Common rail fuel system with injection pump and method of using the same

Abstract

A method of operating an aircraft engine of an aircraft having a common rail fuel injection system for injecting fuel into a combustion chamber of the aircraft engine, the method comprising: pressurizing fuel for circulation through the common rail injection system; circulating a portion of the pressurized fuel through a motive flow inlet of an injection pump; and entraining flow through the injection pump using the portion of the pressurized fuel circulating through the motive flow inlet.

Description

Technical Field

[0001] The present application relates generally to aircraft engines and, more particularly, to fuel systems for use in such aircraft engines. Background Art

[0002] An aircraft engine includes at least one combustion chamber into which fuel is typically provided by a fuel injector. Some fuel injectors, such as common rail injectors, generate a return flow of fuel. The energy of the return flow is typically wasted because the return fuel flow is typically returned directly to the fuel tank. Therefore, better and more efficient fuel management is desired in such fuel systems. Summary of the invention

[0003] In one aspect, a method of operating an aircraft engine of an aircraft having a common rail fuel injection system for injecting fuel into a combustion chamber of the aircraft engine is provided, the method comprising: pressurizing fuel for circulation through the common rail injection system; circulating a portion of the pressurized fuel through a motive flow inlet of a jet pump; and entraining flow through the jet pump using a portion of the pressurized fuel circulated through the motive flow inlet.

[0004] The method of operating an aircraft engine defined above and herein may further comprise, in whole or in part, one or more of the following additional steps and / or features.

[0005] A portion of the pressurized fuel is a return flow of fuel from at least one common rail injector of a common rail fuel injection system, and the method includes circulating the return flow of fuel through a motive flow inlet of an injection pump.

[0006] A portion of the pressurized fuel is diverted from at least one fuel conduit to the injection pump, at least one fuel conduit connecting the high pressure pump to at least one common rail injector of the common rail injection system.

[0007] Fuel is diverted from at least one fuel conduit connecting the high pressure pump to at least one common rail injector of the common rail fuel injection system and entrained flow is achieved using both return flow of fuel and diverted fuel.

[0008] The jet pump is fluidly connected to a fuel source, and the method includes entraining fuel from the fuel source through the jet pump using a portion of the pressurized fuel.

[0009] Regulates the flow rate of the diverted portion of the pressurized fuel.

[0010] Regulating the flow rate includes restricting the flow of the diverted portion of the pressurized fuel.

[0011] Utilizing a portion of the pressurized fuel to entrain the flow through the jet pump includes entraining fuel directly from the fuel tank.

[0012] Entraining the flow through the jet pump with a portion of the pressurized fuel includes drawing the fuel through a main fuel conduit fluidly connecting a source of fuel to the high pressure pump.

[0013] In another aspect, a method of supplying fuel to an aircraft engine having a common rail fuel injection system is provided, the method comprising: pressurizing fuel to circulate through the common rail injection system; injecting a portion of the fuel in a common rail injector of the common rail injection system to generate a return flow of the fuel; and entraining fuel to be pressurized from a fuel source through the injection pump using the return flow of the fuel circulated through a motive flow inlet of the injection pump.

[0014] The method of supplying fuel to an aircraft engine as defined above and herein may further comprise, in whole or in part, one or more of the following additional steps and / or features.

[0015] Fuel is diverted from a fuel conduit connecting a high pressure pump to a common rail injector of a common rail injection system and fuel is entrained using both return flow of fuel and diverted fuel.

[0016] Adjusts the flow rate of the steering fuel.

[0017] Regulating the flow rate includes restricting the flow of the diverted fuel.

[0018] Entraining fuel from a fuel source via a jet pump includes entraining fuel directly from a fuel tank.

[0019] Entraining fuel from a fuel source via the jet pump includes drawing fuel through a main fuel conduit that fluidly connects the fuel source to the high pressure pump.

[0020] In yet another aspect, an aircraft engine is provided, the aircraft engine comprising: at least one combustion chamber; a fuel pump fluidly connected to a fuel source; a common rail injector having an injector inlet fluidly connected to the fuel pump via a fuel conduit, a first injector outlet fluidly connected to the at least one combustion chamber, and a second injector outlet for outputting a return flow of fuel; and a jet pump having a motive flow inlet fluidly connected to one of the second injector outlet and the fuel conduit upstream of the common rail injector and an entrainment flow inlet for receiving fuel to be drawn by the jet pump.

[0021] The fuel system of an aircraft engine as defined above and herein may further comprise, in whole or in part, one or more of the following additional features.

[0022] The motive flow inlet is fluidly connected to both the second injector outlet and the fuel conduit.

[0023] The motive flow inlet is fluidly connected to the fuel conduit via a bypass conduit, and the flow control device is fluidly connected to the bypass conduit.

[0024] The fuel source is a fuel tank, and the injection pump is located in the fuel tank.

[0025] A main fuel conduit fluidly connects the fuel source to the fuel pump, and a boost pump is fluidly connected to the main fuel conduit, with a jet pump connected to the main fuel conduit upstream of the boost pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Referring now to the accompanying drawings, in which:

[0027] Figure 1 is a block diagram of a compound engine system;

[0028] Figure 2 is a schematic cross-sectional view of a rotary internal combustion engine according to certain embodiments;

[0029] Figure 3 is a schematic diagram of an engine assembly according to one embodiment; and

[0030] Figure 4 It is possible to Figure 3 A schematic cross-sectional view of an injection pump used in conjunction with an engine assembly. DETAILED DESCRIPTION

[0031] Reference Figure 1 , schematically showing a compound engine system 8. The system 8 includes a compressor 11 and a turbine 13, which are connected by a shaft 15 and act as a turbocharger for one or more rotary engines 10. The compressor 11 can be a single-stage or multi-stage centrifugal device and / or an axial device. The rotary engine 10 or multiple rotary engines receive compressed air from the compressor 11. The air is optionally circulated through an intercooler between the compressor 11 and the (multiple) rotary engine 10.

[0032] The exhaust gases exiting the rotary engine 10 are supplied to the compressor turbine 13 and also to the power turbine 17, the turbines 13, 17 being shown here arranged in series, i.e., wherein the exhaust gases first flow through one of the two turbines with reduced pressure and then through the other turbine with further reduced pressure. In an alternative embodiment (not shown), the turbines 13, 17 are arranged in parallel, i.e., wherein the exhaust gases are divided and supplied to each turbine at the same pressure. In another alternative embodiment, only one turbine is provided.

[0033] Energy is extracted from the exhaust gases by the compressor turbine 13 to drive the compressor 11 via the connecting shaft 15, and by the power turbine 17 to drive the output shaft 19. The output shaft 19 can be connected to a shaft 22 via a gear system 21, which is connected to the rotary engine(s) 10. The combined output on the shafts 19, 22 can be used to provide propulsion power to the vehicle application in which the system 8 is integrated. This power can be transmitted through a gearbox (not shown) that adjusts the output speed of the shafts 19, 22 to the desired speed on the application. In alternative embodiments, the two shafts 19, 22 can be used independently to drive separate elements, such as propellers, helicopter rotors, load compressors or generators, depending on whether the system is a turboprop engine, a turboshaft engine or an auxiliary power unit (APU).

[0034] Although not shown, the system 8 also includes a cooling system, which includes: a circulation system for a coolant (e.g., water-glycol, oil, air) for cooling the external body of the rotating engine; an oil coolant for the internal mechanical parts of the rotating engine; one or more coolant heat exchangers, etc.

[0035] The compound engine system 8 may be as described in US Pat. No. 7,753,036 issued on Jul. 13, 2010 to Lents et al. or as described in US Pat. No. 7,775,044 issued on Aug. 17, 2010 to Julien et al., both of which are incorporated herein by reference in their entireties.

[0036] The rotary engine 10 forms the core of the combined cycle engine system 8. Figure 2 , schematically shows a rotary internal combustion engine 10 known as a Wankel engine. The rotary internal combustion engine 10 comprises an outer body 12 having axially spaced end walls 14 with a peripheral wall 18 extending therebetween to form a rotor cavity 20. The inner surface of the peripheral wall 18 of the cavity 20 has a profile defining two lobes, the profile preferably being an epitrochoid.

[0037] An inner body or rotor 24 is received within the cavity 20. The rotor 24 has an axially spaced end face 26 adjacent the outer body end wall 14 and a peripheral face 28 extending therebetween. The peripheral face 28 defines three circumferentially spaced tip portions 30 and a generally triangular profile having outwardly arcuate sides 36. The tip portions 30 sealingly engage the inner surface of the peripheral wall 18 to form three rotating combustion chambers 32 between the inner rotor 24 and the outer body 12. The geometric axis of the rotor 24 is offset from and parallel to the axis of the outer body 12.

[0038] The combustion chamber 32 is sealed. In the illustrated embodiment, each rotor tip portion 30 has a tip seal 52 extending from one end face 26 to the other and biased radially outwardly against the peripheral wall 18. An end seal 54 engages each end of each tip seal 52 and is biased against the corresponding end wall 14. Each end face 26 of the rotor 24 has at least one arcuate face seal 60 extending from each tip portion 30 to each adjacent tip portion 30 throughout its length adjacent to the rotor periphery but internal thereto, sealingly engaging the end seal 54 adjacent each end thereof and biased into sealing engagement with the adjacent end wall 14. Alternative sealing arrangements are also possible.

[0039] Although not shown in the drawings, the rotor 24 is journaled on an eccentric portion of the shaft so that the shaft rotates the rotor 24 to orbit within the stator cavity 20. As the rotor 24 rotates around the stator cavity 20, the shaft rotates three times for each complete rotation of the rotor 24. An oil seal is provided around the eccentric to prevent radial outward leakage flow of its lubricating oil between the corresponding rotor end face 26 and the outer body end wall 14. During each rotation of the rotor 24, each chamber 32 has a different volume and moves around the stator cavity 20 to undergo four stages of intake, compression, expansion, and exhaust, which are similar to the strokes in a reciprocating internal combustion engine having a four-stroke cycle.

[0040] The engine includes a main inlet port 40 in communication with an air source, an exhaust port 44, and an optional purge port 42 also in communication with an air source (e.g., a compressor) and located between the inlet port 40 and the exhaust port 44. The ports 40, 42, 44 may be defined in the end wall 14 in the peripheral wall 18. In the illustrated embodiment, the inlet port 40 and the purge port 42 are defined in the end wall 14 and communicate with the same intake duct 34 defined as a passage in the end wall 14, and the exhaust port 44 is defined by the peripheral wall 18. Alternative configurations are possible.

[0041] In certain embodiments, a fuel such as kerosene (jet fuel) or other suitable fuel is delivered to the chamber 32 through a fuel port (not shown) such that the chamber 32 is stratified into a rich fuel-air mixture near the ignition source and a lean mixture elsewhere, and the fuel-air mixture can be ignited within the housing using any suitable ignition system known in the art (e.g., spark plug, glow plug). In certain embodiments, the rotary engine 10 operates under the principles of a Miller or Atkinson cycle with a compression ratio lower than its expansion ratio through appropriate relative positions of the main inlet port 40 and the exhaust port 44.

[0042] Reference Figure 3 , the engine assembly is generally shown as 100. The engine assembly 100 may include the above-referenced Figure 1 The combined cycle engine system 8 described above may include Figure 2 The rotary engine 10 described herein. However, the engine 10 may be any internal combustion engine, such as a gas turbine engine, a piston engine, a rotary engine. The disclosed engine assembly may also be implemented as a gas turbine engine used as an auxiliary power unit (APU) in an aircraft. Therefore, the "internal combustion engine" used herein is understood to include all of these types of engines (reciprocating internal combustion engines such as piston engines, rotary internal combustion engines such as rotary or Wankel engines, continuous flow engines such as gas turbine engines), and is therefore defined as any engine having one or more combustion chambers and having a fuel system that feeds fuel to the combustion chamber(s). As will be further described below, the fuel system of the present engine uses common rail injection.

[0043] The engine assembly 100 includes a fuel injection system 102 for providing fuel to the internal combustion engine 10 from a fuel source S, which in the illustrated embodiment includes a fuel tank. As shown, the fuel injection system 102 includes one or more high pressure pumps 104 and a common rail injector 106. The common rail injector 106 includes a common rail 108 and individual injectors, also referred to as common rail injectors 110. The common rail 108 is in fluid communication with each injector 110.

[0044] In the illustrated embodiment, the engine assembly 100 includes a controller 105, which may be a full authority digital engine control (FADEC). The controller 105 may be operably connected to a power lever 107, which may be manually operated by a pilot of an aircraft equipped with the disclosed engine assembly 100. The controller 105 communicates with a high pressure fuel sensor 109, which is operably connected to the high pressure pump (s) 104 to determine the fuel pressure, and with a speed sensor 111, which is operably connected to the engine 10 to determine the speed of the engine 10. By receiving pressure and speed data from the pressure and fuel sensors 109, 111, the controller 105 controls the amount of fuel to be injected by the injector 110 so that the engine 10 delivers the power required by the pilot via the power lever 107.

[0045] Still refer to Figure 3 Each of the fuel injectors 110 includes an inlet 110a, a first outlet 110b, and a second outlet 110c. In the illustrated embodiment, the inlet 110a is fluidly connected to a fuel source S via (multiple) high pressure pumps 104 and a common rail 108. The first outlet 110b is fluidly connected to the combustion chamber 32 ( Figure 2 The second outlet 110 c is configured to discharge a return flow F of the fuel from the injector 110 .

[0046] In certain embodiments, the injector 110 includes a housing and a piston that can move within the housing from a first position where the piston blocks a first outlet 110b of the injector 110 to a position where the piston is spaced a distance from the first outlet 110b to allow fuel from the fuel source S to be injected into the combustion chamber 32 ( Figure 2 ). The movement of the piston is caused by the pressure difference generated by the high-pressure pump 104. When the piston moves from the first position to the second position, a portion of the fuel entering it through the inlet 110a of the injector 110 is not injected into the combustion chamber 32, but is discharged from the injector 110 while bypassing the combustion chamber 32. The return flow F corresponds to this portion of the fuel discharged through the second outlet 110c of the fuel injector 110.

[0047] As the fuel passes through the high pressure pump(s) 104, the temperature and pressure of the fuel will increase. In use, fuel exiting the injector 110 via the second outlet 110c is typically simply redirected to the fuel source S. As will be seen below, the use of a return flow F of the fuel is proposed herein.

[0048] The fuel injection system 102 further has a fuel circuit C comprising a main conduit 112 for supplying fuel from a fuel source S to the injectors 110 and a return conduit 114 for receiving a return flow F of the fuel.

[0049] The fuel circuit C may include a fuel pump 115, also referred to as a boost pump, which may be fluidly connected to the main conduit 112 and configured to draw fuel from a fuel source (e.g., a fuel tank) S and direct the drawn fuel to the high-pressure pump(s) 104. A metering valve 117 may be fluidly connected to the main conduit 112 upstream of the high-pressure pump 104 to control the flow rate of fuel entering the high-pressure pump 104. As shown, the metering valve 117 is operably connected to the controller 105 to feed data about the flow rate of fuel entering the high-pressure fuel pump 104 to the controller 105. A fuel filter 119 may be fluidly connected to the main conduit 112 upstream of the high-pressure pump 104. In the illustrated embodiment, the fuel filter 119 is located upstream of the pump 115 relative to the flow of fuel from the fuel source S to the high-pressure fuel pump(s) 104.

[0050] In the illustrated embodiment, the pressure regulating valve 120 is fluidly connected to the fuel circuit C. The valve 120 has an inlet 120a and an outlet 120b fluidly connectable to the inlet 120a. The valve 120 further has a control inlet 120c, the function of which is described below.

[0051] The valve 120 has a member 120d movable between a closed position (as shown) and an open position (not shown). In the closed position, fuel is allowed to flow from the main fuel conduit 112 to the return conduit 114. In the open position of the member 120d, the inlet 120a of the valve 120 is fluidly connected to the outlet 120b of the valve 120. In the illustrated embodiment, in the closed position, the member 120d is biased using a biasing member 120e, which may be a spring.

[0052] In the illustrated embodiment, the high pressure pump(s) 104 have a control outlet 104a that is fluidly connected to a control inlet 120c of a pressure regulating valve 120. The pressure of the fuel entering the high pressure pump 104 from the fuel source S is preferably within a given range. If the pressure of the fuel entering the high pressure pump(s) 104 is above a given pressure threshold, the pressure at the control outlet 104a increases and pushes the valve 120 from a closed position to an open position, thereby allowing fuel to flow from the main fuel conduit 112 to the return conduit 114. In other words, the pressure regulating valve 120 provides an escape path for excess fuel that would otherwise increase the inlet fuel pressure of the high pressure pump(s) 104 above a given pressure threshold.

[0053] In the embodiment shown, the high-pressure pump(s) 104 are fluidly connected to the injectors 110 via a fuel conduit 124. Each of the injectors 110 may have its inlet 110a, which is fluidly connected to the high-pressure pump 104 via a respective one of the fuel conduits 124. In the depicted embodiment, a bypass conduit 126 is fluidly connected to the fuel conduit 124. The bypass conduit 126 may have a plurality of upstream connection points 126a, each of which is fluidly connected to a respective one of the fuel conduits 124. The bypass conduit 126 has a downstream connection point 126b that may be connected to the return conduit 114. In the embodiment shown, the downstream connection point 126b of the bypass conduit 126 is fluidly connected to the return conduit 114 downstream of the second outlet 110c of the injector 110, relative to the direction of the return flow F circulating in the return conduit.

[0054] The fuel circulating in the fuel conduit 124 between the high-pressure pump 104 and the injectors 110 is at a high pressure (eg, 500 bar) and a high temperature because it has been compressed by the high-pressure pump(s) 104 .

[0055] In some cases it may be advantageous to use a return flow F of the fuel. Figure 4, the engine assembly 100 includes a jet pump 116. The jet pump 116 can be located upstream of the pump 115 and downstream of the filter 119. Other configurations are also contemplated. For example, the jet pump 116 can be located within the fuel tank. The jet pump 116 has a motive flow inlet 116a, an entrainment flow inlet 116b, and an outlet 116c. The jet pump 116 may include a convergence section 116d for accelerating the fuel received through the motive flow inlet 116a.

[0056] The motive flow inlet 116 a of the injection pump 116 may be connected to the second injector outlet 110 c of the common rail injector 110 , to a fuel conduit 124 connecting the pump 104 to the common rail injector 110 , or to both the second injector outlet 110 c and the fuel conduit 124 .

[0057] In the illustrated embodiment, the motive flow inlet 116a is connected to the second injector outlet 110c of the common rail injector 110 and is selectively connected to the fuel conduit 124 when it is desired to increase the flow rate of the fuel injected into the motive flow inlet 116a. In the depicted embodiment, the motive flow inlet 116a may be fluidly connected to the fuel conduit 124 via the bypass conduit 126 and via the return conduit 114. Other configurations are contemplated without departing from the scope of the present disclosure.

[0058] The injection pump 116 receives a return flow F of fuel and / or a fuel flow from a fuel line 126 that fluidly connects the high pressure pump 104 to the common rail injector 110, and injects the flow through a tube 116e. The tube 116e is fluidly connected to the motive flow inlet 116a, to the entrainment flow inlet 116b, and to the outlet 116c. The injection of fuel from the motive flow inlet 116a into the tube 116e forms a depression around the airflow or jet of fuel injected through the inlet 116a. This depression has a suction effect that draws the fuel flow through the entrainment flow inlet 116b. In other words, the depression formed by the injection of fuel through the motive flow inlet 116a entrains the secondary flow via the entrainment flow inlet 116b. The outlet 116c of the jet pump 116 outputs a flow generated by a combination of the motive flow received via the inlet 116a and the entrained flow received via the entrained flow inlet 116b, and the outlet 116c is defined by the conduit 116e and can define a split section 116f. Therefore, the jet pump 116 is able to use another fuel flow from another source to pump the fuel flow. In a specific embodiment, the split section 116f converts the kinetic energy of the fuel into potential energy. In a specific embodiment, the disclosed system increases or improves the suction lift at the engine inlet by using the wasted energy coming out of the pipeline 110c as a motive flow. Using this usually wasted energy can allow the use of a large pump to draw fuel from the fuel tank to reduce the complexity of the system, and completely operate the system without the need for a pump to meet the suction lift requirements at the engine inlet.

[0059] The motive flow generated by the return flow F of fuel and / or fuel drawn from the fuel line 124 can be used as a motive flow source for an aircraft equipped with the disclosed engine assembly 100. For example, the motive flow source can be used to draw fuel from a fuel tank, increase the flow rate of fuel through a given fuel conduit, displace fuel from a given fuel tank to another fuel tank, and any other suitable application.

[0060] In the present embodiment, the flow control device 113 is fluidly connected to the bypass conduit 126 between the upstream connection point 126a and the downstream connection point 126b. The flow control device 113 may be a variable control orifice and may be used to vary the flow rate of the fuel circulating in the bypass conduit 126. The size of the orifice of the variable control orifice may be manually and / or electronically controlled to control the flow rate in the bypass conduit 126. The flow control device 113 may close the fluid communication between the fuel conduit 124 and the injector 116 via the bypass conduit 126.

[0061] In certain embodiments, the disclosed fuel system allows the use of energy from the return flow coming out of the common rail injector or directly from the common rail fuel line to drive the motive flow within the injection pump. This may allow the use of wasted energy from the common rail system to create a suction effect using motive flow within a low pressure fuel system or directly from the fuel tank. This concept may be applicable to all engine applications such as turboshafts, turboprops, turbofans, and APUs using common rail technology.

[0062] In certain embodiments, the disclosed fuel system utilizes wasted energy out of common rail injectors; allows for simple motive flow replacement of aircraft tank boost pumps to achieve suction lift; and is a low complexity system that is potentially lighter and less expensive than a boost pump.

[0063] To operate the aircraft engine, fuel is pressurized to circulate through common rail injection system 102; a portion of the pressurized fuel is circulated through motive flow inlet 116a of injection pump 116; and a flow is entrained through injection pump 116 using a portion of the pressurized fuel circulated through motive flow inlet 116a.

[0064] Here, a portion of the pressurized fuel is a return flow F of fuel from a common rail injector 110 of the common rail fuel injection system 102. The return flow F of fuel circulates through the motive flow inlet 116a of the injection pump 116. In the embodiment shown, a portion of the pressurized fuel is diverted to the injection pump from at least one fuel conduit 124; at least the fuel conduit 124 connects the high pressure pump 104 to the common rail injector 110 of the common rail injection system 102.

[0065] In the illustrated embodiment, fuel is diverted from at least one fuel conduit 124 and the flow is entrained using both the return flow F of the fuel and the diverted fuel. In the depicted embodiment, the jet pump 116 is fluidly connected to a fuel source S, and fuel from the fuel source is entrained through the jet pump 116 using a portion of the pressurized fuel.

[0066] In the illustrated embodiment, the flow rate of the diverted portion of the pressurized fuel is adjusted. The adjustment of the flow rate can be achieved by restricting the flow of the diverted portion of the pressurized fuel. Here, entraining the flow by using a portion of the pressurized fuel through the jet pump 116 includes entraining fuel directly from the fuel tank S.

[0067] In the illustrated embodiment, entraining the flow with a portion of the pressurized fuel through the jet pump 116 includes drawing fuel through a main fuel conduit 112 that connects the fuel source S to the high-pressure pump 104 .

[0068] In order to supply fuel to an aircraft engine having a common rail fuel injection system 102, the fuel is pressurized to be circulated through the common rail injection system 102; a portion of the fuel is injected in a common rail injector 110 of the common rail injection system 102, thereby generating a return flow F of the fuel; and the fuel to be pressurized is entrained from a fuel source S through the jet pump 116 using the return flow F of the fuel circulated through a motive flow inlet 116 a of the jet pump 116.

[0069] In some cases, fuel is diverted from a fuel conduit 124 that connects the high pressure pump 104 to the common rail injectors 110 of the common rail injection system 102 and entrained with both the return flow F of fuel and the diverted fuel.

[0070] In the illustrated embodiment, the flow rate of the diverted fuel is regulated. The flow rate can be regulated by restricting the flow of the diverted fuel. In the illustrated embodiment, entraining the fuel from the fuel source S by the jet pump 116 includes entraining the fuel directly from the fuel tank. In the illustrated embodiment, entraining the fuel from the fuel source S by the jet pump 116 includes drawing the fuel through the main fuel conduit 112, which fluidly connects the fuel source S to the high pressure pump 104.

[0071] Embodiments disclosed herein include:

[0072] A. A method of operating an aircraft engine of an aircraft, the aircraft engine having a common rail fuel injection system for injecting fuel into a combustion chamber of the aircraft engine, the method comprising: pressurizing fuel for circulation through the common rail injection system; circulating a portion of the pressurized fuel through a motive flow inlet of an injection pump; and entraining flow through the injection pump using a portion of the pressurized fuel circulated through the motive flow inlet.

[0073] B. A method of supplying fuel to an aircraft engine having a common rail fuel injection system, the method comprising: pressurizing fuel to circulate through the common rail injection system; injecting a portion of the fuel in a common rail injector of the common rail injection system to generate a backflow of the fuel; and entraining fuel to be pressurized from a fuel source through a jet pump using the backflow of the fuel circulated through a motive flow inlet of the jet pump.

[0074] Embodiment A and Embodiment B may include any one of the following elements in any combination:

[0075] Element 1: A portion of the pressurized fuel is a return flow of fuel from at least one common rail injector of a common rail fuel injection system, and the method includes circulating the return flow of the fuel through a motive flow inlet of the injection pump. Element 2: Diverting a portion of the pressurized fuel from at least one fuel conduit to the injection pump, at least the fuel conduit connects the high pressure pump to at least one common rail injector of the common rail injection system. Element 3: Diverting fuel from at least one fuel conduit and entraining the flow using both the return flow of the fuel and the diverted fuel, at least the fuel conduit connects the high pressure pump to at least one common rail injector of the common rail fuel injection system. Element 4: The injection pump is fluidly connected to a fuel source, and the method includes entraining fuel from the fuel source through the injection pump using a portion of the pressurized fuel. Element 5: Regulating the flow rate of the diverted portion of the pressurized fuel. Element 6: Regulating the flow rate includes constraining the flow of the diverted portion of the pressurized fuel. Element 7: Entraining the flow through the injection pump using a portion of the pressurized fuel includes entraining fuel directly from a fuel tank. Element 8: Entraining the flow through the injection pump using a portion of the pressurized fuel includes drawing fuel through a main fuel conduit, which fluidly connects the fuel source to the high pressure pump.

[0076] C. An aircraft engine comprising: at least one combustion chamber; a fuel pump fluidly connected to a fuel source; a common rail injector having an injector inlet fluidly connected to the fuel pump via a fuel conduit, a first injector outlet fluidly connected to the at least one combustion chamber, and a second injector outlet for outputting a return flow of fuel; and a jet pump having a motive flow inlet fluidly connected to one of the second injector outlet and the fuel conduit upstream of the common rail injector, and an entrainment flow inlet for receiving fuel to be drawn by the jet pump.

[0077] Embodiment C may include any of the following elements in any combination:

[0078] Element 9: The motive flow inlet is fluidly connected to both the second injector outlet and the fuel conduit. Element 10: The motive flow inlet is fluidly connected to the fuel conduit via a bypass conduit, and the flow control device is fluidly connected to the bypass conduit. Element 11: The fuel source is a fuel tank, and the injection pump is located in the fuel tank. Element 12: The main fuel conduit fluidly connects the fuel source to the fuel pump, and the boost pump is fluidly connected to the main fuel conduit, and the injection pump is connected to the main fuel conduit upstream of the boost pump.

[0079] The above description is exemplary only, and those skilled in the art will recognize that changes may be made to the described embodiments without departing from the scope of the disclosed invention. Other modifications falling within the scope of the invention will be apparent to those skilled in the art upon careful study of the disclosure, and these modifications are intended to fall within the appended claims.

Claims

1. A method of operating an aircraft engine of an aircraft, the aircraft engine having a common rail fuel injection system for injecting fuel into a combustion chamber of the aircraft engine, the method comprising: pressurizing the fuel for circulation through the common rail fuel injection system; circulating a portion of pressurized fuel through a motive flow inlet of an injection pump, wherein the portion of the pressurized fuel is a return flow of fuel from at least one common rail injector of the common rail fuel injection system, the at least one common rail injector being connected to a return conduit for receiving the return flow of the fuel, the method comprising circulating the return flow of the fuel through the motive flow inlet of the injection pump; diverting fuel from a plurality of fuel conduits connecting a high pressure pump to at least one common rail injector of the common rail fuel injection system via a bypass conduit fluidly connected to the fuel conduits, the bypass conduit having a plurality of upstream connection points, each of the plurality of upstream connection points being fluidly connected to a respective one of the fuel conduits, the bypass conduit having a downstream connection point connected to the return conduit; and Flow is entrained through the jet pump utilizing both return flow and diverted fuel of the fuel circulating through the motive flow inlet.

2. The method according to claim 1, wherein: The jet pump is fluidly connected to a fuel source, and the method includes entraining fuel from the fuel source through the jet pump using the portion of the pressurized fuel. 3 . The method of claim 1 , further comprising adjusting a flow rate of the diverted portion of the pressurized fuel.

4. The method according to claim 3, wherein: Adjusting the flow rate includes restricting flow of the diverted portion of the pressurized fuel.

5. The method according to any one of claims 1 to 4, wherein: Entraining the flow through the jet pump using the portion of the pressurized fuel includes entraining fuel directly from a fuel tank.

6. The method according to any one of claims 1 to 4, wherein: Entraining the flow through the jet pump with the portion of the pressurized fuel includes drawing the fuel through a main fuel conduit fluidly connecting a fuel source to a high pressure pump.

7. An aircraft engine, comprising: at least one combustion chamber; a fuel pump fluidly connected to a fuel source; a common rail injector having an injector inlet fluidly connected to the fuel pump via a plurality of fuel conduits (124), a first injector outlet fluidly connected to the at least one combustion chamber, and a second injector outlet for outputting a return flow of fuel; as well as an injection pump having a motive flow inlet and an entrainment flow inlet, the motive flow inlet being fluidly connected to one of the second injector outlet and the fuel conduit upstream of the common rail injector, the entrainment flow inlet being for receiving fuel to be drawn by the injection pump, the motive flow inlet being fluidly connected to both the second injector outlet and the fuel conduit, a bypass conduit being fluidly connected to the fuel conduit, the bypass conduit having a plurality of upstream connection points, each of the plurality of upstream connection points being fluidly connected to a respective one of the fuel conduits, the bypass conduit having a downstream connection point connected to a return conduit receiving a return flow of the fuel, the motive flow inlet being fluidly connected to the fuel conduit via the bypass conduit and via the return conduit.

8. An aircraft engine according to claim 7, wherein: A flow control device is fluidly connected to the bypass conduit.

9. An aircraft engine according to claim 7 or 8, wherein: The fuel source is a fuel tank and the jet pump is located within the fuel tank.

10. The aircraft engine according to claim 7 or 8, further comprising: a main fuel conduit fluidly connecting the fuel source to the fuel pump; and a boost pump fluidly connected to the main fuel conduit, the jet pump being connected to the main fuel conduit upstream of the boost pump.

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