METHOD FOR CONTROLLING AN AIRCRAFT PROPELLER GROUP

Abstract

Aircraft propulsion unit (1) (2) comprising a propeller (3) driven by an electric machine (4) powered by a fuel cell (5) which includes a core (6) generating electrical power, the core (6) being cooled by a cooling circuit (29) and a water injection circuit (61), the cooling circuit (29) comprising a heat exchanger (8) located in a channel (9), the water injection circuit (61) comprising a water reservoir (60) and a water injector (57), the propulsion unit (1) comprising a liquid water recovery system (62) which includes a heat pump (63) comprising a refrigeration circuit (64), the refrigeration circuit (64) comprising a compressor (65), a condenser (66), an expansion valve (67) and an evaporator (68) which exchanges heat with water vapor rejected by the core (6), the reservoir (60) of the injection circuit (61) being supplied at least in part with liquid water from the recovery system (62).Figure for the abridged version: 1.

Description

Title of the invention: METHOD FOR CONTROLLING AN AIRCRAFT PROPELLER GROUP Technical field of the invention

[0001] The present invention relates to a method for controlling an aircraft propulsion unit, as well as to a propulsion unit intended for implementing such a method. 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 which includes, in particular, a cooling circuit in 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.

[0009] To increase the cooling capacity of the cooling system, it is known to supplement it with a liquid water injection circuit which will continuously inject water upstream of the heat exchanger.

[0010] Indeed, the air / water mixture offers a cooling capacity that is superior to air alone, due in particular to the fact that water has a high latent heat of vaporization.

[0011] Such a water injection circuit includes a reservoir which can be supplied by conventional filling when the propulsion unit is stopped and / or by a liquid water recovery system when the propulsion unit is in operation.

[0012] The water recovery system recovers liquid water by condensing the water vapor rejected by the core of the fuel cell, this water vapor being a product of the electrochemical reaction between the fuel and the oxidant.

[0013] Engine manufacturers are currently seeking to optimize the propulsion system described above.

[0014] The objective of the present invention is therefore to provide a simple, efficient, and economical solution to the aforementioned problem. Summary of the invention

[0015] The invention thus proposes a method for controlling an aircraft propulsion unit, the propulsion unit comprising a propeller driven in rotation by an electric machine, the electric machine being powered by a fuel cell comprising an electrical energy generating core, the fuel cell core being cooled by a cooling system comprising a cooling circuit and a water injection circuit, the cooling circuit comprising at least one heat exchanger located in a streamlined and air-supplied channel, the water injection circuit comprising a water reservoir and at least one water injector located in the channel upstream of the heat exchanger, the propulsion unit further comprising a liquid water recovery system comprising a heat pump comprising a refrigeration circuit in which a refrigerant circulates, the refrigeration circuit comprising a compressor, a condenser,an expansion valve and an evaporator that exchanges heat with water vapor rejected by the fuel cell core so that the water vapor condenses into liquid water, the injection circuit reservoir being supplied at least partially with liquid water from the recovery system, the process comprising the step of: a) starting the injector when the temperature of the fuel cell core is above a first predetermined threshold value, the flow rate of water injected by the injector being a function of the temperature of the fuel cell core.

[0016] Such a control method takes into account the temperature of the fuel cell core so as to start the injector only when the injection of water is essential to meet the cooling needs of the fuel cell core.

[0017] When the injector is running, such a control method takes into account the temperature of the fuel cell core so as to rigorously adapt the flow of injected water to the cooling requirements of the fuel cell core.

[0018] Such a control method thus makes it possible to use the water injection only as strictly necessary to meet cooling requirements, and consequently to optimize in particular the size of the injection circuit tank and the water supply requirements of the tank, to the benefit of the overall performance of the propulsion group and the aircraft.

[0019] The control method according to the invention may comprise one or more of the following features and / or steps, taken individually or in combination with each other: - the flow rate of water injected by the injector is maximum when the temperature of the core of the fuel cell is greater than a second predetermined threshold value, the second value being greater than the first value; - The core of the fuel cell comprises membranes moistened by a humidifier, the process including the step of: b) transfer at least some of the liquid water from the recovery system to the humidifier; - the condenser of the refrigeration circuit exchanges heat with a cold source, the process comprising at least one of the following steps: c) heat the aircraft cabin with the thermal energy recovered from the cold source; d) defrost at least one element of the propulsion unit with the thermal energy recovered from the cold source; - The temperature of the fuel cell core is obtained by means of a temperature sensor which is specific to the fuel cell core.

[0020] The present invention also relates to an aircraft propulsion unit intended for implementing the method as described above, the propulsion unit comprising a propeller driven in rotation by an electric machine, the electric machine being powered by a fuel cell which includes an electrical energy generating core, the core of the fuel cell being cooled by a cooling system which includes a cooling circuit and a water injection circuit, the cooling circuit including at least one heat exchanger placed in a streamlined and air-supplied channel, the water injection circuit including a water reservoir and at least one water injector placed in the channel upstream of the heat exchanger, the propulsion unit further including a liquid water recovery system which includes a heat pump having a refrigeration circuit in which a refrigerant circulates,The refrigeration circuit, comprising a compressor, a condenser, an expansion valve, and an evaporator, exchanges heat with water vapor rejected by the core of the fuel cell, thus that the water vapor condenses into liquid water, the injection circuit reservoir being supplied at least in part with liquid water from the recovery system.

[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 core of the fuel cell includes membranes moistened by a humidifier, the humidifier being supplied at least in part with liquid water from the recovery system; - the evaporator of the refrigeration circuit includes a structure carrying at least one tube in which the refrigerant circulates, the condensed liquid water being collected by a collector which is located at the lower part of the evaporator; - the propulsion unit extends around an X axis, the heat exchanger and the duct being annular around the X axis, the duct surrounding a central air-supplied compartment in which the electric machine and the core of the fuel cell are placed, the evaporator of the refrigeration circuit being placed in the compartment downstream of the core of the fuel cell; - the vein includes an inlet which has a variable inlet cross-section.

[0022] The present invention also relates to an aircraft comprising a propulsion unit as described above. 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 detailed view of an axial compressor and a mechanism propulsion unit gears;

[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 detailed flat view of the cooling circuit of a cooling system for the core of a propulsion group fuel cell;

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

[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 a detailed view of a liquid water recovery system for the propulsion group;

[0037] [Fig. 14] the [Fig. 14] is an axial cross-sectional view of the propulsion group according to a first embodiment variant;

[0038] [Fig. 15] [Fig. 15] is an axial cross-sectional view of the propulsion group according to a second embodiment. Detailed description of the invention

[0039] Figure 1 schematically represents a propulsion group 1 of aircraft 2. Aircraft 2 can be, for example, an airplane or a drone.

[0040] According to the invention, the propulsion unit 1 comprises a propeller 3 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 cooling circuit 29 and a water injection circuit 61. The cooling circuit 29 includes at least one heat exchanger 8 located in a shrouded and air-supplied channel 9. The water injection circuit 61 includes a water reservoir 60 and at least one water injector 57 located in the channel 9 upstream of the heat exchanger 8. The propulsion unit 1 further includes a liquid water recovery system 62 which includes a heat pump 63 comprising a refrigeration circuit 64 in which a refrigerant circulates.The refrigeration circuit 64 includes a compressor 65, a condenser 66, an expansion valve 67, and an evaporator 68 which exchanges heat with water vapor rejected by the core 6 of the fuel cell 5, so that the water vapor condenses (liquefies) into liquid water. The reservoir 60 of the injection circuit 61 is supplied at least partially with liquid water from the recovery system 62.

[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 passage 59, in the veins 9, 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] The propulsion group 1 extends around an axis X.

[0045] 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 a passage 59, the ducts 9, and also to a central compartment 12 of the propulsion unit 1.

[0046] Advantageously, as illustrated in the figures, the propulsion group 1 includes a central compartment 12 which is supplied with air and in which are placed the electric machine 4 and the core 6 of the fuel cell 5.

[0047] Advantageously, as illustrated in the figures, the central compartment 12 is defined externally by a housing 17.

[0048] Such a casing 17 can be made of composite material, so as to minimize the overall mass of the propulsion group 1.

[0049] The central compartment 12 may include a convergent portion upstream of its outlet, to generate additional thrust.

[0050] As illustrated in the figures, the central compartment 12 of the propulsion unit 1 houses, from upstream to downstream, an axial compressor 13, a cooler 14, the electric machine 4, a power electronics box 15, an accessory box 16, the core 6 of the fuel cell 5 and the evaporator 68 of the refrigeration circuit 64 of the liquid water recovery system 62.

[0051] 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.

[0052] 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 surface cool the elements which are located in the compartment 12 downstream of the axial compressor 13.

[0053] As illustrated in particular in Figures 1 and 2, the axial compressor 13 is located at the upstream end of the central compartment 12. The axial compressor 13 is supplied with air via an axial inlet which is formed at the upstream end of the compartment 12. The axial compressor 13 includes 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.

[0054] 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.

[0055] As illustrated in particular in figures 1 and 2, the axial compressor 13 here comprises two compression stages arranged axially one after the other.

[0056] 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.

[0057] Advantageously, the timing of the blades of a rectifier 22 is adjusted in a synchronized manner via an adjustment device.

[0058] 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.

[0059] 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 axial 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".

[0060] 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.

[0061] 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.

[0062] Advantageously, as illustrated in the figures, the propulsion unit 1 comprises a cooler 14 located in the compartment 12 between the axial compressor 13 of a on the one hand, the electric machine 4 and the core 6 of the fuel cell 5 on the other hand, the cooler 14 cooling the air which comes out of the axial compressor 13.

[0063] Such a cooler 14 is more commonly known by its English name, "intercooler". Such a cooler 14 cools the air exiting the axial 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.

[0064] Advantageously, such a cooler 14 is an air / air heat exchanger.

[0065] 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.

[0066] The electric machine 4 is electrically powered directly or indirectly (for example via batteries) by the fuel cell 5.

[0067] 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.

[0068] 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.

[0069] As illustrated in the figures, 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.

[0070] As illustrated in the figures, the accessory box 16 is 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.

[0071] The accessory housing 16 can include various pumps (heat transfer fluid pump 30, hydrogen pump, water pump, etc.), a humidifier 69, an oil separator, etc.

[0072] 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.

[0073] Advantageously, the fuel cell 5 is a hydrogen / oxygen fuel cell, in other words, a fuel cell whose fuel is hydrogen and whose oxidant is oxygen. Such a fuel cell 5 is, for example, of the "PEMFC" type, which stands for "Proton Exchange Membrane Fuel Cell".

[0074] The core 6 of the fuel cell 5 is commonly called a “stack” in English.

[0075] Advantageously, the core 6 of the fuel cell 5 is formed of electrochemical cells.

[0076] The core 6 of the fuel cell 5 may comprise one or more stacks 28 of electrochemical cells.

[0077] The core 6 of the fuel cell 5 may include membranes moistened by a humidifier 69. Advantageously, the humidifier 69 is supplied at least in part with liquid water from the recovery system 62.

[0078] The core 6 of a PEMFC-type fuel cell 5 comprises such membranes. In this specific case, each membrane is positioned between a hydrogen-supplied anode and an oxygen-supplied cathode, the membrane's function being to exchange protons from the anode to the cathode. The humidifier 69 injects water into the oxygen supplying the cathode to humidify the membrane.

[0079] 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.

[0080] The core 6 of the fuel cell 5 releases water vapor resulting from the electrochemical reaction between the fuel and the oxidant. The liquid water recovery system 62 condenses this released water vapor into liquid water, to supply, in particular, the reservoir 60 of the injection circuit 61.

[0081] Batteries can be used to store the electrical energy produced by the fuel cell 5.

[0082] As illustrated in particular in Figures 1 and 4, the fuel cell 5 is here a hydrogen / oxygen fuel cell of the "PEMFC" type. 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 system that includes one or more hydrogen tanks and a hydrogen pump. The core 6 is supplied with oxygen by an oxygen supply system that draws air from compartment 12. The oxygen supply system includes a humidifier 69 that humidifies the membranes of the various electrochemical cells. The humidifier 69 is located in the accessory housing 16. The humidifier 69 is supplied with liquid water from the recovery system 62. The outer skin of the core 6 of the fuel cell 5 is surface-cooled by the air circulating in the 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) that allow thermal energy to be dissipated into the air of the compartment 12.

[0083] The cooling circuit 29 includes at least one heat exchanger 8 placed in a faired and air-supplied channel 9.

[0084] The cooling circuit 29 can obviously include several heat exchangers 8, depending in particular on the cooling requirements of the core 6 of the fuel cell 5 and the space available to install them.

[0085] Advantageously, as illustrated in [Fig.1], each heat exchanger 8 is placed in a streamlined vein 9 of its own.

[0086] As illustrated in Figures 1 and 4, the cooling circuit 29 here comprises three heat exchangers 8 each placed in a faired channel 9.

[0087] According to a first embodiment illustrated in [Fig. 14], the cooling circuit 29 comprises a single heat exchanger 8 placed in a faired channel 9.

[0088] According to a second embodiment illustrated in [Fig.15], the cooling circuit 29 comprises two heat exchangers 8 each placed in a faired channel 9.

[0089] Advantageously, the cooling circuit 29 is traversed by a heat transfer fluid, the heat transfer fluid circulating in the cooling circuit 29 by means of a pump 30 (for example a volumetric or centrifugal pump).

[0090] The heat transfer fluid can be, for example, glycol or a glycol / water mixture.

[0091] Advantageously, as illustrated in the figures, the heat exchanger(s) 8 and the vein(s) 9 are annular around the X-axis. This geometric feature not only allows for the installation of one or more large heat exchangers 8 while limiting the negative impacts (drag, mass, etc.) associated with their installation, but also homogenizes the air supply to the heat exchanger(s) 8, thus improving the thermal efficiency of the heat exchanger(s) 8 and, more generally, the overall efficiency of the propulsion unit 1.

[0092] Advantageously, as illustrated in [Fig. 4], the various stacks 28 of the fuel cell core 6 are connected to the cooling circuit 29 in parallel with each other, to limit the flow rate of the 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.

[0093] Advantageously, each heat exchanger 8 comprises two independent paths, namely a first path through which the air from the corresponding vein 9 flows and a second path through which the heat transfer fluid flows.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] Advantageously, a heat exchanger 8 includes fins 32 between the different turns of each tube 31, in order to increase the exchange surface.

[0098] 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 inter-turn spaces to increase the heat exchange surface area.

[0099] Hollow and profiled (or tapered) arms can be introduced into the veins 9 for the passage of the heat transfer fluid pipes.

[0100] The cooling system 7 includes one or more shrouded air channels 9, depending in particular on the cooling requirements of the core 6 of the fuel cell 5 and the space available for implanting them.

[0101] Advantageously, as illustrated in [Fig.1], each vein 9 houses a single heat exchanger 8.

[0102] As illustrated in [Fig.1], the cooling system 7 comprises three separate veins 9, each vein 9 housing a heat exchanger 8.

[0103] According to the first embodiment illustrated in [Fig. 14], the cooling system 7 comprises a single channel 9 housing a heat exchanger 8.

[0104] According to the second embodiment illustrated in [Fig.15], the cooling system 7 comprises two separate veins 9, each vein 9 housing a heat exchanger 8.

[0105] Advantageously, as illustrated in the figures, the vein(s) 9 surround the central compartment 12, so as to minimize the radial bulk of the propulsion group 1.

[0106] Advantageously, when the cooling system 7 includes several veins 9, the veins 9 are coaxial around the X axis, so as also to minimize the radial bulk of the propulsion group 1.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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 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.

[0114] 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.

[0115] 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.

[0116] Advantageously, as illustrated in the figures, the heat exchangers 8 are axially offset from one another.

[0117] 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.

[0118] 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.

[0119] 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).

[0120] Advantageously, the inlet 10 of each channel 9 has a variable inlet cross-section. A variable inlet 10 allows the airflow entering the channel 9 to be precisely adjusted according to cooling requirements, thus minimizing the aerodynamic drag produced by the passage of air through the channel 9 during the different operating regimes of the propulsion unit 1, to the benefit of its overall efficiency.

[0121] The inlet section of each vein 9 thus varies between a minimum section and a maximum section.

[0122] 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.

[0123] 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

[0124] The frame 43 of the nozzle 41 can be made of composite material, so as to minimize the mass of the nozzle 4L

[0125] Similarly, the casing 47 can be made of polymer material, so as to minimize the mass of the nozzle 4L

[0126] 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).

[0127] 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.

[0128] 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.

[0129] The free ends of the bands 45 can be connected to the ring 46 via elastic elements (return springs, polymer blocks) or tie rods.

[0130] 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.

[0131] 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.

[0132] Adjusting the diameter of ring 46 thus allows the opening section of nozzle 4L to be adjusted.

[0133] 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.

[0134] 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.

[0135] A 55 adjustment flap can be movable in translation (sliding flap) or movable in rotation (pivoting flap).

[0136] As illustrated in [Fig.12], the inlet 10 of the vein 9 includes an obturation device 53 comprising two annular rows of rotating movable flaps 55.

[0137] 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.

[0138] The outlets 11 of the veins 9 can also each have a so-called outlet section which is variable. Such an outlet 11 with a variable section allows not only to generating thrust by accelerating the air escaping from vein 9, but also controlling the intensity of this thrust.

[0139] 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.

[0140] The liquid water injection circuit 61 includes a water reservoir 60 and at least one water injector 57 placed in one of the veins 9 upstream of the corresponding heat exchanger 8.

[0141] The air / water mixture offers a cooling capacity that is greater than that of air alone, due in particular to the high latent heat of vaporization of water. The water will vaporize upon contact with the heat exchanger 8, and thus absorb a significant amount of heat from the heat transfer fluid, thereby considerably 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.

[0142] The injection circuit 61 can obviously include one or more water injectors 57 in one or all of the veins 9.

[0143] Advantageously, the injection circuit 61 includes a pump (for example a volumetric or centrifugal pump), so as to move the fluid from the water reservoir 60 to one or more water injectors 57.

[0144] The flow rate of water delivered by the pump can be regulated via an "on / off" type solenoid valve.

[0145] 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.

[0146] Advantageously, the injection circuit 61 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.

[0147] The reservoir 60 of the injection circuit 61 is supplied partially or entirely with liquid water from the recovery system 62. Additionally, the reservoir 60 can be filled via a filling port when the propulsion unit 1 is stopped. Preferably, the filling port is positioned at 12 o'clock, analogous to the face of a clock, to facilitate filling. Also preferably, the water introduced into the reservoir 60 is at a low temperature.

[0148] The tank 60 can be integrated into the nacelle 40 of the propulsion group 1.

[0149] The tank 60 can be associated with a water temperature sensor and a sensor of water level placed inside the tank 60.

[0150] The tank 60 is supplied with liquid water from the recovery system 62 until the water level reaches a predetermined level, the water level being obtained via the water level sensor which is associated with the tank 60.

[0151] The tank 60 may include an isothermal wall, and in other words a thermally insulated wall, in order to limit heat exchange with the external environment.

[0152] The reservoir 60 can be cooled by a cooling device, the cooling device drawing air for example from the air passage 59.

[0153] 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.

[0154] Advantageously, the injection circuit 61 is controlled by a computer, to strictly meet the cooling requirements.

[0155] As illustrated in the figures, for each vein 9, the injection circuit 61 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 veins 9, the radial rows 58 of water injectors 57 are distributed regularly around the X-axis. The injection circuit 61 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 internal fairing 38 of the nacelle 40. The water reservoir 60 is arranged axially between two surface heat exchangers 56.

[0156] 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.

[0157] The liquid water recovery system 62 includes a heat pump 63 comprising a refrigeration circuit 64 in which a refrigerant circulates. The refrigeration circuit 64 includes a compressor 65, a condenser 66, an expansion valve 67 and an evaporator 68 which exchanges heat with water vapor rejected by the core 6 of the fuel cell 5 so that the water vapor condenses into liquid water.

[0158] The recovery system 62 supplies at least part of the reservoir 60 of the injection circuit 61. The recovery system 62 can obviously supply other elements of the propulsion group 1 such as the humidifier 69.

[0159] In the refrigeration circuit 64, more specifically, the compressor 65 compresses the refrigerant (gaseous state) to increase its pressure (and consequently its temperature) before it passes through the condenser 66. The condenser 66 condenses the refrigerant, discharging heat into a cold source 70. The expansion valve 67 expands the refrigerant (liquid state) to lower its pressure (and consequently its temperature) before it passes through the evaporator 68. The evaporator 68 vaporizes the refrigerant by taking heat from the water vapor, the water vapor condensing (or liquefying) into liquid water which is recovered by the recovery system 62 in order to be distributed.

[0160] Advantageously, as illustrated in the figures, the evaporator 68 of the refrigeration circuit 64 is placed in the compartment 12 downstream of the core 6 of the fuel cell 5, so as to capture the maximum amount of water vapor.

[0161] Advantageously, as illustrated in [Fig.13], the evaporator 68 of the refrigeration circuit 64 comprises a structure 71 carrying at least one tube 72 in which the refrigerant circulates, the condensed liquid water being collected by a collector 73 which is disposed at the lower part of the evaporator 68.

[0162] As illustrated in [Fig. 13], more specifically, the structure 71 is in the form of a grid. The tube 72 has a corrugated profile and comprises several segments (or passes) arranged one above the other. Alternatively, the tube 72 could have a spiral profile and comprise several turns arranged one around the other. The collector 73 is in the form of a trough (or gutter), the trough collecting the liquid water condensed by runoff under the effect of gravity.

[0163] Advantageously, the condenser 66 of the refrigeration circuit 64 exchanges heat with a cold source 70. The thermal energy (or heat) recovered by the cold source 70 can be used to heat the cabin of the aircraft 2 and / or defrost at least one element of the propulsion unit 1 (for example, an inlet casing of the nacelle 40).

[0164] Advantageously, the compressor 65 of the refrigeration circuit 64 is controlled according to the different needs (liquid water via the recovery system 62, thermal energy via the condenser 66 of the refrigeration circuit 64, etc.).

[0165] As illustrated in [Fig.1], the propulsion group 1 includes an annular air passage 59 around the X axis, 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.

[0166] 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.

[0167] As illustrated in particular on [Fig.1], 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.

[0168] Advantageously, as illustrated in the figures, the cooling system 7 includes at least one surface heat exchanger 56 which is flush with the internal fairing 38 of the nacelle 40 of the propulsion unit 1.

[0169] 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.

[0170] The cooling system 7 can obviously include several surface heat exchangers 56.

[0171] Advantageously, the surface heat exchanger(s) 56 are part of the cooling circuit 29 which includes the main heat exchangers 8.

[0172] 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.

[0173] As illustrated in the figures, the cooling circuit 29 comprises two surface heat exchangers 56 separated axially from each other by the reservoir 60 of the injection circuit 61. 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.

[0174] 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 14 and 15.

[0175] The propulsion group 1 described above enables the implementation of the control process described below.

[0176] The method for controlling propulsion unit 1 includes the step of: a) to start the injector(s) 57 when the temperature of the core 6 of the fuel cell 5 is above a first predetermined threshold value, the flow rate of water injected by the injector(s) 57 being a function of the temperature of the core 6 of the fuel cell 5.

[0177] By way of example, for a fuel cell 5 whose core 6 has a maximum permissible temperature of 70°C, the first threshold value is equal to 60°C.

[0178] Advantageously, the flow rate of water injected by the injector(s) 57 is maximum when the temperature of the core 6 of the fuel cell 5 is greater than a second predetermined threshold value, the second value being greater than the first value.

[0179] By way of example, for a fuel cell 5 whose core 6 has a maximum permissible temperature of 70°C, the second threshold value is equal to 68°C.

[0180] The activation of the injector(s) 57 during step a) (as well as the flow rate of water injected by the injector(s) 57) can also be determined from one or more of the following additional parameters: - the air temperature upstream of the heat exchangers 8; - the air pressure upstream of the heat exchangers 8; - the flight speed of aircraft 2; - the flight altitude of aircraft 2; - the operating regime of propulsion group 1 (takeoff regime, climb regime, cruise regime, descent regime and landing regime).

[0181] Advantageously, when the core 6 of the fuel cell 5 comprises membranes moistened by a humidifier 69, the process comprises the step of: b) transfer at least part of the liquid water from the recovery system 62 to the humidifier 69.

[0182] Advantageously, when the condenser 66 of the refrigeration circuit 64 exchanges heat with a cold source 70, the process comprises at least one of the steps of: c) heat the aircraft cabin 2 with the thermal energy recovered from the cold source 70; d) defrost at least one element of propulsion group 1 with the thermal energy recovered by the cold source 70.

[0183] Advantageously, the temperature of the core 6 of the fuel cell 5 is obtained by means of a temperature sensor which is specific to the core 6 of the fuel cell 5.

[0184] The control process may also include the step of: e) control the compressor 65 of the refrigeration circuit 64 according to the requirements for liquid water (via the evaporator 68) and thermal energy (via the condenser 66).

Claims

Demands

1. Method for controlling an aircraft propulsion unit (1) (2), the propulsion unit (1) comprising a propeller (3) 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 cooling circuit (29) and a water injection circuit (61), the cooling circuit (29) comprising at least one heat exchanger (8) located in a shrouded and air-supplied channel (9), the water injection circuit (61) comprising a water reservoir (60) and at least one water injector (57) located in the channel (9) upstream of the heat exchanger (8),the propulsion unit (1) further comprising a liquid water recovery system (62) which includes a heat pump (63) having a refrigeration circuit (64) in which a refrigerant circulates, the refrigeration circuit (64) comprising a compressor (65), a condenser (66), an expansion valve (67) and an evaporator (68) which exchanges heat with water vapor rejected by the core (6) of the fuel cell (5) so that the water vapor condenses into liquid water, the reservoir (60) of the injection circuit (61) being supplied at least in part with liquid water from the recovery system (62), the process comprising the step of: a) starting up the injector (57) when the temperature of the core (6) of the fuel cell (5) is above a first predetermined threshold value, the flow rate of water injected by the injector (57) being a function of the temperature of the core (6) of the fuel cell (5).

2. A method according to claim 1, characterized in that the flow rate of water injected by the injector (57) is maximum when the temperature of the core (6) of the fuel cell (5) is greater than a second predetermined threshold value, the second value being greater than the first value.

3. A method according to any one of the preceding claims, characterized in that the core (6) of the fuel cell (5) comprises membranes moistened by a humidifier (69), the method comprising the step of: b) transfer at least a portion of the liquid water from the recovery system (62) to the humidifier (69).

4. A method according to any one of the preceding claims, characterized in that the condenser (66) of the refrigeration circuit (64) exchanges heat with a cold source (70), the method comprising at least one of the steps of: c) heating the cabin of the aircraft (2) with the thermal energy recovered by the cold source (70); d) defrosting at least one element of the propulsion unit (1) with the thermal energy recovered by the cold source (70).

5. A method according to any one of the preceding claims, characterized in that the temperature of the core (6) of the fuel cell (5) is obtained by means of a temperature sensor which is specific to the core (6) of the fuel cell (5).

6. Aircraft propulsion unit (1) (2) for implementing the method according to any one of the preceding claims, the propulsion unit (1) comprising a propeller (3) 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 cooling circuit (29) and a water injection circuit (61), the cooling circuit (29) comprising at least one heat exchanger (8) located in a shrouded and air-supplied channel (9), the water injection circuit (61) comprising a water reservoir (60) and at least one water injector (57) located in the channel (9) upstream of the heat exchanger (8),the propulsion unit (1) further comprising a liquid water recovery system (62) which includes a heat pump (63) having a refrigeration circuit (64) in which a refrigerant circulates, the refrigeration circuit (64) comprising a compressor (65), a condenser (66), an expansion valve (67) and an evaporator (68) which exchanges heat with water vapor rejected by the core (6) of the fuel cell (5) so that the water vapor condenses into liquid water, the reservoir (60) of the injection circuit (61) being supplied at least in part with liquid water from the recovery system (62).

7. Propulsion unit (1) according to the preceding claim, characterized in that the core (6) of the fuel cell (5) comprises membranes moistened by a humidifier (69), the humidifier (69) being supplied at least in part with liquid water from the recovery system (62).

8. Propulsion unit (1) according to any one of claims 6 or 7, characterized in that the evaporator (68) of the refrigeration circuit (64) comprises a structure (71) carrying at least one tube (72) in which the refrigerant circulates, the condensed liquid water being collected by a collector (73) which is disposed at the lower part of the evaporator (68).

9. Propulsion unit (1) according to any one of claims 6 to 8, characterized in that the propulsion unit (1) extends around an axis (X), the heat exchanger (8) and the duct (9) being annular around the axis (X), the duct (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 evaporator (68) of the refrigeration circuit (64) being placed in the compartment (12) downstream of the core (6) of the fuel cell (5).

10. Propulsion unit (1) according to any one of claims 6 to 9, characterized in that the vein (9) comprises an inlet (10) which has a so-called inlet section which is variable.

11. Aircraft (2) comprising a propulsion group (1) according to any one of claims 6 to 10.

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