Aircraft propulsion system comprising an electric propulsion machine powered by a fuel cell

Abstract

An aircraft propulsion system comprising at least one electric propulsion machine (M); a fuel cell (9) for powering the electric propulsion machine (M); and a gas turbomachine (2) comprising: a gas generator (3) including a main drive shaft (4) connected to at least one main compression stage (31) configured to accelerate a main airflow (A1) from a main air inlet (33), and an auxiliary compression stage (5) mounted on an auxiliary drive shaft (6) mechanically connected to the main drive shaft (4), the auxiliary compression stage (5) being configured to accelerate an auxiliary airflow (A2) between an auxiliary air inlet (51) and an auxiliary air outlet (52), the auxiliary air outlet (52) being connected to the air inlet (91) of the fuel cell (9) so as to supply it with a pressurized airflow. Abstract figure: Figure 1

Description

Title of the invention: Aircraft propulsion system comprising an electric propulsion machine powered by a fuel cell technical field

[0001] The present invention relates to the field of propulsion assemblies used for the propulsion of an aircraft and relates in particular to a propulsion assembly comprising an electric propulsion machine powered by a fuel cell.

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the lightening of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electric machines to provide propulsion, in particular, powered by a fuel cell.

[0006] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. For this purpose, The invention relates to the field of aircraft comprising a hybrid propulsion system including an electric propulsion machine powered by a fuel cell.

[0007] In a known manner, an aircraft includes a propulsion system to enable its movement from the acceleration of an airflow.

[0008] In the context of aircraft decarbonization, a so-called "hybrid" architecture is known in which the propulsion system includes an electric propulsion machine powered by a fuel cell. The fuel cell is fueled by hydrogen and reduces kerosene consumption.

[0009] A fuel cell is a device that enables the implementation of an electrochemical reaction to generate electrical energy from a redox reaction. For this purpose, the fuel cell is supplied with an oxidizing fluid and a reducing fluid, for example dihydrogen and dioxygen, which circulate in a plurality of cells and react by means of a catalyst to form the electrochemical reaction and produce electrical energy.

[0010] As is known, the fuel cell must be supplied with a pressurized oxygen flow. Therefore, it is known to provide a compressor to supply a pressurized air flow to the fuel cell and supply it with oxygen.

[0011] However, such a compressor is heavy and bulky, which presents a significant drawback in an aeronautical context that aims to limit aircraft mass to reduce energy consumption and thus their environmental impact. Furthermore, the compressor requires a power supply to operate. This power is generally provided by the fuel cell itself, which limits its efficiency since it supplies less energy to other aircraft equipment. The fuel cell's operating range is also affected because it must supply more energy to power the compressor in parallel.

[0012] The invention thus aims to eliminate at least some of these drawbacks by proposing a propulsion system that is efficient and has increased autonomy, while ensuring that both its mass and size are limited. The propulsion system according to the invention also makes it possible to maintain an optimal level of operational safety while limiting greenhouse gas emissions. PRESENTATION OF THE INVENTION

[0013] The invention relates to an aircraft propulsion system comprising: • at least one electric propulsion machine, • at least one fuel cell configured to generate electrical power to power the electric propulsion machine, the fuel cell including an air inlet, and • a gas turbomachine comprising: • a gas generator comprising a main propulsion shaft connected to at least one main compression stage and at least one turbine stage, the main compression stage being configured to accelerate a main airflow from a main air inlet, • an auxiliary compression stage mounted on an auxiliary drive shaft mechanically connected to the main drive shaft, the auxiliary compression stage being configured to accelerate an auxiliary airflow between an auxiliary air inlet and an auxiliary air outlet, the auxiliary air outlet being connected to the fuel cell air inlet so as to supply it with a pressurized airflow.

[0014] The propulsion system according to the invention allows the gas generator and the fuel cell to be supplied in parallel with two separate air streams accelerated by two separate compression stages integrated into the gas turbomachine. Thanks to the invention, the fuel cell is supplied with a pressurized air stream, eliminating the need for an external compressor, which reduces the mass and size of the propulsion system.

[0015] Thanks to the electric propulsion machine in addition to the gas turbomachine, the propulsion system also has increased autonomy, which allows its performance to be optimized.

[0016] The hydrogen-powered fuel cell supplies the electric propulsion machine with electrical energy, resulting in a propulsion system with significantly limited greenhouse gas emissions.

[0017] In one embodiment, the auxiliary air inlet is combined with the main air inlet. The gas turbomachine thus comprises a single common air inlet for the main compression stage and the auxiliary compression stage, thereby simplifying the architecture of the gas turbomachine.

[0018] In one embodiment, the gas turbomachine includes a disengagement system mechanically linking the main drive shaft and the auxiliary drive shaft. The disengagement system is configured to move between an engaged position, in which the main drive shaft is fixed to the auxiliary drive shaft, and a disengaged position, in which the main drive shaft is disengaged from the auxiliary drive shaft. Advantageously, such a disengagement system allows the two drive shafts to be rotationally separated, enabling each compression stage to operate independently. This ensures an optimal level of operational reliability.

[0019] The disengagement system allows the fuel cell to be supplied with the auxiliary airflow even when the gas generator is not operating, for example in the event of its failure. In this case, the auxiliary compression stage is preferably driven by an electric motor.

[0020] In one embodiment, the propulsion system includes a monitoring system configured to detect when the gas generator is operating, thereby automatically placing the disengagement system in the disengaged position. This ensures the continuity of power supply to the electric propulsion machine.

[0021] In one embodiment, the turbine stage of the gas generator being configured to rotate around the main propulsion shaft at a rotational speed, the disengagement system is configured to evolve between the engaged position and the disengaged position automatically as a function of the rotational speed of the turbine stage of the gas generator, making it possible to ensure the operation of the propulsion assembly.

[0022] In one embodiment, the disengagement system is configured to evolve from the disengaged position and the engaged position when the rotational speed of the gas generator turbine stage is greater than a threshold speed, in particular, when the speed of the main propulsion shaft is greater than that of the auxiliary propulsion shaft.

[0023] Preferably, the disengagement system is a freewheel, allowing the use of a simple system, easily integrated into the enclosure of the gas turbine.

[0024] When the turbine stage of the gas generator is operating at too low a speed, for example when it is shutting down, the disengagement system can automatically switch to the disengaged position to advantageously allow the fuel cell to operate.

[0025] Preferably, the main drive shaft and the auxiliary drive shaft are coaxial, allowing simple integration into the gas turbomachine.

[0026] In a preferred embodiment, the main compression stage and the auxiliary compression stage are oriented in opposite directions, allowing two airflows to be accelerated simultaneously: one in the main compression stage towards the turbine stage of the gas generator and the other in the auxiliary compression stage towards the auxiliary air outlet to supply the fuel cell. The two airflows are thus separate and can supply the compression stages independently without making the gas turbomachine architecture overly complex.

[0027] In one embodiment, the propulsion assembly comprises an auxiliary electric machine connected to the auxiliary propulsion shaft, the electric machine The auxiliary power unit is configured to rotate the auxiliary drive shaft and generate electrical power from its rotation. This auxiliary power unit advantageously supplies the fuel cell with auxiliary airflow even when the gas generator is not operating.

[0028] In one embodiment, the main drive shaft and the auxiliary drive shaft form a single drive shaft.

[0029] In one embodiment, the propulsion assembly comprises an auxiliary electric machine connected to the main drive shaft or the auxiliary drive shaft. The auxiliary electric machine is configured to drive, either directly or via the main drive shaft, the auxiliary drive shaft and the auxiliary compression stage to accelerate the auxiliary airflow and supply the fuel cell. In the event of a failure of the gas turbomachine, the auxiliary electric machine advantageously allows the fuel cell to continue operating by being supplied with the auxiliary airflow. The propulsion electric machine can thus advantageously be powered by the electrical energy generated by the fuel cell.

[0030] Preferably, the gas turbomachine and the fuel cell are powered by the same fuel, simplifying the architecture of the propulsion system, which allows for space and mass savings in the aircraft.

[0031] In one embodiment, the fuel powering the gas turbomachine and the fuel powering the fuel cell are stored in the same tank, in particular dihydrogen, making it possible to limit greenhouse gas emissions from the propulsion system even more significantly.

[0032] Alternatively, the turbomachine is powered by kerosene and the fuel cell by dihydrogen.

[0033] In a preferred embodiment, the gas generator and the auxiliary compression stage are mounted in the same housing. In other words, the gas turbomachine comprises a single casing in which all the elements are mounted, which significantly reduces the overall size of the gas turbomachine.

[0034] In one embodiment, the main propulsion shaft is connected to a propulsion member.

[0035] In one embodiment, the propulsion assembly includes a fuel circuit connecting a cryogenic tank to a fuel inlet of the gas turbomachine and to a fuel inlet of the fuel cell, the propulsion assembly includes at least one mechanical pump mounted on the fuel circuit and configured to circulate a flow of fuel in the circuit of fuel, the mechanical pump is mechanically driven by the gas turbomachine and / or electrically powered by the fuel cell.

[0036] The mechanical pump powered by the fuel cell allows the use of electrical energy directly supplied by the fuel cell, thus eliminating the need for an additional power supply while optimally utilizing the fuel cell's capabilities. Alternatively, the mechanical pump can be mechanically driven by the turbomachine. This improves compactness and reduces the overall size. Furthermore, it makes the propulsion system more self-sufficient.

[0037] In one embodiment in which the propulsion assembly includes an auxiliary electric machine connected to the auxiliary propulsion shaft of the gas turbomachine, the mechanical pump is electrically powered by the auxiliary electric machine.

[0038] In one embodiment, the mechanical pump is mounted directly at the outlet of the cryogenic tank and allows the flow of fuel to circulate in liquid state.

[0039] Alternatively, the propulsion assembly comprising a heat exchanger mounted on the fuel circuit, the mechanical pump is mounted between the heat exchanger and the fuel inlets of the gas generator and the fuel cell, allowing the fuel flow to circulate in the gaseous state.

[0040] Alternatively, the propulsion assembly includes a first mechanical pump and a second mechanical pump mounted respectively upstream and downstream of the heat exchanger, so as to optimize the circulation of the fuel flow in the entire fuel circuit.

[0041] In one embodiment, the propulsion assembly includes an auxiliary airflow humidification device mounted between the auxiliary air outlet of the gas turbomachine and the air inlet of the fuel cell. Such a humidification device ensures that the auxiliary airflow entering the fuel cell, which is particularly dry at the outlet of the gas generator, has an optimal humidity level to guarantee the operation of the fuel cell.

[0042] The invention also relates to an aircraft comprising at least one propulsion assembly as described above.

[0043] Finally, the invention relates to a method for supplying air to a fuel cell of a propulsion system as described above, the method comprising the steps of: • accelerate an auxiliary airflow in the auxiliary compression stage mounted in the gas turbomachine, and • to route the auxiliary airflow via the auxiliary air outlet of the gas turbomachine to the air inlet of the fuel cell to supply it.

[0044] In one embodiment, the main drive shaft being rotationally fixed to the auxiliary drive shaft, the method comprises the steps of • Drive the auxiliary drive shaft via the main drive shaft to accelerate the auxiliary airflow, • Disconnect the main drive shaft from the auxiliary drive shaft, and • drive the auxiliary drive shaft by an auxiliary electric machine to accelerate the auxiliary airflow.

[0045] In one embodiment, the fuel cell air supply method is integrated into a method for powering an electric propulsion machine. The power supply method then includes a step of generating electrical energy in the fuel cell from the auxiliary airflow and a fuel flow to power the electric propulsion machine.

[0046] In one embodiment, the method includes a step of rotating the auxiliary drive shaft from the auxiliary electric machine. In such a configuration, the fuel cell advantageously generates electrical energy to power the auxiliary electric machine, which then drives the auxiliary compression stage and thus provides a pressurized airflow to the fuel cell. PRESENTATION OF THE FIGURES

[0047] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0048] Fig. 1 is a schematic representation of a propulsion assembly according to a first embodiment of the invention.

[0049] Fig. 2 is a schematic representation of a propulsion assembly according to a second embodiment of the invention.

[0050] Fig. 3 is a schematic representation of a propulsion assembly according to a third embodiment of the invention.

[0051] Fig. 4 is a schematic representation of a propulsion assembly of Fig. 2 comprising an airflow humidification device.

[0052] Fig. 5 is a schematic representation of a propulsion assembly of Fig. 2 comprising a mechanical fuel flow circulation pump.

[0053] Fig. 6 is a schematic representation of a propulsion assembly of Fig. 2 according to an alternative embodiment of the invention.

[0054] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0055] With reference to [Fig. 1], a propulsion system 1 for an aircraft is shown according to one embodiment of the invention. The propulsion system 1 extends longitudinally along an axis X and comprises a propulsion element (not shown), configured to contribute to the propulsion of the aircraft by accelerating an airflow circulating from upstream to downstream. The terms "upstream" and "downstream" refer to the axis X extending from the upstream to the downstream end of the propulsion system 1, as shown in [Fig. 1].

[0056] With reference to [Fig.1], the propulsion assembly 1 according to the invention comprises a gas turbine 2, an electric propulsion machine M and a fuel cell 9 to power the electric propulsion machine M.

[0057] The electric propulsion machine M is configured to participate in the propulsion of the aircraft by transferring energy to the propulsion unit in such a way as to drive it into rotation.

[0058] The fuel cell 9 is configured to generate electrical energy Elec to power the electric propulsion machine M.

[0059] As is known, the fuel cell 9 is a device for carrying out an electrochemical reaction to generate electrical energy Elec from a redox reaction. For this purpose, the fuel cell 9 is supplied with an oxidizing fluid and a reducing fluid, for example dihydrogen (H2) and dioxygen (O2), which circulate in a plurality of cells and react by means of a catalyst to form the electrochemical reaction and produce electrical energy Elec.

[0060] To enable the implementation of the redox reaction, the fuel cell 9 is configured to be supplied with a fuel flow Q, preferably dihydrogen (H2). For this purpose, the fuel cell 9 includes a fuel inlet 92 ([Fig. 5]). In this example, the fuel Q is stored in a cryogenic tank R (shown in [Fig. 3]) which allows the dihydrogen to be stored in a liquid state, thus enabling a larger mass of fuel Q to be carried in the aircraft.

[0061] The fuel cell 9 is also configured to be supplied with a pressurized oxygen flow. For this purpose, the fuel cell 9 includes an air inlet 91.

[0062] Still referring to [Fig. 1], the gas turbomachine 2 according to the invention The gas turbine 3 comprises a gas generator 3 including a main drive shaft 4 connected to the propulsion unit, for example, via a gearbox. The gas turbine 3 also includes a main compression stage 31 and a turbine stage 32 connected to the main drive shaft 4 to rotate it and thus drive the propulsion unit. The gas turbine 2 also includes a fuel inlet 21 ([Fig. 3]) to supply the gas turbine 3 with a fuel flow Q.

[0063] The gas generator 3 includes a main air inlet 33 for supplying the main compression stage 31 with a main airflow Al, in particular, from outside. The main compression stage 31 is configured to accelerate the main airflow Al so as to drive the rotation of the turbine stage 32 and thus of the main propulsion shaft 4. The main airflow Al flows, preferably, from upstream to downstream in the gas generator 3, i.e. along the longitudinal axis X.

[0064] The turbine stage 32 drives the main propulsion shaft 4 at a predetermined rotational speed.

[0065] The gas generator 3 also includes an exhaust nozzle 34 through which an exhaust air stream from the combustion between a fuel and the main air stream Al compressed in the main compression stage 31 escapes.

[0066] The operation of such a gas generator 3 is known to those skilled in the art and will not be described in further detail in this document.

[0067] According to the invention, the gas turbomachine 2 comprises an auxiliary compression stage 5 mounted on an auxiliary drive shaft 6.

[0068] The auxiliary drive shaft 6 is mechanically connected to the main drive shaft 4. In a preferred embodiment, the main drive shaft 4 and the auxiliary drive shaft 6 are coaxial and adjacent along the longitudinal axis X, allowing for a simple architecture. In this embodiment, the main drive shaft 4 and the auxiliary drive shaft 6 are rotationally fixed, preferably forming a single drive shaft. It is understood that the main drive shaft 4 and the auxiliary drive shaft 6 could just as easily form a single drive shaft 46, configured to simultaneously drive the main compression stage 31 and the auxiliary compression stage 5 as illustrated in [Fig. 6].

[0069] The auxiliary compression stage 5 comprises an auxiliary air inlet 51 and an auxiliary air outlet 52 and is configured to accelerate an auxiliary airflow A2 flowing from the auxiliary air inlet 51 to the auxiliary air outlet 52. The auxiliary air outlet 52 is connected to the air inlet 91 of the fuel cell 9 so as to supply it with a pressurized airflow. In other words, the compression stage auxiliary 5 mounted in the gas turbomachine 2 allows a pressurized air flow to be generated for the fuel cell 9. Preferably, the auxiliary air inlet 51 takes air from the outside environment.

[0070] In this example, the main compression stage 31, mounted on the main drive shaft 4, and the auxiliary compression stage 5, mounted on the auxiliary drive shaft 6, each comprise a centrifugal wheel for accelerating the main airflow A1 and the auxiliary airflow A2, respectively. The centrifugal wheels are preferably mounted axially in succession along the longitudinal axis X. The airflows A1 and A2 are thus drawn in longitudinally and discharged radially. It is understood, however, that the invention also applies to axial wheels.

[0071] Preferably, the auxiliary air inlet 51 is positioned longitudinally between the main compression stage 31 and the auxiliary compression stage 5. More precisely, in this example, the gas turbomachine 2 comprises, successively from upstream to downstream, the auxiliary air outlet 52, the auxiliary compression stage 5, and the auxiliary air inlet 51. In other words, in this example, the main compression stage 31 and the auxiliary compression stage 5 extend in opposite directions to allow for optimal mechanical integration. The airflows A1 and A2 are conducted respectively from upstream to downstream and from the main air inlet 33, and from downstream to upstream from the auxiliary air inlet 51.

[0072] In a preferred embodiment, as shown in [Fig.2], the auxiliary air inlet 51 is combined with the main air inlet 33, which allows a single air inlet A to supply both the main compression stage 31 with the main airflow A1 and the auxiliary compression stage 5 with the auxiliary airflow A2. This improves compactness and allows the single air inlet to be fitted with an anti-icing debris collection grid.

[0073] Preferably, the gas generator 3 and the auxiliary compression stage 5 are mounted in the same enclosed housing. In other words, the auxiliary compression stage 5 is integrated into the gas turbomachine 2, and the latter comprises a single casing, resulting in significant space savings. The gas turbomachine 2 thus eliminates the need for an external compressor to supply air to the fuel cell 9, thereby reducing the mass and size of the propulsion assembly 1. This is all the more advantageous since the main drive shaft 4 and the auxiliary drive shaft 6 are mechanically connected. Lubrication is advantageously shared within the casing.

[0074] In other words, the gas turbomachine 2 according to the invention makes it possible to supply the gas generator 3 and the fuel cell 9 in parallel with two separate air streams Al, A2 accelerated by two separate compression stages 31.5 mounted in a same enclosure. In this example, the main airflow Al and the auxiliary airflow A2 originate from the same airflow A entering the gas turbomachine 2.

[0075] In one embodiment, with reference to [Fig.4], the propulsion assembly 1 includes a humidification device 10 mounted between the auxiliary air outlet 52 of the gas turbomachine 2 and the air inlet 91 of the fuel cell 9. The humidification device 10 is configured to increase the humidity level of the auxiliary airflow A2 before it enters the fuel cell 9. Indeed, in the gas generator 3, the auxiliary airflow A2 dries out. The humidification device 10 thus makes it possible to supply the fuel cell 9 with a flow of air sufficiently humid to ensure optimal operation of the fuel cell 9. For example, the humidification device 10 is in the form of one or more fluid injector(s), in particular of water vapor, from for example a mixture of water and heat generated by the fuel cell 9 or from heat from the turbine stage 32 of the gas turbomachine 2.It goes without saying that the fluid injector can just as easily inject water from a dedicated reservoir, for example.

[0076] In a preferred embodiment, with reference to [Fig.2], the gas turbomachine 2 includes a disengagement system 7 which mechanically connects the main drive shaft 4 and the auxiliary drive shaft 6. In other words, the disengagement system 7 is at the interface between the two main drive shafts 4 and auxiliary drive shaft 6.

[0077] Advantageously, this allows the auxiliary drive shaft 6 to be driven independently of the main drive shaft 4. This is particularly advantageous when the auxiliary drive shaft 6 is connected to an independent auxiliary electric machine as will be shown later.

[0078] The disengagement system 7 is configured to move between an engaged position in which the main drive shaft 4 is rotationally fixed to the auxiliary drive shaft 6, and a disengaged position in which the main drive shaft 4 is disengaged from the auxiliary drive shaft 6. In other words, the disengagement system 7 is configured to disengage the main drive shaft 4 and the auxiliary drive shaft 6, which allows the fuel cell 9 to be supplied with the auxiliary air flow A2 even when the gas generator 3 is not in operation.

[0079] In particular, in this example, the disengagement system 7 is configured to automatically switch between the engaged and disengaged positions depending on the rotational speed of the turbine stage 32 of the gas generator 3. In one embodiment, the disengagement system 7 is configured to automatically be in the engaged position when the rotational speed of the turbine stage 32 is above a predetermined speed threshold. Similarly, the disengagement system 7 is configured to be in the disengaged position when the rotational speed of the turbine stage 32 is below the predetermined speed threshold. In this example, the engaged position is activated when the speed of the main drive shaft 4 is greater than that of the auxiliary drive shaft 6. Conversely, the disengaged position is activated when the speed of the main drive shaft 4 is less than that of the auxiliary drive shaft 6.

[0080] In summary, in this example, when the gas generator 3 is operating at too low a speed, for example when it is shutting down, the disengagement system 7 is configured to automatically switch to the disengaged position, allowing the fuel cell 9 to continue to operate.

[0081] In this example, the disengagement system 7 is in the form of a freewheel, allowing a simple system and limited space for mounting in the gas turbomachine 2.

[0082] In one embodiment, the propulsion assembly 1 includes a monitoring system (not shown) configured to detect when the gas generator 3 is operating and when it is not operating. The monitoring system is configured to automatically place the disengagement system in the disengaged position if a malfunction of the gas generator 3 is detected, thereby ensuring the supply of electrical power to the electric propulsion machine M and thus guaranteeing the operation of the propulsion unit.

[0083] In one embodiment, with reference to [Fig. 2], the gas turbomachine 2 comprises an auxiliary electric machine 8 connected to the auxiliary drive shaft 6. The auxiliary electric machine 8 is configured to drive the auxiliary drive shaft 6 in rotation, for example, when the disengagement system 7 is in the disengaged position. In other words, when the disengagement system 7 is in the disengaged position, for example, in the event of a failure of the gas generator 3, the fuel cell 9 is configured to supply electrical energy Elec to the auxiliary electric machine 8, which can thus drive the auxiliary compression stage 5. The fuel cell 9 can therefore advantageously be supplied with the auxiliary airflow A2 from the auxiliary compression stage 5, even in the event of a failure of the gas generator 3. Preferably, the auxiliary electric machine 8 is mounted externally to the casing of the gas turbomachine 2.

[0084] An auxiliary electric machine 8 is shown connected to the auxiliary drive shaft 6, however it is understood that the auxiliary electric machine 8 could just as easily be connected to the main drive shaft 4.

[0085] Furthermore, [Fig. 6] shows an example in which the main drive shaft 4 and the auxiliary drive shaft 6 form a single shaft propulsion 46. The auxiliary electric machine 8 is, in this example, connected to the single propulsion shaft 46 and is configured to drive the propulsion shaft 46 in rotation so as to drive the auxiliary compression stage 5 and thus supply the fuel cell 9 with the auxiliary air flow A2, even in the event of failure of the gas generator 3.

[0086] The auxiliary electric machine 8 is also configured to generate electrical energy Elec from the rotation of the auxiliary propulsion shaft 6, so as to power, for example, the electric propulsion machine M in addition to the fuel cell 9.

[0087] In one embodiment, the gas generator 3 and the fuel cell 9 are powered by the same fuel Q, simplifying the gas turbomachine 2 and reducing its size in the aircraft. Preferably, the fuel Q is dihydrogen, providing a clean fuel that helps limit greenhouse gas emissions. It goes without saying that the fuel could be different, for example, a sustainable aviation fuel (SAF). Similarly, it goes without saying that the fuel cell 9 could, for example, be powered by dihydrogen and the gas generator 3 by kerosene.

[0088] With reference to [Fig.3], in this example, the fuel Q, configured to power the gas generator 3 and the fuel cell 9, is stored in a single tank R, preferably a cryogenic tank R, which allows a larger mass of fuel Q to be carried while limiting the mass of the aircraft.

[0089] In such an embodiment, the propulsion assembly 1 includes a fuel circuit 11 for jointly supplying the gas generator 3 and the fuel cell 9. The fuel circuit 11 preferably includes a heat exchanger Ec configured to heat the fuel stream Q and convert it to a gaseous state, so that it does not freeze the air entering the combustion chamber of the gas generator 3 or the fuel cell 9. Complementarily or alternatively, the fuel circuit 11 includes a portion mounted around the nozzle 34 so as to exchange heat between the exhaust stream flowing through the nozzle 34 and the fuel stream Q flowing around the nozzle 34. In one embodiment, the nozzle 34 includes a peripheral channel for circulating the fuel stream Q.The latter is thus configured to be heated directly by the airflow circulating in the gas generator 3, which allows for efficient heating while limiting the need for additional heat exchangers.

[0090] In one embodiment, with reference to [Fig. 5], the fuel circuit 11 connects the cryogenic tank R to the gas turbomachine 2 and the fuel cell 9. The fuel circuit 11 includes a distribution valve 14 configured to divide the fuel flow Q from the cryogenic tank R into a first flow supply Q3 intended for the gas generator 3 and a second supply flow Q9 intended for the fuel cell 9. For this purpose, the fuel circuit 11 is connected to the fuel inlet 21 of the gas turbomachine 2 and to the fuel inlet 92 of the fuel cell 9.

[0091] Preferably, the propulsion assembly 1 comprises a first mechanical pump 12 mounted on the fuel circuit 11 and configured to circulate the fuel flow Q through the fuel circuit 11. In a first embodiment, the first mechanical pump 12 is mounted directly at the outlet of the cryogenic tank R, i.e., between the cryogenic tank R and the heat exchanger Ec, so as to circulate the liquid fuel flow Q to the heat exchanger Ec. In a second embodiment, the first mechanical pump 12 is mounted between the heat exchanger Ec and the fuel inlets 21, 92 of the gas turbomachine 2 and the fuel cell 9, respectively. The first mechanical pump 12 is then configured to circulate the fuel flow Q in a gaseous state to the fuel inlets 21, 92 of the gas turbomachine 2 and the fuel cell 9.In a third embodiment, shown in [Fig. 5], the propulsion assembly 1 comprises both a first mechanical pump 12 mounted on the fuel circuit 11 between the cryogenic tank R and the heat exchanger Ec and a second mechanical pump 13 mounted between the heat exchanger Ec and the fuel inlets 21, 92 of the gas turbomachine 2 and the fuel cell 9. Such an embodiment allows the fuel flow Q in liquid state and the fuel flow Q in gaseous state to circulate efficiently throughout the fuel circuit 11.

[0092] In a first embodiment, each mechanical pump 12, 13 is mechanically driven by the gas turbomachine 2, for example by the rotating gas turbine. The drive of each mechanical pump 12, 13 is, for example, achieved via a gearbox (not shown), which increases compactness and reduces size.

[0093] In a second embodiment, each mechanical pump 12, 13 is electrically powered directly by the fuel cell 9, which increases compactness and reduces size. It is understood that each mechanical pump 12, 13 could just as easily be electrically powered by the aircraft's electrical network or by the auxiliary electric machine 8. It is also understood that the mechanical pumps 12, 13 could just as easily be powered independently of each other, for example, one by the gas turbomachine 2 and the other by the fuel cell 9, depending on the architectural constraints.

[0094] In one embodiment, the propulsion assembly 1 includes a cooling system S configured to cool the engine oil circulating in the turbomachine gas 2 from the cryogenic fuel flow Q at the outlet of tank R.

[0095] A method for supplying power to an electric propulsion machine M of a propulsion unit 1 as described previously, with reference to [Fig. 3], will now be described. The power supply method comprises a process for supplying air to a fuel cell 9 of the propulsion unit 1. In this example, with reference to [Fig. 3], the gas generator 3 and the fuel cell 9 are supplied in parallel with the same fuel Q from the same tank R, in this example dihydrogen. Furthermore, in this example, the disengagement system 7 is initially in the engaged position. In other words, the main drive shaft 4 and the auxiliary drive shaft 6 are initially connected and rotate at the same speed.

[0096] The method includes a first step El of introducing an auxiliary air flow A2 into the gas turbomachine 2, via the auxiliary air inlet 51 mounted, in this example, between the main compression stage 31 and the auxiliary compression stage 5.

[0097] The auxiliary airflow A2 is then accelerated, in a step E2 in the auxiliary compression stage 5 mounted in the housing of the gas turbomachine 2. The main airflow Al is accelerated in the gas generator 3 which drives in rotation the main propulsion shaft 4 and the auxiliary propulsion shaft 6.

[0098] At the outlet of the auxiliary compression stage 5, the pressurized auxiliary airflow A2 is routed, in a step E3, via the auxiliary air outlet 52 to the air inlet 91 of the fuel cell 9 in order to supply it. If the mechanical energy generated exceeds the compression requirements of the auxiliary airflow A2, this mechanical energy can be supplied to a propulsion unit (not shown) or converted into electrical energy by the auxiliary electric machine 8.

[0099] In parallel with the auxiliary air flow A2, in a step E4, a fuel flow Q from the tank R is heated, in this example in a heat exchanger Ec, then routed to the fuel cell 9. Following the redox reaction, the fuel cell 9 generates electrical energy Elec, in a step E5, to power the electric propulsion machine M.

[0100] In one embodiment, when the turbine stage 32 of the gas generator 3 rotates at a speed lower than that of the auxiliary drive shaft 6, the disengagement system 7 is placed in the disengaged position, so as to disconnect the auxiliary drive shaft 6 from the main drive shaft 4. Preferably, the disengagement is performed automatically. The auxiliary electric machine 8, powered by the fuel cell 9 or a battery, drives the auxiliary drive shaft 6 in rotation, so as to supply the fuel cell 9 with a pressurized auxiliary airflow A2. The gas turbomachine 2 is This system is advantageously self-powered by enabling the rotation of the auxiliary drive shaft 6 using electrical energy supplied by the fuel cell 9, while simultaneously supplying the fuel cell 9 with a flow of pressurized air. Advantageously, the main drive shaft 4 is not driven, thus reducing the power required by the auxiliary electric machine 8. However, it is understood that the main drive shaft 4 could be driven, particularly when it is contributing to propulsion.

[0101] Thanks to the invention, the electric propulsion machine is powered by a fuel cell that operates with a fuel whose environmental impact is limited. The addition of an auxiliary compression stage within the gas turbomachine housing allows the fuel cell to be supplied with a flow of pressurized air without the need for an external compressor, for example, as was the case in the prior art. The gas turbomachine thus allows the gas generator and the fuel cell to be supplied in parallel with two separate flows of pressurized air without increasing its size or mass.

Claims

Demands

1. Aircraft propulsion assembly (1) comprising: • at least one electric propulsion machine (M), • at least one fuel cell (9) configured to generate electrical power (Elec) to power the electric propulsion machine (M), the fuel cell (9) comprising an air inlet (91), and • a gas turbomachine (2) comprising: • a gas generator (3) comprising a main drive shaft (4) connected to at least one main compression stage (31) and to at least one turbine stage (32), the main compression stage (31) being configured to accelerate a main airflow (Al) from a main air inlet (33), • an auxiliary compression stage (5) mounted on an auxiliary drive shaft (6) mechanically connected to the main drive shaft (4),the auxiliary compression stage (5) being configured to accelerate an auxiliary airflow (A2) between an auxiliary air inlet (51) and an auxiliary air outlet (52), the auxiliary air outlet (52) being connected to the air inlet (91) of the fuel cell (9) so as to supply it with a pressurized airflow.

2. Propulsion assembly (1) according to claim 1, wherein the gas turbomachine (2) comprises a disengagement system (7) mechanically linking the main drive shaft (4) and the auxiliary drive shaft (6), the disengagement system (7) being configured to move between an engaged position, in which the main drive shaft (4) is integral with the auxiliary drive shaft (6), and a disengaged position, in which the main drive shaft (4) is disengaged from the auxiliary drive shaft (6).

3. Propulsion assembly (1) according to claim 2, wherein the turbine stage (32) of the gas generator (3) is configured to rotate about the main propulsion shaft (4) at a rotational speed, the disengagement system (7) is configured to move between the engaged position and the disengaged position automatically depending on the rotational speed of the turbine stage (32) of the gas generator (3).

4. Propulsion assembly (1) according to claim 3, wherein the disengagement system (7) is configured to evolve from the disengaged position to the engaged position when the rotational speed of the turbine stage (32) of the gas generator (3) is greater than a threshold speed, preferably when the speed of the main propulsion shaft (4) is greater than that of the auxiliary propulsion shaft (6).

5. Propulsion assembly (1) according to any one of claims 1 to 4, wherein the main propulsion shaft (4) and the auxiliary propulsion shaft (6) are coaxial.

6. Propulsion assembly (1) according to any one of claims 1 to 5, comprising an auxiliary electric machine (8) connected to the auxiliary propulsion shaft (6), the auxiliary electric machine (8) being configured to drive the auxiliary propulsion shaft (6) in rotation and generate electrical energy (Elec) from the rotation of the auxiliary propulsion shaft (6).

7. Propulsion assembly (1) according to any one of claims 1 to 5, comprising an auxiliary electric machine (8) connected to the auxiliary drive shaft (6) or to the main drive shaft (4), the auxiliary electric machine (8) being configured to drive in rotation, directly or via the main drive shaft (4), the auxiliary drive shaft (6) and the auxiliary compression stage (5) to accelerate the auxiliary airflow (A2) and power the fuel cell (9).

8. Propulsion assembly (1) according to any one of claims 1 to 7, wherein the gas turbomachine (2) and the fuel cell (9) are powered by the same fuel.

9. Propulsion assembly (1) according to any one of claims 1 to 8, wherein the gas generator (3) and the auxiliary compression stage (5) are mounted in the same enclosure.

10. Propulsion assembly (1) according to claim 9, comprising a fuel circuit (11) connecting a cryogenic tank (R) to a fuel inlet (21) of the gas turbomachine (2) and to a fuel inlet (92) of the fuel cell (9), the propulsion assembly (1) comprising at least one mechanical pump (12, 13) mounted on the fuel circuit (11) and configured to circulate a fuel flow (Q) in the fuel circuit (11), the mechanical pump (12, 13) is driven mechanically by the gas turbomachine (2) and / or powered electrically by the fuel cell (9).

11. Propulsion assembly (1) according to any one of claims 1 to 10, comprising a humidification device (10) for the auxiliary airflow (A2) mounted between the auxiliary air outlet (52) of the gas turbomachine (2) and the air inlet (91) of the fuel cell (9).

12. Aircraft comprising at least one propulsion unit (1) according to any one of claims 1 to 11.

13. Method of supplying air to a fuel cell (9) of a propulsion assembly (1) according to any one of claims 1 to 11, the method comprising the steps of: • accelerating an auxiliary airflow (A2) in the auxiliary compression stage (5) mounted in the gas turbomachine (2), and • routing the auxiliary airflow (A2) via the auxiliary air outlet (52) of the gas turbomachine (2) to the air inlet (91) of the fuel cell (9) to supply it.

14. A feeding method according to claim 13, wherein the main drive shaft (4) is rotationally fixed to the auxiliary drive shaft (6), the method comprises the steps of: • driving the auxiliary drive shaft (6) by the main drive shaft (4) to accelerate the auxiliary airflow (A2), • disengaging the main drive shaft (4) and the auxiliary drive shaft (6), and • driving the auxiliary drive shaft (6) by an auxiliary electric machine (8) to accelerate the auxiliary airflow (A2).

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