FUEL SUPPLY SYSTEM

Abstract

A fuel supply system for fuel injectors of a multi-stage combustor of a gas turbine engine. The fuel supply system includes a metering and splitting arrangement which receives a total fuel flow and controllably meters and splits the received total fuel flow into metered pilot and mains flows. The fuel supply system further includes a de-priming sub-system, one or more fuel lines of a mains fuel distribution pipework being fluidly connected to the mains fuel discharge orifices and extending to the de-priming sub-system, and the de-priming sub-system being configured to remove the mains fuel from the injectors. A re-priming sub-system, the one or more fuel lines of the mains fuel distribution pipework also extending to the re-priming sub-system, and the re-priming sub-system being configured to refill the injectors with mains fuel through the one or more fuel lines when the mains distribution pipework is selected for pilot and mains operation.

Claims

1. A fuel supply system for fuel injectors of a multi-stage combustor of a gas turbine engine, the fuel supply system including: a metering and splitting arrangement which receives a total fuel flow and controllably meters and splits the received total fuel flow into metered pilot and mains flows for injecting respectively at pilot and mains fuel discharge orifices of the injectors to perform staging control of the combustor; and pilot and mains fuel distribution pipeworks respectively distributing fuel from the metering and splitting arrangement to the pilot and mains discharge orifices; wherein the metering and splitting arrangement is operable to select the pilot distribution pipework and deselect the mains distribution pipework for pilot-only operation in which there is a pilot supply to the combustor but no mains supply to the combustor from the injectors, and is operable to select both the pilot and mains distribution pipeworks for pilot and mains operation in which there are pilot and mains supplies to the combustor from the injectors; wherein fuel supply system further includes a de-priming sub-system, one or more fuel lines of the mains fuel distribution pipework being fluidly connected to the mains fuel discharge orifices and extending to the de-priming sub-system, and the de-priming sub-system being configured to remove the mains fuel from the injectors through the one or more fuel lines when the mains distribution pipework is deselected for pilot-only operation; wherein the fuel supply system further includes a re-priming sub-system, the one or more fuel lines of the mains fuel distribution pipework also extending to the re-priming sub-system, and the re-priming sub-system being configured to refill the injectors with mains fuel through the one or more fuel lines when the mains distribution pipework is selected for pilot and mains operation; and wherein the de-priming sub-system includes one or more sinks in which the removed fuel is stored, the re-priming sub-system emptying the sink(s) to perform refilling using the stored fuel.

2. A fuel supply system according to claim 1, wherein the pilot fuel distribution pipework includes a pilot fuel manifold distributing fuel from the metering and splitting arrangement to the pilot discharge orifices.

3. A fuel supply system according to claim 1, wherein the metering and splitting arrangement includes: a metering valve which receives and controllably meters the total fuel flow, and a splitting sub-arrangement which receives the total metered flow from the metering valve and controllably splits the total metered flow into the pilot and mains flows.

4. A fuel supply system according to claim 1, wherein the de-priming sub-system is further configured to remove mains fuel from portions of the mains fuel distribution pipework adjacent the injectors when the mains distribution pipework is deselected for pilot-only operation, and wherein the re-priming sub-system is further configured to refill said portions of the mains fuel distribution pipework with mains fuel when the mains distribution pipework is selected for pilot and mains operation.

5. A fuel supply system according to claim 1, wherein each injector has a dedicated and respective one of the fuel lines, such that each injector can be de-primed and re-primed independently of the other injectors.

6. A fuel supply system according to claim 1, wherein the mains fuel distribution pipework includes plural mains manifolds for the supply of respective groups of the injectors with corresponding portions of the mains flow, each mains manifold having a dedicated and respective one of the fuel lines, such that each group of injectors can be de-primed and re-primed independently of the other groups of injectors.

7. A fuel supply system according to claim 6, wherein the injectors of each group of injectors are neighbouring injectors in the combustor.

8. A fuel supply system according to claim 6, wherein there are just two or just three injectors in each group of injectors.

9. A fuel supply system according to claim 6, wherein there are two injectors in each group of injectors, the two injectors being at the same vertical height in the combustor.

10. A fuel supply system according to claim 1, wherein each of the one or more fuel lines has a top portion at an end thereof and a bottom portion at an opposite end thereof, and is routed such that its injector(s) is at the top end and the de-priming sub-system is at the bottom end.

11. A fuel supply system according to claim 1, wherein there are plural fuel lines, and the re-priming sub-system is configured to perform refilling through the fuel lines at different times and/or different rates for different fuel lines.

12. A fuel supply system according to claim 1, wherein: there are plural fuel lines, the fuel supply system includes plural actuation units which are each controllable to perform both de-priming and re-priming for a respective one of the fuel lines, the actuation units being parts of both the de-priming sub-system and the re-priming sub-system.

13. A fuel supply system according to claim 1, wherein the, or each, fuel line includes a respective pressure and/or flow sensor which issues a signal when the fuel line is primed.

14. A gas turbine engine having a multi-stage combustor and the fuel supply system according to claim 1 for supplying fuel to and performing staging control in respect of pilot and mains fuel discharge orifices of fuel injectors of the combustor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0043] FIG. 1 shows schematically a combustion staging system for a gas turbine engine in pilot and mains operation mode;

[0044] FIG. 2 shows a longitudinal cross-section through a ducted fan gas turbine engine;

[0045] FIG. 3 shows schematically a fuel supply system for fuel injectors of a multi-stage combustor of the gas turbine engine;

[0046] FIG. 4 shows schematically a variant fuel supply system for fuel injectors of the multi-stage combustor;

[0047] FIG. 5 shows schematically a further variant fuel supply system for fuel injectors of the multi-stage combustor; and

[0048] FIG. 6 shows schematically a further variant fuel supply system for fuel injectors of the multi-stage combustor.

[0049] DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

[0050] With reference to FIG. 2, a ducted fan gas turbine engine incorporating the invention is generally indicated at 10 and has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, an intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

[0051] During operation, air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate-pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate-pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high-pressure compressor 14 where further compression takes place.

[0052] The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate-pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

[0053] The combustion equipment 15 of the engine 10 includes a multi-stage combustor. FIG. 3 shows schematically a fuel supply system for fuel injectors of the multi-stage combustor. The engine has a pump system 25 comprising typically a low pressure (LP) pumping stage which draws fuel from a fuel tank of the aircraft and supplies the fuel at boosted pressure to the inlet of a high pressure (HP) pumping stage. The LP stage typically comprises a centrifugal impeller pump while the HP pumping stage may comprise one or more positive displacement pumps, e.g. in the form of twin pinion gear pumps. The LP and HP stages are typically connected to a common drive input, which is driven by the engine HP or IP shaft via an engine accessory gearbox.

[0054] The combustion equipment 15 of the engine 10 includes a multi-stage combustor. A fuel supply system accepts fuel from the HP pumping stage for feeding to the combustor. This system typically has a hydro-mechanical unit (HMU) 27 which performs total metering and comprises a fuel metering valve operable to control the rate at which fuel is allowed to flow to the combustor. The HMU further typically comprises: a pressure drop control arrangement (such as a spill valve and a pressure drop control valve) which is operable to maintain a substantially constant pressure drop across the metering valve, and a pressure raising and shut-off valve at the fuel exit of the HMU which ensures that a predetermined minimum pressure level is maintained upstream thereof for correct operation of any fuel pressure operated auxiliary devices (such as variable inlet guide vane or variable stator vane actuators) that receive fuel under pressure from the HMU. Further details of such an HMU are described in EP 2339147 A (hereby incorporated by reference).

[0055] An engine electronic controller (EEC) commands the HMU fuel metering valve to supply fuel to the combustor at a given flow rate. The metered fuel flow leaves the HMU and arrives at a staging system 30.

[0056] The staging system 30 splits the fuel into two flows: one at a pressure P.sub.p for a pilot flow along pilot fuel distribution pipework to first 31a and second 31b segments of a pilot manifold and the other at a pressure P.sub.m for a mains flow along mains fuel distribution pipework. Fuel injectors 33 (only two being shown in FIG. 3) of a combustor of the engine are split into two groups. Pilot (primary) discharge orifices of the injectors of one group are connected to the first pilot manifold segment 31a, while pilot discharge orifices of the injectors of the other group are connected to the second pilot manifold segment 31b. The mains flow feeds mains (secondary) discharge orifices of the fuel injectors.

[0057] A fuel flow splitting valve (FFSV) 35, or any other suitably-arranged set of valves known to the skilled person and providing a splitting function, receives the metered fuel flow from the HMU 27. Typically, the FFSV has a slidable spool under the control of a servo-valve, the position of the spool determining the outgoing flow split between two outlets forming respectively the pilot flow and the mains flow. The spool can be positioned so that the mains stage is completely deselected, with the entire metered flow going to the pilot stage. An LVDT can provide feedback on the position of the spool to the EEC, which in turn controls staging by control of the servo-valve.

[0058] The pilot fuel distribution pipework has a distributor function 37 to split the pilot flow between the first 31a and second 31b segments of the pilot manifold. The distributor function can be a dedicated unit or can be a functional result of the operation of other parts of the staging system 30. A lean blow out protection valve and a solenoid operated control valve of the type shown in FIG. 1 may be part of the distributor function 37.

[0059] The mains fuel distribution pipework splits the mains flow into sub-flows, one for each injector, or one for each of different groups of the injectors. Each sub-flow is directed to a respective actuation unit 39 which performs de-prime and re-prime functions (discussed in more detail below) on its injector/group of injectors. In the case of each injector having a dedicated actuation unit, a respective fuel line 41 extends from each actuation unit to its injector. In the case of each of different groups of the injectors having a dedicated actuation unit, a respective fuel line 41 extends from each actuation unit to e.g. a manifold or other distributor serving the injectors of the group. Each such group may have just two or three injectors, and these are typically neighbouring injectors in the combustor in order to reduce gravitational head effects between the injectors. However, another option for reducing gravitational head effects is for each group to be formed of two injectors which are at the same vertical height in the combustor, i.e. reflected across the vertical plane containing the engine axis.

[0060] Optionally, each actuation unit 39 can also perform an isolation function. This allows the actuation units to controllably isolate their injector(s) from the mains flow from the FFSV 35, so that the EEC can perform partial mains staging. Typically this involves staging in a subset of the injectors, the injectors of the subset being equally circumferentially spaced around the combustor. Partial mains staging can help to maintain combustion performance at the mains discharge orifices of the injectors at low mains flow conditions.

[0061] The fuel supply system aims to improve on combustion staging systems of the type shown in FIG. 1 by removing a requirement for individual check valves (mains FSVs) at the mains injector heads. As discussed above, FSVs can inadvertently cause injector-to-injector fuel flow variation, which can potentially reduce the life of the combustor and turbine gas path components. Removing FSVs can also provide cost, weight and reliability benefits. The staging system 30 removes the requirement for such valves by de-priming the mains fuel passages of the injectors (and preferably also the fuel lines 41) when the mains flame is staged-out, and then re-priming the mains fuel passages of the injectors (and the fuel lines if necessary) prior to the mains flame being staged back in.

[0062] In particular, the actuation units 39 are under the control of the EEC, which performs a de-prime actuation function 43 and a re-prime actuation function 45. Thus the actuation units 39 and the de-prime actuation function 43 of the EEC together form a de-priming sub-system which removes the mains fuel from the injectors 33 through the fuel lines 41 when the mains distribution pipework is deselected for pilot-only operation, while the actuation units 39 and the re-prime actuation function 45 of the EEC together form a re-priming sub-system which refills the injectors with mains fuel through the fuel lines when the mains distribution pipework is selected for pilot and mains operation. The actuation units typically comprise suitably configured pumps and/or valves to perform these fuel removal and fuel refill functions. They may be pneumatically, hydraulically, mechanically or electrically controlled.

[0063] Each fuel line 41 can be routed vertically with its fuel injector(s) 33 at the top and its actuation unit 39 at the bottom. This helps to ensure that if the fuel line is not fully emptied, then the fuel does not egress into the fuel injector(s), causing coking of the injector nozzle(s).

[0064] The de-priming sub-system may include one or more sinks in which the removed fuel is stored. The re-priming sub-system can then empty the sink(s) to perform refilling using the stored fuel. For example, each actuation unit 39 may comprise a sink in the form of a reservoir, tank, accumulator or lower pressure area, with de-prime being initiated by the actuation unit opening its fuel line 41 to the sink. The fuel removed into the sink can be retained therein to be used for re-priming prior to staging. Advantageously, such an arrangement can reduce the time needed to refill in re-priming, and helps to avoid under- and over-fuelling the pilot and mains flames respectively.

[0065] Another option, however, is for the removed fuel to be recycled by a recuperation system 49 e.g. into the pump system 25, in which case the fuel to be used for refilling on re-priming can be provided by flow from the HMU 27 and the FFSV 35.

[0066] The amount of fuel that is removed during de-priming is dependent on the fuel system architecture. However, enough should be removed to ensure that no fuel can egress into the injectors 33, causing coking. To this end, the amount removed preferably accounts for thermal expansion of fuel remaining in the fuel lines 41 due to heat pick up from the environment, and aircraft manoeuvres. Indeed, one option is simply to remove all the fuel in the fuel lines, although this can increase the time required for re-priming.

[0067] As mentioned above, the fuel supply system permits the removal of mains FSVs and hence mitigates associated issues/risks (e.g. mal-scheduling due to a failed open FSV; nozzle-to-nozzle fuel distribution variation due to FSV-to-FSV component variation; and lifing issues such as seal wear/degradation leading to fuel dribbling and consequent nozzle coking).

[0068] However, a further advantage of the fuel supply system is that it can provide individual flow stream control for re-prime and subsequent staging, which can help to reduce/eliminate fuel dips. It also allows valves to be moved away from the burner head into a more benign environment, providing for improved control of component temperatures, which in turn reduces the risk of degradation in component/system performance due to fuel coking. Further, as discussed above, the actuation units 39 can be configured such that they may be controlled by the EEC to isolate their respective fuel lines 41 from the mains flow from the FFSV 35.

[0069] FIG. 4 shows schematically a variant fuel supply system for fuel injectors of the multi-stage combustor. In the variant system, the EEC has a separate de-prime actuation function 43 for each actuation unit, and also a separate re-prime actuation function 45 for each actuation unit 39. This is particularly advantageous for re-priming, as the refill timings of each fuel line 41 can be staggered to reduce the magnitude of the dips and spikes during mains fuel staging. Also the separate de-prime actuation functions enable the EEC to control partial mains staging.

[0070] FIG. 5 shows schematically a further variant fuel supply system for fuel injectors of the multi-stage combustor. In the further variant system, a pressure sensor and/or a flow sensor 51 is provided in each fuel line 41 to determine when that fuel line is refilled, with a signal being sent to the EEC to initiate re-prime of the next fuel line. Also the pressure/flow sensing can be used by the EEC to determine if there are any failures in the re-prime function.

[0071] Another option, however, is to initiate re-prime all of the fuel lines 41 at the same time but to utilise different lengths of fuel line to reduce the magnitude of the dips and spikes during mains fuel staging (i.e. tuning the architecture of the mains distribution pipework). Yet another option is to control the relative refill rates of the fuel lines 41 to reduce the magnitude of the dips and spikes.

[0072] FIG. 6 shows schematically a further variant fuel supply system for fuel injectors of the multi-stage combustor. In this further variant system, the mains fuel distribution pipework has a single mains manifold 52 which distributes the mains flow to all the injectors 33. A single fuel line 41 extends from a single actuation unit 39 to the manifold. With this system, the de-prime/re-prime functionality of the actuation unit removes fuel from and refills the entire mains manifold in order that no fuel dribbles from a partially drained manifold through to injectors sited below the fuel level.

[0073] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.