FR3001525A1 - Method for managing fuel consumption of twin-engine assembly of helicopter, involves operating engine by supplying fuel throughout start-up injector and by interrupting power supply of main injector in super-idle mode - Google Patents

Abstract

The method involves using a main injector (18) emerging in a combustion chamber (10) and adapted to feed the combustion chamber with fuel when combustion is initiated. A feeding circuit is provided to feed fuels to a start-up injector (17) and the main injector. A turbo-shaft engine (1) is adapted to function in a super-idle mode. The engine is operated by supplying the fuel throughout the start-up injector and by interrupting power supply of the main injector in the super-idle mode. An independent claim is also included for a twin engine assembly.

Description

PRESENTATION OF THE INVENTION The invention relates generally to the field of turbomachines, and more specifically the methods of managing the fuel consumption of an assembly comprising two turbomachines.

The invention also relates to a twin engine assembly adapted for implementing such a management method. STATE OF THE ART It is known from FR2967133 a process for optimizing the fuel consumption of a helicopter comprising two turbomachines, during which one of the two turbomachines is stabilized at a low engine speed called Super Slow-motion, this regime being a zero power regime characterized by a rotational speed of the gas generator significantly lower than the standard idling speed, typically between 0 and 30 to 35% of the rotational speed corresponding to the maximum power of the engine, while the other turbomachine delivers the power necessary for the stabilized flight. This Super Slow motion allows a good operational performance of the helicopter, since the fuel consumption thereof is significantly reduced, while allowing to quickly restore the speed of the turbomachine concerned to a regime of flight at nominal power. The Super Slow-motion system even makes it possible to obtain, almost instantaneously, an operating regime implemented in the case where an engine is inoperative, called the 0E1 scheme (acronym for "One Engine Inoperative" in English), during which the A valid turbine engine provides more power than its rated power to allow the helicopter to continue its flight. However, the operation in Super Slow mode of a turbomachine requires to operate with an extremely low fuel flow, which poses several problems. Referring to Figure 1, there is shown a sectional view of the combustion portion of a turbomachine 1 capable of implementing a super slow speed. This turbomachine comprises a combustion chamber 10 into which a plurality of fuel injectors opens, fed by a fuel supply circuit (not shown). There are two types of fuel injectors: the starter injectors 17, adapted to initiate combustion, and the main injectors 18, which maintain combustion with a higher flow rate when it is initiated. The combustion chamber comprises two outer annular walls 14 and inner 12, extending one inside the other and being connected by an annular bottom wall of chamber 16. The fuel injectors are distributed over the entire circumference of the combustion chamber. However, when a turbomachine is in the Super Slow-motion mode, the fuel flow rates of the injectors are very low, to the point that the effects of gravity are significant between injectors positioned at different altitudes in the operating position of the turbomachine. This generates flow differences between such injectors, which alters the homogeneity of the temperature field of the gases at the chamber outlet. In extreme situations, this can even lead to no longer burning in the upper part of the room. This inhomogeneity generates hot spots in the combustion chamber or in the high-pressure distributor located at the outlet of the chamber, these hot spots can reduce the life of certain parts. In addition, the low fuel flow used during the Super Slow motion increases the risk of coking in the fuel injection circuit and in the injectors, which creates a risk of clogging of these elements.

PRESENTATION OF THE INVENTION The purpose of the invention is to overcome at least one of the aforementioned problems, by proposing a method for managing the fuel consumption of a twin-engine set allowing the operation of a turbomachine in super-idle mode. , without this regime adversely affecting the life of the elements of the turbomachine. In this respect, the invention proposes a method for managing the fuel consumption of a twin-engine set comprising two turbomachines, each turbine engine comprising: a combustion chamber, at least one starter injector opening into said chamber, and adapted to initiate combustion in said chamber, - at least one main injector opening into the combustion chamber, and adapted to supply fuel to the chamber once the combustion has been initiated, and - a fuel supply circuit for the starter injectors and main injectors, wherein each turbomachine is adapted to operate in a so-called super-idle reduced power regime, characterized in that the super-idle speed of a turbomachine is implemented by supplying fuel to all the injectors starting, and interrupting the supply of the main injectors. Advantageously, but optionally, the method according to the invention may further comprise at least one of the following technically compatible features: - the interruption of the feed of the main injectors (18) is followed by the purge of said injectors. - The starter injectors are fed continuously so that said injectors are supplied with fuel both during the initiation of combustion and during the supply of the chamber when the combustion is initiated. the starter injectors are fed during a start-up phase of the turbomachine and during the super-idle speed of the turbomachine, the supply of said starter injectors being interrupted between the start-up phase and the super-speed regime; -slow motion.

The invention also proposes a twin engine assembly adapted to implement the consumption management method, said assembly comprising two turbomachines, each turbomachine comprising: a combustion chamber, comprising two walls of external and internal revolution extending one inside the other and being connected by an annular bottom wall of chamber, - at least one starter injector opening into said chamber, and adapted to initiate combustion in said chamber, - at least one main injector opening into the combustion chamber, and adapted to supply fuel to the chamber once the combustion initiated, and - a fuel supply circuit of the starter injectors and main injectors, the twin engine assembly being characterized in that each turbine engine comprises minus two starter injectors and in that the fuel supply circuit is adapted to supply fuel the starter injectors and interrupting the supply of the main injectors during a so-called super-idle mode, the fuel supply circuit comprising a purge circuit of the main injectors. Advantageously, but optionally, the twin engine assembly according to the invention may further comprise at least one of the following features: - the starter injectors are arranged regularly around the circumference of the combustion chamber. the combustion chamber is of the type with pre-vaporization rods, aerodynamic injector chamber or aeromechanical injector chamber. the main injectors are distinct from the starter injectors, and the starter injectors are oriented towards the chamber bottom wall. - Each starter injector is adapted to diffuse a fuel beam having an angular opening in a first direction between 120 ° and 180 °, and an angular aperture of between 15 and 35 ° in a second direction orthogonal to the first direction. - The assembly comprises a plurality of dual circuit injectors, in each dual circuit injector being integrated a main injector and a starter injector, all the starter injectors being integrated in a dual circuit injector, said dual circuit injectors being adapted to diffuse a conical fuel beam.

The use of the starter injectors during a Super Slow motion makes it possible to maintain a turbomachine at a lower speed than the zero power regime and provides many advantages. The fuel injection pressure of the starter injectors makes it possible to make negligible the effects of gravity on the various positions of the injectors. In addition, the arrangement of the starter injectors allows a carburization of the recirculation core of the primary zone - in the case of a chamber with pre-vaporization rods - and thus to maintain a homogeneous temperature field in the combustion chamber, which maintains the service life of the parts. In addition, the continuous supply of these starter injectors during the Super Slowdown eliminates the risk of coking the main injectors during this phase of operation. The risk of coking starter injectors remains limited because, because of their reduced number, the fuel flow they deliver individually remains consequent which helps to cool them. It should also be noted that, in the event of coking occurring during the super-idling phases: - The detection of clogging can be carried out relatively early by the degradation of the ignition performance that it can induce - The maintenance operation to put back in state the starter injectors is simplified compared to a maintenance operation that would require intervention on all the main injectors. DESCRIPTION OF THE FIGURES Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which: FIG. 1, already described , represents a partial axial sectional view of a turbomachine, - Figure 2 schematically shows a two-engine assembly architecture according to the invention, and - Figure 3a shows in partial sectional view a turbomachine of such a twin-engine set comprising a chamber with pre-vaporization rods. FIG. 3b is a partial sectional view of a turbomachine of a twin engine assembly comprising a chamber with aerodynamic or aeromechanical injectors; FIG. 4 is a partial sectional view of a turbomachine according to another embodiment of the invention; - Figure 5 shows an embodiment of a fuel distribution circuit of a turbomachine. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION There is shown in FIG. 2 an example of a twin-engine assembly 100 adapted to implement a so-called super-idle regime, that is to say a speed or the power of the turbomachine is zero and where the rotational speed of the gas generator is between 0 and 30 to 35%, preferably between 0 and 20%, of the rotational speed of the gas generator (100% corresponding to the maximum power of said turbomachine). This set comprises two turbomachines 1 and 2, each turbine comprising a gas generator 11, 21 and a free turbine 12, 22 supplied by the gas generator to provide the power. The output of the turbomachines is connected to a power transmission box 3. Each gas generator 11, 21 comprises a combustion chamber 10, 20 supplied with fuel by a fuel distribution circuit 40 (not shown in FIG. ). Each turbine engine 1,2 is coupled to drive means E1 and E2 and to emergency assistance devices, U1 and U2. Each drive means E1, E2 in rotation of the respective gas generator 11, 21 may be constituted by a starter respectively powered by a starter / generator device equipping the other turbomachine. The drive means E1, E2, the emergency assistance devices U1, U2 and the controls of the turbomachines 1, 2 are managed by a control system 4. The assembly shown in FIG. 2 is adapted to operate then that one of the turbomachines operates in regime called "Super Slow", that is to say during which a turbomachine operates while the other is maintained in operating state at zero power. The super-idle speed of a turbomachine can be achieved by one of the following ways: by keeping the turbomachine in rotation, whether the corresponding combustion chamber is off or on, the speed of rotation then being in the window of ignition of the combustion chamber if it is extinguished, - with a zero rotation speed with the chamber off, the rotation being then advantageously produced by the own starter of the turbomachine powered by the on-board network, or - with combustion chamber on with a zero rotational speed of the turbomachine, or - with combustion chamber in standby ignition or partially ignited with a zero or no zero rotation speed of the corresponding turbomachine. If the flight conditions become more difficult, rapid reactivation of the turbomachine in super-idle mode, by activation of its assistance device, can be implemented. In addition, in case of failure of one of the turbomachines, the super-idle turbine engine can be quickly reactivated by the corresponding emergency assistance device.

Referring to Figures 3a and 3b, there is shown partially a turbomachine 1, 2 can implement the super-idle regime. This turbomachine comprises a combustion chamber 10 housed in a casing 30. The combustion chamber comprises two external annular walls 14 and internal 12, extending one inside the other and being connected by an annular wall of 16. The turbomachine 1 further comprises a plurality of fuel injectors opening into the combustion chamber, comprising at least one starter injector 17, and a plurality of main injectors 18.

The ignition system consists of 2 spark plugs (not shown) and 2 or more starter injectors. Each candle is able to ignite a fuel mist and thus initiate combustion in the room. In order to ensure the fuel injection during the super-idle speed with the starter injectors, their number may be increased (advantageously 3 or 4 for example). The starter injectors have a flow number, that is to say a ratio flow in L / h on the square root of the pressure difference in bars of the fuel injected between its pressure at the inlet and the outlet of the injector, less than 10 Flow Number of the main injectors for a given turbomachine. The Flow Number of a main injector of a machine is typically 3 to 10 times the Flow Nomber of a starter injector of the same machine. The Flow Number values of the injectors depend on many factors, but mainly on the power, the cycle of each engine and the number of injectors. By way of non-limiting example, the flow number of a starter injector may be between 1 and 4, preferably between 1.5 and 2, while that of a main injector may be greater than 4, for example between 5 and 15, advantageously between 7 and 12. This difference in Flow Number results from a difference in the functionality of the injectors: the initiation of combustion in the chamber by the starter injectors requires a small amount of fuel, while that the continuation by the main injectors of combustion within the chamber to confer power to the turbomachine requires a much higher flow. The starter injectors penetrate inside the combustion chamber through an orifice in the outer wall of the combustion chamber. The combustion chamber 10 may be of the pre-vaporization rod chamber type, as shown in FIG. 3a, in which each main injector 18 opens into a pre-vaporization rod 19, each rod comprising a conduit opening through two orifices in the combustion chamber. . In the case of a chamber with pre-vaporization rods, the rods 19 penetrate inside the chamber through the outer wall 14 or, as illustrated in FIG. 1 through the bottom wall of chamber 16 and are advantageously oriented towards the chamber bottom wall. Alternatively, the chamber 10 may be of the aerodynamic injection chamber or aeromechanical injection chamber type, as shown in FIG. 3b or 4. In addition, the chamber may be of the inverted flow type, as in the case of FIG. , or direct flow. With reference to FIG. 4, according to a particular embodiment, the starting injectors 17 of the turbomachine can be integrated with injectors 18 'called double-circuit, that is to say injectors comprising two coaxial circuits ( not shown), thus a main injection circuit, providing the function of a main injector 18, and a starting injection circuit, providing the function of a starter injector 17. The characteristics of flow and pressure d Injection of the main injection and starting circuits, in particular in terms of Flow Number, are then analogous to the respective characteristics of the corresponding injectors. The two coaxial circuits open into the chamber through a common output port 180 of the injector. Advantageously, the turbomachine 1 comprises at least as many dual-circuit injectors 18 'as starter injectors 17, so that all the starter injectors are integrated with such an injector 18'. When the turbomachine is controlled in super idle mode, the fuel supply of the main injectors 18 is cut off, so that only the starter injectors 17 are powered. It is therefore the starter injectors that ensure the operation of the turbomachine during the super idle regime. In the case where the turbomachine includes 18 'double-circuit injectors, the super idle speed is provided by supplying fuel to the starter circuit of these injectors. The fuel supply of the main circuit is then cut off. For an engine equipped with the super-idle function, the starter injectors can be supplied with fuel continuously, that is to say both during the initiation of combustion and during the feeding of the chamber. when combustion is initiated. It is also possible to stop the supply of the starter injectors as soon as the start-up phase is over and the engine is running at a certain predetermined power level and then to recharge them when the engine is placed at super-idle speed. As previously stated, the flow number of the starter injectors is low, for example between 1 and 4. Therefore, when a low fuel flow is used during the super-idle speed, the dimensioning of these injectors nevertheless allows the pressure of the injected fuel to be sufficient for the effects of gravity to be negligible. By way of non-limiting example, the injection pressure of the fuel in said injectors during the super idle regime, that is to say for a fuel flow of the order of 3LJh per injector, is greater than 3. bars, advantageously between 3 and 10 bars. Thus the temperature field in the combustion chamber remains homogeneous even in the super idle mode. The fact of not fueling the main injectors during the super idle diet involves purging them after the interruption of their diet, in order to avoid their coking and thus their clogging. To do this, the fuel supply circuit 40 of the starter injectors and the main injectors of the turbomachine, shown schematically in FIG. 5, must be adapted.

It comprises a fuel inlet 41 through which the fuel enters the circuit and is redistributed to the injectors by a fuel distribution and purge system 42. The distribution system 42 is connected to the starter injectors by a supply line 43 of the starter injectors, and to the main injectors by a supply line 44 of the main injectors. To allow the purging of the main injectors, the circuit further comprises a purge circuit 45 connected to the system 42 of distribution and purge of the fuel.

In the case where the turbomachine comprises dual circuit injectors 18 ', the purge circuit 45 is adapted to purge the main circuits of these injectors. The supply duct 43 of the starter injectors is a conduit for supplying the starter injection circuit, and the supply duct 44 of the main injectors is a duct making it possible to supply the main injection circuit of the injectors. double circuit 18 '. In the case where the feed of the starter injectors is continuously maintained outside the start-up phase, it is not necessary to purge them, contrary to what is conventionally done.

Returning to FIGS. 3a and 3b, the characteristics of the combustion chamber must also be adapted so that the starter injectors can ensure the operation of the chamber during the super-idle regime. In this regard, the turbomachine comprises from two to four, and preferably at least two starter injectors 17 preferably distributed regularly, that is to say at constant angular interval, around the circumference of the chamber. In addition, in the case where the starter injectors are separate from the main injectors, the starter injectors 17 are oriented towards the wall 16 of the chamber bottom. In this way, the fuel spray injected by the starter injectors best utilizes the aerodynamics in place in the primary zone which maximizes combustion performance during the super idle regime. In addition, "Flat Spray" starter injectors are used, that is to say of the type in which the cross section of the bundle F has a large angular opening in a first direction, between 120 ° and 180 °. °, and a reduced angular aperture in a second direction, orthogonal to the first, between 15 and 35 °. In FIGS. 3a and 3b, the reduced angular aperture is in the plane of section, the large angular aperture being orthogonal to the latter and to the axis of the turbomachine to allow the fuel to be diffused over a large surface area. the bottom wall 16 of the combustion chamber. The orientation of the injectors and their fuel bundle thus makes it possible to feed fuel directly the recirculation thereof, that is to say its trajectory represented by an arrow in the combustion chamber. The residence time in the primary zone of the combustion chamber, that is to say the area where the injection and ignition of the fuel takes place, is thus high enough to allow almost complete combustion of the fuel.

In addition, the fuel being driven by the recirculation, it is distributed in the dilution zone, adjacent to the primary zone, similarly to the fuel that would have come from the main injectors, which limits the influence of the injection. by the starter injectors on the temperature profile of the gases at the outlet of the chamber.

With reference to FIG. 4, when the turbomachine comprises double-circuit injectors 18 'in which the starter injectors are integrated, the orientation of the starter injectors and the main injectors is the same. This orientation is chosen to optimize combustion in the primary zone and thus ensure the best possible performance.

The double-circuit injectors are themselves adapted to diffuse a conical fuel beam, this fuel bundle being the same for the starting injection part and the main injection part of these injectors. As a result, the fuel injected by the dual-circuit injectors is burned perfectly in the combustion chamber.

Claims (10)

REVENDICATIONS1. A method for managing the fuel consumption of a twin engine assembly (100) comprising two turbomachines (1, 2), each turbine engine comprising: a combustion chamber (10, 20), at least one starter injector (17) opening into said chamber, and adapted to initiate combustion in said chamber, - at least one main injector (18) opening into the combustion chamber, and adapted to supply fuel to the chamber once the combustion initiated, and - a circuit of supply (40) of fuel of the starter injectors and main injectors, wherein each turbine engine is adapted to operate in a so-called super-idle mode, characterized in that the super-idle speed of a turbomachine is set works by supplying fuel to all the starter injectors, and by interrupting the supply of the main injectors. 2. The management method according to claim 1, wherein the interruption of the feed of the main injectors (18) is followed by the purge of said injectors. 3. Management method according to one of claims 1 or 2, wherein the starter injectors are fed continuously so that said injectors are fueled both during the initiation of combustion as in the supply to the chamber when combustion is initiated. 4. Management method according to one of claims 1 or 2, wherein the starter injectors are fed during a startup phase of the turbomachine and during the super-idle speed of the turbomachine, the power supply. said starter injectors being interrupted between the starting phase and the super-idle speed. 5. Twin engine assembly (100) adapted to implement the method according to one of the preceding claims, said assembly comprising two turbomachines (1, 2), each turbine engine comprising: - a combustion chamber (10), comprising two walls of external (14) and internal (12) revolution extending one inside the other and being connected by an annular chamber bottom wall (16), - at least one starting injector (17) opening in said chamber, and adapted to initiate combustion in said chamber, - at least one main injector (18, 18 ') opening into the combustion chamber, and adapted to supply fuel to the chamber once the combustion has been initiated, and - a fuel supply circuit (40) for the starting injectors and the main injectors, the twin engine assembly being characterized in that each turbine engine comprises at least two starting injectors (17) and in that the fuel supply circuit ant (40) is adapted to supply fuel to the starter injectors and to interrupt the supply of the main injectors during a so-called super-idle regime, the fuel supply circuit (40) comprising a bleed circuit (45) of the main injectors (18, 18 '). 6. Twin engine assembly according to claim 5, wherein the starter injectors (17) are regularly disposed on the circumference of the combustion chamber (10). 7. A twin engine set according to one of claims 5 or 6, wherein the combustion chamber is of the type pre-vaporization rod chamber, aerodynamic nozzle chamber or aeromechanical injector chamber. 8. Twin engine assembly according to one of claims 5 to 7, wherein the main injectors (18) are separate from the starter injectors (17), and the starter injectors are oriented towards the chamber bottom wall (16). 9. Twin engine assembly according to one of claims 5 to 8, wherein each starter injector (17) is adapted to diffuse a fuel beampresentant an angular aperture in a first direction between 1200 and 180 °, and an angular aperture included between 15 and 35 ° in a second direction orthogonal to the first direction. 10. Twin engine assembly according to one of claims 5 to 7, comprising a plurality of injectors (18 ') with double circuit, in each dual circuit injector (18') being integrated a main injector (18) and a injector start (17), all start injectors (17) being integrated in a dual circuit injector (18 '), said dual circuit injectors (18') being adapted to diffuse a conical fuel beam.