METHOD FOR HEATING THE FUEL OF A FUEL SUPPLY SYSTEM OF A TURBOMACHINE

Abstract

A method for heating the fuel of a fuel supply system (19) of a turbomachine, the turbomachine comprising a heat pump (14) comprising a closed circuit (20) in which a heat transfer fluid circulates, the circuit (20) comprising an evaporator (21) configured to exchange heat with oil of the turbomachine, a first condenser (22) configured to exchange heat with the fuel, an expander (23) configured to expand the heat transfer fluid before entering the evaporator (21) and a compressor (24) configured to compress the heat transfer fluid before entering the first condenser (22), the method comprising the step of: c) heating the fuel by operating the heat pump (14) according to a combined cycle in which the compressor (24) is driven at a rotational speed determined so as to provide excess power to the heat transfer fluid which is intended for heating fuel.Figure for abstract: 2.

Description

Title of the invention: METHOD FOR HEATING THE FUEL OF A FUEL SUPPLY SYSTEM OF A TURBOMACHINE Technical field of the invention

[0001] The present invention relates to a method for heating the fuel of a fuel supply system of a turbomachine, and to a turbomachine intended for implementing this method. Technical background

[0002] A dual-flow turbomachine conventionally comprises a fan driven by a power turbine, and a gas generator whose generated gases are used to drive the power turbine. The gas generator comprises at least one compressor, a combustion chamber and at least one turbine. The fan generates an air flow which is divided into a primary flow intended to supply the gas generator and a secondary flow which contributes predominantly to the thrust provided by the turbomachine.

[0003] The turbomachine also comprises different oil circuits which have the function, for example, of lubricating moving elements (bearings, toothed wheels, etc.) of the turbomachine.

[0004] For the oil to fully perform its functions, it is essential to maintain its temperature within a given range, in particular using a cooling system.

[0005] Engine manufacturers today face a major challenge. Indeed, new turbomachine architectures integrate more oil circuits due in particular to the installation of a reducer (between the power turbine and the fan) and / or increased use of electric generators in order to reinforce the hybridization of the turbomachine.

[0006] These additional oil circuits inevitably imply an increase in the thermal power to be dissipated, and consequently an obligation to review the existing cooling system.

[0007] To meet this need, it is known from document FR2993610A1 in the name of the applicant to cool the oil with a heat pump.

[0008] Such a heat pump comprises a closed circuit in which a heat transfer fluid circulates, the circuit comprising in particular an evaporator, a condenser, a compressor and an expansion valve.

[0009] More precisely, the evaporator vaporizes the heat transfer fluid by taking from the heat in the oil (hot source). The condenser condenses the heat transfer fluid by discharging heat into an air stream (cold source). The compressor compresses the heat transfer fluid (gaseous state) to increase its pressure before it passes through the condenser. The expansion valve expands the heat transfer fluid (liquid state) to lower its pressure before it passes through the evaporator.

[0010] In the aforementioned document, the heat pump is only used to cool the oil.

[0011] However, engine manufacturers note that it could be advantageous to use the heat pump for other functions, including fuel heating.

[0012] Heating the fuel is essential when its temperature is below a critical temperature below which the fuel is subject to icing. Heating the fuel may in particular be necessary when starting the turbomachine when the turbomachine has been stopped for a long time and the external conditions are cold.

[0013] Conventionally, to meet this need, the turbomachine comprises a separate system which is dedicated to heating the fuel, this system comprising in particular a fuel / oil heat exchanger. More precisely, after the oil temperature has risen, the thermal power of the oil is used to heat the fuel via the heat exchanger.

[0014] Engine manufacturers also note that the heat pump compressor is sized to cope with the worst-case scenario, namely a case in which the oil has a significant thermal power to dissipate (for example, a high operating speed combined with a high outside temperature), and the air flow (cold source) has a high temperature. However, in practice, the compressor only operates occasionally at its maximum capacity. Thus, engine manufacturers point out that it could be advantageous to exploit the available compressor capacity for other occasions, and in particular for heating the fuel.

[0015] The objective of the present invention is therefore to optimize the heat pump to allow not only the oil to be cooled but also the fuel to be heated. Summary of the invention

[0016] The invention thus proposes a method for heating the fuel of a fuel supply system of a turbomachine, the turbomachine comprising a heat pump comprising a closed circuit in which a heat transfer fluid circulates, the circuit comprising an evaporator configured to exchange heat with oil of the turbomachine, a first condenser configured to exchange heat with the fuel, an expander configured to expand the heat transfer fluid before entering the evaporator and a compressor configured to compress the heat transfer fluid before entering the first condenser, the method comprising the step of: (c) heating the fuel by operating the heat pump in a combined cycle in which the compressor is driven at a determined rotational speed so as to provide excess power to the heat transfer fluid which is intended for heating the fuel.

[0017] Such a method makes it possible to use the heat pump to heat the fuel.

[0018] The cycle is called a "combined cycle" because it combines both the function of re oil cooling and fuel heating function.

[0019] When the heat pump operates according to the combined cycle, the compressor provides the heat transfer fluid with excess / additional power which is dedicated to heating the fuel. The thermal power taken from the oil is obviously added to the excess power supplied by the compressor, to heat the fuel.

[0020] In other words, when the heat pump operates according to the combined cycle, the compressor provides a power which is greater than the need linked to cooling the oil, to also meet the need linked to heating the fuel.

[0021] The use of the heat pump to heat the fuel makes it possible to eliminate or reduce the system dedicated to this function which is presented in the prior art, to the benefit in particular of the mass, the size, the simplification of the architecture, the specific consumption and the efficiency of the turbomachine.

[0022] Furthermore, heating the fuel with a heat pump proves to be more efficient than the system dedicated to this function which is presented in the prior art, which makes it possible to reduce the overall heating time of the turbomachine. This is all the more true as the drive speed of the compressor is close to its maximum drive speed.

[0023] As a reminder, the takeoff of an aircraft is only authorized from the moment when the temperatures of the oil and fuel of the turbomachine have reached thresholds which guarantee the absence of risks linked to the icing of the latter.

[0024] The method according to the invention may comprise one or more of the following characteristics and / or steps, taken in isolation from one another or in combination with one another: - the determined rotation speed is greater than 50% of the maximum drive speed of the compressor, and preferably greater than 60% of the maximum drive speed of the compressor, and more preferably greater than 70% of the maximum drive speed of the compressor; - the method comprises before step c) a step consisting of: (a) comparing the fuel temperature with a first reference temperature which corresponds to the temperature below which the fuel is subject to icing; the fuel being reheated in step c), if the comparison made in step a) indicates that the temperature of the fuel is lower than the first reference temperature; - the method comprises before step c) a step consisting of: b) compare the oil temperature with a second reference temperature which corresponds to the oil temperature after it has risen in temperature; the fuel being heated in step c), if the comparison made in step b) indicates that the oil temperature is higher than the second reference temperature.

[0025] The present invention also relates to a turbomachine intended for implementing the method as described above, the turbomachine comprising a heat pump comprising a closed circuit in which a heat transfer fluid circulates, the circuit comprising an evaporator configured to exchange heat with oil of the turbomachine, a first condenser configured to exchange heat with the fuel of the fuel supply system, an expander configured to expand the heat transfer fluid before entering the evaporator and a compressor configured to compress the heat transfer fluid before entering the first condenser.

[0026] The turbomachine according to the invention may comprise one or more of the following characteristics and / or steps, taken in isolation from one another or in combination with one another: - the compressor is driven by an electric motor, the electric motor being electrically controlled by a control device; - the circuit comprises a second condenser connected in parallel with the first condenser, the second condenser being configured to exchange heat with a heat source which is separate from the fuel; - the heat transfer fluid circulates only in the first condenser when the heat pump operates according to the combined cycle; - the heat source is an air flow; - the first condenser is part of a first branch of the circuit, the second condenser is part of a second branch of the circuit, the circuit comprising a common part comprising at least the evaporator, the inlets of the branches being connected to the outlet of the common part via a three-way valve. Brief description of the figures

[0027] The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given to by way of non-limiting example and with reference to the attached drawings in which:

[0028] [Fig.l] [Fig.l] is a schematic view in axial half-section of a turbomachine comprising a heat pump according to the invention;

[0029] [Fig.2] [Fig.2] is a detailed view of the heat pump according to a first embodiment;

[0030] [Fig.3] [Fig.3] is a detailed view of the heat pump according to a second embodiment;

[0031] [Fig.4] [Fig.4] is a diagram of a method for heating the fuel of a turbomachine according to the invention. Detailed description of the invention

[0032] In [Fig.l] a turbomachine 1 of an aircraft 2 is partially represented. The aircraft 2 is for example an airplane.

[0033] As illustrated in [Fig.l], the turbomachine 1 is here a double-flow turbojet which conventionally comprises a ducted fan 3, a gas generator 4 and a power turbine 5.

[0034] More precisely, the fan 3 is rotatable about an axis X relative to a fixed structure 6 of the turbomachine 1. The fan 3 is driven in rotation by the power turbine 5 via a speed reducer 7.

[0035] The reducer 7 is for example an epicyclic gear reducer which has the advantage of having a high reduction ratio while being compact. The reducer 7 is housed and lubricated with oil in an enclosure which is commonly called an “oil enclosure”. The oil is more particularly intended to lubricate the moving elements of the reducer 7, and in particular the bearings and the toothed wheels.

[0036] The gas generator 4 here comprises a low-pressure compressor 8, a high-pressure compressor 9, a combustion chamber 10 and a high-pressure turbine 11 (or expansion turbine). The high-pressure compressor 9 is driven in rotation by the high-pressure turbine 11. The low-pressure compressor 8 is driven by the blower 3.

[0037] As illustrated in [Fig.l], the air flow F generated by the fan 3 is divided, by the fixed structure 6 of the turbomachine 1, into a primary flow f1 which enters a primary vein 12 to supply the gas generator 4, and into a secondary flow f2 which flows in a secondary vein 13 around the gas generator 4, to provide the majority of the thrust.

[0038] The example illustrated in [Fig.l] is in no way limiting, the turbomachine 1 could for example be a differently configured turbojet, a turboprop, a turbo-engine or even a turbomachine comprising one or more unducted fans (for example of the UDF type for “Unducted Fan” in English or still of the USF type for “Unducted Single Fan” in English).

[0039] As illustrated in [Fig.l], the turbomachine 1 further comprises a heat pump 14. The heat pump 14 is here arranged in a compartment 15 defined between a casing 16 surrounding the fan 3 (commonly called “fan casing”) and fairings of a nacelle 17 of the turbomachine 1. As a variant, the heat pump 14 could for example be arranged in an inter-vein compartment.

[0040] The heat pump 14 is intended to cool the oil of an oil supply system 18 (commonly called “oil system” and hereinafter called oil system) of the turbomachine 1, when it operates according to a “conventional” cycle.

[0041] According to the invention, the heat pump 14 is also intended to heat the fuel of a fuel supply system 19 (commonly called "fuel system" and hereinafter called fuel system) of the turbomachine 1 while cooling the oil of the oil system 18, when it operates according to a "combined" cycle.

[0042] For this purpose, the heat pump 14 comprises a closed circuit 20 in which a heat transfer fluid circulates. The circuit 20 comprises an evaporator 21 configured to exchange heat with the oil of the oil system 18, a first condenser 22 configured to exchange heat with the fuel of the fuel system 19, an expansion valve 23 configured to expand the heat transfer fluid before entering the evaporator 21 and a compressor 24 configured to compress the heat transfer fluid before entering the first condenser 22.

[0043] By convention, in the present application, the terms “upstream” and “downstream” or even “inlet” and “outlet” are defined in relation to the direction of circulation of the heat transfer fluid in the closed circuit 20 of the heat pump 14.

[0044] As indicated above, the oil cooled by the heat pump 14 comes from an oil system 18.

[0045] The oil system 18 may comprise one or more lubrication circuits in which oil circulates and which are intended to lubricate moving elements of the turbomachine 1.

[0046] The oil system 18 may comprise one or more cooling circuits in which oil circulates and which are intended to cool electrical machines of the turbomachine 1.

[0047] As illustrated in Figures 1 to 3, the oil system 18 comprises at least one lubrication circuit intended to lubricate the reducer 7, and more precisely the bearings and the toothed wheels of the reducer 7. The oil system 18 also comprises at least one cooling circuit intended to cool an electric generator 25 of the turbomachine 1. The electric generator 25 can participate in particular in the hybridization of the turbomachine 1.

[0048] As indicated above, the fuel heated by the heat pump 14 comes from a fuel system 19.

[0049] The fuel system 19 may comprise one or more circuits in which fuel circulates and which are intended to supply variable geometries (for example variable pitch blades or vanes) to actuate them.

[0050] The fuel system 19 may comprise one or more circuits in which fuel circulates and which are intended to supply the combustion chamber 10 of the gas generator 4.

[0051] As illustrated in Figures 1 to 3, the fuel system 19 comprises at least one circuit intended to supply variable geometries and at least one circuit intended to supply the combustion chamber 10.

[0052] Advantageously, the compressor 24 is driven by an electric motor 26, the electric motor 26 being electrically controlled by a control device 27.

[0053] The circuit 20 of the heat pump 14 may comprise a second condenser 28 mounted in parallel with the first condenser 22. The second condenser 28 is configured to exchange heat with a heat source 29 which is distinct from the fuel.

[0054] Advantageously, the heat source 29 is an air flow. The air flow can be taken from one of the veins 12, 13 of the turbomachine 1, or else from outside the turbomachine 1.

[0055] Advantageously, when the circuit 20 comprises first and second condensers 22, 28, the heat transfer fluid circulates only in the first condenser 22 when the heat pump 14 operates according to the combined cycle. Such an adjustment makes it possible to minimize the fuel heating time, and consequently the overall heating time of the turbomachine 1.

[0056] The circuit 20 of the heat pump 14 may comprise a separate compressor for compressing the heat transfer fluid entering the second condenser 28.

[0057] When the circuit 20 comprises first and second condensers 22, 28, the first condenser 22 may be part of a first branch 30 of the circuit 20, the second condenser 28 may be part of a second branch 31 of the circuit 20 and the circuit 20 may comprise a common part 32 comprising at least the evaporator 21. In this specific case, the inlets of the branches 30, 31 may then be connected to the outlet of the common part 32 via a three-way valve 33.

[0058] The three-way valve 33 can occupy predefined positions (three-way valve TOR for “All or Nothing”) or be controlled over a predetermined adjustment range, for example to precisely adjust the flow rate of heat transfer fluid entering each of the branches 30, 31.

[0059] Advantageously, the three-way valve 33 is controlled by the control device 27 as a function in particular of the temperature of the oil to be cooled and the temperature of the fuel to be heated. Other parameters can of course be taken into account by the control device 27 to control the three-way valve 33.

[0060] According to the embodiment illustrated in [Fig.2], the circuit 20 of the heat pump 14 comprises only the first condenser 22 which exchanges heat with the fuel of the fuel system 19.

[0061] The compressor 24 is driven by an electric motor 26, the electric motor 26 being electrically controlled by a control device 27. The control device 27 is a computer which may be a FADEC type computer for “Full Authority Digital Engine Control” in English, or else a separate computer.

[0062] According to the embodiment illustrated in [Fig. 3], the circuit 20 of the heat pump 14 comprises the first condenser 22 which exchanges heat with the fuel of the fuel system 19 and a second condenser 28 which exchanges heat with a heat source 29 which is here an air flow coming from the secondary vein 13.

[0063] More specifically, circuit 20 comprises: - a common part 32 which comprises from upstream to downstream the expander 23, the evaporator 21 and the compressor 24; - first and second branches 30, 31 mounted in parallel with each other, the first branch 30 comprising the first condenser 22 and the second branch 31 comprising the second condenser 28.

[0064] The inputs of branches 30, 31 are connected to the output of the common part 32 via a three-way valve 33.

[0065] The compressor 24 is driven by an electric motor 26.

[0066] The electric motor 26 and the three-way valve 33 are here electrically controlled by a control device 27. The control device 27 is a computer which may be a FADEC type computer for “Full Authority Digital Engine Control” in English, or a separate computer.

[0067] According to the invention, the turbomachines 1 described above are intended for implementing a method for heating the fuel, the method comprising the step consisting of: c) heating the fuel by operating the heat pump 14 according to a combined cycle in which the compressor 24 is driven at a determined rotation speed so as to provide excess power to the heat transfer fluid which is intended for heating the fuel.

[0068] Such a method makes it possible to use the heat pumps 14 described above to re- heat the fuel.

[0069] The cycle is called a "combined cycle" because it combines both the oil cooling function and the fuel heating function.

[0070] When the heat pump 14 operates according to the combined cycle, the compressor 24 provides the heat transfer fluid with excess / additional power which is dedicated to heating the fuel. The thermal power taken from the oil is obviously added to the excess power supplied by the compressor 24, to heat the fuel.

[0071] In other words, when the heat pump 14 operates according to the combined cycle, the compressor 24 provides a power which is greater than the need linked to cooling the oil, to also meet the need linked to heating the fuel.

[0072] The use of the heat pump 14 to heat the fuel makes it possible to eliminate or reduce the system dedicated to this function which is presented in the prior art, to the benefit in particular of the mass, the size, the simplification of the architecture, the specific consumption and the efficiency of the turbomachine 1.

[0073] Furthermore, heating the fuel with a heat pump 14 proves to be more efficient than the system dedicated to this function which is presented in the prior art, which makes it possible to reduce the overall heating time of the turbomachine 1. This is all the more true since the drive speed of the compressor 24 is close to its maximum drive speed.

[0074] Such a reheating method can for example be carried out during a cold start of a turbomachine 1 which is located in an environment whose external conditions are cold.

[0075] The determined rotational speed at which the compressor is driven during the combined cycle depends in particular on the temperature of the fuel.

[0076] Advantageously, the determined rotation speed is greater than 50% of the maximum drive speed of the compressor 24, and preferably greater than 60% of the maximum drive speed of the compressor 24, and more preferably greater than 70% of the maximum drive speed of the compressor 24.

[0077] The method for heating the fuel may comprise, before step c), a step consisting of: (a) comparing the fuel temperature with a first reference temperature which corresponds to the temperature below which the fuel is subject to icing; the fuel being heated in step c), if the comparison made in step a) indicates that the fuel temperature is lower than the first temperature of reference.

[0078] Step a) makes it possible to check whether or not it is necessary to reheat the fuel. A margin can of course be applied to the first reference temperature.

[0079] The method for heating the fuel may comprise, before step c), a step consisting of: b) compare the oil temperature with a second reference temperature which corresponds to the oil temperature after it has risen in temperature; the fuel being heated in step c), if the comparison made in step b) indicates that the oil temperature is higher than the second reference temperature.

[0080] Step b) ensures that the oil has finished heating up before starting to heat the fuel. A margin can of course be applied to the second reference temperature.

[0081] As indicated above, the heat pumps 14 described can also operate according to one or more conventional cycles (depending on the architecture of the heat pump 14), to simply cool the oil.

[0082] According to the example illustrated in [Fig.4], the fuel heating process chronologically comprises steps a), b) and c).

Claims

Claims

1. A method of heating the fuel of a fuel supply system (19) of a turbomachine (1), the turbomachine (1) comprising a heat pump (14) comprising a closed circuit (20) in which a heat transfer fluid circulates, the circuit (20) comprising an evaporator (21) configured to exchange heat with oil of the turbomachine (1), a first condenser (22) configured to exchange heat with the fuel, an expander (23) configured to expand the heat transfer fluid before entering the evaporator (21) and a compressor (24) configured to compress the heat transfer fluid before entering the first condenser (22),the method comprising the step of: c) heating the fuel by operating the heat pump (14) according to a combined cycle in which the compressor (24) is driven at a determined rotation speed so as to provide excess power to the heat transfer fluid which is intended for heating the fuel.,

2. Method according to claim 1, characterized in that the determined rotation speed is greater than 50% of the maximum drive speed of the compressor (24), and preferably greater than 60% of the maximum drive speed of the compressor (24), and more preferably greater than 70% of the maximum drive speed of the compressor (24).

3. Method according to one of the preceding claims, characterized in that the method comprises before step c) a step consisting of: a) comparing the temperature of the fuel with a first reference temperature which corresponds to the temperature below which the fuel is subject to icing; the fuel being reheated in step c) if the comparison carried out in step a) indicates that the temperature of the fuel is lower than the first reference temperature.

4. Method according to one of the preceding claims, characterized in that the method comprises before step c) a step consisting of: b) comparing the temperature of the oil with a second reference temperature which corresponds to the temperature of the oil at the end of its temperature rise; the fuel being reheated in step c) if the comparison carried out at step b) indicates that the oil temperature is higher than the second reference temperature.

5. Turbomachine (1) intended for implementing the method according to one of the preceding claims, the turbomachine (1) comprising a heat pump (14) comprising a closed circuit (20) in which a heat transfer fluid circulates, the circuit (20) comprising an evaporator (21) configured to exchange heat with oil of the turbomachine (1), a first condenser (22) configured to exchange heat with the fuel of the fuel supply system (19), an expander (23) configured to expand the heat transfer fluid before entering the evaporator (21) and a compressor (24) configured to compress the heat transfer fluid before entering the first condenser (22).

6. Turbomachine (1) according to the preceding claim, characterized in that the compressor (24) is driven by an electric motor (26), the electric motor (26) being electrically controlled by a control device (27).

7. Turbomachine (1) according to one of claims 5 or 6, characterized in that the circuit (20) comprises a second condenser (28) mounted in parallel with the first condenser (22), the second condenser (28) being configured to exchange heat with a heat source (29) which is separate from the fuel.

8. Turbomachine (1) according to the preceding claim, characterized in that the heat transfer fluid circulates only in the first condenser (22) when the heat pump (14) operates according to the combined cycle.

9. Turbomachine (1) according to one of claims 7 or 8, characterized in that the heat source (29) is an air flow.

10. Turbomachine (1) according to one of claims 7 to 9, characterized in that the first condenser (22) is part of a first branch (30) of the circuit (20), the second condenser (28) is part of a second branch (31) of the circuit (20), the circuit (20) comprising a common part (32) comprising at least the evaporator (21), the inlets of the branches (30, 31) being connected to the outlet of the common part (32) via a three-way valve (33).

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