules, the measured concentration can be compared to a sulfur concentration typically around 500 ppm (and up to 3000 ppm) of elemental sulfur in a fossil aircraft fuel. By measuring a reduction in sulfur content, the relative amount of SAF present in the fuel as a percentage of the total fuel (e.g. percentage of SAF per unit mass or volume) can therefore be derived (e.g. using the knowing the amount of sulfur (e.g. ppm) in the fossil fuel to derive from a measured amount of sulfur (e.g. ppm) in a fuel mixture the percentage of SAF in that mixture. of trace substances may indicate an absence (within measurable limit) of sulfur molecules in the fuel F, based on which the fuel characteristics determining module 128 may determine that no fossil kerosene (within measurable limits) is present with the fuel.

In the example shown in the , the sensor 127 comprises a fluorescence detection device arranged to measure the quantity of sulfur molecules in the fuel F. As can be seen in the , fuel loaded onto the aircraft passes through sensor 127 where a trace substance measurement is made on the fuel. Sensor 127 includes a fuel inlet 127a and a fuel outlet 127b, and a fuel conduit 127c arranged in fluid communication therebetween. In the present example, the sensor 127 is located on board the aircraft and is arranged to receive the fuel flowing through the fuel transmission line 63, i.e. the fuel flowing from the fuel line connection port 62 to fuel tanks 53, 55. The fluorescence detection device can provide a reliable method for detecting the concentration of sulfur molecules in fuel. Other sensors or measurement techniques may however be used.

The fluorescence detection device comprises an excitation source 129a, such as an LED, which is arranged to emit radiation into the fuel F. The fluorescence detection device further comprises a detector 129b arranged to detect fluorescent light issued. Detector 129b may be in communication with a processor module 129c configured to process a fluorescence signal from detector 129c and calculate a trace substance parameter accordingly.

In the present example, sensor 127 is arranged such that all fuel flowing through transmission line 63 is introduced into sensor inlet 127a, flows through fuel line 127c and exits via fuel outlet 127b to continue to the fuel tanks (i.e. the sensor is connected in series between the fuel line connection port 62 and the fuel tanks). In other examples, sensor 127 may be connected in parallel so that only a portion of the fuel is redirected from transmission line 63, flows through the sensor, and then returned to fuel transmission line 63. or to the fuel tanks. In some examples, the sensor may be a microfluidic (lab-on-a-chip) device through which a small fuel sample can pass to make a measurement of a trace substance parameter.

The fuel characteristics determination module 128 is arranged to transmit the determined fuel characteristic(s) to the electronic engine controller EEC 42 or to another control module of the aircraft. In some examples, the fuel characteristic determination module 128 may be part of the EEC 42 of any one or more of the gas turbine engines of the aircraft. Once received at the EEC, the fuel characteristics can be used to provide information about the fuel that is supplied from the fuel tanks to the engine so that the operation of the gas turbine engine(s) can be adapted accordingly. In yet other examples, determination module 128 may be part of sensor unit 127, which is in communication with the EEC.

In another example, the trace substance parameter may be associated with an aromatics content of the fuel F. In such an example, the trace substance parameter may be a concentration (or other equivalent measure of quantity) of compounds aromatics in the fuel. The inventors have observed that for many SAF production routes, the resulting fuel contains essentially no aromatic compounds. The inventors have determined that this can be used as an alternative indicator of fuel SAF content. In such an example, the sensor 127 is arranged to measure a concentration of aromatic compounds in the fuel F. The system for determining fuel characteristics 126 can, in this example, compare the concentration of aromatic compounds measured with that corresponding to the fuel d of fossil origin in order to determine a percentage of SAF in the fuel F supplied to the aircraft. By measuring a reduction in aromatics content compared to fossil kerosene, the relative amount of SAF present in the fuel as a percentage of the total fuel (e.g. percentage of SAF per unit mass or volume) can therefore be derived. In some instances, the trace substance parameters may indicate a measurable absence of aromatic compounds in the fuel F, based on which the fuel characteristics module may determine that no fossil kerosene is present in the fuel f.

In order to measure a concentration of aromatic compounds in the fuel F, the sensor 127 can comprise a spectroscopy device (instead of the fluorescence device represented in the example of the ). The spectroscopy device may comprise a Fourier Transform Infrared (FT-IR) spectroscopy device or an Ultraviolet-Visible (UV-Vis) spectroscopy device. Such spectroscopy techniques can provide reliable differentiation of aromatic compounds from paraffins and other types of hydrocarbons in aviation fuel. However, other spectroscopy devices and techniques can be used. The spectroscopy device may have a structure similar to the fluorescence device shown in the .

In other examples, other trace substance parameters may be used which are associated with different trace substances to determine fuel characteristics. Appropriate detection devices can be used depending on the relevant trace substance to be measured. In order to determine the one or more fuel characteristics, the determination module 128 may be arranged to compare a measured trace substance parameter to a look-up table of expected trace substance parameter values of fuels with known fuel characteristics. to determine the corresponding characteristics of the fuel F. This can make it possible to determine a variety of different fuel characteristics.

For example, trace substance parameters may be associated with the presence/absence/amount of non-hydrocarbon species in the fuel, including any one or more of the following:

i) Nitrogen

ii) Water

iii) Sulfur

iv) Metals (including any one or more of: Al, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Pt, Sn, Sr, Ti, V and/or Zn); and or

v) Halogens

The inventors have determined that generally SAF is a much purer hydrocarbon fuel with very few trace species, compared to conventional jet fuel processed from a raw source. As SAF is effectively produced by a controlled chemical process, all of the heteroatomic species observed in conventional jet fuel (sulfur, nitrogen, oxygen) or trace metals are present at very low levels (often below the detection limit by analytical techniques). Detecting the presence/absence/concentration of one or more of these species can therefore help to determine whether a fuel is SAF, or is conventional jet fuel from a fossil source.

In the examples given above, the trace substances are inherently present in fuel F. This means that they are trace substances which are not artificially added to the fuel, but which are present (or absent) due to how the fuel is produced or where it comes from. In other examples, the trace substance(s) may be added to fuel for the purpose of providing an indicator for a particular fuel or fuel characteristic (e.g., it is a “tracer” substance). Such tracer substances may be deliberately added for later detection by the present methods. These may provide a binary distinction between SAF fuel or non-SAF fuel by which tracer is present or not, or the amount of trace substance could be added in proportion to some characteristic of the fuel, for example in proportion to the content of SAF or aromatic content. In such an example, the amount of tracer present may then indicate the content of another component of the fuel. For example, a phosphorescent or chemiluminescent species can be used as a tracer species, such as phosphorus or potassium. Such tracer species can be detected using a light or refraction sensor.

In the examples described above, the fuel characteristic determining system 126 is located on board the aircraft 1 so that the fuel in the fuel transmission line 63 flows therethrough before reach the fuel tanks 53, 55. In other examples, the fuel characteristic determining system 126 may be arranged to use fuel within, or sampled from, one of the fuel tanks 53, 55. In such an example, sensor 127 may be located in the fuel tank so that a fluorescence or spectroscopy measurement can be made (or another appropriate measurement depending on the trace substance detected). The sensor 127 can therefore be integrated into an interior wall of the fuel tank so that it is exposed to the fuel inside the tank. In other examples, fuel may be sampled from the tank and passed through sensor 127.

In other examples, the fuel characteristic determining system 126, or at least a portion thereof, may be located separately from the aircraft 1. For example, it may be included in the fuel loading line 61 so that it can detect the properties of the fuel before it reaches the aircraft. In some examples, the sensor 127 may be located in the fuel loading line, or elsewhere separately from the aircraft 1, and arranged to transmit a trace substance parameter to the determination module 128 located on board the aircraft 1 , where it can be communicated to an engine control module (eg the EEC). In yet other examples, the fuel characteristic determining system 126 may be located entirely external to the aircraft. In such an example, the fuel characteristic determination module 128 may determine a fuel characteristic which is then communicated to the aircraft 1 (for example to an engine control module or to the engines 10). In this example, a data transfer link may be provided (eg, wireless or wired data connection) and may be used to communicate fuel characteristics to the aircraft from the fuel characteristic determination system 126. In some examples, the data transfer may be performed manually by a user, for example, a technician or other system operator may obtain the fuel characteristics from the determination system 126 and provide them manually to a order on board the aircraft.

Determination of fuel characteristics in the engine using a trace substance sensor:

There illustrates another example of the fuel characteristic determination system 126 described above. The fuel characteristic determination system 126 of the similarly comprises a sensor 127 and a determination module 128 arranged to measure one or more fuel characteristics based on a trace substance parameter.

There depicts a schematic view of a portion of the aircraft fuel system and combustion equipment 16 of gas turbine engine 10. Combustion equipment 16 includes a plurality of fuel injectors (not shown in there ) arranged to inject fuel into a tubular combustion chamber. Fuel is supplied to the combustion equipment 16 by a fuel delivery controller 107 under the control of the EEC 42. Fuel is delivered to the fuel delivery controller 107 by a fuel pump 108 from a fuel source 109 on board the aircraft 1 (for example one or more fuel tanks as described above). The fuel delivery regulator 107 and combustion equipment 16 may be of known design, and may be arranged for staged (lean burn) combustion or rich burn.

In this example, a trace substance parameter is measured for fuel as it is used by the engine. Sensor 127 in this example is arranged to measure a trace substance parameter at any point in the aircraft fuel system that is upstream of combustion equipment 16 (e.g., upstream of fuel injectors). fuel of the combustion equipment 16) and downstream of the fuel source 109 from which the fuel is supplied (e.g., downstream of the one or more fuel tanks 53, 55 forming the fuel source). In some examples, sensor 127 is located at a point within the engine fuel system, such as in a fuel line within or forming part of gas turbine engine 10 (rather than being on the aircraft 1 on which the gas turbine engine 10 is mounted). In some examples, it is located at a point immediately before fuel combustion (e.g. before entering the combustion chamber). In still other examples, the sensor 127 is located at a point within the aircraft fuel system, for example, before it enters a portion of the gas turbine engine 10 One of the characteristics described above in connection with the example of the can also apply to the example shown in the .

In the example shown in the , the trace sensor 127 is arranged so that all fuel flowing to the combustion chamber 16 passes through it (for example, it is arranged in series). In other examples, only a portion of the fuel may pass through the trace sensor 127. For example, the trace sensor may be located in the fuel system bleed line at which fuel is sampled from the fuel system. fuel supply to the combustion chamber (e.g. before or after fuel mixing).

There illustrates a method 1030 of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft which may be performed by the fuel characteristic determination systems 126 shown in 15, 16 and 17. The method 1030 includes: measuring 1031 one or more trace substance parameters of the fuel, the one or more trace substance parameters each being associated with a respective trace substance in the fuel ; and determining 1032 one or more fuel characteristics of the fuel based on the one or more trace substance parameters. Any of the features described above in connection with Figures 15, 16 and 17 may be incorporated into the method of .

UV-Vis spectroscopy sensor

Determination of fuel characteristics during refueling using a UV-Vis sensor:

With reference to the , another example of a fuel characteristic determination system 130 is illustrated, located on board the aircraft 1. The fuel characteristic determination system 130 in this example is arranged to determine one or more fuel characteristics of the fuel loaded on the aircraft 1, these characteristics being one of those described or claimed here. In this example, the one or more fuel characteristics are determined based on a measurement of the transmittance of UV and visible spectrum (UV-Vis) light through the fuel.

Further details of the fuel characteristic determination system 130 are illustrated in the . The fuel characteristics determining system 130 generally includes a UV-Vis sensor 131, which is arranged to measure one or more UV transmittance parameters of the fuel that is supplied to the aircraft fuel tanks 53, 55.

The fuel characteristic determination system 130 further comprises a fuel characteristic determination module 132 arranged to determine one or more fuel characteristics of the fuel based on the transmittance parameters. The fuel characteristic determination module 132 is arranged to receive the transmittance parameters from the UV-Vis spectrum sensor 131 so that the one or more fuel characteristics can be calculated.

In the example shown in the , the sensor 131 comprises a UV-Vis spectroscopy device arranged to measure the transmittance of light in the UV and visible spectrum by the fuel. As can be seen on the , fuel loaded onto the aircraft passes through sensor 131 where the fuel is irradiated with UV-Vis light. Sensor 131 includes a fuel inlet 131a and a fuel outlet 131b, and a fuel conduit 131c arranged in fluid communication therebetween. In the present example, the sensor 131 is located on board the aircraft and is arranged to receive the fuel flowing through the fuel transmission line 63, that is to say the fuel flowing from the fuel line connection port 62 to fuel tanks 53, 55.

The UV-Vis spectroscopy device includes a light source 133a, such as an LED, arc lamp, etc., which is arranged to emit radiation into the fuel F. In some examples, the light source 133a may include two different or more individual light sources arranged to provide light at different wavelengths which, when combined, provide the desired UV-Vis spectral range. The UV-Vis spectroscopy device further comprises a detector 133b arranged to detect the light transmitted through the fuel from the light source 133a. Detector 133b may include a photodiode or similar sensor arranged to detect light emitted by light source 133a. Detector 133b is in communication with a processor module 133c configured to process a signal from detector 133c and calculate a transmittance parameter accordingly.

The transmittance parameter defines the amount of light absorbance at specific wavelengths of light emitted by light source 133a. The inventors have determined that by measuring a UV-Vis absorption spectrum of the fuel, the fuel characteristics determining module can calculate various characteristics of the fuel.

In one example, the one or more fuel characteristics determined by the fuel characteristics determining module 132 may include a hydrocarbon distribution of the fuel. More specifically, they may include the aromatic hydrocarbon content of the fuel. In some instances, other fuel characteristics may be determined directly from the transmittance parameter, inferred, or determined indirectly from it. For example, the one or more fuel characteristics determined may include the percentage of sustainable aviation fuel in the fuel on which the measurement is made. As described elsewhere herein, SAF is typically associated with essentially zero aromatic content. The fuel characteristics determination system 130 can, in this example, compare the concentration of aromatic compounds measured with that corresponding to the fuel of fossil origin in order to determine a percentage of SAF in the fuel F supplied to the aircraft. By measuring a reduction in aromatics content compared to fossil kerosene, the relative amount of SAF present in the fuel as a percentage of the total fuel (e.g. percentage of SAF per unit mass or volume) can therefore be derived. In some examples, the transmittance parameters may indicate a measurable absence of aromatics in the fuel F, based on which the fuel characteristics determining module 132 may determine that no fossil kerosene is present in the fuel F In other examples, an indication that the fuel is fossil kerosene can be determined.

In order to determine the one or more fuel characteristics, the determination module 132 may be arranged to compare a measured transmittance parameter to a look-up table of expected parameter values of fuels with known fuel characteristics to determine the corresponding characteristics of the fuel. fuel for which the transmittance is measured. This can allow a range of fuel characteristics to be determined based on the transmittance signature as a function of wavelength comparison to those of known fuel types.

In the present example, UV-Vis sensor 131 is arranged such that all fuel flowing through transmission line 63 is introduced into sensor inlet 131a, flows through fuel line 131c, and exits via fuel outlet 131b to continue to the fuel tanks (i.e. the sensor is connected in series between the fuel line connection port 62 and the fuel tanks). In other examples, sensor 131 may be connected in parallel so that only a portion of the fuel is redirected from transmission line 63, flows through the sensor, and then returned to fuel transmission line 63. or to the fuel tanks. In some examples, sensor 131 may be a microfluidic (lab-on-a-chip) device through which a small fuel sample may pass to perform a UV-vis spectroscopy measurement.

The determination module 132 is arranged to communicate the or more fuel characteristics determined to a control module of the gas turbine engine or of the aircraft. In the example described here, the one or more fuel characteristics are transmitted to the electronic engine controller EEC 42. In some examples, the determination module 132 may be part of the EEC 42 of any one or more of the aircraft gas turbine, the control module being a sub-module of the EEC. Once received at the EEC, the fuel characteristics can be used to provide information about the fuel that is supplied from the fuel tanks to the engine so that the operation of the gas turbine engine(s) can be adapted accordingly. In yet other examples, determination module 132 may be part of sensor unit 131, which is in communication with the EEC.

In the examples described above, the fuel characteristic determining system 130 is located on board the aircraft 1 so that the fuel in the fuel transmission line 63 flows therethrough before reach the fuel tanks 53, 55. In other examples, the fuel characteristic determining system 130 may be arranged to use fuel within, or sampled from, one of the fuel tanks 53, 55. In such an example, the UV-Vis sensor 131 may be located in a fuel tank so that a fluorescence or spectroscopy measurement can be made (or other appropriate measurement depending on the trace substance detected ). The UV-Vis sensor 131 can therefore be integrated into an inner wall of the fuel tank so that it is exposed to the fuel inside the tank. In other examples, fuel may be sampled from the tank and passed through sensor 131.

In other examples, the fuel characteristic determining system 130, or at least a portion thereof, may be located separately from the aircraft 1. For example, it may be included in the fuel loading line 61 so that it can detect the properties of the fuel before it reaches the aircraft. In some examples, the UV-Vis sensor 131 may be located in the fuel loading line, or elsewhere separately from the aircraft 1, and arranged to transmit a transmittance parameter to a determination module 132 located on board the aircraft. aircraft 1, where it can be communicated to an engine control module (for example the EEC). In yet other examples, the fuel characteristic determining system 130 may be located entirely external to the aircraft. In such an example, the fuel characteristic determination module can determine a fuel characteristic which is then communicated to the aircraft 1 (for example to an engine control module or to the engines 10). In this example, a data transfer link may be provided (eg, wireless or wired data connection) and may be used to communicate fuel characteristics to the aircraft from the fuel characteristic determination system 130. In some examples, the data transfer may be performed manually by a user, for example, a technician or other system operator may obtain the fuel characteristics from the determination system 130 and provide them manually to a order on board the aircraft.

Determination of fuel characteristics in the engine using a UV-Vis sensor:

There illustrates another example of the fuel characteristic determination system 130 described above. The fuel characteristic determination system 130 of the similarly comprises a UV-Vis sensor 131 and a determination module 132 arranged to measure one or more fuel characteristics based on a transmittance parameter.

There depicts a schematic view of a portion of the aircraft fuel system and combustion equipment 16 of gas turbine engine 10. Combustion equipment 16 includes a plurality of fuel injectors (not shown in there ) arranged to inject fuel into a tubular combustion chamber. Fuel is supplied to the combustion equipment 16 by a fuel delivery controller 107 under the control of the EEC 42. Fuel is delivered to the fuel delivery controller 107 by a fuel pump 108 from a fuel source 109 on board the aircraft 1 (for example one or more fuel tanks as described above). The fuel delivery regulator 107 and combustion equipment 16 may be of known design, and may be arranged for staged (lean burn) combustion or rich burn.

In this example, a transmittance parameter is measured for fuel as it is used by the engine. The UV-Vis sensor 131 in this example is arranged to measure a transmittance parameter at any point inside the fuel system of the aircraft which is upstream of the combustion equipment 16 (for example in upstream of the combustion equipment fuel injectors 16) and downstream of the fuel source 109 from which fuel is supplied (e.g., downstream of the one or more fuel tanks 53, 55 forming the fuel source ). In some examples, the UV-Vis sensor 131 is located at a point within the engine fuel system, such as in a fuel line within or forming part of the gas turbine engine 10 (rather than to be on the aircraft 1 on which the gas turbine engine 10 is mounted). In some examples it is located at a point immediately before the fuel burns (e.g. before it enters the combustion chamber). It can, for example, be included in an engine fuel circuit purge line (for example before or after the fuel mixture). In still other examples, the UV-Vis sensor 131 is located at a point within the aircraft fuel system, for example, before it enters a part of the turbine engine. 10. One of the characteristics described above in connection with the example of the can also apply to the example shown in the .

There illustrates a method 1034 of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft. The method 1034 may be performed by the fuel characteristic determination systems 130 shown in Figures 19, 20 and 21. The method 1030 includes passing UV-visible spectrum light 1035 through the fuel and measuring 1036 d a transmittance parameter indicating the transmittance of light through the fuel. The method further includes determining 1037 one or more fuel characteristics of the fuel based on the transmittance parameter. Once the fuel characteristic is determined, the method 1034 includes communicating 1038 the one or more fuel characteristics to a control module of the gas turbine engine. Any of the features described above in connection with Figures 19, 20 and 21 may be incorporated into the method of .

Determination of fuel characteristics using contrail measurement

There illustrates another example of a fuel characteristic determination system 140, located on board the aircraft 1. The fuel characteristic determination system 140 in this example is arranged to determine one or more fuel characteristics of the fuel on the basis of observations of contrail formation. There shows the aircraft 1 in flight with each gas turbine engine 10 producing exhaust smoke 141. A condensation trail 142 is also formed in the exhaust smoke 141 from each engine 10. The wing fuel tanks of the aircraft 1 are not represented on the for the sake of clarity, but it is understood that these may still be present.

The fuel characteristic determining system 140 comprises a contrail sensor 143 and a fuel characteristic determining module 144. In the present example, the fuel characteristic determining system 140 comprises three contrail sensors 143 , one located on each wing of the aircraft 1 and one on the empennage or the tail assembly of the aircraft. In other examples, a single or other number of contrail sensors may be provided as described below. The contrail sensors are each arranged to determine one or more contrail parameters related to the formation of contrail by the gas turbine engine 1. The contrail sensors 143 are arranged to perform a measurement of sensor on a region behind each gas turbine engine 10 of aircraft 1 in which a contrail 142 is or may be formed, for example, the exhaust fumes 141 from each engine 10.

The contrail parameters measured by the control sensors 143 include a measured value corresponding to the degree of contrail formation occurring in the exhaust smoke 141. In some examples, this may be an indication of the presence or the absence of a contrail 142 in the respective exhaust smoke 141 of each engine 10. In other examples, the contrail parameters may be a variable indicating the relative amount of contrail that is in forming, ranging from no contrail to a maximum degree of contrail formation.

The contrail sensors 143 are in communication with the fuel characteristic determination module 144, which is arranged to receive the contrail parameter(s) from each sensor 143. fuel is arranged to determine one or more characteristics of the fuel based on the received contrail parameters.

The inventors have observed that the presence of a contrail, or the degree to which a contrail is formed, depends (at least in part) on the characteristics of the fuel burned by the combustion chamber of the engines 10. The inventors have determined that the fuel characteristics can be determined on the basis of an active measurement of the formation of contrail in the exhaust smoke of a respective gas turbine engine 10.

In one example, the one or more fuel characteristics determined based on the measured control parameter(s) include a hydrocarbon distribution of the fuel. More specifically, they may include a content of aromatic compounds in the fuel. The inventors have determined that the formation of a contrail depends on the presence of aromatic molecules in the fuel used. The inventors have determined that a reduction in the aromatics content of the fuel results in an increase in an engine's susceptibility to the formation of contrails since the lower aromatics content of the fuel means that the vapor ratio of water/heat added by the engine to the exhaust smoke is increased. This allows the formation of contrails over a wider range of atmospheric conditions compared to fuels with higher aromatic content such as fossil kerosene. Additionally, lower aromatic content may mean fewer soot particles emitted, which should (in most situations) lead to fewer (and therefore individually larger) ice particles in the young contrail.

In some examples, the one or more contrail parameters may include measurements made by the controlling sensors 143 over an extended period of time (rather than an instantaneous observation of a contrail). In some examples, the one or more control parameters may include an extended observation straddling the boundary between the contrail-forming conditions and the contrail-non-forming conditions (or vice versa).

In some examples, other fuel characteristics as defined or claimed elsewhere herein may be determined based on the contrail parameters. In some examples, the SAF content of the fuel can be determined based on the contrail parameters. As the aromatic content of an SAF is generally lower than that of fossil kerosene fuel, the resulting contrail formation will therefore be different and will help determine the SAF content of the fuel. In other examples, the one or more determined fuel characteristics may include an indication that the fuel is fossil kerosene. This can be determined due to the fact that the measured contrail parameters match what would be expected if fossil kerosene were subjected to combustion by the gas turbine engine. In other examples, the hydrocarbon distribution of the fuel can be determined or inferred based on the contrail parameters, for example by referencing the contrail parameters to those expected for a fuel with a hydrocarbon distribution known. Fuel characteristics can be determined using a similar comparison of parameters to those of known fuel types.

In the example shown in the , each of the contrail sensors 143 comprises a contrail detector 143a arranged to detect electromagnetic radiation reflected and/or re-emitted by a contrail 142. Each contrail sensor further comprises an illumination source 143b arranged to emit radiation which is incident on the contrail 142 where it is reflected and/or re-emitted and detected by the detector 143a. In other examples, one of the detectors 143a may be arranged to respond to electromagnetic radiation reflected and/or re-emitted by a contrail 142 in response to ambient lighting (e.g., sunlight), or alternatively by response to infrared (or other) illumination emitted by hot engine exhaust. In such examples, illumination sources 143b may be absent. The radiation detected by the detectors 143a may be infrared wavelength radiation emitted or reflected by a contrail. In other examples, other wavelengths of radiation may be detected.

The sensors 143 each have a field of view 143c in which a signal from a contrail can be received. The sensors may be provided at any convenient location on the aircraft such that the region of contrail formation is within the sensor's field of view. In the present example, the sensors 143 are located on the wings and the empennage of the aircraft. Other sensor locations may however be provided to observe each exhaust smoke separately or together.

In still other examples, other forms of sensor may be used to measure a contrail parameter indicating the presence or absence of a contrail, or the degree to which a contrail is formed. In some examples, the contrail sensors 143 may be arranged to detect sound returned from particles in a contrail. For example, lighting sources can be replaced with sound (or ultrasonic) wave sources, which could include sound generated by the motor in use. The detectors 143a would then be arranged to detect the sound sent back by the ice particles in a contrail.

In yet other examples, sensors 143 may be image sensors. In this example, the sensors may include an imaging device arranged to image the exhaust smoke (e.g. at a location where a contrail may form behind gas turbine engines), and determine at from the image whether or not a contrail has formed, or the degree to which a contrail has formed. This can be done using image processing techniques or an AI (artificial intelligence) algorithm configured to measure the size and shape of any contrail formed, or if a contrail is absent in the images obtained.

The fuel characteristics determination module 144 is arranged to transmit the one or more fuel characteristics determined to the electronic engine controller EEC 42 (not shown in the diagram). ). In some examples, determination module 144 may be part of EEC 42 of any one or more of the gas turbine engines of the aircraft. Once received at the EEC, the fuel characteristics can be used to provide information about the fuel that is supplied from the fuel tanks to the engine so that the operation of the gas turbine engine(s) can be adapted accordingly. In still other examples, the fuel characteristics determining module 144 may be part of one of the sensors 143, which is in communication with the EEC.

In order to determine the one or more fuel characteristics, the determination module 144 may be arranged to compare a measured contrail parameter to a look-up table of expected contrail parameter values of fuels with known fuel characteristics. to determine the corresponding characteristics of the fuel that is used by gas turbine engines.

In some examples, the one or more fuel characteristics are further determined by the fuel characteristic determination module 144 based on one or more ambient atmospheric conditions parameters. Each of these atmospheric conditions parameters indicates the ambient atmospheric conditions in which the gas turbine engines 10 are currently operating. The inventors have determined that the formation of a contrail depends at least in part on the atmospheric conditions under which the respective engine operates, in addition to the characteristics of the fuel which is subjected to combustion. Atmospheric condition parameters may include ambient pressure, temperature and/or vapor pressure (humidity) in which the gas turbine engine operates. By taking more account of ambient conditions, the determination of fuel characteristics can be improved.

In certain examples, the parameters of ambient atmospheric conditions can be obtained from a sensor or sensors located on board the aircraft, which is/are arranged to measure the conditions in the vicinity of the aircraft. This can provide a direct measurement of the current conditions under which the engine is operating. In other examples, ambient condition parameters may be obtained from a weather data source providing real-time or expected information about the ambient conditions in which the engine is operating.

In some examples, the one or more fuel characteristics are further determined based on one or more engine or aircraft operating parameters. Various aircraft or engine operating parameters can affect the formation of a contrail and can therefore be taken into account.

In some examples, the fuel characteristic may be calculated by determining the value of a variable parameter (e.g. an engine operating parameter and/or an ambient condition parameter) at which a contrail is first formed.

In one example, the one or more fuel characteristics may be determined based on a measured contrail parameter during a climb phase of engine operation. For example, the contrail parameter may indicate when a contrail begins to form during a climb phase, and together with the ambient conditions and the engine operating parameter at which the contrail begins to form, a or several characteristics of the fuel can be determined. This can be used to infer fuel properties, in particular the amount of water vapor released by combustion per unit of fuel energy, which in turn is related to fuel characteristics such as mass fraction of hydrogen fuel.

There illustrates a method 1040 of determining a fuel characteristic of an aviation fuel suitable for powering a gas turbine engine of an aircraft that can be performed by the fuel characteristic determining system 140 shown in and described above. Method 1040 includes determining 1041, in use of gas turbine engine 10, one or more contrail parameters. The contrail parameters relate to the formation of contrail by the gas turbine engine 10 as described above. For example, the contrail parameters may include a parameter indicating the degree of contrail formation occurring, or whether contrail is present or absent. Determining 1041 the one or more contrail parameters includes performing 1042 a sensor measurement on a region (e.g., exhaust smoke 141) behind the gas turbine engine in which contrail 142 is or can be formed. The method further includes determining 1043 one or more fuel characteristics of the fuel based on the one or more contrail parameters as described above. Any of the characteristics described above in relation to the can be incorporated into the process of .

Determination of fuel characteristics using exhaust gas measurement

There illustrates another example of a fuel characteristic determining system 150, located on board the aircraft 1. The fuel characteristic determining system 150 in this example is arranged to determine one or more fuel characteristics of the fuel supplied to a gas turbine engine on the basis of measurements of an exhaust gas from this engine 10. The shows the aircraft 1 in flight with each gas turbine engine 10 producing exhaust smoke 141. The wing fuel tanks of the aircraft 1 are not shown in the figure. for the sake of clarity, but it is understood that these may still be present.

The determination system 150 comprises an exhaust sensor 151 and a fuel characteristics determination module 152. In the example represented on the , a fuel characteristic determination system 150 is provided for each engine, but in other examples a single fuel characteristic determination system 150 could be shared between them, with exhaust sensor(s) 151 for each engine 10 providing information to the determination module 152 alone.

The exhaust sensor 151 is arranged to determine one or more exhaust gas content parameters of the exhaust gas produced by the respective gas turbine engine 10. The exhaust sensor is arranged to perform a measurement of the exhaust gas exhaust produced by the engine during use. This may include engine operating conditions corresponding to any phase of flight (eg during cruise), or corresponding to operation while the aircraft is on the ground (eg during start-up or taxiing). The exhaust gas content parameters may indicate the chemical content of the exhaust gas produced by the engine, and may indicate the concentration, presence or absence of respective substances or species in the exhaust gas. In some examples, the exhaust sensor(s) 151 may be located within the respective gas turbine engine 10 such that it is/are arranged to perform a measurement on the exhaust gas before it is emitted by the engine. In some examples, the exhaust sensor may make a measurement on the exhaust gases as they flow through the engine core, or alternatively are sampled from the core stream. In other examples, the exhaust sensor 151 may be arranged to perform a measurement on the exhaust gases once they have left the engine, for example via the core exhaust nozzle 20 (as shown in there ).

The exhaust sensor 151 is in communication with the fuel characteristics determining module 152, which is arranged to receive the exhaust gas content parameter(s) therefrom. The fuel characteristics determining module 152 is then arranged to determine one or more fuel characteristics based on the received exhaust gas content parameters.

The inventors have determined that the characteristics of the fuel supplied to the gas turbine engine and subjected to combustion by its combustion chamber can be determined during engine operation by active measurement of the properties of the exhaust gas produced. In this example, the exhaust content parameters include exhaust gas properties other than the presence of a contrail.

In one example, the one or more exhaust gas content parameters include a parameter indicating the nvPM content of the exhaust gas. The inventors have determined that by actively measuring the nvPM content of the exhaust gas, various characteristics of the fuel F can be determined. By measuring the nvPM content, for example, a hydrogen to carbon ratio of fuel F subjected to combustion can be determined. The inventors have observed that a lower hydrogen to carbon ratio (e.g. compared to fossil kerosene) is associated with a higher level of nvPM production, and the dependence between them can be used to determine the fuel characteristic.

In another example, a naphthalene content can be determined based on the measured nvPM content. In this example, a high naphthalene content (eg relative to fossil kerosene fuel) is associated with a higher level of nvPM production. This dependence between nvPM production and naphthalene content can be used to determine the naphthalene content of fuel F.

In yet another example, an aromatic content (eg, aromatic mass fraction) of the fuel F can be determined based on the measured nvPM content. In this example, a high aromatics content (e.g. relative to fossil kerosene fuel) is associated with a higher level of nvPM production. This dependence between nvPM production and aromatics content can be used to determine the aromatics content of fuel F.

In order to measure the nvPM content of the exhaust gas, the exhaust sensor 151 may, in one example, comprise a laser induced glow (LII) meter arranged to determine the volume concentration of nvPM in the exhaust gas. exhaust. The LII measuring device can be arranged to trigger a very short, high energy pulse of a 1064 nm laser at the level of particles in the exhaust gas. This results in nvPM particles heating up and glowing in the visible spectrum. The maximum luminescence is directly related to the volume concentration of nvPM. The density of the material can then also be used for a conversion into mass concentration of nvPM.

In other examples, the exhaust sensor 151 may include a Condensation Particle Count (CPC) meter arranged to determine an nvPM number in the exhaust gas. The CPC device is arranged to count particles using laser scattering after the particles have been magnified by passing them through a cloud of butanol vapor. This condenses to make the particles large enough to be counted using laser scattering measurement. In this example, a volatile particle separator may be required upstream of the CPC measuring device to separate all volatile particles from the exhaust gas.

In addition to, or alternative to the nvPM content, the one or more exhaust gas content parameters may include a parameter indicating SO ₂ , CO ₂ or CO gas in the exhaust gas. Based on a measurement of the SO ₂ content of the exhaust gas, the elemental sulfur content of the fuel can be determined by the fuel characteristics determination module. For example, because the SO ₂ content of the exhaust gas comes from the oxidation of the sulfur content of the fuel. Similarly, based on a measurement of CO ₂ or CO in the exhaust gas, the fuel characteristics determination module can determine the carbon content in the hydrocarbon content of the fuel. The carbon content can be determined based on the oxidation of the carbon content of the fuel. In other examples, the exhaust gas content parameters indicate the sulfate aerosol content of the exhaust gas. These exhaust gas content parameters can be used to determine a fuel characteristic: fuel sulfur content F.

In order to measure the SO ₂ , CO ₂ or CO gas content of the exhaust gas, the exhaust sensor 151 can comprise a device for measuring non-dispersive absorption in the infrared (NDIR). In order to measure the sulphate aerosol mass content of the exhaust gas, the sensor 151 may comprise an aerosol mass spectrometer (AMS) device. The AMS device can be arranged to direct aerosols onto a hot plate (for example at 600° C.) and measure a resulting molecular mass spectrum. The AMS device can be arranged to sum all the spectral peaks associated with the sulfates. This method does not take into account the sulfur nucleation peak if there is one in the cooled smoke. The particle size distributions (electrical mobility) can be measured either by a Scanning Electric Mobility Analyzer (SMPS) type measurement, or by a Differential Electric Mobility Analyzer (DMS) type measurement that can determine a sulfur nucleation peak of ~ 10nm. The AMS measurement can be performed using a cooled sample of exhaust gas from the engine exhaust.

The exhaust sensor types listed above are intended to be examples only, and other sensor types may be used to determine the nvPM and sulfur content of exhaust gas. In yet other examples, other exhaust gas content properties may be determined, using suitable sensors, so that various other fuel characteristics are determined (e.g. one of those defined elsewhere herein).

In some instances, other fuel characteristics as defined or claimed elsewhere herein may be determined based on the exhaust gas parameters. In some examples, the SAF content of the fuel can be determined based on the exhaust gas parameters. As, for example, the aromatics content of an SAF is generally lower than that of fossil kerosene fuel, the resulting exhaust gas properties (e.g. nvPM content) will therefore be different and will help determine the content. in fuel SAF. In other examples, the one or more determined fuel characteristics may include an indication that the fuel is fossil kerosene. This can be determined from the fact that the measured exhaust gas content parameters correspond to what would be expected if fossil kerosene were subjected to combustion by the gas turbine engine.

In order to determine the one or more fuel characteristics, the determination module 152 may be arranged to compare a measured exhaust gas parameter or parameters to a look-up table of expected exhaust gas parameter values of fuels with known fuel characteristics to determine the corresponding fuel characteristics used by gas turbine engines. For example, the measured exhaust gas parameters can be compared to a baseline that would be expected for a fuel of known characteristics, such as kerosene or standard Jet A-1 fuel.

In some examples, the one or more fuel characteristics are further determined by the determination module 152 based on one or more ambient atmospheric conditions parameters. Each of the atmospheric conditions parameters indicates the ambient atmospheric conditions in which the gas turbine engine is currently operating. The inventors have determined that the properties of exhaust gases depend at least in part on the atmospheric conditions in which the engine is operating, in addition to the characteristics of the fuel undergoing combustion. Atmospheric condition parameters may include ambient pressure, temperature and/or vapor pressure (humidity) in which the gas turbine engine operates. By taking more account of ambient conditions, the determination of fuel characteristics can be improved.

In certain examples, the parameters of ambient atmospheric conditions can be obtained from a sensor or sensors on board the aircraft which are arranged to measure the conditions in the vicinity of the aircraft. This can provide a direct measurement of the current conditions under which the engine is operating. In other examples, ambient condition parameters may be obtained from a weather data source providing real-time or expected information about the ambient conditions in which the engine is operating.

In some examples, the one or more fuel characteristics are further determined based on one or more engine or aircraft operating parameters. The motor operating parameters may for example include the power setting of the motor.

Exhaust gas content parameters can be measured at any time during aircraft operation. In some examples, exhaust gas content parameters may be measured during an operating phase prior to aircraft take-off so that a fuel parameter may be determined for later use during gas turbine operation for this specific flight. In some examples, the exhaust gas content parameters can be measured during a start-up or taxiing phase of engine operation.

In yet other examples, exhaust gas content parameters may be measured under a first engine operating condition, which is associated with high levels of emission of the relevant substance in the produced exhaust gas, relative to an engine operating condition in which one would expect them to be lower. For example, if the exhaust gas content parameters relate to the nvPM content of the exhaust gas, they can be measured during a phase of engine operation in which nvPM production is expected to be inherently high relative to to other low nvPM emission phases. The first engine operating condition may, for example, be low engine power, relative to a second operating condition which may be a relatively higher engine power operating condition.

In some examples, the fuel characteristic determination module 152 may base the determination of fuel characteristics on a comparison of exhaust gas content parameters measured under different engine operating conditions. For example, the determination of fuel characteristics can be based on a comparison of exhaust gas content parameters measured at different engine power levels.

There illustrates a method 1050 of determining a fuel characteristic of an aviation fuel suitable for powering a gas turbine engine of an aircraft that can be performed by the fuel characteristic determining system 150 shown in and described above. Method 1050 includes determining 1051, in use of gas turbine engine 10, one or more exhaust gas content parameters. The one or more exhaust gas parameters are determined by performing 1052 a sensor measurement on an exhaust gas from the gas turbine engine 10 as described above. The method 1050 further includes determining 1053 one or more fuel characteristics of the fuel based on the one or more exhaust gas parameters.

The method 1050 may include measuring exhaust gas content parameters in a first engine operating condition in which the emission of the respective measured substance is greater than that in a second engine operating condition. The first engine operating condition may correspond to a lower engine power than the second. In yet other examples, the one or more fuel characteristics may be determined based on a comparison of exhaust gas content parameters determined under different engine operating conditions (e.g., the first and second conditions engine operation).

Determination of fuel characteristics using engine performance measurements

There illustrates another example of a fuel characteristic determining system 155, located on board the aircraft 1. The fuel characteristic determining system 155 in this example is arranged to determine one or more fuel characteristics of the fuel supplied to a gas turbine engine of the aircraft on the basis of measurements of the performance parameters of this engine 10.

The determination system 150 comprises a performance parameter sensor 156 and a fuel characteristics determination module 157. In the example represented on the , a fuel characteristic determination system 155 is provided for each engine, but in other examples, a single fuel characteristic determination system 155 could be shared between them, with the performance 156 for each engine 10 providing information to the determination module 157 alone.

The fuel characteristics determination module 157 is arranged to determine one or more performance parameters of the respective gas turbine engine 10 measured during a first period of engine operation (e.g. during operation under a first engine operating condition). ). The performance parameters can be obtained from a measurement made by the sensor 156. In the example described, the fuel characteristics determination module 157 is arranged to obtain the performance parameters directly from the sensor 156. In For other examples, sensor 156 may be in communication with EEC 42 of motor 10, and may be used as part of an existing motor control method. The fuel characteristic determination module 157 can, in such an example, obtain performance parameters from the EEC 42. This can allow the fuel characteristic determination system 155 to use existing sensors already provided on the gas turbine engine 10. While the represents the fuel characteristics module 157 which is separate from and in communication with the EEC 42, it may, in some examples, be part of the EEC.

The one or more fuel characteristics may be determined by the fuel characteristics determination module 157 after being received from the sensor 156. The fuel characteristics may, in some instances, be determined during a second subsequent period of operation (e.g. during operation in a second engine operating condition, different from the first) after they have been collected during the first period of operation. In other examples, the determination may be made during the first period of operation. The inventors have determined that certain engine performance parameters will depend on the characteristics of the fuel used, and that this can be used to determine various fuel characteristics.

The first operating period during which the performance parameters are measured can be a first flight phase, for example a take-off or climb phase. The second period of operation during which one or more fuel characteristics can then be determined (and possibly on which it is possible to act by controlling the engine accordingly) can be a second phase of flight which occurs later in a mission. operation or flight relative to the first. The second flight phase can be a cruise phase. By using performance parameters measured during a takeoff or climb phase, the engine can be operated under an engine operating condition in which a greater variation in performance resulting from fuel characteristics can be observed. For example, during the climb phase, a steerable inlet guide vane (VIGV) of the engine may be in a fully opened state, which would correspond to a greater observable dependence of performance on fuel characteristics.

Various engine performance parameters may be measured by the sensor(s) 156. The performance parameters may be determined directly by a sensor measurement, or may be determined indirectly from a dependency on another parameter. In order to determine the one or more fuel characteristics, the fuel characteristics determination module 157 can be arranged to compare a measured performance parameter to a look-up table of expected performance parameter values corresponding to fuels with characteristics of known fuel under the corresponding engine operating condition to determine the characteristics of the fuel used. For example, the measured performance parameters can be compared to a baseline that would be expected for a fuel of known characteristics, such as kerosene or standard Jet A-1 fuel.

Various fuel characteristics as defined or claimed elsewhere herein may be determined based on the performance parameters in this manner. In some examples, the SAF content of the fuel can be determined based on the performance parameters. In other examples, the one or more determined fuel characteristics may include an indication that the fuel is fossil kerosene. This can be determined from the fact that the measured performance parameters correspond to what would be expected if fossil kerosene were subjected to combustion by the gas turbine engine.

In one example, the performance parameters provided to the fuel characteristics determining module 157 may include the rotational speed of the fan 23 and the flow rate of fuel delivered to the engine. The speed of rotation of the fan 23 may be determined by the speed of rotation of the turbine/low pressure compressor N1, which will be the same as the speed of the fan 23 for an architecture without gearhead, or linked to the speed of the fan by the ratio d gear box 30. The variation of fan speed with fuel characteristics may be related to the different fuel energy per unit volume and/or per unit mass of different fuel types. The engine fuel system includes a fuel flow meter arranged to measure the rate (e.g. by mass or volume) at which fuel is delivered to the engine, which, if combined with knowledge of the resulting fan speed, can help determine the fuel benefit (i.e. more fuel energy per unit time results in faster fan speed). Based on the fan speed and the fuel flow rate, the fuel characteristic determination module can be arranged to calculate the amount of fuel energy that is introduced into the combustion chamber per unit mass or per unit volume of fuel flow, and thus infer fuel characteristics, for example, whether the fuel supplied is SAF, fossil or a percentage mixture of the two (i.e. determine the percentage SAF content).

In other examples, the performance parameters provided to the fuel characteristics determining module 157 may include a turbine inlet temperature (TET). The TET may be as defined elsewhere herein, and may in this example be measured at the first rotor of the first turbine 17 in a direction downstream of the combustor 16 (e.g. at the level of the furthest pressure turbine). high). The TET can be measured directly, or more in some examples be measured indirectly based on a measurement further downstream in the core airflow, for example at the second turbine 19. The inventors have determined that the calorific value of the fuel burned by the combustion chamber has an effect on the TET. A measurement of the TET may therefore be used by the fuel characteristic determination module to determine one or more fuel characteristics of the fuel by comparison with the expected TET for known fuel types. For example, the inventors determined that an increase in fuel calorific value would result in an increase in TET. This can be used as a method to determine if the fuel being used is SAF, as SAF generally has a higher calorific value than kerosene. In some examples, an increase in TET of approximately 3K can be observed when using SAF compared to kerosene.

In another example, the determination of fuel characteristics may be based on a combustion chamber fuel/air ratio. This can be determined by the mass of fuel flow to the combustion chamber versus core airflow. The inventors have determined that this ratio will decrease with the use of a fuel such as SAF, and therefore may provide another means of determining that SAF is being used by the engine.

In still other examples, other engine performance parameters may be used, including body speed HP, T30 and/or T40 (as defined elsewhere herein). In other examples, the fuel flow required to achieve a desired fan speed under the current ambient conditions and the aircraft forward speed (airspeed) can be used to determine the characteristics of the fuel delivered to the engine. For SAF, the fuel flow required to reach a given fan speed will be lower (relative to mass) or higher (relative to volume) than the fossil fuel flow required to reach the same fan speed under the same operating conditions. functioning. Similar comparisons between measured and expected performance parameters for known fuel characteristics can be used to determine a variety of fuel characteristics.

The fuel characteristic determination module 157 may be arranged to determine each fuel characteristic based on a plurality of different engine performance parameters. The plurality of performance parameters may include at least two different performance parameters, and preferably at least three different performance parameters. The fuel characteristic can be determined on the basis of a comparison of these different performance parameters with each other. By using more than one performance parameter, the accuracy or reliability of determining fuel characteristics can be improved.

In response to the fuel characteristic(s) determined by the fuel characteristic determining module, the operation of the gas turbine engine (or aircraft) may be adjusted or modified accordingly during the second period of operating time. For example, it is possible to act on engine performance parameters, obtained during the take-off or climb phase, during operation in cruise or during descent.

In the present example, wherein the aircraft includes fuel tanks that can be configured to store fuel having different fuel characteristics, the gas turbine engine only operates according to the one or more fuel characteristics during the second period of time only if the fuel is used from the same fuel tank, or is a fuel known to have the same fuel characteristics, as during the first time period. This means that engine operation changes only if the same fuel is used, so that the change in fuel response is appropriate.

In one example, an engine fuel consumption parameter or characteristic may be controlled based on the determined fuel characteristic. For example, the engine may be controlled during the cruise operating phase from a fuel consumption perspective based on the fuel characteristics determined from the take-off/climb phase performance parameters. In other examples, the rotational speed N1 of the high pressure turbine/compressor may be varied in response to the one or more fuel characteristics. For example, the rotation speed N1 can be reduced during the climb so that the resulting TET is identical to the temperature corresponding to that when operating on kerosene (in such an example, the first phase of flight can be takeoff, and the second a rising phase). In other examples, the rotational speed N1 during cruise may be changed in response to fuel characteristics determined during takeoff. In yet another example, the rotational speed N1 can be modified during a descending phase of flight based on the determined fuel characteristics, again modifying the rotational speed N1 to correspond to that which would be expected if the engine ran on kerosene. The rotational speed N1 in these examples can be changed by changing the corresponding rating tables in the motor control unit (e.g. EEC 42).

There illustrates a method 1058 of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft that may be performed by the fuel characteristic determination system 155 shown in there and described above. The method 1058 includes determining 1059 one or more gas turbine engine performance parameters measured during a first period of gas turbine engine operating time. Once the performance parameters are determined, the method includes determining 1060 one or more fuel characteristics of the fuel based on the one or more performance parameters. In some examples, the one or more fuel characteristics are determined during a second operating period as described above, or may be determined during the first operating period.

In some examples, method 1058 is part of a method of operating an aircraft having the gas turbine engine (e.g., method 1065 described below), and therefore may include a step 1061 of operating the engine at gas turbine engine or the aircraft according to the one or more fuel characteristics during the second operating time period. Operation of the aircraft or gas turbine engine may include changing a control parameter in response to fuel characteristics determined as described below.

One of the characteristics described above in relation to the fuel characteristic determination system 157 with reference to the example shown in the can be incorporated into the process of .

Operation of the aircraft according to a fuel characteristic or parameter on which the determination of fuel characteristics is based

The fuel characteristics determined using one of the fuel characteristic determination systems or methods for determining a fuel characteristic in the examples herein may be used in the operation of the aircraft, and more specifically the operation of the / of the gas turbine engine(s) of the aircraft. This can make it possible to modify the operation of the aircraft 1 in response to the determined fuel characteristic.

The present application therefore further provides a method 1065 of operating an aircraft 1 powered by one or more gas turbine engines 10 as illustrated in the . The method 1065 can be a method of operating the aircraft 1 of one of the examples described here. The method 1065 includes determining 1066 one or more fuel characteristics. This may include using any of the methods described herein. The method 1065 further includes operating 1067 the aircraft 1 according to the one or more fuel characteristics. Operation of aircraft 1067 may more specifically include operation of the gas turbine engine(s) 10 mounted on aircraft 1, but may include operation of other parts of the aircraft.

Once one or more fuel characteristics are known, the gas turbine engine 10 or aircraft more generally can be controlled or operated in a variety of different ways to take advantage of that knowledge. The operating step 1067 of the gas turbine engine or the aircraft may comprise modifying 1067a a control parameter of the aircraft, and specifically a control parameter of the gas turbine engine, in response to the one or more fuel characteristics. Changing the command parameter may include one or more of the following:

i) Changing a control parameter of a gas turbine engine thermal management system (e.g., fuel-oil heat exchanger 118) based on the one or more fuel characteristics. By altering the operation of the heat exchanger 118, the temperature of the fuel supplied to the combustion chamber 16 of the engine 10 can be changed. In one example, modifying the operation of the thermal management system or changing the temperature of the fuel may include increasing the temperature of the fuel if the fuel characteristics indicate that the fuel can tolerate higher temperature operation without risk of coking or thermal breakdown.

ii) When more than one fuel is stored on board an aircraft 1, the modification of a control parameter which controls a selection of the fuel to be used for this or that operation (for example for ground operations as opposed to flight, for low temperature start-up, or for operations with different thrust demands) based on fuel characteristics such as % SAF, nVPM generation potential, viscosity and calorific value. A fuel delivery system of the aircraft can therefore be appropriately controlled based on the fuel characteristics. The fuel delivery system can be controlled to supply the engine with fuel having a fuel characteristic different from that measured. This may include, for example, providing a fuel with a relatively lower aromatics content; supply of fuel with low SAF content; or the supply of fossil kerosene fuel. The fuel supply can be controlled by switching between fuel tanks or by changing a fuel mixture ratio.

iii) The modification of a control parameter to adjust one or more flight control surfaces of the aircraft 1, so as to change route and/or altitude on the basis of knowledge of the fuel.

iv) Changing a control parameter to change a fuel pump's spill percentage (i.e. the proportion of fuel pumped back into circulation instead of being delivered to the combustion chamber) of a fuel system of the aircraft according to the one or more fuel characteristics, for example based on the % SAF of the fuel. The pump and/or one or more valves can therefore be appropriately controlled based on the fuel characteristics.

v) Modification of a control parameter to change the programming of steerable inlet guide vanes (VIGV) based on fuel characteristics. The VIGVs may be moved, or a movement of the VIGVs may be canceled, as appropriate based on fuel characteristics.

In the examples above, the gas turbine engine or the aircraft operates according to the one or more fuel characteristics by making changes to the way the aircraft or the gas turbine engine is controlled during its use. This can be done, for example, by an engine control system (such as the EEC 42) making changes to various engine control parameters. Similar changes may be implemented by other aircraft control systems during use (e.g. during flight). The EEC may be more generally referred to as an example of a control system 42 arranged to control the operation of the aircraft (for example, it may be a control module of a control system).

The present application further provides an aircraft 1 having a fuel characteristic determination system according to any one or more of the examples disclosed or claimed herein. The aircraft further comprises a control system arranged to control the operation of the aircraft according to one or more fuel characteristics determined by the fuel characteristic determining system. The control system may include the EEC engine 42, with which the fuel characteristic determination system may be in communication or partially integrated therewith. In other examples, other aircraft control systems may have fuel characteristics and the aircraft may be controlled accordingly. The control system may be arranged to control the operation of the aircraft according to a parameter on which a determination of fuel characteristics is based directly, rather than requiring that a fuel characteristic be determined as described below.

The step of operating 1067 the gas turbine engine or aircraft according to the one or more fuel characteristics may be performed automatically in response to determining the fuel properties without any pilot intervention. In some instances, it may be performed after approval by a pilot, following notification to the pilot of a proposed change. In some examples, step 1067a may consist of automatically performing certain changes and requesting others, depending on the nature of the change. In particular, changes that are "transparent" to the pilot – such as internal changes to engine flow rates that do not affect engine power output and would not be noticed by a pilot – can be made automatically, whereas any changes the pilot notices can be notified to the pilot (i.e. a notification that the change will occur unless the pilot decides otherwise) or suggested to the pilot (i.e. that the change will not happen without a positive input from the pilot). In implementations where a notification or suggestion is provided to a pilot, this may be provided on a cockpit screen of the aircraft and/or sent to a separate device such as a portable tablet or other computing device, and/or announced via an audible signal such as synthesized speech or a recorded message or a particular tone indicating the proposed/notified change.

In other examples, the step of operating 1067 the gas turbine engine according to the one or more fuel characteristics may include supplying 1067b to the gas turbine engine a fuel having characteristics different from those of the fuel for which the one or more fuel characteristics were measured in step 1066. This provisioning of a different fuel may include loading a fuel having different fuel characteristics into the fuel tanks of the aircraft when refueling the aircraft. 'aircraft.

In some examples, aircraft operation may be altered in response to one or more of the parameters disclosed herein based on which fuel characteristics are determined. This may include, for example, the vibration parameter, the swelling parameter, the trace substance parameter, the UV-Vis transmittance parameter, the contrail parameter, the exhaust parameter and the engine performance. The aircraft can therefore be controlled on the basis of such parameters, without a fuel characteristic necessarily also being calculated.

In such an example, the operation of the aircraft can be modified in response to the one or more contrail parameters, without a fuel characteristic being determined. An example of such a process is shown in . There illustrates a method 1070 of operating an aircraft 1 having a gas turbine engine 10. The method 1070 includes: determining 1071, while operating the gas turbine engine 10, one or more drag parameters associated with the formation of contrail by the gas turbine engine 10. Determining 1071 the one or more contrail parameters includes performing 1073 a sensor measurement on a region behind the gas turbine engine 10. gas in which a contrail is or may be formed as described above in connection with the example shown in the . The contrail parameters are determined in step 1071 during variable operation of the aircraft (eg during a period of variable engine operating parameter and/or ambient condition parameter). The determined contrail parameters may indicate the value of a variable parameter at which a contrail is first formed. Once the one or more contrail parameters thus determined, the method 1070 further comprises controlling 1074 an operating parameter of the aircraft according to the one or more contrail parameters and the value of the variable parameter to be which they correspond. As discussed above, this may involve measuring engine performance parameters and/or ambient conditions under which contrail formation begins during a climb phase of aircraft operation. Aircraft control may additionally or alternatively include any of the examples of aircraft control in response to the fuel characteristics described above.

Another example in which the aircraft is controlled based on a sensor parameter rather than a fuel characteristic is shown in . In this example, steps 1026, 1027 and 1028 of method 1025 shown in figure are incorporated into a method of operating an aircraft. Therefore, in this example, the illustrates a method of operating an aircraft 1090 which includes measuring 1091 a swelling parameter of a sealing material (which is the same material as that of the other seals 125 provided on the aircraft 1) using the steps of the method 1025. The method 1090 further includes operating 1092 the aircraft according to the inflation parameter. Operating 1092 of the aircraft according to the inflation parameter may include supplying 1093, to the one or more gas turbine engines, a fuel having a different characteristic compared to the fuel for which the inflation parameter was measured. Fuel having a different characteristic may be supplied by refueling the aircraft with fuel having a different characteristic than that already in its fuel tank(s), or by supplying fuel from a different fuel tank to board of the aircraft that contains fuel with a different characteristic. Supplying fuel from a different fuel source on board the aircraft may include changing a mixture of fuels from different fuel sources, or switching between fuels with different characteristics. Providing a fuel having a different characteristic may include any one or more of: i) providing a fuel having a relatively higher aromatics content; (ii) supply of fuel with low SAF content; (iii) supply of kerosene. This may allow the seal swell to be increased if it is determined that operation using the current fuel is providing inadequate seal swell, which could result in reduced seal performance.

In the examples previously described, the various fuel characteristic determining systems are arranged to determine the one or more fuel characteristics based only on the respective parameter described in each example (for example, based on only one of a vibration parameter, a swelling parameter, a trace substance parameter, a UV-Vis transmittance parameter, a contrail parameter, an exhaust parameter or an engine performance parameter). In other examples, one of the fuel characteristic determination modules or methods for determining one or more fuel characteristics described or claimed herein may be arranged to base the fuel characteristics on any one or more parameters described herein, i.e. any one or more of vibration parameter, swelling parameter, trace substance parameter, UV-Vis transmittance parameter, contrail parameter , the exhaust parameter and the engine performance parameter. This may allow a wider range of fuel characteristic types to be determined, or may improve the accuracy or reliability of the fuel characteristic determination.

In one of the examples described here, the characteristics of fuel as it is loaded onto the aircraft can be determined (for example, as shown in the examples of Figures 5, 9, 13, 15 and 19). In such instances, the determined fuel characteristic(s) may be communicated to the EEC 42 directly if it is operating when fueling, or may otherwise be stored and communicated to the EEC when activated. If EEC is not active when fuel characteristics are determined, they may be communicated to another aircraft control system.

When the fuel characteristics are determined for the fuel loaded on the aircraft, this fuel can be mixed with fuel already present in the fuel tanks (for example from previous flights). The fuel characteristics determined can therefore be combined with those determined from previous instants when the aircraft was refueled in order to determine the characteristics of the fuel stored in the fuel tanks of the aircraft. This can be done using a summation method in which the amount of fuel loaded into the tanks, the amount of fuel used during each flight, and the corresponding characteristics of the fuel loaded are recorded and combined to determine the fuel characteristics of the fuel actually stored. in aircraft fuel tanks at any given time.

Generation of maintenance program according to fuel characteristics

The one or more fuel characteristics determined using one of the methods described or claimed herein may be used in the generation of a maintenance program for the respective gas turbine engine, or more generally the aircraft on which the engine gas turbine is mounted.

There illustrates an example of a method 1080 for generating a maintenance program for an aircraft. The aircraft includes one or more gas turbine engines, and may be the aircraft 1 described with respect to one of the other examples herein. The method 1080 includes determining 1081 one or more fuel characteristics of a fuel with which the gas turbine engine has been, or is to be, fueled. The one or more fuel characteristics may be those of a fuel or fuels used during previous uses of the gas turbine engine, or of a fuel contained in the fuel tanks of the aircraft. The one or more fuel characteristics can be determined using any of the methods described herein, but are not limited to the methods alone in other examples. Fuel characteristics can be determined as described herein and provided automatically to a maintenance schedule determination module without human intervention. In certain other examples, determining the one or more fuel characteristics may involve entering them manually into a maintenance program determination module, for example when refueling the aircraft. This may include reading fuel characteristics from a fuel specification, or from the output of a fuel characteristic determination system, and manually entering them by a human user into the program determination module of maintenance. The method 1080 further includes generating 1082 a maintenance schedule based on the one or more fuel characteristics. In other examples, one or more maintenance programs (eg one for each engine) can be determined.

The inventors have determined that the characteristics of the fuel that has been used to power the gas turbine have an effect on the operation of the gas turbine engine and the aircraft in general and therefore may necessitate a change in a maintenance program. for this gas turbine engine or aircraft. Changing the maintenance schedule may include changing scheduled maintenance operations and/or changing the time/frequency at which maintenance operations are performed. In some examples, generating a maintenance schedule may include modifying an existing schedule in response to fuel characteristics, or generating a new schedule.

The generation step 1082 of the maintenance program may include comparing 1083 the determined fuel characteristic(s) with an expected fuel characteristic, and modifying 1084 a maintenance program accordingly. An existing predefined maintenance schedule for a gas turbine engine, or an aircraft in general, may be associated with an expected fuel characteristic. For example, the maintenance schedule can be determined according to a specified type of fuel to be used by the aircraft so that maintenance can be performed based on how the engine is expected to operate using that fuel. The existing maintenance program may be modified in response to the determination that a deviation from expected fuel characteristics has occurred. This can allow the maintenance schedule to be tailored to the fuel that was actually used, rather than assuming that the specified fuel was used.

In one example, the existing maintenance program may specify the operation of the aircraft 1 using a fuel having a specific SAF content, for example, a high SAF fuel having a certain proportion of SAF compared to fossil kerosene, or require the use of 100% SAF fuel. Deviation from the use of fuel with the specified SAF content, as indicated by the determined fuel characteristics, may result in a change in the maintenance schedule to account for out-of-specification operation. In other instances, modification of the maintenance schedule may be based on other fuel characteristics as defined elsewhere herein. For example, the aromatics content of the fuel, or an indication that fossil kerosene has been used, can be determined and the maintenance schedule can be modified or otherwise generated accordingly.

In some examples, periodic measurement of fuel characteristics may be made upon which the determination of the maintenance schedule is based. This can allow the maintenance schedule to be generated based on an effect on engine or aircraft performance that may occur during an extended period of use with fuel having certain properties. This can allow slow changes in engine performance to be taken into account, rather than using a "real time" modification of the maintenance schedule based on a single determination of real time fuel characteristics. For example, the one or more fuel characteristics determined in step 1081 may indicate that a threshold level of fuel coking or thermal degradation has occurred. This can lead to the buildup of surface deposits in gas turbine engine components over time (e.g. fuel injectors), and may require more frequent maintenance or the replacement or cleaning of sensitive components. By using periodic determination of fuel characteristics, the level of coking can be monitored over time and the maintenance schedule can be adapted accordingly.

In some examples, determining the one or more fuel characteristics may include measuring a change in the properties of a sensor component, which is exposed to the fuel used to power the engines 10 of the aircraft. The sensor component may, in some examples, be a piezoelectric crystal, which is exposed to fuel loaded onto the aircraft or used by the gas turbine engine, as discussed in connection with the examples shown in Figures 5 through 8. In this example, the method 1080 can therefore use the fuel determination system 114 described in the examples above. Determining the one or more fuel characteristics in such an example may include measuring a mode of vibration of the piezoelectric crystal, which provides an indication of a surface deposit formed on the crystal. The maintenance schedule may be modified based on the detection of such surface deposit indicating that a fuel having a characteristic causing surface deposits to form in the engine or fuel system has been used, and maintenance must be carried out accordingly. The maintenance program can be modified according to the exceeding of a threshold level of coking or thermal degradation of fuel. In such an example, the fuel characteristic may be an indication that the fuel has caused a surface deposit, rather than requiring a further determination of a fuel characteristic which is associated with the discovery of such surface deposit formation. surface. This can allow the maintenance program to be modified based on a formed surface deposit, regardless of the mechanism by which it formed.

In other examples, method 1081 may use the detection device 120 illustrated in Figures 10, 11 and 13 and described above. In this example, the sensor component that is exposed to fuel and on which a determination of fuel characteristics is based includes a sealing material 121. This may be a sealing material, which is the same as one or more seals used in the gas turbine engine fuel system 10 as described above in connection with Figures 13 and 14. As discussed above, one or more fuel characteristics may be determined based on a swelling parameter of the sealing material. The inventors have determined that the one or more fuel characteristics determined in this manner can be used to generate a maintenance schedule based on the effect the fuel characteristics will have on the seals that are exposed to fuel on board the vehicle. aircraft (for example, in the fuel circuit arranged to store and supply fuel to the gas turbine engine, and in the engine itself). In this example, the one or more fuel characteristics based on which the maintenance schedule is generated indicate whether a threshold level of sealant swelling is reached. If swelling has not exceeded a predetermined threshold, this may indicate that sealing performance may have been inhibited and the maintenance schedule should be generated or modified accordingly.

The method 1080 of generating a maintenance program for an aircraft can be part of a method for maintaining an aircraft. An example of such a process 1085 is illustrated in . The method 1085 of maintaining an aircraft includes generating 1086 a maintenance program using the method 1080 described above. Once the maintenance schedule has been generated, the method 1085 includes performing 1087 maintenance on the aircraft according to the maintenance schedule. Performing maintenance may include performing maintenance on the gas turbine engine(s) 10, or on the aircraft more generally. The step of performing the maintenance may include steps performed by a technician in response to the generated maintenance schedule. In other examples, the maintenance steps can be carried out automatically without the intervention of a technician. For example, software updates or changes to control programs (eg those of the EEC) can be performed automatically during the maintenance process without human intervention.

There illustrates an example of an aircraft 1 having a maintenance program generation system 160 arranged to carry out the method 1085 of the . The maintenance program generation system 160 in this example includes a fuel characteristics determination module 117 corresponding to the example described above, in which the fuel characteristics are determined on the basis of a vibration parameter d a piezoelectric crystal (eg, using a sensor 115, which includes a piezoelectric crystal 116 as described above). The fuel characteristic determining module, however, may be any one or more of those disclosed or claimed elsewhere herein.

The maintenance program generation system 160 further comprises a maintenance program generation module 162 in communication with the fuel characteristics determination module 117 and configured to generate a maintenance program according to the one or more fuel characteristics received. of this one. The maintenance program generation module 162 can be configured to generate the maintenance program as described above.

The maintenance program generation system 160 can be located on board the aircraft 1 as represented in the example of the . In this example, a separate maintenance program generation system 160 is provided for each engine 10. In other examples, a single system may be provided, for example having a single generation module 162 configured to receive fuel characteristics a single fuel characteristics determination module on board the aircraft, or separate fuel characteristics determination modules provided for each engine. A single maintenance program for the aircraft 1 as a whole can be produced, or separate maintenance programs for each engine 10 can be produced accordingly.

In other examples, the maintenance generation system 160 can be located at least partially outside the aircraft 1. For example, the maintenance program generation module 162 can be located separately from the aircraft 1 , and may be configured to communicate via a wired or wireless data link connection with a fuel characteristic determination module so that the one or more fuel characteristics can be received and a maintenance schedule can be generated accordingly .

The maintenance program generation module 162 can be arranged to output a maintenance program to a technician carrying out maintenance on the aircraft 1, or to an aircraft condition monitoring system arranged to manage the maintenance of the aircraft 1 (or the engines 10 separately). In some examples, the maintenance generation module 162 may be in communication with the EEC 42 so that updates or reconfiguration of control parameters stored in the EEC may be performed (e.g., automatically).

It will be understood that the invention is not limited to the examples described above and that various modifications and improvements can be made without departing from the concepts described here. Unless mutually excluded, any of the Features may be used separately or in combination with any other Feature and the Disclosure extends to and includes all combinations and sub-combinations of one or more Features described herein.

Claims (22)

A method (1040) of determining one or more fuel characteristics of an aviation fuel (F) suitable for powering a gas turbine engine (10) of an aircraft (1), the method comprising:
determining (1041), during use of the gas turbine engine (10), one or more contrail parameters related to the formation of contrail by the gas turbine engine (10), in wherein determining (1041) the one or more contrail parameters comprises performing (1042) a sensor measurement on a region behind the gas turbine engine in which contrail is or may be formed; And
determining (1043) one or more fuel characteristics of the fuel (F) based on the one or more contrail parameters. The method (1040) of claim 1, wherein the one or more contrail parameters includes a parameter indicative of the degree of contrail formation occurring, preferably the presence or absence of contrail. condensation produced by the gas turbine engine. The method (1040) of claim 1 or 2, wherein determining (1041) the one or more contrail parameters comprises measuring electromagnetic radiation reflected and/or re-emitted by a contrail. The method (1040) of one of the preceding claims, wherein determining (1041) the one or more contrail parameters includes detecting the presence or absence of contrail, or the degree to which a contrail is formed, in an image of the region behind the gas turbine engine. The method (1040) of one of the preceding claims, wherein the one or more fuel characteristics are further determined based on one or more ambient atmospheric conditions parameters, each indicative of the ambient atmospheric conditions in which the engine gas turbine is currently operating. The method (1040) of claim 5, further comprising obtaining the one or more ambient atmospheric conditions from a weather data source providing real-time or expected information about the ambient atmospheric conditions. The method (1040) of claim 5 or 6, further comprising obtaining the one or more ambient atmospheric conditions from a sensor arranged to measure ambient conditions in the vicinity of the aircraft. The method (1040) of one of the preceding claims, wherein the one or more fuel characteristics are further determined based on one or more engine or aircraft operating parameters. The method (1040) of claim 8, wherein the one or more fuel characteristics are determined based on measuring the value of a variable parameter at which contrail formation begins, preferably an operating parameter of the variable motor and/or a variable ambient condition parameter. The method (1040) of one of the preceding claims, wherein the one or more fuel characteristics determined comprises any one or more of:
(i) a distribution of hydrocarbons from the fuel (F);
(ii) a percentage of sustainable aviation fuel in the fuel (F);
(iii) an aromatic hydrocarbon content of the fuel (F); and or
(iv) an indication that the fuel (F) is a fossil fuel, for example kerosene. A fuel characteristic determination system (140) for determining one or more fuel characteristics of an aviation fuel (F) suitable for powering a gas turbine engine (10) of an aircraft (1), the system including:
a contrail sensor (143) arranged to determine one or more contrail parameters related to the formation of contrail by the gas turbine engine (10), the contrail sensor (143) being arranged to perform a sensor measurement on a region behind the gas turbine engine in which a contrail (142) is or may be formed; And
a fuel characteristics determining module (144) arranged to determine one or more fuel characteristics of the fuel (F) based on the one or more contrail parameters. The fuel characteristic determining system (140) of claim 11, wherein the one or more contrail parameters includes a parameter indicative of the degree of contrail formation occurring, preferably the presence or absence of a condensation trail produced by the gas turbine engine. The fuel characteristics determining system (140) of claim 11 or 12, wherein the contrail sensor (143) is arranged to measure electromagnetic radiation reflected and/or re-radiated by a contrail. The fuel characteristic determining system (140) of one of claims 11 to 13, wherein the contrail sensor (143) is arranged to detect the presence or absence of a contrail, or the degree to which a contrail is formed, in an image of the region behind the gas turbine engine. The fuel characteristic determining system (140) of one of claims 11 to 14, wherein the fuel characteristic determining module (144) is further arranged to determine the one or more fuel characteristics based on one or more ambient atmospheric conditions parameters, each indicative of the ambient atmospheric conditions in which the gas turbine engine is currently operating, and optionally the fuel characteristics determining module (144) is further arranged to:
a) obtain the one or more ambient atmospheric conditions from a meteorological data source providing real-time or expected information on the ambient atmospheric conditions; and or
b) obtaining the or several ambient atmospheric conditions from a sensor arranged to measure the ambient conditions in the vicinity of the aircraft. The fuel characteristics determining system (140) of one of claims 11 to 15, wherein the fuel characteristics module (144) is further arranged to determine the one or more fuel characteristics based on a or more engine or aircraft operating parameters, and possibly:
wherein the one or more fuel characteristics are determined based on measuring the value of a variable parameter at which contrail formation begins, preferably a variable engine operating parameter and/or a condition parameter variable ambient. The fuel characteristic determining system (140) of one of claims 11 to 16, wherein the determined one or more fuel characteristics includes any one or more of:
(i) a distribution of hydrocarbons from the fuel (F);
(ii) a percentage of sustainable aviation fuel in the fuel (F);
(iii) an aromatic hydrocarbon content of the fuel (F); and or
(iv) an indication that the fuel (F) is a fossil fuel, for example kerosene. A method (1065) of operating an aircraft (1) having a gas turbine engine (10), the method comprising:
determining (1066) one or more fuel characteristics using the method of one of claims 1 to 10; And
the operation (1067) of the aircraft (1) according to the one or more fuel characteristics. The method of claim 18, wherein operating the aircraft (1) according to the one or more fuel characteristics comprises any one or more of:
i) changing an operating parameter of a thermal management system of the gas turbine engine;
ii) changing a fuel temperature of the fuel in the gas turbine engine; and or
iii) the change of a flight characteristic of the aircraft, preferably an altitude of the aircraft, more preferably a cruising altitude. A method (1070) of operating an aircraft having a gas turbine engine, the method comprising:
determining (1071), during use of the gas turbine engine (10), one or more contrail parameters related to the formation of contrail by the gas turbine engine (10), in wherein determining (107) the one or more contrail parameters comprises performing (1073) a sensor measurement on a region behind the gas turbine engine in which a contrail is or may be formed, and wherein the one or more control parameters are determined during variable operation of the aircraft and correspond to a value of a variable parameter at which contrail begins to form; And
controlling (1074) the operating parameter of the aircraft or gas turbine engine according to the one or more contrail parameters. The method of claim 20, wherein the variable aircraft operation may be a climb phase of the aircraft operation. Aircraft (1) comprising the fuel characteristic determining system (140) of one of claims 11 to 17, further comprising a control system arranged to control the operation of the aircraft (1) or of the turbine engine according to the one or more fuel characteristics determined by the fuel characteristic determining system (140).