DE102018222158A1 - Method for operating a fuel system and fuel system - Google Patents

Abstract

The invention relates to a method for operating a fuel system for supplying an internal combustion engine with fuel, in particular natural gas, in which the fuel is stored in a tank (1), fed to a rail (3) by means of a pump (2) and with the aid of at least one the rail (3) connected, electrically controllable injector (4) is metered and in which the following steps are carried out before the fuel metering: a) determining the speed of sound (c) in the fuel, b) measuring the pressure (p) and the temperature ( T) of the fuel, c) determining the fuel composition by comparing the determined speed of sound (c) with the speed of sound (c) of known fuel compositions at a given pressure (p) and a given temperature (T), d) determining material data of the fuel composition that is suitable for the For fuel metering are relevant, e) use the determined substance data as correction variables for the fuel add The invention further relates to a fuel system for supplying an internal combustion engine with fuel.

Description

The invention relates to a method for operating a fuel system for supplying an internal combustion engine with fuel, in particular with natural gas. The invention further relates to a fuel system for supplying an internal combustion engine with fuel, in particular with natural gas. The fuel system according to the invention is particularly suitable for performing the method according to the invention.

State of the art

Natural gas is a gas mixture containing hydrocarbons, the chemical composition of which - depending on the source - can fluctuate considerably. The main component of natural gas is methane. In addition, higher-chain hydrocarbons such as ethane and / or propane can be included. Natural gas can also contain low-boiling substances, such as nitrogen.

Legislation requires that internal combustion engines that run on natural gas, regardless of the fuel composition in their area of application, must comply with the existing emission limit values. To ensure this with changing fuel quality, the quality must first be determined, for example with the help of a special sensor. The determined quality can then be set manually by the driver or communicated to an engine control unit which adapts the operation of the internal combustion engine accordingly. As an alternative or in addition, compliance with the emission limit values can be ensured by an exhaust gas aftertreatment system, which must be dimensioned sufficiently large for this.

In a fuel system of the type mentioned at the outset, fuel is generally metered using one or more fuel injectors. When metering the fuel, the fuel quality, in addition to other parameters, in particular the pressure and the temperature, represents a variable influencing the flow through the injector. For precise metering, it is therefore necessary to know the qualitative composition of the fuel. The accuracy of the metering in turn has a decisive influence on the safety, smooth running, consumption and pollutant emissions of the internal combustion engine.

The invention is therefore based on the object of increasing the metering accuracy of a fuel system when supplying an internal combustion engine with fuel, in particular with natural gas.

To achieve the object, the method for operating a fuel system with the features of claim 1 is proposed. Advantageous developments of the invention can be found in the subclaims. In addition, the fuel system with the features of claim 10 is proposed.

Disclosure of the invention

1. a) Ermitteln der Schallgeschwindigkeit c im Kraftstoff,
2. b) Messen des Drucks p und der Temperatur T des Kraftstoffs,
3. c) Bestimmen der Kraftstoffzusammensetzung mittels Abgleichen der ermittelten Schallgeschwindigkeit c mit der Schallgeschwindigkeit c bekannter Kraftstoffzusammensetzungen bei gegebenem Druck p und gegebener Temperatur T,
4. d) Ermitteln von Stoffdaten der Kraftstoffzusammensetzung, die für die Zumessung von Kraftstoff relevant sind,
5. e) Verwenden der ermittelten Stoffdaten als Korrekturgrößen für die Kraftstoffzumessung.

In the proposed method for operating a fuel system for supplying an internal combustion engine with fuel, in particular with natural gas, the fuel is stored in a tank, fed to a rail by means of a pump and metered with the aid of at least one electrically controllable injector connected to the rail. The following steps are also carried out before the fuel metering:

1. a) determining the speed of sound c in the fuel,
2. b) measuring the pressure p and the temperature T of the fuel,
3. c) determining the fuel composition by comparing the determined speed of sound c with the speed of sound c of known fuel compositions at a given pressure p and a given temperature T,
4. d) determining substance data of the fuel composition that are relevant for the metering of fuel,
5. e) Using the determined substance data as correction variables for the fuel metering.

The method according to the invention accordingly comprises method steps in which a fuel composition and specific substance data of the fuel composition are determined in order to optimize the fuel metering on the basis of these substance data, which are substance data relevant to metering. The fuel composition and the substance data are determined on the basis of the speed of sound in the fuel. From the ascertained speed of sound in connection with the measured pressure and the measured temperature, in turn all material data relevant for the metering can be determined, and preferably arithmetically.

The method according to the invention has the advantage that the metering or the flow rate through the injector can be controlled on the basis of the data relevant to metering in such a way that the consumption and pollutant emissions of the internal combustion engine are minimized. This in turn has the consequence that a system provided for aftertreatment of exhaust gases from the internal combustion engine can be made smaller. Furthermore, about the Flow rate the amount of energy is determined, which is entered into the internal combustion engine. In particular, the amount of energy entered can be limited in order to meet safety requirements and / or to protect the internal combustion engine.

To determine the speed of sound in step a) of the proposed method, a measurement of the transit time t at a defined barrel length L is carried out with the aid of a sensor, preferably with the aid of an ultrasound sensor. On the basis of the measured or known data, the speed of sound c can then be calculated using the following formula: $$\text{c}=\text{L}/\Delta \text{t}$$

Furthermore, steps a) and b) are preferably carried out at the same time and / or at the same location, preferably in the tank and / or in a high-pressure store, the so-called buffer store, upstream of the rail. The tank and / or the high-pressure accumulator are particularly well suited for transit time measurements to determine the speed of sound, since their dimensions are known. The run length L of the measuring section can thus be easily defined. In addition, the tank and / or the high-pressure accumulator generally already has sensors for measuring the pressure p and / or the temperature T, so that these can be used to carry out step b) of the method according to the invention. The use of additional sensors for measuring the pressure p and / or the temperature T can thus be dispensed with.
Steps a) and b) are advantageously carried out in a pressure and / or temperature range which shows the greatest characteristic differences for a specific fuel composition. The greater the differences, the more precisely the fuel composition can be determined in step c) by means of comparisons. This means that the reliability of the statement made in step c) increases.

As an alternative or in addition, it is proposed that steps a) and b) are each carried out at several locations and / or in different states. The various measurements can be used to check the plausibility, so that the reliability is further increased. For example, measurements can be carried out in the tank and in the high pressure accumulator. Since there are usually different pressures and temperatures in the tank and in the high-pressure accumulator, the conditions at the two measuring locations are different at the same time.

wobei die gemessene Schallgeschwindigkeit mit den hinterlegten Stoffdatenkennfeldern verglichen wird. Anhand der Stoffdatenkennfelder können im Folgenden alle für den Durchfluss durch den Injektor relevanten Stoffdaten als Funktion der Schallgeschwindigkeit c sowie des zugehörigen Drucks p und der zugehörigen Temperatur T ermittelt werden. Die ermittelten Stoffdaten werden vorzugsweise im Steuergerät abgelegt. Dabei kann es sich insbesondere um ein Steuergerät handeln, das auch zur Ansteuerung des mindestens einen Injektors verwendet wird.Steps c) and d) are preferably carried out with the aid of material data maps which are stored in a control unit. The exact substance data are determined by comparison according to the formula: $${\text{c}}_{\text{Measurement}}=\text{c}\left(\text{p}\begin{array}{ccc},& \text{T},& \text{composition}\end{array}\right),$$

whereby the measured speed of sound is compared with the stored material data maps. All material data relevant to the flow through the injector can be determined as a function of the speed of sound c as well as the associated pressure p and the associated temperature T on the basis of the material data characteristic fields. The determined substance data are preferably stored in the control unit. In particular, this can be a control device that is also used to control the at least one injector.

In step d) of the proposed method, the fuel density and / or the calorific value are preferably determined. In addition to the speed of sound, the fuel density represents a variable that determines the flow through the injector. Therefore, knowledge of the fuel density is important for controlling the injector. The calorific value of the fuel composition determines the energy content or the amount of energy that is entered into the internal combustion engine with the metering of fuel. Depending on the composition of the fuel, the energy content must be limited for safety reasons and / or to protect the internal combustion engine, so that, knowing the calorific value, this variable can also be used as a correction value or correction variable when metering the fuel.

The substance data determined in step d) are preferably used in step e) to adapt the control parameters, in particular the electrical control duration, of the at least one injector. The flow through the injector can be varied via the electrical activation duration, so that the optimal electrical activation duration can be selected depending on the respective fuel composition. This is preferably done automatically with the aid of the control unit, so that no more settings have to be made manually or manually.

In a development of the invention, it is proposed that the substance data of the fuel composition determined in step d) be made available to further functions. The substance data are preferably made available via the control unit, in which the substance data are preferably stored.

The proposed fuel system to supply a Internal combustion engine with fuel, in particular with natural gas, comprises a tank for storing the fuel, a pump by means of which the fuel can be fed from the tank to a rail and at least one electrically controllable injector connected to the rail for metering fuel. The fuel system further comprises at least one sensor, in particular an ultrasonic sensor, for determining the speed of sound c and at least one sensor for measuring the pressure p and the temperature T of the fuel, the sensors in the area of the tank and / or in the area of a high-pressure accumulator upstream of the rail arranged and connected in a data-transmitting manner to a control device.

The proposed fuel system has all the components required to carry out the method according to the invention described above, so that the fuel system is suitable for carrying out this method. This means that the same advantages can be achieved with the aid of the proposed fuel system. In this regard, reference is made to the corresponding statements in connection with the description of the method according to the invention. In addition, the proposed fuel system is characterized in that it does not require any complex sensors, in particular no expensive quality sensor, to estimate the qualitative fuel composition. The required pressure and temperature measurements can be carried out using the existing sensors. Only an additional sensor, preferably an ultrasonic sensor, is to be provided for determining the speed of sound. This is preferably arranged in the area of the tank or the high pressure accumulator. A sensor can also be arranged in the area of the tank and in the area of the high-pressure accumulator, for example, to enable the measurements to be checked for plausibility. In this context, “in the area” means on or in the tank or high-pressure accumulator, so that the pressure and / or the temperature and / or the speed of sound can be measured in the respective container.

• 1 eine schematische Darstellung eines erfindungsgemäßen Kraftstoffsystems zur Versorgung eines Verbrennungsmotors mit Erdgas,
• 2 ein Diagramm zur Darstellung der Schallgeschwindigkeit in unterschiedlichen Erdgaszusammensetzungen in Abhängigkeit vom Druck, bei einem Druckbereich von 5 bis 20 bar, und
• 3 ein Diagramm zur Darstellung der Schallgeschwindigkeit in unterschiedlichen Erdgaszusammensetzungen in Abhängigkeit vom Druck, bei einem Druckbereich von 200 bis 500 bar.

The invention is explained below with reference to the accompanying drawings. These show:

• 1 1 shows a schematic illustration of a fuel system according to the invention for supplying an internal combustion engine with natural gas,
• 2nd a diagram showing the speed of sound in different natural gas compositions depending on the pressure, at a pressure range of 5 to 20 bar, and
• 3rd a diagram showing the speed of sound in different natural gas compositions depending on the pressure, at a pressure range of 200 to 500 bar.

Detailed description of the drawings

That in the 1 schematically illustrated fuel system for supplying an internal combustion engine with natural gas comprises a tank 1 , in which the natural gas is stored in liquid form. In the tank 1 is a pump 2nd arranged, with the help of natural gas indirectly via a high pressure accumulator 6 a rail 3rd is fed. The high pressure accumulator 6 is a heat exchanger 9 upstream for heating the natural gas. Both in the tank 1 as well as in the high pressure accumulator 6 the pressure and temperature with the help of a sensor 8th monitors, each of which is a pressure and temperature sensor. Alternatively, the pressure and temperature can also be measured using individual sensors. The sensors 8th are about control lines 10th with a control unit 7 connected so that by means of the sensors 8th measured data to the control unit 7 can be transmitted.

The control unit 7 is used for the electrical control of several injectors 4th that to the rail 3rd are connected. The injectors 4th are also for this purpose via control lines with the control unit 7 connected in a data-transferring manner (not shown). The control unit 7 determines the electrical activation duration of the injectors 4th for the required amount of fuel depending on the composition, pressure and temperature of the fuel.

In the tank 1 and in the high pressure accumulator 6 is another sensor 5 arranged, each in the present case an ultrasonic sensor for determining the speed of sound in the fuel. With the help of the sensors 5 are runtime measurements over a defined run length in the tank 1 or in the high pressure accumulator 6 carried out. The sensors 5 are also via control lines to the control unit 7 connected (not shown), so that this data is sent to the control unit 7 be available.

Based on the determined speed of sound, which is compared with material data maps, in the control unit 7 are then all the flow through the injectors 4th influencing material data determined as a function of the speed of sound and the associated pressure or temperature. These substance data include in particular the density and the calorific value of the fuel or the fuel composition. The electrical control of the injectors can then be based on this material data 4th be adapted so that the fuel metering is optimized with regard to the consumption and pollutant emissions of the internal combustion engine. Furthermore, the energy content entered via the metering of fuel can be limited, for example to increase safety.

In the 2nd and 3rd exemplary characteristic curves for the speed of sound c in natural gas as a function of pressure p are shown. The parameter of the family of curves is the fuel composition. A specific composition of the natural gas can be concluded by comparing a determined speed of sound with corresponding characteristic curves. In the 2nd the speed of sound c for liquid natural gas (LNG) is shown at 113 k over a pressure range of 5 to 20 bar. The pressure p in a tank is usually within this pressure range 1 for liquid natural gas. In the 3rd the speed of sound c is given for gaseous natural gas (NG) at 273 K over a pressure range of 200 to 500 bar. The pressure p in a high-pressure accumulator is usually within this pressure range 6 .

Claims (10)

Method for operating a fuel system for supplying an internal combustion engine with fuel, in particular natural gas, in which the fuel is stored in a tank (1), fed to a rail (3) by means of a pump (2) and to the rail (3 ) connected, electrically controllable injector (4) and in which the following steps are carried out before the fuel metering: a) determining the speed of sound (c) in the fuel, b) measuring the pressure (p) and the temperature (T) of the fuel, c) determining the fuel composition by comparing the determined speed of sound (c) with the speed of sound (c) of known fuel compositions at a given pressure (p) and a given temperature (T), d) determining substance data of the fuel composition that are relevant for the metering of fuel, e) Using the determined substance data as correction variables for the fuel metering. Procedure according to Claim 1 , characterized in that to determine the speed of sound in step a), with the aid of a sensor (5), preferably with the aid of an ultrasound sensor, a transit time measurement (t) is carried out at a defined barrel length (L). Procedure according to Claim 1 or 2nd , characterized in that steps a) and b) are carried out simultaneously and / or at the same location, preferably in the tank (1) and / or in a high-pressure accumulator (6) upstream of the rail (3). Method according to one of the preceding claims, characterized in that steps a) and b) are carried out in a pressure and / or temperature range which shows the greatest characteristic differences for a specific fuel composition. Method according to one of the preceding claims, characterized in that steps a) and b) are each carried out at several locations and / or in different states. Method according to one of the preceding claims, characterized in that steps c) and d) are carried out with the aid of material data maps which are stored in a control unit (7) which is preferably used to control the at least one injector (4). Method according to one of the preceding claims, characterized in that the fuel density and / or the calorific value is or are determined in step d). Method according to one of the preceding claims, characterized in that the substance data determined in step d) are used in step e) to adapt the control parameters, in particular the control duration, of the at least one injector (4). Method according to one of the preceding claims, characterized in that the substance data of the fuel composition determined in step d) are made available to further functions, the substance data preferably being made available via the control unit (7). Fuel system for supplying an internal combustion engine with fuel, in particular with natural gas, comprising a tank (1) for storing the fuel, a pump (2) by means of which the fuel from the tank (1) can be fed to a rail (3) and at least one the rail (3) connected, electrically controllable injector (4) for metering fuel, further comprising at least one sensor (5), in particular an ultrasonic sensor, for determining the speed of sound (c) and at least one sensor (8) for measuring the pressure (p) and the temperature (T) of the fuel, the sensors (5, 8) being arranged in the region of the tank (1) and / or in the region of a high pressure accumulator (6) upstream of the rail (3) are connected to a control device (7) in a data-transmitting manner.

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