ELECTRIC PROPULSION SYSTEM FOR AN AIR VEHICLE

Description

[0001] The invention relates to the field of electric propulsion of aircraft. An electrically powered aircraft comprises, for example, electric propulsion systems attached to its wings. Such an electric propulsion system generally comprises a propulsion propeller driven in rotation by one or more electric motors powered by a set of fuel cells. The electric motor(s) and the fuel cells are, for example, integrated into a nacelle. During their operation, the fuel cells release heat that must be evacuated. For this, one solution uses a fuel cell cooling circuit, this circuit comprising a heat exchanger cooled by means of air outside the aircraft circulating in an air duct.Air outside the aircraft enters the air duct through air inlets arranged on a side face of the nacelle and exits through scoops or air outlets ("exhausts" in English) of the nacelle. The need for cooling the fuel cells is all the greater as the thrust provided by the propulsion system is high, for example during takeoff of the aircraft. However, the sizing of the fuel cell cooling circuit must allow sufficient evacuation of the heat produced by the fuel cells in all phases of use of the aircraft, which is complex, especially since it is necessary to avoid degrading the aerodynamic performance of the aircraft.

[0002] Document US 2020 / 277069 A1 describes an aircraft nacelle 26a comprising a set of fuel cells 26d intended to electrically power an engine 26i driving a propulsion propeller. An air channel 26w allows on the one hand the supply of oxygen and on the other hand the cooling of the fuel cells. The set of fuel cells may comprise a heat exchanger to improve the cooling of the fuel cells. An opening 26x of the air channel opens at the front end of the nacelle. As shown in the figure 5 , the air channel extends laterally along one side of the fuel cells 26d, from the opening 26x located at the forward end of the nacelle. Such a configuration is not optimal from the point of view of the aerodynamic performance of the nacelle and consequently of the aircraft. DISCLOSURE OF THE INVENTION:

[0003] The present invention aims in particular to provide a solution to this problem. It relates to an aircraft propulsion system comprising: an electricity production system comprising a set of fuel cells; at least one electric motor powered by electricity from at least a portion of the fuel cells; a propulsion propeller mechanically coupled to the at least one electric motor; and a nacelle housing at least the electricity production system and the at least one electric motor, said nacelle comprising an air circulation channel provided to allow the electricity production system to be cooled, in which: the air circulation channel extends inside the nacelle from a first end of said air circulation channel located at a first longitudinal end of the nacelle; the air circulation channel receives a heat exchanger provided to allow cooling of the electricity production system; and the propulsion propeller is located near the first longitudinal end of the nacelle.

[0004] The propulsion system is remarkable in that at least a portion of the airflow channel adjacent the first end of the airflow channel is delimited by a cylindrically shaped outer surface surrounding the longitudinal axis of the nacelle, the outer surface being located inside the nacelle.

[0005] The fact that the airflow channel extends inside the nacelle from the first longitudinal end of the nacelle allows the circulation of a high air flow rate in the airflow channel, in order to meet the cooling needs of the electricity generation system to ensure its efficiency. The fact that the at least part of the airflow channel contiguous to the first end of the airflow channel is delimited by a cylindrically shaped outer surface surrounding the longitudinal axis of the nacelle allows axial symmetry of the propulsion system. This makes it possible to minimize the aerodynamic blocking effects and therefore the aerodynamic drag of the nacelle, by optimizing the pressure losses due to the cooling of the electricity generation system.Thus, the propulsion system according to the invention makes it possible to meet the cooling needs of the electricity production system while maintaining satisfactory aerodynamic drag characteristics.

[0006] According to different embodiments which can be taken individually or in combination: in at least one part of the nacelle, considered along the length of the nacelle, the air circulation channel is unique, of circular section and houses a fan provided to promote the circulation of air in this air circulation channel. Preferably, this circular section is centered on the longitudinal axis of the nacelle; the fan is housed in the air circulation channel, between the first end of the air circulation channel and the heat exchanger; the propulsion propeller is rotatably mounted around the nacelle; the propulsion system comprises an air flow adjustment device, associated with the first end of the air circulation channel; the propulsion propeller is mounted integral with a drive shaft whose longitudinal axis corresponds to the longitudinal axis of the nacelle;the heat exchanger is installed in a portion of the air circulation channel in which a section of the air circulation channel through a plane perpendicular to the longitudinal axis of the nacelle is crown-shaped; the heat exchanger is installed in a portion of the air circulation channel in which the air circulation channel is of circular section; the air circulation channel is of cylindrical shape and extends along the length of the nacelle, between the first end of the air circulation channel and a second end of the air circulation channel opening near a second longitudinal end of the nacelle, opposite the first longitudinal end of the nacelle;a second end of the air circulation channel opens through a side wall of the nacelle, between the first longitudinal end of the nacelle and a second longitudinal end of the nacelle, opposite the first longitudinal end of the nacelle; the propulsion system comprises a hydrogen tank housed in the nacelle between the second end of the air circulation channel and the second longitudinal end of the nacelle; the propulsion system comprises an air flow adjustment device, associated with the second end of the air circulation channel; the first longitudinal end of the nacelle corresponds to a front longitudinal end of the nacelle; the first longitudinal end of the nacelle corresponds to a rear longitudinal end of the nacelle; the propulsion system comprises two propulsion propellers mounted counter-rotating close to each other;in addition to the propulsion propeller, the propulsion system includes a propeller mounted fixed relative to the nacelle, close to the propulsion propeller. ;

[0007] The invention also relates to an aircraft comprising such a propulsion system. DETAILED DESCRIPTION:

[0008] The invention will be better understood by reading the following description and examining the attached figures. There figure 1 illustrates an aircraft equipped with a propulsion system according to an embodiment of the invention. The figure 2A schematically illustrates, seen in longitudinal section, a propulsion system of an aircraft according to a first embodiment of the invention. The figure 2B is a detail view of the propulsion system of an aircraft illustrated in the figure 2A . There figure 2C , similar to the figure 2B , schematically illustrates a particular embodiment of the propulsion system of an aircraft in accordance with the first embodiment of the invention. The figure 2D schematically illustrates a propulsion system of an aircraft in accordance with a variant of the first embodiment of the invention. The figure 3A schematically illustrates, seen in longitudinal section, a propulsion system of an aircraft according to a second embodiment of the invention. The figure 3B schematically illustrates a propulsion system of an aircraft in accordance with a variant of the second embodiment of the invention. The figure 4A schematically illustrates, seen in longitudinal section, a propulsion system of an aircraft according to a third embodiment of the invention. The figure 4B schematically illustrates a propulsion system of an aircraft in accordance with a variant of the third embodiment of the invention. The figure 5A schematically illustrates, seen in longitudinal section, a propulsion system of an aircraft according to a fourth embodiment of the invention. The figure 5B schematically illustrates a propulsion system of an aircraft in accordance with a variant of the fourth embodiment of the invention.

[0009] Aircraft 1 shown on the figure 1 comprises a fuselage 2 and propulsion systems 3. In the example illustrated in the figure, the propulsion systems are fixed under the wings of the aircraft. However, this characteristic is not limiting of the invention which also covers other arrangements of the propulsion systems, which can in particular be fixed on the wings of the aircraft, integrated into the wings, be fixed to the fuselage, etc.

[0010] A propulsion system 3 of an aircraft, as illustrated in the figures 2A à 5B , comprises a nacelle 20 which houses an electricity production system 10, which comprises a set of fuel cells 15 labeled FC in the figure (for “Fuel Cells” in English) as well as a set 14 of equipment auxiliary to the fuel cells, labeled BOP in the figure (for “Balance Of Plant” in English). The nacelle 20 also houses at least one electric motor 16 supplied with electricity by at least part of the fuel cells (by electrical connections not shown in the figures). The nacelle comprises an air circulation channel 22 provided to allow the electricity production system 10 to be cooled. The air circulation channel receives a heat exchanger 30 provided to allow the electricity production system 10 to be cooled.The air circulation channel 22 extends inside the nacelle 20 from a first end 25 of said air circulation channel located at a first longitudinal end 24 of the nacelle. At least a portion of the air circulation channel 22, contiguous to the first end 25 of the air circulation channel, is delimited by an outer surface 28 of cylindrical shape surrounding the longitudinal axis X of the nacelle 20. This cylindrical shape preferably corresponds to a cylinder with a circular base (cylinder of revolution) or an elliptical base. This makes it possible to have a symmetry of the nacelle 20 with respect to its longitudinal axis X in order to minimize the drag of the nacelle. The propulsion system 3 further comprises a propulsion propeller 18 mechanically coupled to the at least one electric motor 16. This propulsion propeller is located near the first longitudinal end 24 of the nacelle.In a particular and non-limiting manner of the invention, the propulsion propeller 18 can be mechanically coupled to the at least one electric motor 16 via a reducer or a gearbox.

[0011] Advantageously, in at least one part 35 of the nacelle, considered along the length of the nacelle, the air circulation channel 22 is unique, of circular section and houses a fan 12 provided to promote the circulation of air in this air circulation channel. Preferably, as shown in the figures, this circular section is centered on the longitudinal axis of the nacelle. In particular, the fan 12 is housed in the air circulation channel 22, between the first end 25 of the air circulation channel and the heat exchanger 30.

[0012] Advantageously, the nacelle 20 houses a tank 40 of dihydrogen H2, also called hydrogen in the remainder of the description. In particular, the hydrogen is stored in the liquid state in the tank 40, labeled LH2 in the figures. The hydrogen contained in the tank 40 makes it possible to supply the fuel cells 15 with hydrogen. However, without departing from the scope of the invention, the propulsion system 3 may not include such a hydrogen tank. The fuel cells 15 are then supplied with hydrogen from a hydrogen tank external to the propulsion system 3, for example a hydrogen tank located in the fuselage 2 or in a wing of the aircraft.

[0013] In the various figures, the broken line arrows illustrate the direction of air circulation in the air circulation channel 22. The thick line arrows, marked with the symbol F and parallel to the longitudinal axis X of the nacelle 20, illustrate the orientation of the nacelle 20 when it is installed on an aircraft 1: the tip of an arrow F indicates the front of the nacelle (on the left in the figures) when the aircraft is in flight. The length of the nacelle extends between its first longitudinal end 24 and a second longitudinal end 26. In the remainder of the description, the concepts of front and rear are expressed relative to the direction of forward movement of the aircraft 1 when it is in flight.

[0014] In the first embodiment illustrated in the figure 2A , as well as in the third embodiment illustrated in the figure 4A , the propulsion propeller 18 is rotatably mounted around the nacelle 20, close to its first longitudinal end 24. The electric motor (or a set of electric motors) 16 is arranged in the shape of a crown at the periphery of the nacelle (in a plane perpendicular to the longitudinal axis X of the nacelle). A stator S of the motor 16 is secured to the nacelle. Blades of the propulsion propeller 18 are secured to a rotor R designed to rotate around the stator S during operation of the motor 16. This arrangement of the propulsion propeller 18 and the electric motor 16 has the advantage of not requiring the integration of any motorization element inside the first end 25 of the air circulation channel 22 which is thus completely free for the circulation of air.

[0015] In a variant not shown in the figure, the blades of the propulsion propeller are mounted integrally with a crown mounted to rotate around the nacelle. This crown is mechanically coupled to the at least one motor 16 by a gear system.

[0016] In an advantageous embodiment illustrated in the figure 2C , the propulsion system 3 comprises an air flow adjustment device 32 associated with the first end 25 of the air circulation channel 22. This device 32 is designed to be moved in translation along the longitudinal axis X of the nacelle 20, as illustrated by the bidirectional arrow T. The position of the device 32 is controlled so as to optimize the flow of cooling air in the air circulation channel 22 according to the need for cooling, in order to minimize as much as possible the aerodynamic drag of the nacelle. The mechanical connections between the device 32 and the nacelle are not shown in the figure. A translation (to the right in the figure) of the device 32 having the effect of bringing it closer to the first end 25 of the air circulation channel 22 makes it possible to reduce the air flow in the air circulation channel 22.A translation (to the left in the figure) of the device 32 having the effect of moving it away from the first end 25 of the air circulation channel 22 makes it possible to increase the air flow in the air circulation channel 22. The air flow adjustment device 32 corresponds for example to a shutter (“plug” or “spinner” in English) provided to partially close the first end 25 of the air circulation channel 22 when it is brought closer to said end.

[0017] In the second embodiment illustrated in the figure 3A , as well as in the fourth embodiment illustrated in the figure 5A , the propulsion propeller 18 is mounted integral with a drive shaft 19 whose longitudinal axis corresponds to the longitudinal axis X of the nacelle 20. The drive shaft 19 is mechanically coupled to the at least one electric motor 16, which is integrated into a motor system 31. In a particular embodiment, the motor system 31 further comprises a gearbox not shown in the figures. When the propulsion system 3 comprises several electric motors 16, the drive shaft 19 is mechanically coupled to these electric motors via the gearbox.

[0018] The engine system 31 is mounted at least partly inside the nacelle 20, at its first end 24, centered on the longitudinal axis X of the nacelle. Thus, the first end 25 of the air circulation channel 22 is such that the outer surface 28 of the air circulation channel 22, of cylindrical shape, surrounds the engine system 31. Advantageously, the engine system 31 comprises a fairing provided to facilitate the flow of air along said engine system. When the outer surface 28 of the air circulation channel 22 is of circular cylindrical shape, a section of the air circulation channel 22 through a plane perpendicular to the longitudinal axis X of the nacelle is then crown-shaped. At its first end 25, the air circulation channel is then comprised between its outer surface 28 on the one hand and the engine system 31 on the other hand.In order not to overload the figures, the mechanical connections between the engine system 31 and the nacelle are not shown. In operation, the rotation of the propulsion propeller 18 promotes the introduction of air into the first end 25 of the air circulation channel 22. The air circulates in the air circulation channel 22, between the cylindrical outer surface 28 and the engine system 31. The air then arrives in the part 35 of the air circulation channel 22 in which the air circulation channel 22 is single, of circular section and comprises the fan 12. The fan 12 promotes the circulation of air in the air circulation channel.

[0019] In the first embodiment illustrated in the figure 2A , as well as in the second embodiment illustrated in the figure 3A , a second end 27b of the air circulation channel 22 opens through a side wall 21 of the nacelle, between the first longitudinal end 24 of the nacelle and a second longitudinal end 26 of the nacelle, opposite the first longitudinal end of the nacelle. The second end 27b is for example scoop-shaped. The heat exchanger 30 is installed between the part 35 of the air circulation channel 22 and its second end 27b. According to a first alternative, the second end 27b of the air circulation channel 22 extends substantially over the entire perimeter of the side wall 21 of the nacelle. The heat exchanger 30 is then installed in a part of the air circulation channel 22 in which a section of the air circulation channel by a plane perpendicular to the longitudinal axis of the nacelle is crown-shaped.According to a second alternative, the air circulation channel 22 comprises several independent branches between its part 35 and its second end 27b. The second end 27b then comprises several independent parts distributed along the perimeter of the side wall 21 of the nacelle. The different independent parts each correspond to one of the branches of the air circulation channel 22 and they are preferably distributed symmetrically over the perimeter of the side wall 21 of the nacelle. The heat exchanger 30 then comprises several parts arranged in the different branches of the air circulation channel 22. In a variant, the heat exchanger 30 is installed in a part of the air circulation channel in which the air circulation channel is of circular section, for example in the part 35.

[0020] When the nacelle 20 houses a hydrogen tank 40, this hydrogen tank is for example housed in a part of the nacelle between the second end 27b of the air circulation channel 22 and the second longitudinal end 26 of the nacelle. In particular, as shown in the figures 2A And 3A , the fuel cell assembly 15 as well as the assembly 14 of auxiliary equipment are also housed in the part of the nacelle between the second end 27b of the air circulation channel 22 and the second longitudinal end 26 of the nacelle.

[0021] In a particular and non-limiting manner of the invention, the propulsion system 3 comprises an air flow adjustment device, not shown in the figures, associated with the second end 27b of the air circulation channel 22. This air flow adjustment device corresponds for example to a set of flaps whose position can be adjusted to vary the air flow in the air circulation channel 22, in particular according to the cooling requirements of the electricity production system 10.

[0022] In the third embodiment illustrated in the figure 4A , the air circulation channel is cylindrical in shape and extends along the length of the nacelle, between the first end 25 of the air circulation channel 22 and a second end 27a of the air circulation channel opening near a second longitudinal end 26 of the nacelle, opposite the first longitudinal end 24 of the nacelle. When this cylindrical shape is of circular section, the part 35 of the air circulation channel 22 then extends over almost the entire length of the nacelle 20. The heat exchanger 30 is then of circular section. The cylindrical shape of the air circulation channel 22 makes it possible to promote the flow of air in this air circulation channel and consequently to improve the cooling of the electricity production system 10. Advantageously, the propulsion system 3 comprises a device 33 for adjusting the air flow rate associated with the second end 27a of the air circulation channel 22.This air flow adjustment device 33 corresponds for example to a set of flaps whose position can be adjusted to vary the air flow in the air circulation channel 22, in particular depending on the cooling requirement of the electricity production system 10. The fuel cells 15 and the set of auxiliary equipment 14 are housed in the nacelle around the air circulation channel 22, between the air circulation channel 22 and the side wall 21 of the nacelle.

[0023] In the fourth embodiment illustrated in the figure 5A , the air circulation channel 22 is similar to that of the third embodiment, except with regard to the first end 25 already described.

[0024] On the figures 2A , 3A , 4A And 5Aalready described, the first end 24 of the nacelle corresponds to the front of the nacelle and the second end 26 corresponds to the rear of the nacelle. The propulsion propeller 18 is therefore located close to the front of the nacelle. In operation, the air enters the air circulation channel 22 through the first end 25 and exits through the second end 27a or 27b. The air exits through the second end 27a or 27b after being heated by the heat exchanger 30, which makes it possible to create an auxiliary thrust, additional to the main thrust produced by the propulsion propeller.

[0025] THE figures 2B , 3B , 4B And 5B correspond to variants of the embodiments illustrated on the figures 2A , 3A , 4A And 5A, in which the first end 24 of the nacelle corresponds to the rear of the nacelle and the second end 26 corresponds to the front of the nacelle. The propulsion propeller 18 is therefore located near the rear of the nacelle. In operation, the air enters the air circulation channel 22 through the second end 27a or 27b and exits through the first end 25. The air exits through the first end 25 after having been heated by the heat exchanger 30, which makes it possible to create an auxiliary thrust, additional to the main thrust produced by the propulsion propeller.

[0026] In a particular embodiment, the propulsion system 3 comprises two propulsion propellers mounted counter-rotating close to each other.

[0027] In another embodiment, in addition to the propulsion propeller 18, the propulsion system 3 comprises a propeller mounted fixed relative to the nacelle, close to the propulsion propeller.

Claims

1. Propulsion system (3) of an aircraft (1), comprising: - a system for producing electricity (10) comprising a set of fuel cells (15); - at least one electric motor (16) supplied with electricity by at least some of the fuel cells; - a propeller (18) mechanically coupled to the at least one electric motor; and - a nacelle (20) housing at least the system for producing electricity (10) and the at least one electric motor (16), said nacelle comprising an air circulation channel (22) provided to allow the system for producing electricity (10) to be cooled, wherein: - the air circulation channel (22) extends inside the nacelle from a first end (25) of said air circulation channel that is situated at a first longitudinal end (24) of the nacelle (20); - the air circulation channel receives a heat exchanger (30) provided to allow the system for producing electricity (10) to be cooled; and - the propeller (18) is situated near the first longitudinal end (24) of the nacelle, characterized in that at least a part of the air circulation channel that is contiguous with the first end of the air circulation channel is delimited by an outer surface (28) of cylindrical shape that surrounds the longitudinal axis (X) of the nacelle, the outer surface (28) being situated inside the nacelle.

2. Propulsion system according to Claim 1, characterized in that in at least a part (35) of the nacelle, considered along the length of the nacelle, there is only one air circulation channel (22), which is of circular section and houses a fan (12) provided to promote the circulation of air in this air circulation channel.

3. Propulsion system according to Claim 2, characterized in that the fan (12) is housed in the air circulation channel, between the first end (25) of the air circulation channel and the heat exchanger (30).

4. Propulsion system according to one of Claims 1 to 3, characterized in that the propeller (18) is mounted so as to be able to rotate about the nacelle (20).

5. Propulsion system according to the preceding claim, characterized in that it comprises a device for adjusting the air flow rate (32), which is associated with the first end (25) of the air circulation channel.

6. Propulsion system according to one of Claims 1 to 3, characterized in that the propeller (18) is mounted secured to a drive shaft (19), of which the longitudinal axis corresponds to the longitudinal axis of the nacelle.

7. Propulsion system according to any one of the preceding claims, characterized in that the heat exchanger (30) is installed in a part of the air circulation channel (22), in which a section of the air circulation channel on a plane perpendicular to the longitudinal axis of the nacelle is in the shape of a ring.

8. Propulsion system according to any one of Claims 1 to 6, characterized in that the heat exchanger (30) is installed in a part of the air circulation channel, in which the air circulation channel is of circular section.

9. Propulsion system according to the preceding claim, characterized in that the air circulation channel is of cylindrical shape and extends along the length of the nacelle, between the first end (25) of the air circulation channel and a second end (27a) of the air circulation channel that opens near a second longitudinal end (26) of the nacelle, which is opposite the first longitudinal end (24) of the nacelle.

10. Propulsion system according to any one of Claims 1 to 8, characterized in that a second end (27b) of the air circulation channel (22) opens through a lateral wall (21) of the nacelle, between the first longitudinal end (24) of the nacelle and a second longitudinal end (26) of the nacelle, which is opposite the first longitudinal end of the nacelle.

11. Propulsion system according to the preceding claim, characterized in that it has a hydrogen reservoir (40) housed in the nacelle between the second end (27b) of the air circulation channel and the second longitudinal end (26) of the nacelle.

12. Propulsion system according to any one of the preceding claims, characterized in that it comprises a device (33) for adjusting the air flow rate, which is associated with the second end (27a, 27b) of the air circulation channel (22).

13. Propulsion system according to any one of the preceding claims, characterized in that the first longitudinal end (24) of the nacelle corresponds to a front longitudinal end of the nacelle.

14. Propulsion system according to any one of Claims 1 to 12, characterized in that the first longitudinal end (24) of the nacelle corresponds to a rear longitudinal end of the nacelle.

15. Aircraft, characterized in that it comprises a propulsion system (3) according to any one of the preceding claims.