Patent Description:
Aircraft engines use heat exchangers for various reasons. Such an aircraft engine heat exchanger may include a fuel-oil heat exchanger (FOHE), sometimes referred to as a fuel/oil cooler, which is typically used to simultaneously heat the fuel prior to its injection into a combustion chamber and cool bearing oil. In an aircraft, costs, maintenance, weight and size can be important considerations when designing the fluid systems. The size of the heat exchanger is typically directly related to its heat exchange capacity. There is an ever-present need for improvements in the field of aircraft heat exchangers and their methods of use. Document <CIT> discloses a heat exchanger system according to the prior art.

There is accordingly provided a heat exchange system for an aircraft engine, comprising: a heat exchanger having at least one first conduit and at least one second conduit in heat exchange relationship with the at least one first conduit; a main conduit directing a main flow of fuel from a fuel source to a combustion chamber of the aircraft engine; a pump hydraulically connected to the main conduit for driving the main fuel flow through the main conduit to the combustion chamber; a return conduit receiving excess fuel outputted by the pump and exceeding a fuel requirement of the combustion chamber, the return conduit having a return inlet hydraulically connected to the main conduit downstream of the pump and a return outlet hydraulically connected to the main conduit upstream of the pump, the return conduit hydraulically connected to the at least one second conduit of the heat exchanger; and an actuator having an actuator inlet hydraulically connected to the main conduit downstream of the pump and an actuator outlet hydraulically connected to the main conduit upstream of the pump while bypassing the heat exchanger, wherein a pressure differential between the actuator inlet and the actuator outlet remains substantially unchanged with variations of a fuel flow through the at least one second conduit of the heat exchanger.

The heat exchange system for an aircraft engine as defined above and herein may further include one or more of the following additional elements, in whole or in part, and in any combination.

In certain embodiments, the pump is a high-pressure pump, a low-pressure pump located upstream of the high-pressure pump and hydraulically connected on the main conduit.

In certain embodiments, the return conduit is hydraulically connected to the main conduit between the high-pressure pump and the low-pressure pump.

In certain embodiments, the low-pressure pump includes an impeller and wherein the high-pressure pump is a fixed-displacement pump.

In certain embodiments, the actuator outlet is hydraulically connected to the return conduit at a connection point downstream of the heat exchanger.

In certain embodiments, a bypass conduit is provided having a bypass inlet hydraulically connected to the return conduit upstream of the heat exchanger and a bypass outlet hydraulically connected to the main conduit upstream of the pump.

In certain embodiments, a controlled orifice is provided between the bypass inlet and the bypass outlet.

In certain embodiments, the controlled orifice is variable in size for controlling a flow of a fluid flowing into the bypass conduit.

There is also provided a method of operating a heat exchange system of an aircraft engine, as set forth in claim <NUM>.

The method as defined above and herein may further include one or more of the following additional elements and/or steps, in whole or in part, and in any combination.

In certain embodiments, reinjecting the spill flow includes flowing the spill flow into a return conduit in fluid flow communication with the heat exchanger.

In certain embodiments, injecting of the output fuel flow from the actuator includes injecting the output fuel flow into the return conduit at a connection point on the return conduit and located downstream of the heat exchanger.

In certain embodiments, feeding of the fuel to the combustor includes drawing fuel from a fuel source with a second pump, the reinjecting of the spill flow includes reinjecting the spill flow into a main fuel conduit at a connection point between the pump and the second pump.

In certain embodiments, the method further includes flowing a portion of the spill flow outside the heat exchanger such that the portion of the spill flow bypasses the heat exchanger.

In certain embodiments, the method further includes injecting the portion of the spill flow upstream of the pump.

In certain embodiments, the method further includes controlling a mass flow rate of the portion of the spill flow.

In certain embodiments, controlling of the mass flow rate includes flowing the portion of the spill flow through a controlled orifice.

In certain embodiments, the method further includes varying a size of the controlled orifice to vary a mass flow rate of fuel through the heat exchanger.

In certain embodiments, flowing of the spill flow of the pump through the heat exchanger to exchange heat between the spill flow and another fluid includes exchanging heat between the fuel and oil via the heat exchanger.

In certain embodiments, the method further includes receiving a sensor signal from at least one sensor, the sensor signal indicative of a temperature of the fuel fed to the combustor being lower than a temperature threshold, the method comprising increasing a mass flow rate of the fuel flowing through the heat exchanger.

In certain embodiments, increasing of the mass flow rate includes increasing an output mass flow rate of the pump and/or decreasing a bypass mass flow rate of fuel that bypasses the heat exchanger.

<FIG> illustrated an aircraft engine depicted as a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. More specifically, the gas turbine engine <NUM> has a core gas path including an intake <NUM> for receiving air. The compressor section <NUM> has at least one compressor <NUM> extending across the core gas path and the turbine section <NUM> has at least one turbine <NUM> extending across the core gas path, with the at least one compressor <NUM> and the at least one turbine <NUM> being rotatable with a rotary shaft <NUM> supported within the gas turbine engine <NUM> by bearings <NUM>. An oil system <NUM> is provided for circulating oil to the bearings <NUM> and back to an oil reservoir <NUM>. It will be appreciated that the principles of the disclosure apply to any aircraft engines, such as internal combustion engines (e.g., piston engine, rotary engine), any type of gas turbine engines, (e.g., turbofan, turboshaft, and turboprop), and auxiliary power unit.

In the embodiment shown, the gas turbine engine <NUM> has a heat exchange system <NUM> that is used to exchange heat between different fluids for proper operation of the gas turbine engine <NUM>. In the present case, the heat exchange system <NUM> includes a heat exchanger <NUM>, which may be referred to as a fuel-oil heat exchanger (FOHE), used for transferring heat from the oil of the oil system <NUM> to fuel flowing from a fuel tank <NUM>, or any other fuel source, to the combustor <NUM> of the gas turbine engine <NUM> for combustion. Preheating the fuel as such may increase efficiency of the combustion of the fuel and may cool down the oil that heats up while lubricating the bearings <NUM>. In some cases, the heat exchanger <NUM> may be used to transfer or extract heat to/from an aircraft system S in need.

Referring now to <FIG>, a more detail view of the heat exchange system <NUM> is provided. The heat exchange system <NUM> includes a main fuel conduit (or simply "main conduit") <NUM> that has an inlet 42A hydraulically connected to the fuel tank <NUM> and an outlet 42B hydraulically connected to the combustor <NUM>. A first pump <NUM> is used to draw fuel from the fuel tank <NUM> and hydraulically connected to the main fuel conduit <NUM> to generate a fuel flow F0 and to increase fluid pressure. The first pump <NUM> may be referred to as a low-pressure pump since a mass flow rate outputted by the first pump <NUM> may vary as a function of a pressure in the main fuel conduit <NUM> downstream of the first pump <NUM>. In other words, a pressure rise provided by the first pump <NUM> may vary as a function of a mass flow rate in the main fuel conduit <NUM> flowing through the low pressure pump <NUM>. Typically, such a low-pressure pump includes an impeller rotatable to create a pressure rise between a first pump inlet 43A and a first pump outlet 43B of the first pump <NUM> to draw the fuel from the fuel tank <NUM>. The first pump <NUM> may be used to support the functionality of the system downstream of the first pump <NUM>, such as providing the second pump with the necessary inlet pressure.

The heat exchange system <NUM> includes a second pump <NUM> hydraulically connected to the main fuel conduit <NUM> downstream of the first pump <NUM>. The second pump <NUM> may be referred to as a high-pressure pump due to the relatively high pressure rise it offers in relation to the low pressure pump located upstream in order to condition the fuel for combustion. The pressure generated by the second pump <NUM> may also be used to support downstream component and system functionality. A mass flow rate outputted or generated by the second pump <NUM> may not vary as a function of a pressure in the main fuel conduit <NUM> downstream of the second pump <NUM>. Such a high-pressure pump is sometimes referred to as a fixed-displacement pump (e.g., gear pump). At a given rotational speed, a fixed mass flow rate is drawn from a second pump inlet 44A of the second pump <NUM> to a second pump outlet 44B thereof.

As shown in <FIG>, an actuator <NUM> is in fluid flow communication with the main fuel conduit <NUM>. It will be appreciated that more than one actuator may be in fluid flow communication with the main fuel conduit <NUM>. The actuator <NUM> is referred below in the singular form although more than one actuator may be used. The actuator <NUM> is driven by a pressure differential between its actuator inlet 45A and its actuator outlet 45B. The actuator <NUM> may be, for instance, an active clearance control (ACC) actuator, a high-pressure compressor stator vane actuator (HPC SVA), and/or a low-pressure compressor bleed valve actuator (LPC BVA). The actuator <NUM>, by being driven by a force resulting from a pressure differential between its actuator inlet 45A and actuator outlet 45B, is dependent upon where it is connected on the heat exchange system <NUM>. For instance, if the actuator inlet 45A is at a too similar pressure compared to that of the actuator outlet 45B, the actuator <NUM> may not be able to carry its function since not enough actuation force is provided resultant of a low fuel pressure differential. The actuator <NUM> is fed with an actuator fuel flow F2 drawn from the main fuel conduit <NUM> downstream of the second pump <NUM> an upstream of the combustor <NUM>.

In the embodiment shown, a return conduit <NUM> stems from the main fuel conduit <NUM> at a first connection point P1, which corresponds to an inlet (or "return inlet") of the return conduit <NUM>, and is hydraulically connected (i.e. at a "return outlet") to the main fuel conduit <NUM> at a second connection point P2 on the main fuel conduit <NUM> and located upstream of the first connection point P1. Since a mass flow rate outputted by the second pump <NUM> may be substantially higher than necessary for combustion, the return conduit <NUM> may allow to redirect excess flow, or spill flow F1, from the second pump <NUM>. In other words, there may be a mismatch between the mass flow rate of fuel generated by the second pump <NUM> and a fuel requirement of the combustor <NUM>. The fuel flow rate to the combustor <NUM> may be governed by valves (not shown). These valves may be located at location P1. The return conduit <NUM> diverts the fuel that is not need by the combustor <NUM> back to the main fuel conduit <NUM> upstream of the second pump <NUM>. In the embodiment shown, the second connection point P2 is located downstream of the first pump <NUM> and upstream of the second pump <NUM>. A pressure regulating valve (PRV) may be hydraulically connected on the return conduit <NUM> upstream of the heat exchanger <NUM>. A metering valve may be hydraulically connected on the main conduit <NUM> downstream of a connection point between the actuator inlet 45A and the main conduit <NUM>. The pressure regulating valve may be hydraulically connected to the metering valve such that the PRV perceives upstream and downstream pressure of the metering valve.

The heat exchanger <NUM> includes at least one first conduit 41A for flowing oil from the oil system <NUM> (<FIG>) and at least one second conduit 41B for flowing fuel. The heat exchanger <NUM> is used to warm up the fuel and cool down the oil by providing a heat exchange relationship between the at least one first conduit 41A and the at least one second conduit 41B. The return conduit <NUM> is in fluid flow communication with the at least one second conduit 41B of the heat exchanger <NUM> for flowing a flow F3 that will exchange heat with the oil through the heat exchanger <NUM>. Therefore, the spill flow F1 generated by the second pump <NUM> and not required by the combustor <NUM> is leveraged to cool down the oil of the oil system <NUM> and heat up the fuel flowing in the main fuel conduit <NUM>.

The heat exchange system <NUM> further includes a bypass conduit <NUM> that stems from the return conduit <NUM> at a third connection point P3 located downstream of the first connection point P1 and upstream of the heat exchanger <NUM>. The bypass conduit <NUM> has a bypass inlet at the third connection point P3 and an bypass outlet connected to the main fuel conduit <NUM>. In the present case, the bypass conduit <NUM> is hydraulically connected to the main fuel conduit <NUM> through a fuel filter housing <NUM>, but other configurations are contemplated. The bypass conduit <NUM> may be hydraulically connected to the main fuel conduit <NUM> downstream of the second connection point P2 and upstream of the second pump <NUM>.

A controlled orifice <NUM> is hydraulically connected to the bypass conduit <NUM> between the third connection point P3 and the bypass outlet of the bypass conduit <NUM>. The controlled orifice <NUM> is used to restrict a flow passage area such that a mass flow rate of a bypass flow F4 flowing into the bypass conduit <NUM> remains below a given threshold. In use, the spill flow F1 from the second pump <NUM> flowing in to the return conduit <NUM> is divided in two flows: the flow F3 that flows into the heat exchanger <NUM> for picking up heat from the oil; and the bypass flow F4 that flows into the bypass conduit <NUM> thereby bypassing the heat exchanger <NUM>. The controlled orifice <NUM> may be variable in size to vary the mass flow rate of fuel that flows into the bypass conduit <NUM>. The smaller the size of the controlled orifice <NUM>, the greater the mass flow rate of fuel that will flow into the at least one second conduit 41B of the heat exchanger <NUM>. To the contrary, the larger the controlled orifice <NUM>, the greater the mass flow rate of the fuel that will flow into the bypass conduit <NUM> since the restriction across the bypass conduit <NUM> may be lower compared to that across the at least one second conduit 41B of the heat exchanger <NUM>. The resulting pressure loss the bypass conduit <NUM> and the return conduit <NUM> may be lower in such a case, however the heat transfer rate between the fuel and oil may be diminished with the reduction in fuel flow through the heat exchanger <NUM>. The disclosed configuration may keep the actuator force margin unaffected regardless of the size of the orifice <NUM>. In some embodiments, the controlled orifice <NUM> and the bypass conduit <NUM> may be omitted. In some cases, the controlled orifice <NUM> may be actuated such that a dimension of the controlled orifice may be varied as a function of heat requirements of the fuel. In some cases, the controlled orifice <NUM> may be closed such that all of the spill flow F1 from the second pump <NUM> is routed through the heat exchanger <NUM>. In an alternate embodiment, the controlled orifice <NUM> may be alternatively connected to the return conduit <NUM> downstream of the third connection point P3 and upstream of the heat exchanger <NUM>. In an alternate embodiment, the controlled orifice <NUM> may be alternatively connected to the return conduit <NUM> downstream of the fourth connection point P4 and upstream of the fuel filter <NUM>.

As shown in <FIG>, at least one sensor <NUM> may be operatively connected to a controller <NUM>. The at least one sensor <NUM> may send a signal to the controller <NUM> indicative of a temperature of the fuel fed to the combustor <NUM> being lower than a temperature threshold. In some cases, the at least one sensor <NUM> may send a signal to the controller <NUM> indicative of a temperature of the fuel fed to the fuel filter <NUM> being lower than a temperature threshold. In response thereto, the controller <NUM> may trigger increase a mass flow rate of the fuel flowing through the heat exchanger <NUM>. This may be done by increasing an output mass flow rate of the second pump <NUM> and/or by decreasing a bypass mass flow rate of fuel that bypasses the heat exchanger <NUM> by decreasing a size of the controlled orifice <NUM>.

Referring back to <FIG>, when it is desired to increase a heat transfer between the fuel and the oil to increase a temperature of the fuel fed to combustor <NUM>, the second pump <NUM> may be operated to increase its output mass flow rate. Alternatively, or in combination, the controlled orifice <NUM> may be made smaller to force a greater flow across the heat exchanger <NUM>. However, because of this increased flow rate through the heat exchanger <NUM>, a pressure drop across the heat exchanger <NUM> may increase. This may have the effect of increasing a pressure at an inlet of the at least one second conduit 41B of the heat exchanger <NUM>.

Typically, the actuator outlet 45B of the actuator <NUM> is hydraulically connected to the return conduit <NUM> downstream of the first connection point P1 and upstream of the heat exchanger <NUM>. If the pressure drop across the heat exchanger <NUM> increases, which, as explained above, increases the pressure at the inlet of the heat exchanger <NUM>, a pressure differential between the actuator inlet 45A and the actuator outlet 45B of the actuator <NUM> may become below a given threshold. This may impede proper operation of the actuator <NUM>.

In the embodiment shown, the actuator outlet 45B is hydraulically connected to the return conduit <NUM> at a fourth connection point P4 downstream of an outlet of the at least one second conduit 41B of the heat exchanger <NUM> and upstream of the second connection point P2 between the return conduit <NUM> and the main fuel conduit <NUM>. It will be appreciated that other locations for the fourth connection point P4 are contemplated. For instance, the fourth connection point P4 may be located directly on the main fuel conduit <NUM>, upstream or downstream of the second connection point P2. The fourth connection point P4 may be located upstream or downstream of the fuel filter <NUM> and may be located upstream of the first pump <NUM> in some embodiments. In the depicted embodiment, the actuator <NUM> is hydraulically connected to an actuator conduit 45C that has an inlet on the main fuel conduit <NUM> downstream of the first connection point P1 and upstream of the outlet 42B of the main fuel conduit <NUM>. The actuator conduit 45C has an outlet hydraulically connected to the return conduit <NUM> at the fourth connection point P4.

Consequently, re-routing the outlet of the actuator conduit 45C to a location downstream of the heat exchanger <NUM> may allow to increase a pressure differential between the actuator inlet 45A and the actuator outlet 45B thanks to the pressure on the return conduit <NUM> being lower downstream of the heat exchanger <NUM> than that upstream of the heat exchanger <NUM>. This is caused by the pressure drop observed by the fuel through the at least one second conduit 41B of the heat exchanger <NUM>. Hence, the disclosed heat exchange system <NUM> may allow the increasing of the heat transfer between the fuel and the oil through the heat exchanger <NUM> while maintaining the pressure differential across the actuator <NUM> within an acceptable range. This may be done through a selection of a size of the orifice <NUM>, or by actively controlling at least one dimension of the orifice <NUM> while not affecting the pressure differential across the actuator <NUM>. In other words, the proposed heat exchange system <NUM> that connects the actuator outlet 45B downstream of the heat exchanger <NUM> may allow to maintain a force margin on the actuator <NUM> within an acceptable range independently of an increase of the mass flow rate of the fuel across the heat exchanger <NUM>.

Referring now to <FIG>, a method for operating the heat exchange system <NUM> is shown at <NUM>. The method <NUM> includes feeding fuel to the combustor <NUM> with the second pump <NUM> at <NUM>; flowing the spill flow F1 of the second pump <NUM> through the heat exchanger <NUM> to exchange heat between the spill flow F1 and oil at <NUM>; reinjecting or merging the spill flow F1 upstream of the second pump <NUM> at <NUM>; feeding the actuator <NUM> with fuel outputted by the second pump <NUM> at <NUM>; and injecting the fuel flow F2 of the actuator <NUM> at a location upstream of the second pump <NUM> and downstream of the heat exchanger <NUM>.

In the present embodiment, the reinjecting or merging the spill flow F1 includes flowing the spill flow F1 into the return conduit <NUM> in fluid flow communication with the heat exchanger <NUM>. The injecting of the fuel flow F2 of the actuator includes injecting the fuel flow F2 of the actuator <NUM> into the return conduit <NUM> at the fourth connection point P4 on the return conduit <NUM> and located downstream of the heat exchanger <NUM>. In the embodiment shown, the feeding of the fuel to the combustor <NUM> includes drawing fuel from the fuel tank <NUM> with the first pump <NUM> and the reinjecting of the spill flow F1 includes reinjecting the spill flow F1 into the main fuel conduit <NUM> at the second connection point P2 between the first pump <NUM> and the second pump <NUM>.

In the embodiment shown, the method <NUM> includes flowing a portion F4 of the spill flow F1 outside the heat exchanger <NUM> such that the portion F4 of the spill flow F1 bypasses the heat exchanger <NUM>. This may include injecting the portion F4 of the spill flow F1 upstream of the second pump <NUM>.

In the embodiment shown, the method <NUM> comprises controlling a mass flow rate of the portion F4 of the spill flow F1. This may be done by flowing the portion F4 of the spill flow F1 through the controlled orifice <NUM>. To vary the flow rate of the portion F4 of the spill flow F1 through the bypass conduit <NUM>, a size of the controlled orifice <NUM> may be varied.

As shown in <FIG>, the method <NUM> may include receiving a sensor signal from at least one sensor <NUM>, the sensor signal indicative of a temperature of the fuel fed to the combustor <NUM> being lower than a temperature threshold. At which point, a mass flow rate of a fuel flow F3 flowing through the heat exchanger <NUM> may be varied. This may be done by increasing an output mass flow rate of the second pump <NUM> and/or by decreasing a bypass mass flow rate of fuel that bypasses the heat exchanger <NUM>.

With reference to <FIG>, an example of a controller <NUM> is illustrated. The controller <NUM> may include more computing devices operable to exchange data. The controller <NUM> may be the same or different types of devices. The controller <NUM> may be implemented with one or more controller <NUM>. Note that the controller <NUM> can be implemented as part of a full-authority digital engine controls (FADEC) or other similar device, including electronic engine control (EEC), engine control unit (ECU), electronic propeller control, propeller control unit, and the like. In some embodiments, the controller <NUM> is implemented as a Flight Data Acquisition Storage and Transmission system, such as a FASTTM system. The controller X may be implemented in part in the FASTTM system and in part in the EEC. Other embodiments may also apply.

The controller <NUM> comprises a processing unit <NUM> and a memory <NUM> which has stored therein computer-executable instructions <NUM>. The processing unit <NUM> may comprise any suitable devices configured to implement the method <NUM> such that instructions <NUM>, when executed by the controller <NUM> or other programmable apparatus, may cause the functions/acts/steps performed as part of the method <NUM> as described herein to be executed.

The memory <NUM> may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

The methods and systems for operating the heat exchange system <NUM> described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the controller <NUM>. Alternatively, the methods and systems for operating the heat exchange system <NUM> may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems for operating the heat exchange system <NUM> may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems for operating the heat exchange system <NUM> may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit <NUM> of the controller <NUM>, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method <NUM>.

Claim 1:
A heat exchange system (<NUM>) for an aircraft engine (<NUM>), comprising:
a heat exchanger (<NUM>) having at least one first conduit (41A) and at least one second conduit (41B) in heat exchange relationship with the at least one first conduit (41A);
a main conduit (<NUM>) directing a main flow of fuel from a fuel source (<NUM>) to a combustion chamber of the aircraft engine (<NUM>);
a pump (<NUM>) hydraulically connected to the main conduit (<NUM>) for driving the main fuel flow through the main conduit (<NUM>) to the combustion chamber;
a return conduit (<NUM>) receiving excess fuel outputted by the pump (<NUM>) and exceeding a fuel requirement of the combustion chamber, the return conduit (<NUM>) having a return inlet hydraulically connected to the main conduit (<NUM>) downstream of the pump (<NUM>) and a return outlet hydraulically connected to the main conduit (<NUM>) upstream of the pump (<NUM>), the return conduit (<NUM>) hydraulically connected to the at least one second conduit (41B) of the heat exchanger (<NUM>); the system being characterised in that
an actuator (<NUM>) has an actuator inlet (45A) hydraulically connected to the main conduit (<NUM>) downstream of the pump (<NUM>) and an actuator outlet (45B) hydraulically connected to the main conduit (<NUM>) upstream of the pump (<NUM>) while bypassing the heat exchanger (<NUM>), and in that the system is configured such that a pressure differential between the actuator inlet (45A) and the actuator outlet (45B) remains substantially unchanged with variations of a fuel flow through the at least one second conduit (41B) of the heat exchanger (<NUM>).