FUEL SUPPLY SYSTEM

Abstract

A fuel supply system includes a metering and splitting arrangement receiving a fuel flow and controllably meters and splits the received fuel flow into metered pilot and mains flows for injecting at injector pilot and mains fuel discharge orifices to perform combustor staging control. The system includes an ecology valve having a piston chamber and a piston slidably movable in the chamber between de-prime and re-prime positions, the chamber forming a fuel sink to one side of the piston which increases in volume when the piston moves to its de-prime position and reduces in volume when the piston moves to its re-prime position. The system includes an actuator for actuating the piston. The valve is fluidly connected to a mains fuel distribution for operating the piston to its de-prime position to remove the mains fuel from the injectors through the mains fuel distribution pipework and into the fuel sink.

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 the fuel supply system further includes an ecology valve having a piston chamber and a piston slidably movable in the chamber between de-prime and re-prime positions, the chamber forming a fuel sink to one side of the piston which increases in volume when the piston moves to its de-prime position and reduces in volume when the piston moves to its re-prime position; wherein the fuel supply system further includes an actuator for actuating the piston; and wherein the ecology valve is fluidly connected to the mains fuel distribution pipework such that for pilot-only operation the actuator moves the piston to its de-prime position to remove the mains fuel from the injectors through the mains fuel distribution pipework and into the fuel sink, and such that for pilot and mains operation the actuator moves the piston to its re-prime position to refill the injectors with mains fuel from the fuel sink.

2. A fuel supply system according to claim 1, wherein the metering and splitting arrangement is configured to fluidly isolate the mains fuel distribution pipework from the received total fuel flow and the pilot supply during pilot-only operation.

3. A fuel supply system according to claim 1, wherein the metering and splitting arrangement includes: a total metering valve which receives and controllably meters the total fuel flow, and a splitting sub-arrangement which receives the total metered flow from the total 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 metering and splitting arrangement includes: a pilot metering valve which receives and controllably meters a portion of the fuel flow for onward flow to the pilot distribution pipework, and a mains metering valve in parallel to the pilot metering valve, the mains metering valve receiving and controllably metering a different portion of the fuel flow for onward flow to the mains distribution pipework, and wherein the relative values of the fuel flows controllably metered by the pilot and mains metering valves determine the staging control split of the pilot and mains flows.

5. A fuel supply system according to claim 1, wherein moving the piston to its de-prime position also removes mains fuel from the mains fuel manifold, and moving the piston to its re-prime position refills the mains fuel manifold with mains fuel.

6. A fuel supply system according to claim 1, wherein the actuator is a positive displacement pump which is operable in one direction to send fuel into the fuel sink from the mains fuel distribution pipework prior to pilot-only operation, and is operable in the opposite direction to send fuel from the fuel sink into the mains fuel distribution pipework prior to pilot and mains only operation.

7. A fuel system according to claim 6, wherein the positive displacement pump is electrically powered.

8. A fuel supply system according to claim 6, wherein the piston is spring biased towards its de-prime position.

9. A fuel system according to claim 6, wherein the ecology valve is positioned between the positive displacement pump and the mains fuel distribution pipework, and the piston chamber forms a variable volume control chamber on the opposite side of the piston to the fuel sink, the positive displacement pump pumping fuel from the control chamber prior to pilot-only operation to move the piston to its de-prime position, and the positive displacement pump pumping fuel into the control chamber prior to pilot and mains operation to move the piston to its re-prime position,

10. A fuel system according to claim 6, wherein the positive displacement pump is positioned between the ecology valve and the mains fuel distribution pipework, the positive displacement pump pumping fuel from the mains fuel distribution pipework into the fuel sink prior to pilot-only operation to move the piston to its de-prime position, and the positive displacement pump pumping fuel from the fuel sink into the mains fuel distribution pipework prior to pilot and mains operation to move the piston to its re-prime position,

11. A fuel system according to claim 1, wherein the actuator is an electro-mechanical actuator which is operable in one direction to drive the piston to its de-prime position and is operable in the opposite direction to drive the piston to its re-prime position.

12. A fuel system according to claim 1, wherein the ecology valve has a position sensor which senses the position of the piston, the position sensor sending signals to switch off the actuator when the piston reaches its de-prime and/or re-prime positions.

13. A fuel system according to claim 1, wherein the ecology valve has a latching port which admits relatively high pressure fuel into the piston chamber on the opposite side of the piston to the fuel sink to latch the piston in its re-prime position.

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

[0044] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0045] FIG. 1 shows schematically a combustion staging system for a gas turbine engine in pilot and mains operation mode;

[0046] FIG. 2 shows a longitudinal cross-section through a ducted fan gas turbine engine;

[0047] FIG. 3 shows schematically a pump system and a fuel supply system for fuel injectors of a multi-stage combustor of the gas turbine engine with the fuel supply system providing pilot-only operation;

[0048] FIG. 4 shows schematically the pump system and the fuel supply system of FIG. 3 but with the fuel supply system providing pilot and mains operation;

[0049] FIG. 5 shows schematically the pump system and a variant of the fuel supply system with the fuel supply system providing pilot and mains operation;

[0050] FIG. 6 shows schematically the pump system and a further variant of the fuel supply system with the fuel supply system providing pilot-only operation;

[0051] FIG. 7 shows schematically the pump system and the fuel supply system of FIG. 6 but with the fuel supply system providing pilot and mains operation;

[0052] FIG. 8 shows schematically the pump system and a further variant of the fuel supply system with the fuel supply system providing pilot-only operation;

[0053] FIG. 9 shows schematically an overview of a variant configuration with parallel pilot and mains metering paths from separate HMUs, and an ecology system on the mains path for mains manifold de-priming/re-priming;

[0054] FIG. 10 shows schematically a configuration similar to that of FIG. 9 but also with separate HP pumping stages for the two paths and independent and respective spill controls; and

[0055] FIG. 11 shows schematically an overview of a further variant configuration with parallel pilot and mains metering paths from a single HMU, and an ecology system on the mains path for mains manifold de-priming/re-priming.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The combustion equipment 15 of the engine 10 includes a multi-stage combustor. FIGS. 3 and 4 show schematically a pump system and a fuel supply system for fuel injectors of the multi-stage combustor. In FIG. 3 the fuel supply system is shown in pilot-only operation with mains supply off and the mains fuel passages of the injectors and the connecting mains manifold de-primed. In FIG. 4 the fuel supply system is shown in pilot and mains operation with the mains fuel passages and mains manifold re-primed and mains supply on.

[0060] The pump system 24 comprises 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.

[0061] 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) 25 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).

[0062] 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 of the fuel supply system.

[0063] The staging system 30 splits the fuel into two flows: one for a pilot flow along pilot fuel distribution pipework 34 to first 31a and second 31b segments of a pilot manifold and the other for a mains flow along mains fuel distribution pipework 32 to mains manifold 29. Each fuel injector 33 of the combustor of the engine has a fuel spray nozzle (FSN) containing a pilot (primary) discharge orifice and a mains (secondary) discharge orifice. The injectors are split into two groups. The pilot discharge orifices of the FSNs of the injectors of one group are connected to the first pilot manifold segment 31a, while pilot discharge orifices of the FSNs of the injectors of the other group are connected to the second pilot manifold segment 31b. The mains flow from the mains manifold feeds the mains discharge orifices of the FSNs of both groups of the fuel injectors. The pilot and mains discharge orifices may have respective weight distribution valves (WDVs) to reduce gravitational head effects between the injectors.

[0064] On entry into the staging system 30, the metered fuel flow first passes through a flow washed filter (FWF) 26, thereby providing scouring flow for the filter. Servo flows to various internal servo orifices and control valves are taken through a fine mesh of the FWF.

[0065] A pilot (secondary) metering valve (PMV) 27 meters the total pilot flow to the pilot fuel distribution pipework 34, thereby controlling the overall pilot/mains flow split. This is achieved by modulating the PMV to vary the opening of a metering port. A typical arrangement is to have a metering piston moving within a sleeve of the PMV to vary the opening of a metering profile cut into the sleeve. The piston can be actuated by a servo-valve in response to a demand signal from the EEC, with valve position feedback provided by a position sensor.

[0066] The pressure drop across the metering profile is regulated to a nominally constant value so that the metered pilot flow is principally a function of the PMV piston position. A mains spill valve 28 controls the pressure drop across the PMV by spilling the portion of total metered flow not required by the pilot discharge orifices of the injectors to the mains fuel distribution pipework 32. For example, an inner piston of the mains spill valve senses the PMV pressure drop and adjusts a pressure drop control orifice of the mains spill valve (via a poppet valve) so that an outer spill piston of the mains spill valve moves to maintain a constant pressure drop across the PMV.

[0067] Downstream of the PMV, the total pilot flow in the pilot fuel distribution pipework 34 can be split between the first 31a and second 31b segments of the pilot manifold. A lean blow out protection valve 37 and e.g. a solenoid-operated control valve (not shown) may be located between the pilot fuel distribution pipework and the first pilot manifold segment 31a. When activated, the lean blow out protection valve can restrict the portion of pilot fuel flow passing to the FSNs connected to the first manifold segment 31a so that a higher proportion of the total pilot flow passes to a reduced number of FSNs connected to the second manifold segment 31b, ensuring that the latter receive sufficient fuel to avoid lean blow out. The lean blow out protection valve and the associated twin segment pilot manifold arrangement are optional features; the total pilot flow can be fed to a single manifold (no lean blow out protection valve required) or indeed multiple pilot manifolds via multiple valve arrangements.

[0068] Under pilot-only operation (FIG. 3), the PMV 27 is driven wide open, causing the pressure drop across the PMV to decrease. This is sensed by the mains spill valve 28, which responds by moving to close off the flow to the mains fuel distribution pipework 32, thereby deselecting the mains manifold 29 and the mains discharge orifices of the injectors 33. The mains spill valve provides a drip tight seal between the upstream PMV and the downstream mains fuel distribution pipework. This can be achieved via a face seal, which contacts the end of the mains spill valve piston and a further dynamic seal on the piston itself. Drip tight sealing prevents ingress of fuel into the mains manifold and subsequently into the injectors, and thus helps to prevent coking of the small mains fuel passages of the injectors. Such coking can increase injector-to-Injector fuel maldistribution and reduce overall injector life.

[0069] The staging system 30 has an ecology valve 35 comprising a piston chamber and a piston slidably movable in the piston chamber between de-prime and re-prime positions. The piston chamber forms a fuel sink in the form of a spring chamber to one side of the piston and a control chamber on the other side of the piston. This sink increases in volume when the piston moves to its de-prime position and reduces in volume when the piston moves to its re-prime position. On closing off the mains supply in pilot-only operation, an ecology pump 36 (illustrated here as a gear pump, but it could be a different type of positive displacement pump, such as a piston pump), which is driven by an electric motor in a reverse sense direction, drains a fixed volume of fuel from the mains fuel distribution pipework 32 into the fuel sink. More particularly, the ecology pump draws fuel from a variable volume control (non-spring) chamber of the ecology valve on the opposite side of the piston to the spring chamber (fuel sink), so that the pressure in the valve spring chamber falls to the combustion chamber pressure (P40) and the pressure in the control chamber (Pev) rises to a level above P40, which is set by the ecology valve force balance. This is insufficient to open an ecology pump relief valve, which remains closed throughout the de-priming process.

[0070] The flow drawn by the ecology pump 36 and returned to LP causes displacement of the piston of the ecology valve 35 to the left (as illustrated in FIG. 3), closing off a high pressure line from a latching port 38 of the ecology valve. As the piston moves it draws the fixed volume of fuel from the mains fuel distribution pipework 32 into the spring chamber (sink) so that (i) the injectors 33 are fully emptied of mains fuel, and (ii) the mains manifold 29 is emptied sufficiently to avoid any subsequent ingress of fuel into the mains passages of the injectors should the remaining fuel in the mains fuel distribution pipework/manifold expand under temperature during pilot-only operation or be displaced during aircraft manoeuvres.

[0071] When the piston of the ecology valve 35 reaches its final de-prime position (left hand hard stop), the pressure (Pev) falls towards vapour pressure. A position sensor on the ecology valve provides an indication to the EEC that the valve has reached the hard stop. Once this is confirmed, the ecology pump can be de-powered to reduce power consumption and to avoid heat generation. The pressure Pev then rises to LP and the ecology valve spring, which is sized to hold the valve closed against the maximum LP-P40 pressure, maintains the piston in this position until the next time that mains flow is required. A combination of, for example, a left hand face seal and dynamic piston seal within the ecology valve can create a drip tight seal across the valve. This prevents ingress of LP fuel into the mains manifold 29 when LP exceeds P40, as well as preventing ingress of hot combustion gas (P40) back into the fuel system at conditions where P40 exceeds LP.

[0072] When the system is shut down on the ground, but the aircraft tank pumps are left running for maintenance purposes, the spring of the ecology valve 35 can hold the piston at its final de-prime position against any LP pressure so that the mains manifold 29 does not refill. The shut-off valve in the HMU 25, along with seals in the PMV 27 and the mains spill valve 28 also prevent fuel ingress into the pilot manifold 31 and the mains manifold 29.

[0073] When mains flow is required (FIG. 4), the ecology pump 36 is powered by the electric motor in a forward sense to drive the piston of the ecology valve 35 to its final re-prime position (to the right as illustrated), thereby displacing fuel from the ecology valve spring chamber (sink) into the main fuel distribution pipework 32 to refill the mains manifold 29 and the mains passages of the injectors 33. Advantageously, the electric motor can accelerate the ecology pump quickly to provide a fast re-prime capability.

[0074] As the ecology pump 36 pumps fuel at LP from the inlet of the HP pumping stage of the pump system 24 into the non-spring chamber of the ecology valve 35, the pressure Pev in the non-spring chamber rises above LP to a level above P40, set by the valve force balance. This is insufficient to open the ecology pump relief valve, which remains closed as the piston moves. The movement of the piston to the right displaces the fixed volume of fuel in the spring chamber (sink) back into the main fuel distribution pipework 32 so that the mains manifold 29 and the mains passages of the injectors 33 become fully re-primed prior to the demand for mains flow. The mains discharge orifices WDVs limit any pre-leakage from the injectors.

[0075] The position sensor of the ecology valve 35 provides an indication that the piston has reached its right-hand stop (indicating that the injectors 33 are fully re-primed with mains fuel). The electric motor drive to the ecology pump 36 can then be switched off with the ecology pump relief valve cracking to prevent any over-pressurisation prior to the pump being switched off. The latching port 38 in the ecology valve opens as the piston reaches its right-hand stop. This admits HMU high pressure (HP) fuel to the control (non-spring) chamber of the ecology valve via a latching feed orifice 39. The HP fuel holds the piston in position once the ecology pump is de-powered. A second face seal at the right hand end of the valve, together with the piston dynamic seal can prevent leakage across the ecology valve to, or from, the mains fuel distribution pipework 32. Any parasitic leakage from HP to LP through the latching port is limited by the size of the latching feed orifice and the ecology pump itself.

[0076] Once re-priming indication is confirmed, the metering piston of the PMV 27 is commanded off its wide open stop, back towards a partially open condition at the correct opening for the demanded pilot flow. The resultant increase in PMV pressure drop is sensed by the mains spill valve 28, which opens to restore the correct PMV pressure drop and to simultaneously allow the correct mains flow to spill into the mains fuel distribution pipework 32.

[0077] Being able to displace a known fixed volume of fuel (set by the piston chamber diameter and piston travel of the ecology valve 35) during both de-priming and re-priming is particularly advantageous. This volume is sufficiently large so that (i) a full de-prime of the mains fuel from the injectors 33 and mains manifold 29 is achieved for pilot-only operation, (ii) in pilot-only operation, any expansion of residual fuel at high temperatures does not result in fuel ingress into the mains passages of the injectors, and (iii) in pilot-only operation, any aircraft manoeuvres do not result in flow spilling into the mains injector passageways. However, the volume is preferably as low as possible to minimise re-prime time, so that the engine can achieve acceleration performance requirements.

[0078] Many variants of the fuel supply system are possible. For example, the system shown in FIGS. 3 and 4 can be reconfigured to meter mains flow and spilling to pilot. As another example, the PMV/spill valve arrangement could be replaced by a splitter valve. Such a variant is shown schematically in FIG. 5 under pilot and mains operation. A fuel flow splitting valve (FFSV) 40, 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 25. 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. A position sensor can provide a feedback signal indicating the position of the spool to the EEC, which in turn controls the staging split ratio by sending a signal to the servo-valve to drive the splitter valve to a demanded position. The FFSV includes a sealing arrangement for drip tight mains sealing during pilot-only operation.

[0079] FIGS. 6 and 7 show schematically the pump system and a further variant of the fuel supply system under respectively pilot-only operation and pilot and mains operation. In this variant the ecology valve 35 is moved to the other side of the ecology pump 36, and an ecology latch 41 in the form servo-valve or similar device varies the pressure in the non-fuel sink chamber of the ecology valve to provide fuel-draulic latching of the valve. In FIG. 6 (pilot-only operation), the ecology pump and the ecology valve act in a similar manner to that previously described in respect of FIGS. 3 and 4 to de-prime the mains manifold 29 the mains passages of the injectors 33. The ecology valve is latched in position using the servo-valve 41 to port fuel at LP from the inlet to the HP pumping stage of the pump system 24 to the non-fuel sink chamber. The control (fuel sink) chamber on the other side of the piston is pressurised by the ecology pump, which is left running at a low speed/flow to spill flow through a low pressure relief valve once the ecology valve has moved to its de-prime (left-hand) position, as indicated by the ecology valve position sensor. The mains manifold 29 does not refill as there is fixed recirculating flow around the ecology pump.

[0080] In FIG. 7 (pilot and mains operation) the ecology pump 36 and ecology valve 35 combine to re-prime the mains manifold/injectors. More particularly, the piston of the ecology valve is fuel-draulically latched into its re-prime position by using the servo-valve 41 to feed HMU high pressure (HP) fuel to the non-fuel sink chamber. With the valve piston in this position, the ecology pump can be de-powered.

[0081] A potential benefit of this variant is a reduction in HP to LP parasitic leakage, which has an impact on main engine pump sizing. There is also potential to reference the latching servo-valve 41 to another low pressure sink instead of LP (e.g. atmosphere or low pressure pump inlet pressure (Pinlet)), as long as high pressure fuel leakage to such a sink via the servo-valve can be avoided.

[0082] The staging system 30 can be re-configured to use a directly-driven ecology valve 35 to perform the de-priming/re-priming. One example is illustrated in FIG. 8 in which a stepper motor 42 is used to drive the ecology valve via e.g. a ball screw or rack and pinion 43. Potential benefits of this variant are that the directly-driven ecology valve requires no additional latching features, and that there are no additional HP to LP parasitic leakages

[0083] All the above systems have the HMU 25 acting upstream of and in series with the staging system 30 which controls the pilot/mains split. However, the fuel supply system can be reconfigured to a parallel arrangement whereby two parallel HMUs, or a single HMU with parallel metering paths, provide the total flow and pilot/mains split control. This is illustrated schematically in FIGS. 9 to 11 for three possible reconfigurations. FIG. 9 shows a system with parallel pilot and mains metering paths from separate HMUs, and an ecology system on the mains path for mains manifold de-priming/re-priming. FIG. 10 shows a system similar to that of FIG. 9 but also with separate HP pumping stages for the two paths and independent and respective spill controls. FIG. 11 shows a system with parallel pilot and mains metering paths from a single HMU, and an ecology system on the mains path for mains manifold de-priming/re-priming.

[0084] 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.