Patent Description:
Aircraft engines include at least one combustion chamber into which fuel is provided, typically by a fuel injector. Some fuel injectors, such as common-rail injectors, generate a backflow of fuel. The energy of the backflow is typically wasted, as the fuel backflow is usually returned directly back to the fuel tank. Better and more efficient fuel management in such fuel systems is therefore desirable.

<CIT> discloses a prior art method for monitoring and controlling fuel injector in common rail injection systems. <CIT> discloses a rotary internal combustion engine comprising common fuel injectors, and bypass lines to recirculate overflow fuel from a fuel injection system.

In one aspect, there is provided a method of operating an aircraft engine of an aircraft as recited in claim <NUM>.

The method of operating an aircraft engine as defined above and herein may further include, one or more of the following additional steps and/or features.

The ejector pump is fluidly connected to a source of fuel, the method comprising entraining fuel from the source of fuel through the ejector pump using the portion of the pressurized fuel.

Regulating a flow rate of the diverted portion of the pressurized fuel.

Regulating the flow rate includes constricting a flow of the diverted portion of the pressurized fuel.

Entraining the flow through the ejector pump with the portion of the pressurized fuel includes entraining fuel directly from a fuel tank.

Entraining the flow through the ejector pump with the portion of the pressurized fuel includes suctioning the fuel through a main fuel conduit fluidly connecting the source of fuel to a high-pressure pump.

In yet another aspect, there is provided an aircraft engine as recited in claim <NUM>.

The aircraft engine and fuel system as defined above and herein may further include, one or more of the following additional features.

The source of fuel is a fuel tank, the ejector pump located within the fuel tank.

A main fuel conduit fluidly connecting the source of fuel to the fuel pump, and a boost pump fluidly connected to the main fuel conduit, the ejector pump being connected to the main fuel conduit upstream of the boost pump.

Referring to <FIG>, a compound engine system <NUM> is schematically shown. The system <NUM> includes a compressor <NUM> and a turbine <NUM> which are connected by a shaft <NUM>, and which act as a turbocharger to one or more rotary engines <NUM>. The compressor <NUM> may be a single-stage or multiple-stage centrifugal device and/or an axial device. A rotary engine <NUM>, or a plurality of rotary engines, receives compressed air from the compressor <NUM>. The air optionally circulates through an intercooler <NUM> between the compressor <NUM> and the rotary engine(s) <NUM>.

The exhaust gas exiting the rotary engine <NUM> is supplied to the compressor turbine <NUM> and also to a power turbine <NUM>, the turbines <NUM>, <NUM> being shown here in series, i.e. with the exhaust gas flowing first through one of the two turbines where the pressure is reduced, and then through the other turbine, where the pressure is further reduced. In an alternate embodiment (not shown), the turbines <NUM>, <NUM> are arranged in parallel, i.e. with the exhaust gas being split and supplied to each turbine at same pressure. In another alternate embodiment, only one turbine is provided.

Energy is extracted from the exhaust gas by the compressor turbine <NUM> to drive the compressor <NUM> via the connecting shaft <NUM>, and by the power turbine <NUM> to drive an output shaft <NUM>. The output shaft <NUM> may be connected via a gear system <NUM> to a shaft <NUM> connected to the rotary engine(s) <NUM>. The combined output on the shafts <NUM>, <NUM> may be used to provide propulsive power to a vehicle application into which the system <NUM> is integrated. This power may be delivered through a gearbox (not shown) that conditions the output speed of the shafts <NUM>, <NUM> to the desired speed on the application. In an alternate embodiment, the two shafts <NUM>, <NUM> may be used independently to drive separate elements, e.g. a propeller, a helicopter rotor, a load compressor or an electric generator depending whether the system is a turboprop, a turboshaft or an Auxiliary Power Unit (APU).

Although not shown, the system <NUM> also includes a cooling system, including a circulation system for a coolant to cool the outer body of the rotary engine (e.g. water-ethylene, oil, air), an oil coolant for the internal mechanical parts of the rotary engine, one or more coolant heat exchangers, etc..

The compound engine system <NUM> may be as described in Lents et al. 's <CIT>'s <CIT>.

The rotary engine <NUM> forms the core of the compound cycle engine system <NUM>. Referring to <FIG>, the rotary internal combustion engine <NUM>, known as a Wankel engine, is schematically shown. The rotary combustion engine <NUM> comprises an outer body <NUM> having axially-spaced end walls <NUM> with a peripheral wall <NUM> extending therebetween to form a rotor cavity <NUM>. The inner surface of the peripheral wall <NUM> of the cavity <NUM> has a profile defining two lobes, which is preferably an epitrochoid.

An inner body or rotor <NUM> is received within the cavity <NUM>. The rotor <NUM> has axially spaced end faces <NUM> adjacent to the outer body end walls <NUM>, and a peripheral face <NUM> extending therebetween. The peripheral face <NUM> defines three circumferentially-spaced apex portions <NUM>, and a generally triangular profile with outwardly arched sides <NUM>. The apex portions <NUM> are in sealing engagement with the inner surface of peripheral wall <NUM> to form three rotating combustion chambers <NUM> between the inner rotor <NUM> and outer body <NUM>. The geometrical axis of the rotor <NUM> is offset from and parallel to the axis of the outer body <NUM>.

The combustion chambers <NUM> are sealed. In the embodiment shown, each rotor apex portion <NUM> has an apex seal <NUM> extending from one end face <NUM> to the other and biased radially outwardly against the peripheral wall <NUM>. An end seal <NUM> engages each end of each apex seal <NUM> and is biased against the respective end wall <NUM>. Each end face <NUM> of the rotor <NUM> has at least one arc-shaped face seal <NUM> running from each apex portion <NUM> to each adjacent apex portion <NUM>, adjacent to but inwardly of the rotor periphery throughout its length, in sealing engagement with the end seal <NUM> adjacent each end thereof and biased into sealing engagement with the adjacent end wall <NUM>. Alternate sealing arrangements are also possible.

Although not shown in the Figures, the rotor <NUM> is journaled on an eccentric portion of a shaft such that the shaft rotates the rotor <NUM> to perform orbital revolutions within the stator cavity <NUM>. The shaft rotates three times for each complete rotation of the rotor <NUM> as it moves around the stator cavity <NUM>. Oil seals are provided around the eccentric to impede leakage flow of lubricating oil radially outwardly thereof between the respective rotor end face <NUM> and outer body end wall <NUM>. During each rotation of the rotor <NUM>, each chamber <NUM> varies in volumes and moves around the stator cavity <NUM> to undergo the four phases of intake, compression, expansion and exhaust, these phases being similar to the strokes in a reciprocating-type internal combustion engine having a four-stroke cycle.

The engine includes a primary inlet port <NUM> in communication with a source of air, an exhaust port <NUM>, and an optional purge port <NUM> also in communication with the source of air (e.g. a compressor) and located between the inlet and exhaust ports <NUM>, <NUM>. The ports <NUM>, <NUM>, <NUM> may be defined in the end wall <NUM> of in the peripheral wall <NUM>. In the embodiment shown, the inlet port <NUM> and purge port <NUM> are defined in the end wall <NUM> and communicate with a same intake duct <NUM> defined as a channel in the end wall <NUM>, and the exhaust port <NUM> is defined through the peripheral wall <NUM>. Alternate configurations are possible.

In a particular embodiment, fuel such as kerosene (jet fuel) or other suitable fuel is delivered into the chamber <NUM> through a fuel port (not shown) such that the chamber <NUM> is stratified with a rich fuel-air mixture near the ignition source and a leaner mixture elsewhere, and the fuel-air mixture may be ignited within the housing using any suitable ignition system known in the art (e.g. spark plug, glow plug). In a particular embodiment, the rotary engine <NUM> operates under the principle of the Miller or Atkinson cycle, with its compression ratio lower than its expansion ratio, through appropriate relative location of the primary inlet port <NUM> and exhaust port <NUM>.

Referring to <FIG>, an engine assembly is generally shown at <NUM>. The engine assembly <NUM> may incorporate the compound cycle engine system <NUM> described herein above with reference to <FIG> and may include the rotary engine <NUM> described above with reference to <FIG>. The engine <NUM> may however be any combustion engine, such as a gas turbine engine, a piston engine, a rotary engine, and so on. The disclosed engine assembly may also be implemented as a gas turbine engine used as an Auxiliary Power Unit (APU) in an aircraft. Accordingly, the term "combustion engine" as used herein is understood to include all of these types of engines (reciprocating combustion engines such as piston engines, rotating combustion engines such as rotary or Wankel engines, continuous flow engines such as gas turbine engines, etc.), and is therefore defined as any engine having one or more combustion chambers and having a fuel system feeding fuel to the combustion chamber(s). As will be described further below, the fuel system of the present engines uses common rail injection.

The engine assembly <NUM> includes a fuel injection system <NUM> for providing fuel to the combustion engine <NUM> from a fuel source S, which, in the embodiment shown, comprises a fuel tank. As shown, the fuel injection system <NUM> includes one or more high-pressure pump(s) <NUM> and a common-rail injector <NUM>. The common-rail injector <NUM> includes a common rail <NUM> and individual injectors, also referred to as common-rail injectors <NUM>. The common-rail <NUM> is in fluid communication with each of the injectors <NUM>.

In the embodiment shown, the engine assembly <NUM> includes a controller <NUM>, which may be a Full Authority Digital Engine Control (FADEC). The controller <NUM> may be operatively connected to a power lever <NUM>, which may be manually operable by a pilot of an aircraft equipped with the disclosed engine assembly <NUM>. The controller <NUM> communicates with a high pressure fuel sensor <NUM>, which is operatively connected to the high-pressure pump(s) <NUM> for determining fuel pressure, and with a speed sensor <NUM>, which is operatively connected to the engine <NUM> for determining a speed of the engine <NUM>. By receiving pressure and speed data from the pressure and fuel sensors <NUM>, <NUM>, the controller <NUM> controls an amount of fuel to be injected by the injectors <NUM> so that the engine <NUM> delivers the power required by the pilot via the power lever <NUM>.

Still referring to <FIG>, each of the fuel injectors <NUM> includes an inlet 110a, a first outlet 110b, and a second outlet 110c. The inlet 110a is fluidly connected to the source S of fuel, in the embodiment shown via the high-pressure pump(s) <NUM> and the common rail <NUM>. The first outlet 110b is fluidly connected to the combustion chamber <NUM> (<FIG>) of the internal combustion engine <NUM>. The second outlet 110c is configured for expelling a backflow F of fuel from the injectors <NUM>.

In a particular embodiment, the injector <NUM> includes housings and pistons movable within the housings from a first position in which the piston blocks the first outlet 110b of the injector <NUM> to a second position in which the piston is distanced from the first outlet 110b for allowing the fuel from the source of fuel S to be injected in the combustion chamber <NUM> (<FIG>). Movement of the piston is induced by a pressure differential created by the high-pressure pumps <NUM>. When the piston moves from the first position to the second position, a portion of the fuel that enters the injector <NUM> via its inlet 110a is not injected in the combustion chamber <NUM> and is expelled out of the injector <NUM> while bypassing the combustion chamber <NUM>. The backflow F corresponds to this portion of the fuel that is expelled via the second outlet 110c of the fuel injector <NUM>.

The temperature and pressure of the fuel increases as a result of its passage through the high-pressure pump(s) <NUM>. In use, the fuel that exits the injector <NUM> via the second outlet 110c is typically simply redirected toward the source of fuel S. As will be seen herein below, it is herein proposed to use the backflow F of fuel.

The fuel injection system <NUM> further has a fuel circuit C including a main conduit <NUM>, for suppling the fuel from the source of fuel S to the injector <NUM>, and a return conduit <NUM> for receiving the backflow F of fuel.

The fuel circuit C may include a fuel pump <NUM>, also referred to as a boost pump, which may be fluidly connected on the main conduit <NUM> and configured to draw fuel from the fuel source (e.g., fuel tank) S and to direct the drawn fuel to the high-pressure pump(s) <NUM>. A metering valve <NUM> may be fluidly connected to the main conduit <NUM> upstream of the high-pressure pumps <NUM> for controlling a flow rate of fuel entering the high-pressure pumps <NUM>. As shown, the metering valve <NUM> is operatively connected to the controller <NUM> for feeding data thereto about a flow rate of fuel entering the high-pressure fuel pumps <NUM>. A fuel filter <NUM> may be fluidly connected to the main conduit <NUM> upstream of the high-pressure pump <NUM>. In the embodiment shown, the fuel filter <NUM> is located upstream of the pump <NUM> relative to a flow of fuel from the fuel source S to the high-pressure fuel pump(s) <NUM>.

In the embodiment shown, a pressure regulating valve <NUM> is fluidly connected to the fuel circuit C. The valve <NUM> has an inlet 120a and an outlet 120b fluidly connectable to the inlet 120a. The valve <NUM> further has a control inlet 120c whose function is described below.

The valve <NUM> has a member 120d movable between a close position (as shown) and an open position (not shown). In the close position, a flow of fuel from the main fuel conduit <NUM> to the return conduit <NUM> is permitted. The inlet 120a of the valve <NUM> is fluidly connected to the outlet 120b of the valve <NUM> in the open position of the member 120d. In the embodiment shown, the member 120d is biased in the close position using a biasing member 120e, which may be a spring.

In the embodiment shown, the high-pressure pump(s) <NUM> have a control outlet 104a fluidly connected to the control inlet 120c of the pressure regulating valve <NUM>. The pressure of the fuel entering the high-pressure pumps <NUM> from the fuel source S is preferably within a given range. If the pressure of the fuel entering the high-pressure pump(s) <NUM> is above a given pressure threshold, a pressure at the control outlet 104a increases and pushes the valve <NUM> from the close position to the open position thereby allowing fuel to flow from the main fuel conduit <NUM> to the return conduit <NUM>. In other words, the pressure regulating valve <NUM> provides an escape route for excess fuel that would otherwise increase inlet fuel pressure of the high-pressure pump(s) <NUM> above the given pressure threshold.

In the embodiment shown, the high-pressure pump(s) <NUM> is fluidly connected to the injectors <NUM> via fuel conduits <NUM>. Each of the injectors <NUM> has its inlet 110a fluidly connected to the high-pressure pump <NUM> via a respective one of the fuel conduits <NUM>. In the depicted embodiment, a bypass conduit <NUM> is fluidly connected to the fuel conduits <NUM>. The bypass conduit <NUM> has a plurality of upstream connection points 126a each being fluidly connected to a respective one of the fuel conduits <NUM>. The bypass conduit <NUM> has a downstream connection point 126b that is connected to the return conduit <NUM>. In the embodiment shown, the downstream connection point 126b of the bypass conduit <NUM> is fluidly connected to the return conduit <NUM> downstream of the second outlets 110c of the injectors <NUM> relative to a direction of the backflow F circulating in the return conduit <NUM>.

The fuel circulating in the fuel conduits <NUM> between the high pressure pump <NUM> and the injectors <NUM> is at high pressure (e.g., <NUM> bars) and at high temperature as it has been compressed by the high pressure pump(s) <NUM>.

In some cases, it might be advantageous to leverage the backflow of fuel F. Referring also to <FIG>, the engine assembly <NUM> includes an ejector pump <NUM>. The ejector pump <NUM> may be located upstream of the pump <NUM> and upstream of the filter <NUM>. Other configurations are contemplated. For instance, the ejector pump <NUM> may be located within the fuel tank. The ejector pump <NUM> has a motive flow inlet 116a, an entrained flow inlet 116b and an outlet 116c. The ejector pump <NUM> may include a converging section 116d for accelerating the fuel received through the motive flow inlet 116a.

The motive flow inlet 116a of the ejector pump <NUM> is connected to the second injector outlets 110c of the common-rail injectors <NUM>, to the fuel conduits <NUM> connecting the pump <NUM> to the common-rail injectors <NUM>, or to both of the second injector outlets 110c and the fuel conduits <NUM>.

In the embodiment shown, the motive flow inlet 116a is connected to the second injector outlets 110c of the common-rail injectors <NUM> and selectively connected to the fuel conduits <NUM> when it is required to increase a flow rate of fuel injected to the motive flow inlet 116a. In the depicted embodiment, the motive flow inlet 116a is fluidly connected to the fuel conduits <NUM> via the bypass conduit <NUM> and via the return conduit <NUM>.

The ejector pump <NUM> receives the backflow F of fuel and/or a flow of fuel from the fuel lines <NUM> fluidly connecting the high-pressure pump <NUM> to the common-rail injectors <NUM> and injects said flow through a conduit 116e. The conduit 116e is fluidly connected to the motive flow inlet 116a, to the entrained flow inlet 116b, and to the outlet 116c. Injection of the fuel from the motive flow inlet 116a into the conduit 116e creates a depression around a stream or jet of the fuel injected through the inlet 116a. This depression has a suctioning effect that draws a flow of fuel through the entrained flow inlet 116b. In other words, the depression created by the injection of the fuel through the motive flow inlet 116a entrains a secondary flow via the entrained flow inlet 116b. The outlet 116c of the ejector pump <NUM>, which is defined by the conduit 116e and which may define a diverging section 116f, outputs a flow resulting from a combination of the motive flow received via the inlet 116a and the entrained flow received via the entrained flow inlet 116b. Consequently, the jet pump <NUM> is able to pump a flow of fuel using another flow of fuel from another source. In a particular embodiment, the divergent section 116f transfers kinetic energy of the fuel to potential energy. In a particular embodiment, the disclosed system takes advantage of waste energy coming out of lines 110c by bringing it as a motive flow to increase or improve suction lift at the engine inlet. Using this usually wasted energy may allow to avoid using an oversized pump to draw the fuel from the fuel tank, to reduce the complexity of the system, and to completely operate the system without the pump to meet suction lift requirements at engine inlet.

The motive flow created by the backflow of fuel F and/or by the fuel drawn from the fuel conduits <NUM> may be used as a motive flow source to the aircraft equipped with the disclosed engine assembly <NUM>. For instance, the motive flow source may be used to suctioned fuel from a fuel tank, to increase a flow rate of fuel through a given fuel conduit, to displace fuel from a given fuel tank to another, and any other suitable applications.

In the present embodiment, a flow control device <NUM> is fluidly connected to the bypass conduit <NUM> between the upstream and downstream connection points 126a, 126b. The flow control device <NUM> may be a variable control orifice and may be used to vary a flow rate of the fuel circulating within the bypass conduit <NUM>. A size of the orifice of the variable control orifice may be controlled manually and/or electronically to control a flow rate in the bypass conduit <NUM>. The flow control device <NUM> may close fluid communication between the fuel conduits <NUM> and the ejector <NUM> via the bypass conduit <NUM>.

The disclosed fuel system allows to use the energy of the return flow coming out of the common rail injectors or directly from the common rail fuel lines to drive a motive flow within an ejector pump. This might allow to take advantage of the waste energy from the common rail system to create a suction effect within the low pressure fuel system or directly from the fuel tank using a motive flow. This concept might be applicable for all engine applications such as turboshaft, turboprop, turbofan and APU using common rail technology.

The disclosed fuel system takes advantage of the waste energy coming out of the common rail injectors; allow the possibility to replace the aircraft fuel tank boost pump by a simple motive flow to fulfill the suction lift; and is a low complexity system, which may be lighter and less expensive than boost pumps.

For operating the aircraft engine, the fuel is pressurized for circulation through the common-rail injection system <NUM>; a portion of the pressurized fuel is circulated through the motive flow inlet 116a of the ejector pump <NUM>; and a flow is entrained through the ejector pump <NUM> with the portion of the pressurized fuel circulating through the motive flow inlet 116a.

Herein, the portion of the pressurized fuel is the backflow of fuel F from the common-rail injector <NUM> of the common-rail fuel injection system <NUM>. The backflow of fuel F is circulated through the motive flow inlet 116a of the ejector pump <NUM>. In the embodiment shown, the portion of the pressurized fuel is diverted from at least one fuel conduit <NUM> to the ejector pump; the at least fuel conduit <NUM> connecting the high-pressure pump <NUM> to the common-rail injector <NUM> of the common-rail injection system <NUM>.

In the embodiment shown, fuel is diverted from at least one fuel conduit <NUM> and the flow is entrained with both of the backflow of fuel F and the diverted fuel. In the depicted embodiment, the ejector pump <NUM> is fluidly connected to the source of fuel S, fuel from the source of fuel is entrained through the ejector pump <NUM> using the portion of the pressurized fuel.

In the embodiment shown, a flow rate of the diverted portion of the pressurized fuel is regulated. The regulation of the flow rate may be achieved by constricting the flow of the diverted portion of the pressurized fuel. Herein, entraining the flow through the ejector pump <NUM> with the portion of the pressurized fuel includes entraining fuel directly from the fuel tank S.

In the embodiment shown, entraining the flow through the ejector pump <NUM> with the portion of the pressurized fuel includes suctioning the fuel through the main fuel conduit <NUM> that fluidly connects the source of fuel S to the high-pressure pump <NUM>.

For supplying fuel to the aircraft engine having the common-rail fuel injection system <NUM>, fuel is pressurized to circulate through the common-rail injection system <NUM>; a portion of the fuel is injected in the common-rail injectors <NUM> of the common-rail injection system <NUM> thereby generating the backflow of fuel F; and fuel to be pressurized is entrained from the source of fuel S though the ejector pump <NUM> with the backflow of fuel F circulating through the motive flow inlet 116a of the ejector pump <NUM>.

In some cases, fuel is diverted from the fuel conduits <NUM> and the fuel is entrained with both of the backflow of fuel F and the diverted fuel; the fuel conduits <NUM> connecting the high-pressure pump <NUM> to the common-rail injectors <NUM> of the common-rail injection system <NUM>.

In the embodiment shown, a flow rate of the diverted fuel is regulated. The flow rate may be regulated by constricting a flow of the diverted fuel. In the embodiment shown, entraining the fuel from the source of fuel S through the ejector pump <NUM> includes entraining the fuel directly from the fuel tank. In the illustrated embodiment, entraining the fuel from the source of fuel S through the ejector pump <NUM> includes suctioning the fuel through the main fuel conduit <NUM> fluidly connecting the source of fuel S to the high-pressure pump <NUM>.

Claim 1:
A method of operating an aircraft engine (<NUM>, <NUM>) of an aircraft, the aircraft engine (<NUM>, <NUM>) having a common-rail fuel injection system (<NUM>) for injecting fuel into a combustion chamber (<NUM>) of the aircraft engine (<NUM>, <NUM>), the method comprising:
pressurizing fuel for circulation through the common-rail fuel injection system (<NUM>);
circulating a portion of the pressurized fuel through a motive flow inlet (116a) of an ejector pump (<NUM>), wherein the portion of the pressurized fuel is a backflow (F) of fuel from at least one common-rail injector (<NUM>, <NUM>) of the common-rail fuel injection system (<NUM>), connected to a return conduit (<NUM>) for receiving the backflow (F) of fuel, the method including circulating the backflow (F) of fuel through the motive flow inlet (116a) of the ejector pump (<NUM>);
diverting fuel from a plurality of fuel conduits (<NUM>) via a bypass conduit (<NUM>), the fuel conduits (<NUM>) connecting a high-pressure pump (<NUM>) to at least one common-rail injector (<NUM>, <NUM>) of the common-rail fuel injection system (<NUM>), the bypass conduit (<NUM>) fluidly connected to the fuel conduits (<NUM>), the bypass conduit (<NUM>) having a plurality of upstream connection points (126a) each being fluidly connected to a respective one of the fuel conduits (<NUM>), the bypass conduit (<NUM>) having a downstream connection point (126b) connected to the return conduit (<NUM>); and
entraining a flow through the ejector pump (<NUM>) with both of the backflow (F) of fuel and the diverted fuel circulating through the motive flow inlet (116a).