Patent Description:
Fuel delivery systems for gas turbine engines sometimes require an ecology function to remove a set quantity of fuel from the engine fuel manifolds after engine shutdown. While ecology systems are known, there is a continued demand for the provision of a compact, economical ecology function for fuel supply systems.

<CIT> discloses a prior art fuel system having the features of the preamble of claim <NUM>. <CIT> discloses another prior art fuel system.

In one aspect of the present invention, there is provided a fuel system for an aircraft engine, in accordance with claim <NUM>.

In an embodiment of any of the above embodiments, the flow restrictor includes a check valve, the check valve configured to restrict fuel flow from the fuel metering unit to the ecology outlet port of the flow divider.

In an embodiment of any of the above embodiments, the flow restrictor is a passive flow restrictor.

In an embodiment of any of the above embodiments, the discharge pressurizing valve is a <NUM>-way, <NUM>-position valve having a first position in which the inlet port of the discharge pressurizing valve is fluidly connected to the inlet/outlet port and the ecology outlet port of the discharge pressurizing valve is closed, and a second position in which the inlet port of the discharge pressurizing valve is closed and the inlet/outlet port is fluidly connected to the ecology outlet port of the discharge pressurizing valve.

In an embodiment of any of the above embodiments, the flow divider includes a <NUM>-way, <NUM>-position valve having a first position in which the inlet port of the flow divider is fluidly connected to the primary and secondary fuel manifolds and the ecology outlet port of the flow divider is closed, and a second position in which the inlet port of the flow divider is closed and the ecology outlet port is fluidly connected to the primary and secondary fuel manifolds.

In an embodiment of any of the above embodiments, the discharge pressurizing valve has a first position in which its inlet port is fluidly connected to its inlet/outlet port while its ecology outlet port is closed, and a second position in which its inlet port is closed and its inlet/outlet port is fluidly connected to its ecology outlet port, wherein the flow divider has a first position in which its inlet port is fluidly connected to the primary and secondary fuel manifolds while its ecology outlet port is closed, and a second position in which its inlet port is closed while its ecology outlet port is fluidly connected to the primary and secondary fuel manifolds, wherein the discharge pressurizing valve is in its first position when the flow divider is in its first position, and wherein the discharge pressurizing valve is in its second position when the flow divider is in its second position.

In an embodiment of any of the above embodiments, the fuel line is an external fuel line configured to be mounted outside of the aircraft engine.

In an embodiment of any of the above embodiments, the flow restrictor is a tesla valve.

In an embodiment of any of the above embodiments, the flow divider is positioned adjacent to the primary and secondary fuel manifolds.

<FIG> illustrates an aircraft engine <NUM> comprising a fuel system <NUM> having fuel supply and ecology functions. According to some embodiments, the engine <NUM> is provided in the form of a gas turbine engine configured for use in subsonic flight, and generally comprising a compressor section for pressurizing the air, a combustor in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section for extracting energy from the combustion gases. However, it is understood that the engine <NUM> can adopt various forms and is, thus, not strictly limited to gas turbine engines. For instance, the engine <NUM> could be provided in the form of a hybrid electric aircraft engine or a compounded engine including an internal combustion engine compounding power with a gas turbine engine.

The fuel system <NUM> of the engine <NUM> generally comprises a fuel metering unit (FMU) <NUM> fluidly connected to a flow divider <NUM> configured to split the fuel flow from the FMU <NUM> between a primary and a secondary fuel manifold <NUM>, <NUM> (<FIG> and <FIG>). As will be seen hereinafter, the FMU <NUM> and the flow divider <NUM> cooperate to sequence and schedule the fuel flow between the primary and secondary fuel manifolds <NUM>, <NUM>. The term "fluidly connected" as used herein is intended to mean either an indirect or a direct fluid communication. Thus, if a first device fluidly connects to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections.

According to the illustrated embodiment, the FMU <NUM> and the flow divider <NUM> are two separate units installed at remote locations along the engine <NUM>. As exemplified in <FIG>, the FMU <NUM> can be installed at the rear end of the engine <NUM>, whereas the flow divider <NUM> may be disposed adjacent the fuel manifolds <NUM>,<NUM> in the combustor section of the engine <NUM>. The FMU <NUM> is fluidly connected to the flow divider <NUM> via a single fuel line <NUM>. As will be seen hereinafter, the fuel line <NUM> is used to both supply fuel to the fuel manifolds <NUM>, <NUM> during engine operation and to withdraw fuel from the manifolds <NUM>, <NUM> at engine shutdown. In other words, the same fuel line <NUM> is selectively used as a fuel supply line (<FIG>) and an ecology line (<FIG>). As exemplified in <FIG>, the fuel line <NUM> may be provided in the form of an external line extending along a length of the engine <NUM> between the FMU <NUM> and the flow divider <NUM>. It is understood that the fuel line <NUM> can include various components, such as conduit sections, pipes, hoses, fittings, connectors, etc., for carrying a fuel flow from one location to another.

Referring to <FIG> and <FIG>, it can be appreciated that the FMU <NUM> comprises a discharge pressurizing valve <NUM> and an ecology ejector <NUM>. According to the illustrated embodiment, the discharge pressurizing valve <NUM> is embodied in the form of a <NUM>-way, <NUM>-position directional control valve having a pressure or inlet port 24a, an inlet/outlet port 24b and an ecology outlet port 24c. The inlet port 24a is fluidly connected to a fuel source, such as the engine fuel tank (not shown) via one or more fuel pumps (not shown). The inlet/outlet port 24b is, in turn, fluidly connected to the fluid line <NUM>. And the ecology port 24c is fluidly connected to a suction inlet port 26a of the ecology ejector <NUM>. As depicted in <FIG>, in the first position (i.e. the fuel supply mode), the inlet port 24a is fluidly connected to the inlet/outlet port 24b and the ecology port 24c is disabled/closed. In the second position (i.e. the ecology mode) shown in <FIG>, the inlet/outlet port 24b is fluidly connected to ecology outlet port 24c and the inlet port 24a is closed. A translating spool or the like may serve as the valve member and determines the position that the valve is in. As schematically illustrated in <FIG> and <FIG>, the valve member/spool may be biased towards the second position by a biasing member 24d (e.g. a spring or a hydraulic/pneumatic member). Alternatively, the valve member/spool may be electric or electronically controlled, like a solenoid. As schematically shown at 24e, the valve member may also be fluidly connected to the pressure side of the valve <NUM> so that when the pressure at the inlet port 24a reaches a predetermined value sufficient to overcome the biasing force of the biasing member 24d, the valve member is hydraulically pushed against the biasing member 24d to the first position illustrated in <FIG>. At engine shutdown, the fuel pump is stopped, the pressure acting on the valve member thus drop, and the biasing member 24d returns the valve member to its second position as shown in <FIG>, thereby fluidly connecting the fuel line <NUM> to the ejector <NUM>.

In addition to the suction inlet port 26a, the ecology ejector <NUM> has a motive flow inlet 26b fluidly connected to a high pressure motive fluid source (i.e. pressurized fuel) and a discharge or outlet port 26c fluidly connected to a fuel tank, such as the engine main fuel tank. As shown in <FIG>, following engine shutdown, the motive flow 26d flowing through the motive flow inlet 26b creates a suction at the suction inlet port 26a to draw fuel from the manifolds <NUM>,<NUM>, via the flow divider <NUM>, the fuel line <NUM> and the discharge pressurizing valve <NUM>.

Still referring to <FIG> and <FIG>, it can be appreciated that according to some embodiments, the flow divider <NUM> comprises a <NUM>-way, <NUM>-position valve having an inlet port 20a, a primary fuel port 20b, a secondary fuel port 20c, and an ecology outlet port 20d. The inlet port 20a is fluidly connected to the fuel line <NUM>. The primary fuel port 20b and the secondary fuel port 20c are respectively fluidly connected to the primary and secondary fuel manifolds <NUM>, <NUM>. The ecology outlet port 20d is, in turn, fluidly connected to the fuel line <NUM> via a flow restrictor <NUM>, which can form part of the flow divider <NUM>. According to the illustrated embodiment, the flow restrictor <NUM> is provided in the form of a one-way valve or check valve configured to allow fuel flow from the ecology outlet port 20d towards the FMU <NUM> and to block fuel flow from the fuel line <NUM> to the ecology outlet port 20d. It is understood that the flow restrictor <NUM> could consist of various forms of valves including active valves, switch valves, on/off control valves, <NUM>-way valves just to name a few.

Instead of a valve, in some applications, the flow restrictor <NUM> could be embodied in the form of a passive restrictor like an orifice defining a throat/ restricted orifice or a Tesla valve or a similar flow restrictor that would allow sufficiently low (acceptable) fluid resistance in the ecology direction (<FIG>) to empty the manifolds <NUM>, <NUM>, and sufficiently high (acceptable) fluid resistance in the normal operating direction (<FIG>) to force the flow divider valve to move to the first position (i.e. the fuel supply mode). According to these alternatives, the sealing once ecology is done would not be provided, but could be regarded as optional.

As shown in <FIG>, when the divider valve is in its first position (i.e. the fuel supply mode), the inlet port 20a is fluidly connected to both the primary and secondary fuel ports 20b, 20c to split the incoming fuel flow according to a predetermined ratio between the primary and secondary fuel manifolds <NUM>, <NUM>. It is understood that the divider valve can have an infinite number of intermediate positions between open to primary only, and fully open to primary and secondary. In the second position (i.e. ecology mode) shown in <FIG>, the primary and secondary fuel ports 20b, 20c are rather fluidly connected to the ecology outlet port 20d to permit drainage of the fuel manifolds <NUM>, <NUM> after the engine has been shut down or during the process of shutting down the engine, or as the engine spools down following a commanded engine shutdown. In an alternative configuration, only a selected one of the two manifolds <NUM>, <NUM> could be emptied by the system. Accordingly, the second position or an intermediate position could be used to selectively connect one or both fuel manifolds to the ecology port 20d. A translating spool or the like may serve as the valve member and determines the position that the divider valve is in. As schematically illustrated in <FIG> and <FIG>, the valve member/spool may be biased towards the second position (<FIG>) by a biasing member 20e (e.g. a spring, a hydraulic/pneumatic member or a solenoid). As schematically shown at 20f, the valve member may also be fluidly connected to the pressure side of the divider valve so that when the pressure at the inlet port 20a reaches a predetermined value sufficient to overcome a biasing force of the biasing member 20e, the valve member is hydraulically pushed against the biasing member 20e to the first or open position illustrated in <FIG>. At engine shutdown, the fuel pump is stopped, the pressure acting on the valve member thus drops, and the biasing member 20e returns the valve member to its second or closed position as shown in <FIG>, thereby fluidly connecting the fuel manifolds <NUM> and <NUM> to the ejector <NUM> via the flow divider valve, the fuel line <NUM> and the discharge pressurizing valve <NUM>.

As shown in <FIG>, during engine operation, the fuel system <NUM> is in a fuel supply mode for supplying fuel to the primary and secondary fuel manifolds <NUM>, <NUM>. In this mode, fuel pressure in the system maintains the discharge pressuring valve <NUM> and the flow divider valve <NUM> in their first or open position. As depicted by the flow arrows in <FIG>, in this mode of operation, fuel is allowed to flow from the discharge pressuring valve <NUM> through the fuel line <NUM> and the inlet port 20a of the flow divider <NUM> to the primary and secondary fuel manifolds <NUM>, <NUM>. The manifolds <NUM>,<NUM> feed respective groups of primary and secondary fuel nozzles (not shown) disposed for injecting fuel in the combustion chamber (not shown) of the engine <NUM>. The primary fuel flow may be used to initiate the combustion process during engine start-up, while the secondary fuel flow may be used to supplement and intensify the combustion process once the primary flow is burning steadily.

In the fuel supply mode of the fuel system <NUM>, the ecology port 24c of the discharge pressurizing valve <NUM> is closed, thereby disconnecting the ecology ejector <NUM> from the fuel line <NUM>. Fuel flow through the ecology port 20d of the flow divider <NUM> is prevented by the flow restrictor <NUM> (the check valve in the illustrated embodiment).

At engine shutdown, operation of the fuel pump is terminated, thereby causing the fuel pressure in the system to drop. This causes the fuel system <NUM> to fall into its ecology mode for draining the fuel manifolds <NUM>,<NUM>. The drop in fluid pressure in the system causes the discharge pressuring valve <NUM> and the flow divider <NUM> to close as illustrated in <FIG>. In this second or closed position, the fuel manifolds <NUM>, <NUM> are fluidly connected to the ecology port 20d of the flow divider <NUM> and the fuel line <NUM> is fluidly connected to the ecology ejector <NUM> via the ecology port 24c of the discharge pressurizing valve <NUM>. A motive flow 26d through the ejector <NUM> is used to entrain an ecology flow through the fuel line <NUM> to drain the fuel manifolds <NUM>, <NUM>. In the ecology mode, fuel is thus allowed to flow from the fuel manifolds <NUM>, <NUM> through the ecology port 20d of the flow divider <NUM>, the flow restrictor <NUM> (e.g. the check valve), the fuel line <NUM>, the ecology port 24c of the discharge pressuring valve <NUM> and to the suction inlet port 26a of the ejector <NUM> where the fuel withdrawn from the manifolds <NUM>, <NUM> is discharged at 26c into a tank or the like.

In view of the foregoing, it can be appreciated that a single fluid line <NUM> can be used to both supply fuel to and withdraw fuel from the manifolds <NUM>, <NUM>. It eliminates the need for a dedicated ecology line between the FMU <NUM> and the flow divider <NUM>. This is particularly advantageous when the flow divider <NUM> and the FMU <NUM> are located at spaced-apart locations along the engine <NUM>. It reduces part counts, weight and facilitate assembly.

The FMU <NUM> further comprises a flow restrictor <NUM>, such as a check valve or the like, for preventing the fuel to backflow from the ecology ejector <NUM> in the ecology mode. Such a check valve could be installed in a line between the suction inlet 26a of the ejector <NUM> and the ecology port 24c of the discharge pressurizing valve <NUM>.

Under certain conditions, if the performance of the ecology system is too good, the fuel line <NUM> between the FMU <NUM> and the flow divider <NUM> (also used for ecology) could be fully emptied during the ecology sequence. The consequence is that the fuel line <NUM> would have to be refilled with fuel during the next engine start, which makes it more difficult to start the engine, the fuel pump capacity at start being limited. To avoid oversizing the fuel pump, the FMU <NUM> could be operated by a suitable control system to send fuel to the engine at the very beginning of the start procedure, or as early as the pump bearings can support a sufficient load. In addition, the ecology system could be configured to ensure that the fuel line <NUM> is not completely emptied during ecology.

According to other embodiments outside the wording of the claims, instead of integrating an ecology function to the discharge pressuring valve <NUM>, a separate ecology valve could be provided in the FMU <NUM> to selectively fluidly connect the ecology ejector <NUM> to the fuel line <NUM>.

According to at least some embodiments, the discharge pressurizing valve and/or the flow divider valve could be controlled to switch to the ecology mode electronically instead of hydraulically.

According to one embodiment or more, suction is not needed to draw the fuel out of the manifolds at engine shutdown because the fuel lines are such that gravity combined (or not) with the residual air/gas pressure in the engine combustor as the engine spools down are sufficient to push the fuel contained in the manifolds back through the flow divider, the fuel line, the discharge pressurizing valve to the port 26b. The port 26b could be directly connected to the aircraft fuel tank or like, or any other low pressure point in the fuel system.

Claim 1:
A fuel system (<NUM>) for an aircraft engine (<NUM>), comprising:
a fuel metering unit (<NUM>) fluidly connectable to a fuel source of the aircraft engine (<NUM>);
a flow divider (<NUM>) separate from the fuel metering unit (<NUM>) and mountable to the aircraft engine (<NUM>) at a location remote from the fuel metering unit (<NUM>), the flow divider (<NUM>) having a fuel inlet port (20a) fluidly connected to the fuel metering unit (<NUM>) via a fuel line (<NUM>); and
a primary and a secondary fuel manifold (<NUM>, <NUM>) fluidly connected to the flow divider (<NUM>);
wherein the fuel metering unit (<NUM>) and the flow divider (<NUM>) are configured to be operated in a fuel supply mode in which fuel is allowed to flow in a first direction through the fuel line (<NUM>) from the fuel metering unit (<NUM>) to the flow divider (<NUM>) to feed the primary and secondary fuel manifolds (<NUM>, <NUM>),
characterised in that:
the fuel metering unit (<NUM>) and the flow divider (<NUM>) are configured to be operated in an ecology mode in which fuel is allowed to flow in a second direction through the fuel line (<NUM>) from the flow divider (<NUM>) towards the fuel metering unit (<NUM>);
the fuel system (<NUM>) further comprises an ecology ejector (<NUM>);
the fuel metering unit (<NUM>) includes a discharge pressurizing valve (<NUM>) having an inlet port (24a) fluidly connectable to a source of fuel, an ecology outlet port (24c) fluidly connected to a suction inlet port (26a) of the ecology ejector (<NUM>), and an inlet/outlet port (24b) selectively connectable in flow communication to either one of the inlet port (24a) or the ecology outlet port (24c) of the discharge pressurizing valve (<NUM>);
the fuel inlet port (20a) of the flow divider (<NUM>) is selectively fluidly connectable to the primary and the secondary fuel manifold (<NUM>, <NUM>), the flow divider (<NUM>) having an ecology outlet port (20d) selectively fluidly connectable to the primary and secondary fuel manifolds (<NUM>, <NUM>), and a flow restrictor (<NUM>) fluidly connected to the ecology outlet port (20d); and
the fuel line (<NUM>) extends from the inlet/outlet port (24b) of the discharge pressurizing valve (<NUM>) to the inlet port (20a) of the flow divider (<NUM>), the ecology outlet port (20d) of the flow divider (<NUM>) fluidly connected to the fuel line (<NUM>) via the flow restrictor (<NUM>).