METHOD FOR CONTROLLING AN AIRCRAFT PROPULSION UNIT

Abstract

Propulsion unit (1) of an aircraft (2) comprising a propeller (3) driven by an electric machine (4) powered by a fuel cell (5) which comprises a core (6) generating electrical energy, 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) placed in a vein (9), the water injection circuit (61) comprising a water tank (60) and a water injector (57), the propulsion unit (1) comprising a liquid water recovery system (62) which comprises a heat pump (63) comprising a refrigeration circuit (64), the refrigeration circuit (64) comprising a compressor (65), a condenser (66), an expander (67) and an evaporator (68) which exchanges heat with water vapor discharged by the core (6), the tank (60) of the injection circuit (61) being supplied at least in part with liquid water from the recovery system (62).Figure for abstract: 1.

Description

Title of the invention: METHOD FOR CONTROLLING AN AIRCRAFT PROPULSION 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 comprise a propulsion unit equipped with an electric thruster comprising a propeller driven by an electric motor.

[0003] The electrical energy required to power the electric thruster is provided in part or in full by one or more electrical 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 “PAC” 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 / oxidant pair (for example the hydrogen / oxygen pair) into electrical energy. The fuel cell comprises in particular an electrical energy generating core which is formed of electrochemical cells.

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

[0008] For this purpose, it is known to cool the core of the fuel cell with a cooling system which notably comprises a cooling circuit in which a heat transfer fluid circulates. To evacuate the thermal energy of the heat transfer fluid into the external environment, the cooling circuit comprises a heat exchanger placed in a ducted air stream.

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

[0010] Indeed, the air / water mixture offers a cooling capacity which is greater than air alone, in particular because water has a high latent heat of vaporization.

[0011] Such a water injection circuit comprises 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 discharged by the core of the fuel cell, this water vapor resulting from the electrochemical reaction between the fuel and the oxidizer.

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

[0014] The objective of the present invention is therefore to provide a simple, effective and economical solution to address 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 which comprises a core generating electrical energy, the core of the fuel cell being cooled by a cooling system which comprises a cooling circuit and a water injection circuit, the cooling circuit comprising at least one heat exchanger placed in a streamlined vein and supplied with air, the water injection circuit comprising a water tank and at least one water injector placed in the vein upstream of the heat exchanger, the propulsion unit further comprising a liquid water recovery system which comprises a heat pump comprising a refrigeration circuit in which a refrigerant circulates, the refrigeration circuit comprising a compressor, a condenser,an expander and an evaporator which exchanges heat with water vapor discharged by the core of the fuel cell so that the water vapor condenses into liquid water, the reservoir of the injection circuit being supplied at least in part with liquid water from the recovery system, the method comprising the step of: a) starting the injector when the temperature of the core of the fuel cell is higher than a first predetermined threshold value, the flow rate of water injected by the injector being a function of the temperature of the core of the fuel cell.

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

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

[0018] Such a control method thus makes it possible to use water injection to the strict minimum 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 unit and the aircraft.

[0019] The control method according to the invention may comprise one or more of the following characteristics and / or steps, taken in isolation from one another or in combination with one another: - the 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 method comprising the step of: (b) transferring at least a portion of the liquid water from the recovery system to the humidifier; - the condenser of the refrigeration circuit exchanges heat with a cold source, the method comprising at least one of the steps consisting of: (c) heating the aircraft cabin with the thermal energy recovered by the cold source; d) defrost at least one element of the propulsion group with the thermal energy recovered by 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 comprises a core generating electrical energy, the core of the fuel cell being cooled by a cooling system which comprises a cooling circuit and a water injection circuit, the cooling circuit comprising at least one heat exchanger placed in a streamlined vein and supplied with air, the water injection circuit comprising a water tank and at least one water injector placed in the vein upstream of the heat exchanger, the propulsion unit further comprising a liquid water recovery system which comprises 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 which exchanges heat with water vapor discharged by the core of the fuel cell so that, 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 characteristics and / or steps, taken in isolation from one another or in combination with one another: - the core of the fuel cell comprises 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 comprises a structure carrying at least one tube in which the refrigerant circulates, the condensed liquid water being collected by a collector which is arranged at the level of the lower part of the evaporator; - the propulsion unit extends around an axis X, the heat exchanger and the vein being annular around the axis X, the vein surrounding a central compartment supplied with air 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 comprises an inlet which has a so-called inlet section which is variable.

[0022] The present invention finally relates to an aircraft comprising a propulsion unit as described previously. Brief description of the figures

[0023] The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

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

[0025] [Fig.2] [Fig.2] is a detail view of an axial compressor and a mechanism to propulsion unit gears;

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

[0027] [Fig.4] [Fig.4] is a flat detail view of the cooling circuit of a cooling system for the core of a fuel cell of the propulsion group;

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

[0029] [Fig.6] [Fig.6] is a detail 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 of the 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 sectional view of a device for closing an entrance to a vein;

[0036] [Fig. 13] [Fig. 13] is a detailed view of a liquid water recovery system of the propulsion unit;

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

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

[0039] In [Fig. 1] a propulsion unit 1 of an aircraft 2 is schematically represented. The aircraft 2 may 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 comprises a core 6 generating electrical energy. The core 6 of the fuel cell 5 is cooled by a cooling system 7 which comprises a cooling circuit 29 and a water injection circuit 61. The cooling circuit 29 comprises at least one heat exchanger 8 placed in a stream 9 which is shrouded and supplied with air. The water injection circuit 61 comprises a water tank 60 and at least one water injector 57 placed in the stream 9 upstream of the heat exchanger 8. The propulsion unit 1 further comprises a liquid water recovery system 62 which comprises a heat pump 63 comprising a refrigeration circuit 64 in which a refrigerant circulates.The refrigeration circuit 64 comprises a compressor 65, a condenser 66, an expansion valve 67 and an evaporator 68 which exchanges heat with water vapor discharged 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 in part with liquid water from the recovery system 62.

[0041] By convention in the present application, the terms “upstream” and “downstream” are defined in relation to the direction of circulation of the air 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 operates in “propulsor” mode.

[0042] Furthermore, by convention in the present application, “axial” or “axially” means any direction parallel to the X axis of the propulsion group 1, and “radial” or “radially” means any direction perpendicular to the X axis of the 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 [Fig. 1], the propeller 3 is here unducted and rotatable about the axis X in a plane of rotation P which is perpendicular to the axis X. The propeller 3 is here 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 veins 9 but also to a central compartment 12 of the propulsion unit 1.

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

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

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

[0049] The central compartment 12 may comprise a converging 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 accessories 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 bars), but also to cool on the surface 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 comprises a rotor 18 driven in rotation around the axis X 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 comprising a bladed moving wheel 21 which forms part of the rotor 18 and a bladed fixed rectifier 22 which forms 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 row of variable-pitch vanes. Such variable-pitch vanes are better known by the English acronym “VSV” for “Variable Stator Vanes”. Such variable-pitch vanes make it possible to adapt the flow rate and the compression ratio of the axial compressor 13, depending on the power supply requirements of the core 6 of the fuel cell 5.

[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 which is common to all of the blades and a connecting rod which is specific to each of the blades. The ring is driven in rotation by one or more actuators. Each connecting rod comprises one end which is linked in rotation with the corresponding blade and one end which is articulated with the ring. The rotational driving of the ring by the actuator(s) makes it possible to adjust in a synchronized manner the setting of all of 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 even upstream of the axial compressor 13.

[0061] As illustrated in Figures 2 and 3, the gear mechanism 23 comprises an epicyclic train comprising a crown 24 secured to the rotor 20 of the electrical machine 4, an annular row of external satellites 25, an annular row of internal satellites 26 and a sun gear 27 secured to the rotor 18 of the axial compressor 13. The external satellites 25 are meshed (or engaged) with both the crown 24 and the internal satellites 26. The internal satellites 26 are meshed with both the external satellites 25 and the sun gear 27.

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

[0063] Such a cooler 14 is better known by the English designation “intercooler”. Such a cooler 14 cools the air leaving the axial compressor 13, in order not only to supply the core 6 of the fuel cell 5 according to the desired conditions, but also to effectively cool the surface of the elements which are 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 the compartment 12 downstream of the axial compressor 13 and upstream of the electrical 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 electrical machine 4 is placed in the compartment 12 downstream of the cooler 14 and upstream of the core 6 of the fuel cell 5. The electrical 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 electrical machine 4 is cooled on the surface by the air circulating in the compartment 12. The outer skin of the stator of the electrical machine 4 may comprise fins, in order to increase the exchange surface with the air.

[0068] The electrical machine 4 can be reversible, and thus be capable of operating in “motor” mode to produce mechanical energy (in particular to drive 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 electrical machine 4 and the core 6 of the fuel cell 5, so as to reduce the length of the cables connecting the electrical machine 4 and the core 6 of the fuel cell 5. The power electronics box 15 may comprise 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 connects in rotation the electric machine 4 and the various accessories of the accessory box 16.

[0071] The accessory box 16 may 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 “PAC” or the English term “fuel cell”. The fuel cell 5 produces the electrical energy necessary in particular for the electrical power supply of the electric machine 4.

[0073] 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. Such a fuel cell 5 is for example of the “PEMFC” type which stands for “Proton Exchange Membrane Fuel Cell” in English.

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

[0075] Advantageously, the core 6 of the fuel cell 5 is formed from 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 comprise membranes humidified 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 arranged between an anode supplied with hydrogen and a cathode supplied with oxygen, the membrane having the function of exchanging protons from the anode to the cathode. The humidifier 69 here injects water into the oxygen which supplies the cathode to humidify the membrane.

[0079] The core 6 of the fuel cell 5 has a maximum admissible temperature which is predefined (for example 70°C). This maximum admissible temperature must be respected to allow its proper operation and maximize its lifespan.

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

[0081] Batteries may 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 cell of the “PEMFC” type. The core 6 of the fuel cell 5 is placed in the compartment 12 downstream of the electrical machine 4. The core 6 of the fuel cell 5 comprises several stacks 28 of electrochemical cells which are arranged axially one after the other. The core 6 is supplied with hydrogen by a hydrogen supply system which comprises one or more hydrogen tanks and a hydrogen pump. The core 6 is supplied with oxygen by an oxygen supply system which takes air from the compartment 12. The oxygen supply system comprises a humidifier 69 which humidifies the membranes of the various electrochemical cells. The humidifier 69 is arranged in the accessory box 16. The humidifier 69 is here supplied with liquid water from the recovery system 62. The outer skin of the core 6 of the fuel cell 5 is cooled on the surface by the air circulating in the compartment 12. The outer skin of the core 6 of the fuel cell 5 may comprise fins, in order to increase the exchange surface with the air. The core 6 of the fuel cell 5 may comprise internal galleries (or passages) which allow thermal energy to be evacuated into the air of the compartment 12.

[0083] The cooling circuit 29 comprises at least one heat exchanger 8 placed in a streamlined vein 9 supplied with air.

[0084] The cooling circuit 29 can of course comprise several heat exchangers 8, depending in particular on the cooling requirements of the core 6 of the fuel cell 5 and the space available for installing them.

[0085] Advantageously, as illustrated in [Fig.l], each heat exchanger 8 is placed in a streamlined vein 9 which is specific to it.

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

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

[0088] According to a second variant embodiment illustrated in [Fig.15], the cooling circuit 29 comprises two heat exchangers 8 each placed in a streamlined vein 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 may 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 axis X. Such a geometric characteristic not only makes it possible to install one or more large heat exchangers 8 while limiting the negative impacts (drag, mass, etc.) which are linked to their installation, but also to homogenize the air supply to the heat exchanger(s) 8, for the benefit of 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 different 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 rate of heat transfer fluid flowing in each of the stacks 28, and thus reduce the 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 in which the air from the corresponding vein 9 circulates and a second path in which the heat transfer fluid circulates.

[0094] The paths of a heat exchanger 8 may each comprise fins, in order to increase the exchange surface, for 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 noted 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 for example obtained by bending.

[0097] Advantageously, a heat exchanger 8 comprises 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 tubes 31 wound in a spiral, the tubes 31 being arranged axially one after the other and fixed to each other (for example by welding or brazing). Each tube 31 here comprises six turns spaced radially from each other. The turns of a tube 31 are held in position relative to each other via four supports 33 (or reinforcements) distributed regularly around the axis X. Each tube 31 comprises fins 32 arranged in the interturn spaces, in order to increase the exchange surface.

[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 comprises one or more streamlined air streams 9, depending in particular on the cooling requirements of the core 6 of the fuel cell 5 and the space available for installing them.

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

[0102] As illustrated in [Fig.l], 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 vein 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 size of the propulsion unit 1.

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

[0107] Advantageously, as illustrated in [Fig.l], 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 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 10 m / 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.l], 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 is defined in an axial half-section of the propulsion group 1 which passes through the axis X.

[0110] The reference point Pr is here the radially median point of the inlet 10, when the inlet 10 has an inlet section which is minimal.

[0111] Such 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 10 m / 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 an inlet section that is maximum. Or, the reference point Pr could be the radially inner point (or the radially outer point) of the inlet 10, when the inlet 10 has an inlet section that is minimum or maximum.

[0113] Advantageously, as illustrated in the figures, each vein 9 comprises a divergent 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 thrust.

[0114] The diverging portion 34 of the vein 9 forms a diffuser. The diverging portion 34 has a flow section which increases from upstream to downstream. The reduction in the air speed makes it possible to reduce the pressure losses linked to the passage of air in the heat exchanger 8.

[0115] The converging portion 35 of the vein 9 forms a converging nozzle. The converging portion 35 has a flow section which decreases from upstream to downstream. Such a converging nozzle makes it possible to accelerate the air escaping from the vein 9 and to generate thrust, the thrust at least partly compensating for the drag generated by the passage of the air in the heat exchanger 8.

[0116] Advantageously, as illustrated in the figures, the heat exchangers 8 are axially offset relative to each other.

[0117] Such an axial offset makes it possible to locate the diverging and converging portions 34, 35 of the veins 9, while minimizing the radial size 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 delimited radially 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 vein 9 has a so-called inlet section which is variable. An inlet 10 with a variable section makes it possible to precisely adapt the flow of air entering the vein 9 according to the cooling requirements, and thus minimize the aerodynamic drag produced by the passage of air in the vein 9, during the different operating regimes of the propulsion unit 1, for 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 internal wall 36 or the external wall 37 of the vein 9.

[0123] Advantageously, as illustrated in Figures 7 to 11, a nozzle 41 with variable section comprises a frame 43 (or armature) comprising a base 44 from which extends an annular row of independent strips 45. The free ends of the strips 45 are connected in common to a ring 46 whose diameter is adjustable. The frame 43 is covered at least partially with an envelope 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] In the same way, 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 type electric 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 driving screw 51 which is driven in rotation by the actuator 49, and two receiving nuts 52 engaged with the screw 51, each of the nuts 52 being fixed to a free end 50 of the ring 46. The rotational driving of the screw 51 by the actuator 49 causes the translation of each of the nuts 52 relative to each other, so as to increase or decrease the diameter of the ring 46 depending on the direction of rotation.

[0128] A nozzle 41 with variable section may comprise a defrosting device. The defrosting device comprises, for example, heating resistors distributed regularly around the periphery of the frame 43.

[0129] The free ends of the strips 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 may 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.l 1] 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 the ring 46 thus makes it possible to adjust the opening section of the nozzle 4L.

[0133] The ring 46 of a nozzle 41 can form the upstream end of the internal wall 36 or of the external wall 37 of a vein 9, thus the adjustment of the diameter of the ring 46 makes it possible to adjust 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 comprise a closing device 53 comprising at least one adjustable flap 55.

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

[0136] As illustrated in [Fig.12], the inlet 10 of the vein 9 comprises a closing device 53 comprising two annular rows of flaps 55 movable in rotation.

[0137] The inlet section of the vein 9 is minimal when the shutters 55 of the closure device 53 are closed. And conversely, the inlet section of the vein 9 is maximal ([Fig. 12]) when the shutters 55 of the closure device 53 are open.

[0138] The outlets 11 of the veins 9 may also each have a so-called outlet section which is variable. Such an outlet 11 with variable section not only makes it possible to generate thrust by accelerating the air escaping from vein 9, but also to control 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 section. Alternatively, the outlet 11 of the vein 9 could comprise a closure device 53 comprising at least one adjustable flap 55.

[0140] The liquid water injection circuit 61 comprises 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 air alone, in particular because water has a high latent heat of vaporization. The water will vaporize on contact with the heat exchanger 8, and thus absorb a significant amount of heat from the heat transfer fluid, so as to significantly reduce the temperature of the heat transfer fluid at the outlet of the heat exchanger 8. The water vapor created is evacuated through the outlet 11 of the vein 9.

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

[0143] Advantageously, the injection circuit 61 comprises 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 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 lower than a predetermined value (for example 30°C). Low temperature water makes it possible to benefit from the high latent heat of vaporization of the water but also from the high heat capacity of the water.

[0146] Advantageously, the injection circuit 61 comprises 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 in part or in full with liquid water from the recovery system 62. In addition, the reservoir 60 can be filled via a filling orifice when the propulsion unit 1 is stopped. Preferably, the filling orifice is positioned at 12 o'clock by analogy with the dial of a clock, so as to facilitate filling. Also preferably, the water introduced into the reservoir 60 has 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 water level placed inside the tank 60.

[0150] The reservoir 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 reservoir 60.

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

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

[0153] The water injector(s) 57 may be inclined relative 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 here comprises several radial rows 58 of water injectors 57, the water injectors 57 being placed 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 axis X. The injection circuit 61 comprises a water reservoir 60 which is annular around the axis X. 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 pipes of the injector(s) 57.

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

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

[0159] In the refrigeration circuit 64, more precisely, 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 by evacuating 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 arranged at the level of 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 chute (or gutter), the chute 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.l], the propulsion group 1 comprises 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.

[0166] The air passage 59 is delimited radially by the external wall 37 of the external vein 9 and an internal fairing 38 of the nacelle 40.

[0167] As illustrated in particular in [Fig.l], the nacelle 40 of the propulsion unit 1 surrounds the veins 9, and is delimited radially by the internal fairing 38 and an external fairing 39 facing each other.

[0168] Advantageously, as illustrated in the figures, the cooling system 7 comprises 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 of course comprise several surface heat exchangers 56.

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

[0172] Advantageously, the surface heat exchanger(s) 56 are integrated or form part of the nacelle 40 of the propulsion unit 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 axially separated from each other by the reservoir 60 of the injection circuit 61. The surface heat exchangers 56 are annular around the axis X. 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.l] as well as to the variant embodiments illustrated in Figures 14 and 15.

[0175] The propulsion group 1 described above makes it possible to implement the control method described below.

[0176] The method for controlling the propulsion unit 1 comprises the step of: a) starting the injector(s) 57 when the temperature of the core 6 of the fuel cell 5 is higher than 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] For example, for a fuel cell 5 whose core 6 has a maximum admissible 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] For example, for a fuel cell 5 whose core 6 has a maximum admissible temperature of 70°C, the second threshold value is equal to 68°C.

[0180] The starting 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 unit 1 (take-off regime, climb regime, cruise regime, descent regime and landing regime).

[0181] Advantageously, when the core 6 of the fuel cell 5 comprises membranes humidified by a humidifier 69, the method comprises the step consisting of: b) transferring at least a portion 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 method comprises at least one of the steps consisting 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 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 method may also comprise the step of: e) controlling 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

Claims

1. Method for controlling a propulsion unit (1) of an aircraft (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) which comprises a core (6) generating electrical energy, the core (6) of the fuel cell (5) being cooled by a cooling system (7) which comprises a cooling circuit (29) and a water injection circuit (61), the cooling circuit (29) comprising at least one heat exchanger (8) placed in a stream (9) faired and supplied with air, the water injection circuit (61) comprising a water tank (60) and at least one water injector (57) placed in the stream (9) upstream of the heat exchanger (8),the propulsion unit (1) further comprising a liquid water recovery system (62) which comprises a heat pump (63) comprising 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 discharged 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 method comprising the step of: a) starting the injector (57) when the temperature of the core (6) of the fuel cell (5) is greater than 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. 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. Method according to one of the preceding claims, characterized in that the core (6) of the fuel cell (5) comprises membranes humidified by a humidifier (69), the method comprising the step of: b) transferring at least a portion of the liquid water from the recovery system (62) to the humidifier (69).

4. Method according to 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 consisting 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. Method according to 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. Propulsion unit (1) of an aircraft (2) intended for implementing the method according to 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) which comprises a core (6) generating electrical energy, the core (6) of the fuel cell (5) being cooled by a cooling system (7) which comprises a cooling circuit (29) and a water injection circuit (61), the cooling circuit (29) comprising at least one heat exchanger (8) placed in a stream (9) faired and supplied with air, the water injection circuit (61) comprising a water tank (60) and at least one water injector (57) placed in the stream (9) upstream of the heat exchanger (8),the propulsion unit (1) further comprising a liquid water recovery system (62) which comprises a heat pump (63) comprising 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 discharged 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 humidified 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 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 arranged at the level of the lower part of the evaporator (68).

9. Propulsion unit (1) according to one of claims 6 to 8, characterized in that the propulsion unit (1) extends around an axis (X), the heat exchanger (8) and the vein (9) being annular around the axis (X), the vein (9) surrounding a central compartment (12) supplied with air 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 group (1) according to 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 unit (1) according to one of claims 6 to 10.

Images