FR3087876A1 - COMBUSTION CHAMBER ASSEMBLY - Google Patents

Abstract

The invention relates to an assembly (1) for an annular combustion chamber with a longitudinal axis (A) for a turbomachine comprising an annular chamber bottom wall (8) through which a plurality of fuel injectors (14) are distributed regularly around it. the longitudinal axis (A) and connected to fuel supply means, characterized in that it comprises means for controlling individual means for controlling the fuel flow (28) of each injector (14).

Description

DOMAIN COMBUSTION CHAMBER KIT

[1] The present invention relates to combustion chambers for a turbomachine, such as a turbojet or an aircraft turboprop.

CONTEXT

[2] A major stake in the development of turbomachines is to reduce fuel consumption, mainly for economic but also ecological reasons.

Since the reduction in fuel consumption must not have an impact on the operability of the turbomachine, that is to say the various desired operations of the turbomachine, techniques such as sectored combustion have been developed.

[3] Sector burning has been used on certain aircraft turbomachines and on land turbines.

This technique is based on the use of two fuel rails each supplying part of the injectors, in combination with a valve for opening / closing the fuel flow in the second supply rail of the associated injectors.

Such a technique makes it possible to reduce carbon monoxide (CO) emissions when the turbomachine is operating at idle speed and to limit the risks of the combustion chamber going out by preventing the supply of the injectors connected to the second rail.

[4] However, this type of sectorized combustion has drawbacks.

In fact, when the supply is interrupted in the second rail via the valve, the injectors connected to this rail which do not deliver fuel may be subject to the formation of coke under certain operating conditions of the chamber of 2. combustion.

Such coking can lead to the obstruction of these injectors, impacting the operability of the turbomachine.

[5] In addition, the supply of the injectors does not make it possible to optimize the performance of the turbomachine during these different operating speeds.

[6] The object of the invention is in particular to provide a simple, effective and economical solution to the drawbacks of the current technique described above.

SUMMARY OF THE INVENTION 10

To this end, there is proposed an annular combustion chamber assembly with a longitudinal axis for a turbomachine comprising an annular chamber bottom wall through which a plurality of fuel injectors are distributed regularly around the longitudinal axis and connected. to fuel supply means, characterized in that it comprises means for controlling individual means for controlling the flow of fuel from each injector.

[8] Such an assembly, having individualized means dedicated to adjusting the flow rate of each injector, makes it possible to modify the richness of the air-fuel mixture of each sector of the combustion chamber 20 with which one or more injectors is associated, that is, that is to say the proportion of air relative to the proportion of fuel, and thus to optimize the performance of the combustion chamber.

Furthermore, this assembly makes it possible to reduce the risks of extinction, non-ignition and combustion instability, while reducing the emissions of smoke and polluting gases (for example CO, CH, NOx).

[9] Depending on the desired performance, this assembly makes it possible to control the operating richness of the sectors of the combustion chamber, independently of the overall richness of the combustion chamber.

Thus, this assembly allows operation of the 3rd combustion chamber in lean overall richness during speeds close to full throttle in order to limit smoke and NOx emissions.

Also, the whole ensures sufficiently high local wealth in the fuel injection sector of an injector during 5 intermediate speeds and speeds close to idling to limit CO and CH emissions while preserving the chamber from unwanted extinction.

[10] According to an additional characteristic, the supply means may comprise a single annular fuel supply rail connected to each of the means for controlling the fuel flow of an injector.

[11] The assembly only requires a supply ramp, unlike the combustion chambers of the prior art where the sectorization is performed by associating each sector with a supply ramp.

In all 15 proposed here, the individual control means make it possible, with a single ramp, to manage the control of the richness in each combustion sector.

[12] In addition, said flow control means may be a solenoid valve.

[13] Furthermore, said control means can be integrated into a computer of a turbomachine, such as for example a FADEC system (in English, Full Authority Digital Engine Control).

[14] Such an integration thus allows dynamic control of the ignition of the injectors as well as their fuel flow according to predefined cycles in response to a setpoint relating to the operating speed of the engine (idle, full throttle, cruising, deceleration). and external conditions (temperature, pressure, speed and flow).

[15] A method of supplying fuel to a combustion chamber is also proposed for an assembly as described above as well as two internal and external coaxial annular shrouds connected at their upstream ends to the annular chamber bottom wall.

The method comprises the following steps: 4 a) Determining the engine speed; b) Control the supply of part of the injectors by means of individual flow control means.

[16] By engine speed is meant the speed of rotation of the shaft of the high pressure compressor.

The engine speed can, for example, be measured by means of a tone wheel.

[17] Such a method makes it possible to individually control the flow of fuel injected by each of the injectors, thus making it possible to adapt, to the engine speed, in a finer manner than in the prior art, the richness of the air-mixture. fuel by fuel injection sector, the sectors also being modular by changing the patterns of the injectors delivering fuel.

[18] Furthermore, step b) can be carried out by keeping constant the total flow rate of the fuel conveyed to all the individual means for controlling the flow rate.

[19] Thus, the process makes it possible to vary the local richness of the sectors while maintaining the overall richness of the combustion chamber adapted to the engine speed.

[20] Also, for a combustion chamber further comprising at least one spark plug, step a) can be preceded by the steps: Controlling the individual flow control means so that only a first injector, arranged circumferentially near the spark plug 25 of the combustion chamber, is supplied with fuel; Controlling the flow control means so that at least one second injector circumferentially adjacent to said first injector is supplied; Control the individual flow control means 30 so that the remaining injectors are successively supplied with fuel in a circumferential direction from said at least one second injector.

[21] This makes it possible to optimize combustion, while maintaining a margin in relation to the risks of extinction, but also to limit combustion instabilities by modifying the flame response to acoustic disturbances or by eliminating the circumferential periodicity of the temperature. and chamber pressure.

[22] According to additional characteristics, step b) can vary according to a period dt. 10

[023] The invention will be better understood and other details, characteristics and advantages of the invention will become apparent on reading the following description given by way of non-limiting example with reference to the appended drawings.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic sectional view of an assembly according to the invention; - Figure 2 is a schematic view of an assembly for a combustion chamber; FIGS. 3A, 3B, 3C and 3D are diagrams of examples of injection patterns in static mode; FIG. 4 is a diagram of an example of a periodically variable injection pattern, in dynamic mode.

DETAILED DESCRIPTION

[024] FIG. 1 illustrates an assembly 1 comprising an annular combustion chamber 25 2 for a turbomachine, such as for example an airplane turbojet or turboprop.

The annular combustion chamber 2 comprises two rings or annular walls, internal 4 and external 6, substantially frustoconical, the section of which increases towards 6 downstream, and coaxial with a longitudinal axis extending downstream and being connected at their ends. upstream to an annular chamber bottom wall 8.

An annular fairing or cowling 10 fixed to the bottom of the chamber 8 extends upstream and comprising passage orifices 12 of the heads 5 of injectors 14.

[25] The terms upstream and downstream are defined with respect to the direction of gas flow within the turbomachine.

The terms axial and radial are defined with respect to the axis A of the turbomachine.

[26] The fairing 10 guides the flow of air leaving the high pressure compressor 10 upstream of the turbomachine and divides it into a central air flow which supplies the combustion chamber 2 and into two peripheral annular veins which bypass the combustion chamber. combustion 2.

[27] The air coming from the compressor is brought into the combustion chamber 2, in particular through augers 16, and mixed with the fuel coming from the 15 injectors 14.

The combustion of the air-fuel mixture is initiated by at least one spark plug 18 mounted on an outer casing 20, passing through the outer annular shell 6 and emerging between the inner 4 and outer annular rings 6 in the annular injection space. fuel. 20

[028] As can be seen in FIG. 2, each injector 14 of the assembly passes through the annular chamber bottom wall 8, and the injectors 14 are regularly distributed around the longitudinal axis A of the combustion chamber 2.

The injectors 14 are connected to fuel supply means which comprise a single annular fuel supply rail 22, of longitudinal axis A, and disposed radially outside the outer casing 20.

The supply means also comprise individual supply conduits 24 of each injector 14, connecting the annular supply rail 22 to each of the injectors 14.

FIG. 2 also shows the mounting plates or flanges 26 of each injector 14 on the radially outer face of the outer casing 20. 7

[29] In particular, between each individual duct 24 and the annular feed rail 22, there are individual means for controlling the flow 28, making it possible in particular to control the fuel flow from the feed rail 22, conveyed by through the individual duct 24 to the injector 14.

[30] The individual flow control means 28 are thus dedicated control means for each injector 14, individualized, so that the flow of fuel conveyed to each injector 14 can be controlled independently of each other. 10

[031] The individual flow control means 28 may for example be solenoid valves.

The solenoid valves can be of the all or nothing type, that is to say can take two positions: open or closed.

For more precise control of the flow, the solenoid valves can be of the proportional type, the opening of which is proportional to the electric current supplied.

[32] Thus, each of the individual means for controlling the flow 28 of fuel conveyed to the injectors 14 is connected to the annular fuel supply rail 22 of the assembly.

[33] Each of these individual flow control means 28 is controlled by means of control means, making it possible to send each of the instructions relating to the desired fuel flow rate, conveyed to the injectors 14, as a function of the operating speed. operation of the turbomachine.

[34] The electrical control means can for example be integrated into an onboard computer of the turbomachine, in particular into a FADEC system allowing the interface between the cockpit and the engine of the aircraft.

The control means send instructions to the individual flow control means 28 taking into consideration the speed of the turbomachine. 30

[035] This assembly 1 allows the implementation of methods of supplying fuel to a combustion chamber 2. 8

[36] The common point of these processes is to vary locally, in certain sectors of the combustion chamber, the richness of the air-fuel mixture while maintaining the same overall richness value.

[37] As illustrated by FIG. 2, the injectors 14 are regularly distributed around the longitudinal axis A of the combustion chamber.

The sectors of the combustion chamber 2, visible in FIGS. 3A, 3B, 3C and 3D, are the angular portions comprising one or more injectors 14 of which the individual flow control means 28 are in the same state, with respect to the 'longitudinal axis A. 10

[038] As detailed above, the individual control means 28 are able to assume two states, a closed state where the fuel flow is zero, and an open state, where the fuel flow is non-zero.

Each of the individual driving means 28 is controllable so that, independently of each other, they can be switched from a closed state to an open state and vice versa.

[39] As can be seen in Figures 3A, 3B, 3C and 3D, some of the injectors 14 are powered (shown in white), and others are not powered (shown in black), depending on the state (open or closed) of the individual control means 28 to which the injectors 14 20 are connected.

[40] The sectors are defined as the angular sectors of the combustion chamber 2, comprising one or more consecutive injectors 14 being in the same state, that is to say supplied or not supplied. 25

[041] The position and condition of all the injectors 14 of the combustion chamber 2 is called a “pattern”.

These patterns can be static (static mode), or variable as a function of time (dynamic mode).

[042] In general, the methods of supplying an assembly as described above comprise the following steps: a) determining the engine speed; 9 b) Control the supply of part of the injectors 14 by means of the flow control means 28.

[043] The steps of this method can be partially or fully supervised by the FADEC system of the aircraft. 5

[044] Thus, the computer, integrating the control means, determines, by recovering a multitude of control data, the operating speed of the engine.

[45] By taking into account the engine operating speed, a fuel pattern for the injectors 14 is chosen in static mode or in dynamic mode.

The solenoid valves 28 are thus controlled and synchronized by means of the computer, as a function of the environment as well as the performance of the desired engine.

[46] Step b) can also be carried out by maintaining constant the total flow rate of the fuel conveyed to the flow control means.

To do this, the opening and closing of the solenoid valves 28 of each injector 14 are slightly offset in time to limit the phenomenon of "water hammer", that is to say to limit the strong variations in pressure in the ramp 22 supplying the tank. 'set of injectors 14.

[47] Step b) consists in authorizing or not the supply of certain injectors 14, so that certain injectors 14 are debiting and others not debiting.

[48] The number of non-flowable injectors 14, as well as the pattern, is chosen so as to ensure the best compromise between the desired combustion performance and the circumferential heterogeneities, in particular in temperature, which may affect modules located downstream of the combustion chamber. the combustion chamber 2, such as for example the high pressure turbine.

Thus, this choice depends on the operating speed of the engine which may be transient (ignition, winding, acceleration, deceleration) or stabilized, on the fuel flow rate and on environmental parameters such as temperature, pressure and humidity. 10

[049] Examples of patterns in static mode are illustrated in Figures 3A, 3B, 3C and 3D.

These figures illustrate examples of patterns for twelve injectors 14 flow, that is to say supplied, and six injectors 14 non-flow, that is to say not supplied. 5

[050] The pattern of FIG. 3A is an example of a pattern making it possible to promote combustion, in particular when the aircraft is in the descent phase.

An injector 14 does not flow over three successive injectors 14 circumferentially.

[51] The pattern of Figure 3B has an advantage when the engine speed operation is at idle, for example on the ground.

This pattern is characterized by two successive injectors 14 which do not flow on six successive injectors 14.

In particular, it makes it possible to limit CO emissions when the aircraft is on the ground.

[52] Figure 3C also illustrates a pattern for reducing CO emissions at engine idle speed, the pattern being distinguished from 3B by its non-periodicity.

[53] Figure 3D illustrates a pattern to promote flame propagation after ignition of the turbomachine.

This pattern is characterized by an angular sector of the combustion chamber 2 in which none of the 20 injectors 14 is discharging.

[54] In general, axisymmetric and non-axisymmetric patterns of flow and non-flow injectors 14 can be considered depending on the operating speed and the desired performance of the turbomachine. 25

[055] The number of non-outputting injectors 14 can vary dynamically and periodically for an engine operating speed, in particular when it is transient.

[056] For example, step b) of the process can vary according to a period dt.

Among other things, the period dt is adapted to the operating speed of the engine, as well as to the desired performance. 11

[57] In a particular example, when the turbomachine is started, when the combustion chamber 2 is ignited, the number of non-flow injectors 14 can vary dynamically but not periodically.

Step a) of the feed method described above can be preceded by the following steps, for ignition of the combustion chamber 2: Control the flow control means 28 so that a first injector 14, arranged nearby the ignition plug 18 of the combustion chamber 2 is supplied with fuel; Control the flow control means 28 so that at least one second injector 14 circumferentially adjacent to said first injector 14 is supplied; Control the flow control means 28 so that the remaining injectors 14 are successively supplied with fuel in the circumferential direction from said at least one second injector 14.

[58] In other words, during ignition, the injectors 14 close to the spark plug 18 are controlled to be debiting, then the solenoid valves 28 are individually controlled so that the neighboring injectors 14 step by step and circumferentially are debiting to ensure the flame spread throughout the chamber.

[59] Apart from the particular case of the ignition phase of the combustion chamber 2, the dynamic management of the injectors 14 discharging and non-discharging, allows, with constant combustion chamber 2 richness, to vary the local richness in the sectors where the injectors 14 are discharging, that is to say supplied.

This control of the local richness thus makes it possible to optimize the combustion in the following areas: the extinction margin, the ignition capacity, the emission of particles and gaseous pollutants, the combustion instability margin.

[60] The dynamic control of the richness by sector, makes it possible, during a prolonged operation, to control the duration of cut-off of the supply of each of the injectors 14, according to a pattern and a periodicity of the sectorized combustion.

FIG. 4 illustrates an example of a dynamic mode of periodic variation of the pattern of an assembly 1, comprising eighteen injectors 14.

Each injector 14 is supplied, therefore discharging, for two periods, that is to say 2 x dt and not supplied, therefore not discharging, for a period cit.

The period dt as well as the pattern are chosen so as to obtain the best combustion performance, also depending on the flow rate of the feed fuel, on the pressure and on the temperature of the chamber 2.

The feed and cut-off times of the injectors 14 are also chosen so as to ensure a satisfactory self-ignition delay when the injectors 14 are refueled.

[061] The dynamic control of the injectors 14 can therefore be based both on pre-established laws, stored in the memory of the FADEC system or of a computer, based on the operating speed of the engine 15 (for example taking into account the conditions. speed, stabilized or transient engine operating speed, water ingestion, icing conditions) but also on laws based on real-time monitoring of the thermal state of the engine, of the supply conditions of the engine. combustion chamber 2 (fuel flow) and engine response 20 (speed gradients, downstream gas chamber temperatures,

Claims (8)

CLAIMS 1. Assembly (1) of annular combustion chamber (2) of longitudinal axis (A) for a turbomachine comprising an annular chamber bottom wall (8) through which a plurality of fuel injectors (14) are regularly distributed around the longitudinal axis (A) and connected to fuel supply means, characterized in that it comprises means for controlling individual means for controlling the fuel flow (28) of each injector (14). 2. Assembly (1) according to claim 1, characterized in that the supply means comprise a single annular fuel feed rail (22) connected to each of the individual means for controlling the fuel flow (28) of an injector (14). 3. Assembly (1) according to claim 1 or 2, characterized in that said individual flow control means (28) is a solenoid valve. 4. Assembly (1) according to one of claims 1 to 3, characterized in that said control means are integrated into a computer of a turbomachine. 5. A method of supplying fuel to a combustion chamber (2) comprising an assembly (1) according to one of the preceding claims, comprising the following steps: a) determining the engine speed; b) Controlling the supply of part of the injectors (14) by means of the individual flow control means (28). 6. The supply method according to claim 5, wherein step b) is carried out by maintaining constant the flow rate of the fuel conveyed to the individual flow control means (28). 7. A method of supplying according to claim 5 or 6 of a combustion chamber (2) further comprising at least one spark plug (18), wherein step a) is preceded by steps: individual flow control means (28) so that a first injector (14), arranged circumferentially close to the spark plug (18) of the combustion chamber (2), is supplied with fuel; Controlling the individual flow control means (28) so that at least one second injector (14) circumferentially adjacent to said first injector (14) is supplied; Control the individual flow control means (28) so that the remaining injectors (14) are successively supplied with fuel in the circumferential direction 1c from said at least one second injector (14). 8. Feeding method according to one of claims 5 to 7, wherein step b) varies according to a period dt.