AIRCRAFT PROPEL GROUP INCLUDING A FUEL CELL

Abstract

Aircraft propulsion system (1) (2) comprising a propeller (3) driven in rotation by an electric machine (4), the electric machine (4) being powered by a fuel cell (5) comprising a core (6), the core (6) being cooled by a cooling system (7) comprising a first heat exchanger (8) located in a first ducted channel (9) through which air flows, characterized in that the cooling system (7) comprises a second heat exchanger (8) located in a second ducted channel (9) through which air flows, the heat exchangers (8) and the channels (9) being annular, the channels (9) surrounding a central air-supplied compartment (12) in which the electric machine (4) and the fuel cell core (6) (5) are located, the inlets (10) of the channels (9) preferably each having a variable inlet cross-section. Figure for the abstract: 1

Description

Title of the invention: AIRCRAFT PROPELLER GROUP COMPRISING A FUEL CELL Technical field of the invention

[0001] The present invention relates to an aircraft propulsion unit comprising a fuel cell whose core is cooled by a cooling system, and to a method for adjusting such a cooling system. Technical background

[0002] An aircraft may include a propulsion unit equipped with an electric propulsion system comprising a propeller driven by an electric motor.

[0003] The electrical energy required to power the electric propulsion system is supplied in part or in full by one or more electric generators.

[0004] In the remainder of the application, we will focus on the particular case where the electric generator is a fuel cell, better known by the acronym "FPC" or the English term "fuel cell".

[0005] A fuel cell has the advantage of producing few polluting and noise emissions.

[0006] Such a fuel cell converts the chemical energy contained in a fuel / oxidizer pair (for example, the hydrogen / oxygen pair) into electrical energy. The fuel cell includes, in particular, an electrical energy-generating core made up of electrochemical cells.

[0007] The electrochemical reaction of the fuel / oxidizer couple produces not only electricity but also heat which is important to remove, in order to allow its proper functioning and maximize its lifespan.

[0008] To achieve this, it is known to cool the core of the fuel cell with a cooling system that includes, in particular, a cooling circuit through which a heat transfer fluid circulates. To dissipate the thermal energy of the heat transfer fluid into the external environment, the cooling circuit includes a heat exchanger located in a shrouded air duct. The air duct is generally circular in cross-section and positioned below the electric propulsion unit.

[0009] Engine manufacturers note that such a propulsion group architecture is not optimal.

[0010] Indeed, following various studies, engine manufacturers have found that in order to meet the cooling needs of the core in the most unfavorable case (namely a takeoff in a hot environment), it is necessary to implant a large heat exchanger, and consequently to have a large vein.

[0011] The implantation of a large circular cross-sectional stream under the electric thruster would not only result in significant aerodynamic drag but also in a non-homogeneous supply of the stream (portions of the stream located in the wake of the propeller and portions of the stream located outside the wake of the propeller), to the detriment of the thermal efficiency of the heat exchanger and more generally of the overall efficiency of the propulsion group.

[0012] Furthermore, it is known to implant a flap in the duct to limit the aerodynamic drag generated by the passage of air through the duct. The flap is generally in two states, namely open when the fuel cell is active and closed when the fuel cell is inactive.

[0013] Motor manufacturers note that such a shutter can be improved.

[0014] Indeed, for certain operating regimes such as the cruise regime, the flow of air entering the duct is too high and only a part of this air is needed to cool the core of the fuel cell, the excess part of the air generating an aerodynamic drag which is undesirable.

[0015] The objective of the present invention is therefore to provide a simple, effective and economical solution to address the aforementioned problems. Summary of the invention

[0016] The invention thus proposes an aircraft propulsion unit extending around an axis X, the propulsion unit comprising a propeller which is mobile in rotation around the axis X and driven in rotation by an electric machine, the electric machine being powered by a fuel cell which includes a core generating electrical energy, the core of the fuel cell being cooled by a cooling system which includes a first heat exchanger placed in a first ducted channel through which air flows from an inlet of the first channel to an outlet of the first channel, characterized in that the cooling system includes a second heat exchanger placed in a second ducted channel through which air flows from an inlet of the second channel to an outlet of the second channel, the heat exchangers and the channels being annular around the axis X,The veins surrounding a central, air-supplied compartment in which the electric machine and the fuel cell core are placed, the inlets of the veins preferably each having a variable inlet cross-section.

[0017] Having several heat exchangers in separate channels allows each heat exchanger to be supplied with fresh air (in other words, air not previously heated by passing through a previous heat exchanger), thus providing a cooling system with a capacity high cooling capacity compared in particular to a cooling system comprising a single thick heat exchanger or to a cooling system comprising several heat exchangers placed in the same row one after the other.

[0018] Having heat exchangers and annular veins allows for the implantation of large heat exchangers while limiting the negative impacts (drag, mass, etc.) associated with their implantation.

[0019] Such annular veins also allow each of the heat exchangers to be supplied homogeneously, with all the veins being in the wake of the propeller, to the benefit of the thermal efficiency of each of the heat exchangers and more generally of the overall efficiency of the propulsion group.

[0020] Variable section inlets allow the airflows entering each of the veins to be precisely adapted according to the cooling needs of the core, and thus minimize the aerodynamic drag produced by the passage of air in each of the veins, during the different operating regimes of the propulsion group, to the benefit of its overall efficiency.

[0021] The propulsion unit according to the invention may comprise one or more of the following features and / or stages, taken individually or in combination with each other: - the helix is ​​mobile in rotation in a plane called rotation P which is perpendicular to the axis X, the inlets of the veins being arranged downstream of the helix, the axial dimension Da between the plane of rotation P of the helix and the inlet of each vein being between 0.1 x R and 0.6 x R, where R is the radius of the helix; - the inlet of each vein presents a reference point Pr whose radial dimension Dr with respect to the X axis is between 0.4 x R and 0.95 x R, where R is the radius of the propeller, the reference point Pr being defined in an axial half-section of the propulsion group which passes through the X axis; - each vein includes a diverging portion located directly upstream of the corresponding heat exchanger, so as to slow down the speed of the air entering the heat exchanger, and a convergent portion located directly upstream of the outlet of the vein, so as to accelerate the air escaping from the vein and generate a thrust; - at least one of the vein inlets is formed by a variable section nozzle, the nozzle comprising a framework having a base from which extends an annular row of independent bands, the free ends of the bands being connected in a common way to a ring whose diameter is adjustable, the framework being covered at least partially with a casing, so as to seal the nozzle; - at least one of the vein inlets includes an obturation device comprising at least one adjustable flap; - the cooling system includes a surface heat exchanger that is flush with an internal fairing of a nacelle of the propulsion unit; - the cooling system includes at least one water injector which is placed in one of the veins upstream of the corresponding heat exchanger; - the propulsion unit includes an axial compressor located in the compartment upstream of the electric machine and the core of the fuel cell, the axial compressor being supplied with air and comprising a rotor driven in rotation by the electric machine; - the propulsion unit includes a cooler placed in the compartment between the axial compressor on one side and the electric machine and the core of the fuel cell on the other, the cooler cooling the air which exits the axial compressor; - the heat exchangers are axially offset from each other; - the cooling system includes a third heat exchanger placed in a third ducted channel through which air flows from an inlet of the third channel to an outlet of the third channel, the third heat exchanger and the third channel being annular around the X axis, the third channel surrounding the central compartment, the inlet of the third channel preferably having an inlet section which is variable.

[0022] The present invention also relates to a method for adjusting the cooling system of a propulsion unit as described above, the method comprising the step of: a) adjust the inlet section of the veins from a measurement of the temperature of the core of the fuel cell, so as to adjust the airflows entering the veins according to the cooling requirements. Brief description of the figures

[0023] The invention will be better understood and other details, features and advantages of the invention will become more apparent upon reading the following description, given by way of non-limiting example and with reference to the accompanying drawings in which:

[0024] [Fig-1] [Fig.1] is an axial cross-sectional view of a propulsion unit according to the invention;

[0025] [Fig.2] [Fig.2] is a detail view of [Fig.1] showing an axial compressor of the propulsion unit and its drive via a gear mechanism;

[0026] [Fig.3] [Fig.3] is a side view of the gear mechanism illustrated on the [Fig.2];

[0027] [Fig.4] [Fig.4] is a flat view of a core cooling system of a fuel cell of the propulsion group illustrated in [Fig.1];

[0028] [Fig.5] [Fig.5] is a side view of a heat exchanger of the cooling system;

[0029] [Fig.6] [Fig.6] is a detailed view of the heat exchanger illustrated in [Fig.5]

[0030] [Fig.7] [Fig.7] is a partial perspective view of a variable section nozzle;

[0031] [Fig.8] [Fig.8] is a perspective view of the variable section nozzle;

[0032] [Fig.9] [Fig.9] is a detail view illustrating the actuation of an adjustable ring variable section nozzle;

[0033] [Fig. 10] [Fig. 10] is a front view of the nozzle with a maximum opening section;

[0034] [Fig. 11] [Fig. 11] is a front view of the nozzle with a minimum opening section;

[0035] [Fig. 12] [Fig. 12] is an axial cross-sectional view of a device for obturating an inlet of a vein;

[0036] [Fig. 13] [Fig. 13] is an axial cross-sectional view of the propulsion unit according to a first embodiment variant;

[0037] [Fig. 14] [Fig. 14] is an axial cross-sectional view of the propulsion group according to a second embodiment. Detailed description of the invention

[0038] Figure 1 schematically represents a propulsion group 1 of aircraft 2. Aircraft 2 can be, for example, an airplane or a drone.

[0039] The propulsion unit 1 extends around an axis X. The propulsion unit 1 comprises a propeller 3 which is free to rotate about the axis X and is driven in rotation by an electric machine 4. The electric machine 4 is powered by a fuel cell 5 which includes a core 6 generating electrical energy. The core 6 of the fuel cell 5 is cooled by a cooling system 7 which includes a first heat exchanger 8 located in a first shrouded channel 9 through which air flows from an inlet 10 of the first channel 9 to an outlet 11 of the first channel 9.

[0040] According to the invention, the cooling system 7 comprises a second heat exchanger 8 placed in a second shrouded channel 9 through which air flows from an inlet 10 of the second channel 9 to an outlet 11 of the second channel 9. The heat exchangers 8 and the channels 9 are annular around the X-axis. The channels 9 surround a central air-supplied compartment 12 in which are placed the electric machine 4 and the core 6 of the fuel cell 5. The inlets 10 of the veins 9 preferably each have an inlet section which is variable.

[0041] By convention in this application, the terms "upstream" and "downstream" are defined with respect to the direction of airflow around the fairings 38, 39 of the nacelle 40, in the veins 9, in the passage 59 and in the compartment 12, when the propulsion unit 1 is operating in "propulsor" mode.

[0042] Furthermore, by convention in the present application, "axial" or "axially" means any direction parallel to the X axis of propulsion group 1, and "radial" or "radially" means any direction perpendicular to the X axis of propulsion group 1.

[0043] Finally, in the present application, the elements common to the different embodiments bear identical numerical references.

[0044] As illustrated in the figures, and in particular in [Fig. 1], the propeller 3 is shown here unfaired and free to rotate about the X-axis in a plane of rotation P that is perpendicular to the X-axis. The propeller 3 is driven in rotation directly by the electric machine 4. Alternatively, the propeller 3 could be driven indirectly by the electric machine 4, for example via a gear mechanism. The propeller 3 supplies air to the vents 9 as well as to the central compartment 12 of the propulsion unit 1.

[0045] As illustrated in the figures, the central compartment 12 of the propulsion group 1 is centered on the X axis and houses, from upstream to downstream, an axial compressor 13, a cooler 14, the electric machine 4, a power electronics box 15, the core 6 of the fuel cell 5 and an accessory box 16.

[0046] Advantageously, as illustrated in the figures, the central compartment 12 is defined externally by a housing 17.

[0047] Such a casing 17 can be made of composite material, so as to minimize the overall mass of the propulsion group 1.

[0048] The central compartment 12 may include a convergent portion upstream of its outlet, to generate additional thrust.

[0049] Advantageously, as illustrated in the figures, the propulsion unit 1 comprises an axial compressor 13 placed in the compartment 12 upstream of the electric machine 4 and the core 6 of the fuel cell 5. The axial compressor 13 is supplied with air and comprises a rotor 18 driven in rotation by the electric machine 4.

[0050] Such an axial compressor 13 compresses the air entering the compartment 12, in order not only to supply the core 6 of the fuel cell 5 according to the desired conditions (for example air supply between 1.5 and 2.5 bar) but also to cool the surface of the elements which are located in the compartment 12 downstream of the axial compressor 13.

[0051] As illustrated in the figures, the axial compressor 13 is located at the upstream end of the central compartment 12. The compressor 13 is supplied with air via an inlet axial which is formed at the upstream end of compartment 12. The axial compressor 13 comprises a rotor 18 driven in rotation around the X axis by the electric machine 4 and a stator 19 which is integral with the casing 17.

[0052] Advantageously, the axial compressor 13 comprises at least one compression stage including a bladed rotating wheel 21 which is part of the rotor 18 and a bladed fixed rectifier 22 which is part of the stator 19.

[0053] As illustrated in the figures and in particular in [Fig.2], the axial compressor 13 here comprises two compression stages arranged axially one after the other.

[0054] Advantageously, the rectifier 22 of each stage comprises an annular array of variable-pitch vanes. Such variable-pitch vanes are better known by the English acronym "VSV" for "Variable Stator Vanes". Such variable-pitch vanes allow the flow rate and compression ratio of the axial compressor 13 to be adapted according to the supply requirements of the fuel cell core 6.

[0055] Advantageously, the timing of the blades of a rectifier 22 is adjusted in a synchronized manner via an adjustment device.

[0056] The adjustment device comprises, for example, a rotating movable ring common to all the blades and a connecting rod specific to each blade. The ring is driven in rotation by one or more actuators. Each connecting rod has one end that is rotationally linked to the corresponding blade and one end that is articulated with the ring. The rotational drive of the ring by the actuator(s) allows for the synchronized adjustment of the pitch of all the blades of the rectifier 22.

[0057] Advantageously, as illustrated in Figures 2 and 3, the rotor 18 of the axial compressor 13 is driven in rotation by the electric machine 4 via a gear mechanism 23. The gear mechanism 23 has a transmission ratio greater than 1, so that the rotational speed of the rotor 18 of the compressor 13 is greater than the rotational speed of the rotor 20 of the electric machine 4. Such a gear mechanism 23 is also called a "multiplier".

[0058] The gear mechanism 23 can be arranged axially between the axial compressor 13 and the electric machine 4, or upstream of the axial compressor 13.

[0059] As illustrated in Figures 2 and 3, the gear mechanism 23 comprises an epicyclic train having a ring gear 24 fixed to the rotor 20 of the electric machine 4, an annular row of external planet gears 25, an annular row of internal planet gears 26 and a sun gear 27 fixed to the rotor 18 of the axial compressor 13. The external planet gears 25 are meshed (or in engagement) with both the ring gear 24 and the internal planet gears 26. The internal planet gears 26 are meshed with both the external planet gears 25 and the sun gear 27.

[0060] Advantageously, as illustrated in the figures, the propulsion unit 1 includes a cooler 14 placed in the compartment 12 between the compressor 13 on one side and the electric machine 4 and the core 6 of the fuel cell 5 on the other, the cooler 14 cooling the air which exits the compressor 13.

[0061] Such a cooler 14 is more commonly known by the English term "intercooler". Such a cooler 14 cools the air exiting the compressor 13, in order not only to supply the core 6 of the fuel cell 5 under the desired conditions, but also to efficiently cool the surface of the elements located in the compartment 12 downstream of the cooler 14.

[0062] Advantageously, such a cooler 14 is an air / air heat exchanger.

[0063] As illustrated in the figures, the cooler 14 is placed in compartment 12 downstream of the axial compressor 13 and upstream of the electric machine 4.

[0064] The electric machine 4 is electrically powered directly or indirectly (for example via batteries) by the fuel cell 5.

[0065] As illustrated in the figures, the electric machine 4 is placed in compartment 12 downstream of the cooler 14 and upstream of the core 6 of the fuel cell 5. The electric machine 4 comprises a rotor 20 which directly drives the propeller 3 and indirectly drives the rotor 18 of the axial compressor 13 via the gear mechanism 23. The outer skin of the stator of the electric machine 4 is surface-cooled by the air circulating in compartment 12. The outer skin of the stator of the electric machine 4 may include fins, in order to increase the surface area for heat exchange with the air.

[0066] The electric machine 4 can be reversible, and thus be able to operate in "motor" mode to produce mechanical energy (to drive in particular the propeller 3 and the rotor 18 of the axial compressor 13) and in "generator" mode to produce electrical energy.

[0067] The power electronics box 15 is arranged axially between the electric machine 4 and the core 6 of the fuel cell 5, so as to reduce the length of the cables connecting the electric machine 4 and the core 6 of the fuel cell 5. The power electronics box 15 can include various converters, batteries, etc.

[0068] The fuel cell 5 is better known by the acronym "FC" or the English term "fuel cell". The fuel cell 5 produces the electrical energy necessary, in particular, for powering the electric machine 4.

[0069] Advantageously, the fuel cell 5 is a hydrogen / oxygen cell, and in other words a cell whose fuel is hydrogen and whose oxidant is oxygen.

[0070] Fuel cell 5 is for example a fuel cell known by the English acronym "PEMFC" for "Proton Exchange Membrane Fuel Cell".

[0071] The core 6 of the fuel cell 5 is commonly referred to as the "stack" in English.

[0072] Advantageously, the core 6 of the fuel cell 5 is formed of electrochemical cells.

[0073] The core 6 of the fuel cell 5 may comprise one or more stacks 28 of electrochemical cells.

[0074] The core 6 of the fuel cell 5 has a predefined maximum permissible temperature (for example, 70°C). This maximum permissible temperature must be respected to ensure its proper operation and maximize its lifespan.

[0075] Batteries can be used to store the electrical energy produced by the fuel cell 5.

[0076] As illustrated in the figures, the fuel cell 5 is here a hydrogen / oxygen fuel cell. The core 6 of the fuel cell 5 is located in compartment 12 downstream of the electric machine 4. The core 6 of the fuel cell 5 comprises several stacks 28 of electrochemical cells arranged axially one after the other. The core 6 is supplied with hydrogen by a hydrogen supply device connected to one or more hydrogen tanks. The core 6 is supplied with oxygen by an oxygen supply device that draws air from compartment 12. The outer skin of the core 6 of the fuel cell 5 is surface-cooled by the air circulating in compartment 12. The outer skin of the core 6 of the fuel cell 5 may include fins to increase the surface area for heat exchange with the air.The core 6 of the fuel cell 5 may include internal galleries (or passages) which allow thermal energy to be evacuated into the air of compartment 12.

[0077] As illustrated in the figures, the accessory housing 16 is arranged axially downstream of the core 6 of the fuel cell 5.

[0078] The accessory housing 16 can include various pumps (heat transfer fluid pump 30, oil pump, hydrogen pump, water pump, etc.), a humidifier, an oil separator, etc.

[0079] Alternatively, the accessory box 16 could be arranged axially between the electric machine 4 and the core 6 of the fuel cell 5, so as to reduce the axial dimension of the transmission shaft which links in rotation the electric machine 4 and the various accessories of the accessory box 16.

[0080] As indicated above, according to the invention, the heat exchangers 8 are annular around the X axis.

[0081] Each heat exchanger 8 allows the thermal energy from the core 6 of the fuel cell 5 to be evacuated into the air which passes through the corresponding vein 9.

[0082] Generally, the cooling system 7 can include between 2 and 6 heat exchangers 8, depending in particular on the cooling requirements of the core 6 of the fuel cell 5 and the space available for their installation.

[0083] As illustrated in [Fig.1], the cooling system 7 comprises two heat exchangers 8 each placed in a faired channel 9.

[0084] Alternatively, as illustrated in Figures 13 and 14, the cooling system 7 comprises three heat exchangers 8 each placed in a faired channel 9.

[0085] Advantageously, as illustrated in [Fig.4], the heat exchangers 8 are part of a cooling circuit 29 in which a heat transfer fluid circulates by means of a pump 30 (for example a volumetric or centrifugal pump).

[0086] The heat transfer fluid can be, for example, glycol or a glycol / water mixture.

[0087] Advantageously, as illustrated in [Fig.4], the various stacks 28 of the core 6 of the fuel cell 5 are connected to the cooling circuit 29 in parallel with each other, to limit the flow of heat transfer fluid flowing into each of the stacks 28, and thus reduce pressure losses and consequently the consumption of the heat transfer fluid pump 30.

[0088] Advantageously, each heat exchanger 8 comprises two independent paths, namely a first path in which the air from the corresponding vein 9 flows and a second path in which the heat transfer fluid flows.

[0089] The paths of a heat exchanger 8 can each include fins, in order to increase the exchange surface, to the benefit of the thermal efficiency of the heat exchanger 8 and the reduction of pressure losses.

[0090] Advantageously, the axial dimension of a heat exchanger 8 is less than or equal to 100 mm. It is observed that beyond the aforementioned axial dimension, the thermal efficiency of the heat exchanger 8 no longer increases.

[0091] Advantageously, a heat exchanger 8 comprises at least one tube 31 wound in the form of a spiral. Such a heat exchanger 8 is obtained, for example, by bending.

[0092] Advantageously, a heat exchanger 8 includes fins 32 between the different turns of each tube 31, in order to increase the exchange surface.

[0093] As illustrated in the figures, and in particular Figures 5 and 6, the heat exchanger 8 comprises six spirally wound tubes 31, the tubes 31 being arranged axially one after the other and fixed to each other (for example, by welding or brazing). Each tube 31 comprises six turns spaced radially apart. The turns of a tube 31 are held in position relative to each other by means of four supports 33 (or reinforcements) distributed regularly around the X-axis. Each tube 31 includes fins 32 arranged in the spaces between the turns, in order to increase the exchange surface area.

[0094] Hollow and profiled (or tapered) arms can be introduced into the veins 9 for the passage of the heat transfer fluid pipes.

[0095] As indicated above, according to the invention, the veins 9 in which the heat exchangers 8 are placed are also annular around the axis X. The veins 9 surround the central compartment 12, and preferably each have an inlet section which is variable.

[0096] The inlets 10 of the veins 9 can also each have an inlet section which is fixed (or non-variable), depending on the requirements.

[0097] As illustrated in [Fig.1], the cooling system 7 comprises two distinct and coaxial veins 9 around the X axis, each vein 9 housing a heat exchanger 8.

[0098] Alternatively, as illustrated in Figures 13 and 14, the cooling system 7 comprises three distinct and coaxial veins 9 around the X axis, each vein 9 housing a heat exchanger 8.

[0099] Advantageously, as illustrated in [Fig.1], the inlets 10 of the veins 9 are arranged downstream of the helix 3. The axial dimension Da between the plane of rotation P of the helix 3 and the inlet 10 of each vein 9 is between 0.1 x R and 0.6 x R, where R is the radius of the helix 3.

[0100] Such an axial positioning of the inlet 10 of each vein 9 makes it possible to capture air having an optimal speed (namely between 50 and 1 lOm / s), so as to efficiently evacuate the thermal energy of the heat transfer fluid into the air of the vein 9.

[0101] Advantageously, as illustrated in [Fig.1], the inlet 10 of each vein 9 has a reference point Pr whose radial dimension Dr with respect to the X axis is between 0.4 x R and 0.95 x R, where R is the radius of the propeller 3. The reference point Pr is defined in an axial half-section of the propulsion group 1 which passes through the X axis.

[0102] The reference point Pr is here the radially median point of the inlet 10, when the inlet 10 has an inlet section that is minimal.

[0103] Such a radial positioning of the inlet 10 of each vein 9 makes it possible to capture air having an optimal speed (namely between 50 and 1 lOm / s), so as to efficiently evacuate the thermal energy of the heat transfer fluid into the air of the vein 9.

[0104] Alternatively, the reference point Pr could be the radially median point of the inlet 10, when the inlet 10 has a maximum inlet cross-section. Or, the reference point Pr could be the radially internal (or radially external) point of the inlet 10, when the inlet 10 has a minimum or maximum inlet cross-section.

[0105] Advantageously, as illustrated in the figures, each vein 9 comprises a diverging portion 34 located directly upstream of the corresponding heat exchanger 8, so as to slow down the speed of the air entering the exchanger of heat 8, and a convergent portion 35 located directly upstream of the outlet 11 of the vein 9, so as to accelerate the air escaping from the vein 9 and generate a thrust.

[0106] The diverging portion 34 of the vein 9 forms a diffuser. The diverging portion 34 has a flow cross-section that increases from upstream to downstream. Reducing the air velocity helps to reduce the pressure losses associated with the passage of air through the heat exchanger 8.

[0107] The converging portion 35 of the vein 9 forms a converging nozzle. The converging portion 35 has a flow cross-section that decreases from upstream to downstream. Such a converging nozzle accelerates the air escaping from the vein 9 and generates thrust, the thrust at least partially compensating for the drag generated by the passage of the air through the heat exchanger 8.

[0108] Advantageously, as illustrated in the figures, the heat exchangers 8 are axially offset from each other.

[0109] Such an axial offset allows the divergent and convergent portions 34, 35 of the veins 9 to be implanted, while minimizing the radial bulk of the propulsion group 1.

[0110] Advantageously, as illustrated in the figures, each vein 9 comprises an upstream part located upstream of the corresponding heat exchanger 8 and a downstream part located downstream of the corresponding heat exchanger 8.

[0111] Advantageously, as illustrated in the figures, each vein 9 is radially delimited by an internal wall 36 (or an internal conduit) and an external wall 37 (or an external conduit).

[0112] When the inlet 10 of each vein 9 has a variable inlet section, the inlet section varies between a minimum section and a maximum section.

[0113] To adjust the inlet section of a vein 9, the inlet 10 of the vein 9 can be formed by one or two nozzles 41 with variable section, each nozzle 41 forming at least in part the inner wall 36 or the outer wall 37 of the vein 9.

[0114] Advantageously, as illustrated in Figures 7 to 11, a variable-section nozzle 41 comprises a frame 43 (or armature) having a base 44 from which extends an annular row of independent strips 45. The free ends of the strips 45 are commonly connected to a ring 46 whose diameter is adjustable. The frame 43 is at least partially covered by a casing 47 (or membrane), so as to seal the nozzle 4L

[0115] The frame 43 of the nozzle 41 can be made of composite material, so as to minimize the mass of the nozzle.

[0116] Similarly, the casing 47 can be made of polymer material, so as to minimize the mass of the nozzle.

[0117] Advantageously, as illustrated in Figures 7 to 11, the diameter of the ring 46 is adjustable via a mechanism 48 driven by an actuator 49 (for example, a stepper motor).

[0118] As illustrated in [Fig. 9], the ring 46 is split and thus comprises two free ends 50 facing each other. The mechanism 48 comprises a drive screw 51 which is rotated by the actuator 49, and two receiving nuts 52 meshing with the screw 51, each nut 52 being fixed to a free end 50 of the ring 46. The rotation of the screw 51 by the actuator 49 causes each of the nuts 52 to translate relative to each other, so as to increase or decrease the diameter of the ring 46 depending on the direction of rotation.

[0119] A variable-section nozzle 41 may include a defrosting device. The defrosting device includes, for example, heating elements distributed regularly around the periphery of the frame 43.

[0120] The free ends of the bands 45 can be connected to the ring 46 via elastic elements (return springs, polymer blocks) or tie rods.

[0121] The free ends of the bands 45 can each be in the form of a loop, the ring 46 passing through each of the loops.

[0122] Fig. 10 is a front view of the nozzle 41 with a maximum opening section, the ring 46 having a maximum diameter. Fig. 11 is a front view of the nozzle 41 with a minimum opening section, the ring 46 having a minimum diameter.

[0123] Adjusting the diameter of ring 46 thus allows the opening section of nozzle 4L to be adjusted.

[0124] The ring 46 of a nozzle 41 can form the upstream end of the inner wall 36 or the outer wall 37 of a vein 9, so adjusting the diameter of the ring 46 allows adjusting the inlet section of the vein 9.

[0125] Alternatively, to adjust the inlet section of a vein 9, the inlet 10 of the vein 9 may include a closure device 53 comprising at least one adjustable flap 55.

[0126] A 55 adjustment flap can be movable in translation (sliding flap) or movable in rotation (pivoting flap).

[0127] As illustrated in [Fig. 12], the inlet 10 of the vein 9 comprises a device shutter 53 comprising two annular rows of rotating movable flaps 55.

[0128] The inlet cross-section of vein 9 is minimal when the flaps 55 of the obturation device 53 are closed. Conversely, the inlet cross-section of vein 9 is maximal ([Fig. 12]) when the flaps 55 of the obturation device 53 are open.

[0129] The outlets 11 of the veins 9 can also each have a variable outlet cross-section. Such a variable outlet cross-section not only allows generating thrust by accelerating the air escaping from vein 9, but also controlling the intensity of this thrust.

[0130] To adjust the outlet section of a vein 9, the outlet 11 of the vein 9 could be formed by one or two nozzles 41 with variable cross-section. Alternatively, the outlet 11 of the vein 9 could include a shut-off device 53 comprising at least one adjustable flap 55.

[0131] As illustrated in the figures, the propulsion group 1 includes an annular air passage 59 around the axis X, this air passage 59 being arranged radially between the veins 9 (and more precisely the external vein 9) and a nacelle 40 of the propulsion group 1.

[0132] The air passage 59 is radially delimited by the outer wall 37 of the outer vein 9 and an inner fairing 38 of the nacelle 40.

[0133] Advantageously, as illustrated in the figures, the cooling system 7 includes a surface heat exchanger 56 which is flush with the internal fairing 38 of the nacelle 40 of the propulsion unit 1.

[0134] Such a surface heat exchanger 56 provides additional cooling capacity for the core 6 of the fuel cell 5 while having a low impact on drag.

[0135] The cooling system 7 can obviously include one or more surface heat exchangers 56.

[0136] Advantageously, the surface heat exchanger(s) 56 are integrated into or form part of the nacelle 40 of the propulsion group 1, and in other words, the surface heat exchanger(s) 56 are carried by the nacelle 40.

[0137] Advantageously, the surface heat exchanger(s) 56 are part of the cooling circuit 29 which includes the main heat exchangers 8.

[0138] As illustrated in [Fig.1], the cooling system 7 comprises a single surface heat exchanger 56 which is annular around the X axis. The surface heat exchanger 56 is integrated into the nacelle 40 and is flush with the internal fairing 38 of the nacelle 40.

[0139] As illustrated in [Fig. 13], the cooling system 7 comprises three surface heat exchangers 56 arranged axially one after the other. The surface heat exchangers 56 are annular around the X-axis. The surface heat exchangers 56 are integrated into the nacelle 40 and are flush with the internal fairing 38 of the nacelle 40. Unlike the cooling system 7 illustrated in [Fig. 13], the cooling system 7 illustrated in [Fig. 14] comprises only two surface heat exchangers 56, one of which has been replaced by a water reservoir 60, as described below.

[0140] As illustrated in the figures, the nacelle 40 of the propulsion group 1 surrounds the veins 9, and is radially delimited by the inner fairing 38 and an outer fairing 39 facing each other.

[0141] Advantageously, the cooling system 7 includes at least one water injector 57 which is placed in one of the veins 9 upstream of the corresponding heat exchanger 8.

[0142] The air / water mixture offers a superior cooling capacity compared to air alone. The water vaporizes upon contact with the heat exchanger 8, thereby absorbing a significant amount of heat from the heat transfer fluid, thus noticeably reducing the temperature of the heat transfer fluid at the outlet of the heat exchanger 8. The resulting water vapor is discharged through the outlet 11 of the stream 9.

[0143] The cooling system 7 can obviously include one or more water injectors 57 in one or all of the veins 9.

[0144] Advantageously, the injector(s) 57 are variable flow, so as to be able to adapt the flow of injected water according to the cooling requirements.

[0145] Advantageously, the injector(s) 57 are part of a water circuit which includes a pump (for example a positive displacement or centrifugal pump) and one or more water reservoirs 60.

[0146] Advantageously, the temperature of the injected water is low and below a predetermined value (for example, 30°C). Low-temperature water allows us to benefit from the high latent heat of vaporization of water as well as the high specific heat capacity of water.

[0147] Advantageously, the cooling system 7 includes at least one radial or annular row 58 of water injectors 57 which is placed in one of the veins 9 upstream of the corresponding heat exchanger 8.

[0148] The water injected by the injectors 57 can be produced in part or in whole by the fuel cell 5, and resulting from the reaction between hydrogen and oxygen

[0149] Water can be stored in one or more tanks 60. The tank(s) 60 can be filled periodically, for example, before each takeoff. The tank(s) 60 are, for example, integrated into the nacelle 40. Each tank 60 can be associated with a water temperature sensor and a water level sensor. Each tank 60 can include an isothermal wall, i.e., a thermally insulated wall. The tank(s) 60 can be cooled by a cooling device, the cooling device drawing, for example, air from the air passage 59. Each tank 60 can include a filling port positioned at 12 o'clock, analogous to the face of a clock, to facilitate filling.

[0150] The water injector(s) 57 can be inclined with respect to the X axis along the direction of air flow in the vein 9, so as to limit pressure losses (in particular aerodynamic disturbances) and optimize the homogeneity of the air / water mixture.

[0151] As illustrated in [Fig. 14], for each channel 9, the cooling system 7 comprises several radial rows 58 of water injectors 57, the water injectors 57 being located upstream of the corresponding heat exchanger 8. In each of the channels 9, the radial rows 58 of water injectors 57 are evenly distributed around the X-axis. The cooling system 7 includes a water reservoir 60 which is annular around the X-axis. The water reservoir 60 is integrated into the nacelle 40 and is flush with the inner fairing 38 of the nacelle 40. The water reservoir 60 is arranged axially between the two surface heat exchangers 56.

[0152] Hollow and profiled (or tapered) arms can be introduced into the veins 9 for the passage of the water supply lines of the injector(s) 57.

[0153] By way of example, the cooling system 7 of [Fig. 1] is intended for a propulsion unit 1 whose thrust-to-weight ratio varies between 0.2 and 0.25. And the cooling systems 7 of Figures 13 and 14 are intended for a propulsion unit 1 whose thrust-to-weight ratio is greater than 0.25.

[0154] The general characteristics described above (concerning, for example, the heat exchangers 8, the veins 9, etc.) can be applied to the embodiment illustrated in [Fig. 1] as well as to the variant embodiments illustrated in Figures 13 and 14.

[0155] According to the invention, the cooling system 7 is configured to be adjusted by an adjustment method.

[0156] The adjustment process includes the step of: a) adjust the inlet section of the veins 9 from a measurement of the temperature of the core 6 of the fuel cell 5, so as to adjust the air flow rates entering the veins 9 according to the cooling requirements.

[0157] Such an adjustment method takes into account the temperature of the core 6 of the fuel cell 5 so as to adapt quickly and precisely the airflows entering the veins 9 according to the cooling requirements of the core 6, and thus minimize the aerodynamic drag produced by the passage of air in the different veins 9, during the different operating regimes of the propulsion group 1, to the benefit of the overall performance of the propulsion group 1 and of the aircraft 2 (consumption, flight range, etc.).

[0158] The inlet sections of the veins 9 during step a) can be adjusted from additional parameters such as the air temperature upstream of the heat exchangers 8, the air pressure upstream of the heat exchangers 8, the velocity flight of aircraft 2, flight altitude of aircraft 2, operating regime of propulsion group 1 (takeoff regime, climb regime, cruise regime, descent regime and landing regime).

[0159] Advantageously, the temperature measurement of the core 6 of the fuel cell 5 which is used in step a) can be obtained by means of a temperature sensor which is specific to the core 6 of the fuel cell 5.

[0160] By way of example, the minimum cross-sectional area of ​​the inlet 10 of a vein 9 is equal to 0.05 x Sech, where Sech is the frontal cross-sectional area of ​​the corresponding heat exchanger 8. And the maximum cross-sectional area of ​​the inlet 10 of a vein 9 is equal to 0.8 x Sech-

[0161] For a fuel cell 5 whose core 6 has a maximum allowable temperature of 70°C, the inlet area of ​​each vein 9 is approximately equal to 0.5 x Sech when the temperature of the core 6 is equal to 60°C, and the inlet area of ​​each vein 9 is approximately equal to 0.8 x Sech when the temperature of the core 6 is equal to 68°C.

[0162] When the cooling system 7 includes at least one water injector 57, the adjustment process includes a step consisting of: b) adjust the flow rate of water injected by injector 57 into vein 9 from a measurement of the temperature of the core 6 of the fuel cell 5.

[0163] The flow rate of water injected during step b) can be adjusted from additional parameters such as the air temperature upstream of the heat exchangers 8, the air pressure upstream of the heat exchangers 8, the flight speed of the aircraft 2, the flight altitude of the aircraft 2, the operating regime of the propulsion unit 1 (take-off regime, climb regime, cruise regime, descent regime and landing regime).

[0164] By way of example, for a fuel cell 5 whose core 6 has a maximum permissible temperature of 70°C, the injector(s) 57 are set as follows: - zero flow when the temperature of the core 6 of the fuel cell 5 is below a first predetermined threshold value (for example 60°C); - controlled flow when the temperature of the core 6 of the fuel cell 5 is between the first threshold value and a second predetermined threshold value (for example 68°C); - maximum flow rate when the core temperature 6 is above the second threshold value.

Claims

Demands

1. An aircraft propulsion unit (1) (2) extending about an axis (X), the propulsion unit (1) comprising a propeller (3) that is rotatable about the axis (X) and driven in rotation by an electric machine (4), the electric machine (4) being powered by a fuel cell (5) comprising an electrical power-generating core (6), the core (6) of the fuel cell (5) being cooled by a cooling system (7) comprising a first heat exchanger (8) located in a first ducted channel (9) through which air flows from an inlet (10) of the first channel (9) to an outlet (11) of the first channel (9), characterized in that the cooling system (7) comprises a second heat exchanger (8) located in a second ducted channel (9) through which air flows from an inlet (10) of the second channel (9) and up to an exit (11) of the second vein (9),the heat exchangers (8) and the veins (9) being annular around the axis (X), the veins (9) surrounding a central air-supplied compartment (12) in which the electric machine (4) and the core (6) of the fuel cell (5) are placed, the inlets (10) of the veins (9) preferably each having a so-called inlet section which is variable.

2. Propulsion unit (1) according to claim 1, characterized in that the propeller (3) is mobile in rotation in a plane called rotation (P) which is perpendicular to the axis (X), the inlets (10) of the veins (9) being arranged downstream of the propeller (3), the axial dimension (Da) between the plane of rotation (P) of the propeller (3) and the inlet (10) of each vein (9) being between 0.1 x R and 0.6 x R, where R is the radius of the propeller (3).

3. Propulsion unit (1) according to any one of the preceding claims, characterized in that the inlet (10) of each vein (9) has a reference point (Pr) whose radial dimension (Dr) with respect to the axis (X) is between 0.4 x R and 0.95 x R, where R is the radius of the propeller (3), the reference point (Pr) being defined in an axial half-section of the propulsion unit (1) which passes through the axis (X).

4. Propulsion unit (1) according to any one of the preceding claims, characterized in that each vein (9) comprises a diverging portion (34) located directly upstream of the interchange of corresponding heat (8), so as to slow down the speed of the air entering the heat exchanger (8), and a convergent portion (35) located directly upstream of the outlet (11) of the vein (9), so as to accelerate the air escaping from the vein (9) and generate a thrust.

5. Propulsion unit (1) according to any one of the preceding claims, characterized in that at least one of the inlets (10) of the veins (9) is formed by a nozzle (41) with variable cross-section, the nozzle (41) comprising a frame (43) having a base (44) from which extends an annular row of independent bands (45), the free ends of the bands (45) being connected in a common way to a ring (46) whose diameter is adjustable, the frame (43) being covered at least partially with a casing (47), so as to seal the nozzle (41).

6. Propulsion unit (1) according to any one of the preceding claims, characterized in that at least one of the inlets (10) of the veins (9) comprises a closing device (53) having at least one adjustable flap (55).

7. Propulsion unit (1) according to any one of the preceding claims, characterized in that the cooling system (7) comprises a surface heat exchanger (56) which is flush with an internal fairing (38) of a nacelle (40) of the propulsion unit (1).

8. Propulsion unit (1) according to any one of the preceding claims, characterized in that the cooling system (7) includes at least one water injector (57) which is placed in one of the veins (9) upstream of the corresponding heat exchanger (8).

9. Propulsion unit (1) according to any one of the preceding claims, characterized in that the propulsion unit (1) comprises an axial compressor (13) placed in the compartment (12) upstream of the electric machine (4) and the core (6) of the fuel cell (5), the axial compressor (13) being supplied with air and comprising a rotor (18) driven in rotation by the electric machine (4).

10. Propulsion unit (1) according to the preceding claim, characterized in that the propulsion unit (1) comprises a cooler (14) placed in the compartment (12) between the axial compressor (13) on the one hand and the electric machine (4) and the core (6) of the fuel cell (5) on the other hand, the cooler (14) cooling the air exiting the axial compressor (13).

11. Propulsion unit (1) according to any one of the preceding claims, characterized in that the heat exchangers (8) are axially offset from each other.

12. Propulsion unit (1) according to any one of the preceding claims, characterized in that the cooling system (7) comprises a third heat exchanger (8) placed in a third duct (9) shrouded in which air flows from an inlet (10) of the third duct (9) to an outlet (11) of the third duct (9), the third heat exchanger (8) and the third duct (9) being annular around the axis (X), the third duct (9) surrounding the central compartment (12), the inlet (10) of the third duct (9) preferably having an inlet section which is variable.

13. Method of adjusting the cooling system (7) of a propulsion unit (1) according to any one of the preceding claims, the method comprising the step of: a) adjusting the inlet section of the veins (9) from a measurement of the temperature of the core (6) of the fuel cell (5), so as to adjust the air flow rates entering the veins (9) according to the cooling requirements.

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