IGNITION SYSTEM FOR A COMBUSTION CHAMBER OF A TURBOSHAFT ENGINE

Abstract

A system for igniting a combustion chamber of a turboshaft engine, comprising: a plurality of start-up injectors which are suitable for injecting fuel into said chamber during a combustion-initiating phase; a circuit for supplying fuel to said start-up injectors, comprising a first sub-circuit, referred to as the primary start-up circuit, designed to supply fuel to some of said plurality of start-up injectors; a second sub-circuit, referred to as the secondary start-up circuit, designed to supply fuel to the other start-up injectors of said plurality.

Claims

1. System for igniting a combustion chamber of an aircraft turboshaft engine, comprising: a plurality of start-up injectors which lead into said combustion chamber and are configured to inject fuel into said chamber during a combustion-initiating phase; a start-up circuit configured to supply fuel to said start-up injectors; and a plurality of main injectors which lead into said combustion chamber and are configured to inject fuel into said combustion chamber so as to maintain the combustion once said combustion has been initiated by said start-up injectors; wherein said start-up circuit comprises: a first primary sub-circuit, configured to supply fuel to a subset of said plurality of start-up injectors; a secondary sub-circuit, configured to supply fuel to the remaining start-up injectors of said plurality of start-up injectors; and wherein said primary sub-circuit and said secondary sub-circuit each comprise a solenoid start-up valve configured to be controlled by a control unit so as to allow or prevent the supply of fuel to said start-up injectors.

2. System according to claim 1, wherein said solenoid valves are controlled by said control unit using a sequential or simultaneous procedure, the procedure being selected according to the flight conditions of said aircraft.

3. System according to claim 1, wherein said solenoid valves are controlled by said control unit such that, on the ground, each sub-circuit is used alternately for each flight so as to limit dormancy of a possible failure to a single flight.

4. System according to claim 1, wherein each start-up injector is associated with a rail for supplying fuel to said injector, said supply rail of one start-up injector of the subset of start-up injectors having a lower volume than said supply rail of a start-up injector of the remaining start-up injectors so as to be able to be filled up with fuel more quickly.

5. System according to claim 1, further comprising one spark plug opposite each start-up injector, which spark plug is configured to supply a spark for setting alight the fuel in said combustion chamber.

6. System according to claim 1, wherein the subset of said plurality of start-up injectors comprises two start-up injectors and wherein the remaining start-up injectors comprise two start-up injectors.

7. Turboshaft engine comprising a combustion chamber, wherein said engine comprises a system for igniting said combustion chamber according to claim 1.

8. An aircraft, comprising: at least one turboshaft engine, the at least one turboshaft engine including: a plurality of start-up injectors which lead into said combustion chamber and are configured to inject fuel into said chamber during a combustion-initiating phase; a start-up circuit configured to supply fuel to said start-up injectors; and a plurality of main injectors which lead into said combustion chamber and are configured to inject fuel into said combustion chamber so as to maintain the combustion once said combustion has been initiated by said start-up injectors; wherein said start-up circuit comprises: (i) a primary sub-circuit, configured to supply fuel to a subset of said plurality of start-up injectors; (ii) a secondary sub-circuit, configured to supply fuel to the remaining start-up injectors of said plurality of start-up injectors; wherein said primary sub-circuit and said secondary sub-circuit each comprise a start-up valve configured to be controlled by a control unit so as to allow or prevent the supply of fuel to said start-up injectors.

9. The aircraft according to claim 8, wherein said start-up valves are controlled by said control unit using a sequential or simultaneous procedure, the procedure being selected according to the flight conditions of said aircraft.

10. The aircraft according to claim 8, wherein said start-up valves are controlled by said control unit such that, on the ground, each sub-circuit is used alternately for each flight so as to limit dormancy of a possible failure to a single flight.

11. The aircraft according to claim 8, wherein each start-up injector is associated with a rail for supplying fuel to said injector, said supply rail of one start-up injector of the subset of start-up injectors having a lower volume than said supply rail of a start-up injector of the remaining start-up injectors so as to be able to be filled up with fuel more quickly.

12. The aircraft according to claim 8, further comprising one spark plug opposite each start-up injector, which spark plug is configured to supply a spark for setting alight the fuel in said combustion chamber.

13. The aircraft according to claim 8, wherein the subset of said plurality of start-up injectors comprises two start-up injectors and wherein the remaining start-up injectors comprise two start-up injectors.

Description

5. LIST OF FIGURES

[0046] Other aims, features and advantages of the invention will emerge from reading the following description, which is given purely by way of non-limiting example and relates to the accompanying FIG. 1, which is a schematic view of an ignition system according to an embodiment of the invention.

6. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0047] In the figure, the scales and proportions are not respected for the sake of illustration and clarity.

[0048] FIG. 1 is a schematic view of a system for igniting a combustion chamber 2 of a turboshaft engine.

[0049] The system comprises start-up injectors 21a, 21b, 31a, 31b which lead into the combustion chamber 2 and are suitable for injecting fuel into the chamber 2 during a combustion-initiating phase.

[0050] The system also comprises main injectors 12 which lead into the combustion chamber 2 and are suitable for injecting fuel into the chamber 2 at a higher flow rate once combustion has been initiated.

[0051] The combustion chamber 2 is shown schematically by a rectangle in FIG. 1 for the sake of clarity. In practice, the combustion chamber generally comprises two annular walls, namely an outer wall and an inner wall, which extend one inside the other and are connected by an annular bottom wall of the chamber. The fuel injectors are distributed over the entire circumference of the combustion chamber.

[0052] The system also comprises a circuit for supplying fuel to the main injectors 12, referred to as the main circuit 5, and a circuit for supplying fuel to the start-up injectors 21, 31, referred to as the start-up circuit 6.

[0053] These two circuits are connected to a fuel inlet 7 which is supplied with fuel by a pump designed to withdraw fuel from a fuel reservoir (not shown in FIG. 1).

[0054] According to the invention, the start-up circuit 6 for supplying fuel to the start-up injectors 21, 31 is formed of two sub-circuits, namely a first sub-circuit, referred to as the primary start-up circuit 20, which is designed to supply fuel to the injectors 21, referred to as the primary start-up injectors, and a second sub-circuit, referred to as the secondary start-up circuit 30, which is designed to supply fuel to the start-up injectors 31, referred to as the secondary start-up injectors.

[0055] The primary start-up circuit 20 also comprises a solenoid valve 22 controlled for example by the engine electronic control unit (better known by the acronym EECU) of the helicopter. The secondary start-up circuit 30 also comprises a solenoid valve 32 controlled by the EECU. The solenoid valve 22 is designed to allow or prevent the supply of fuel to the primary start-up injectors 21. The solenoid valve 32 is designed to allow or prevent the supply of fuel to the primary start-up injectors 31.

[0056] The primary start-up injectors 21 have fuel supply rails that have a volume that is smaller than the volume of the rails for supplying fuel to the secondary start-up injectors 31. This means that, when the solenoid valves are open, the primary injectors 21 are quickly activated and initiate combustion in the combustion chamber 2. The secondary injectors 31 continue the combustion once the corresponding rails are filled, and this process takes slightly longer for said secondary injectors than for the primary injectors owing to said secondary injectors having a larger volume.

[0057] Once the start-up injectors 21, 31 are active, the combustion in the combustion chamber is maintained by the activation of the injectors 12 of the main circuit combined with the spreading of the flame from the start-up injectors 31, 21 to the main injectors 12. Once the main injectors 12 have taken over from the start-up injectors 21, 31, the primary and secondary start-up circuits are bled and the fuel residue is discharged to a collector via channels 25, 35. Bleeding the start-up injectors after they have stopped supplying fuel makes it possible to avoid coking (carbonisation of the fuel in the pipes) and therefore prevents the injectors from becoming clogged.

[0058] According to the embodiment of FIG. 1, each start-up injector 21a, 21b, 31a, 31b is associated with a spark plug 23a, 23b, 33a, 33b arranged opposite the injector. Each spark plug 23a, 23b, 33a, 33b is supplied with electricity from an electrical circuit 24, 34 comprising a high-voltage electrical power source. Each spark plug is designed to produce a spark that sets alight the mixture of air and fuel in the combustion chamber 2.

[0059] There being one spark plug per start-up injector makes it possible to reduce the time taken for the flame to spread towards the main injectors, and therefore to ultimately reduce the start-up time of the turboshaft engine provided with an ignition system of this kind.

[0060] The invention is not limited to the described embodiment. In particular, according to other embodiments, the ignition system may comprise more than four start-up injectors and/or a different number of primary start-up injectors and secondary start-up injectors.