Fuel Cell Systems

Abstract

The system 1 comprises a fuel cell stack 100, a cooling fluid tank 305, a heat exchanger 320, an exhaust 325, a controller 395, and a valve 315 having an inlet 316 and first and second outlets 317, 318. Cooling fluid is transported from the tank to the stack through a supply line 340 and from the stack to the inlet through a discharge line 345. The controller controls the valve to either discharge the cooling fluid at the first outlet so that it returns to the tank on a recirculation line 330 via the heat exchanger, or discharge the cooling fluid at the second outlet so that it flows to the exhaust and leaves the system. The controller is configured to select the first or second outlet depending on the heat load required across the stack and the heat load available across the heat exchanger. The gravimetric power density of the system is higher than that of a comparable system with only closed circuit cooling.

Description

[Technical field]

[0001] The present invention relates to fuel cell systems, and more particularly to cooling subsystems within fuel cell systems, such as, but not limited to, hydrogen fuel cell systems. [Background technology]

[0002] Thermal management of a fuel cell (FC) can be provided by a separate cooling circuit forming part of the fuel cell system or by evaporative cooling.

[0003] When a separate cooling circuit is used for thermal management of the fuel cells, liquid water or other coolant circulates through flow paths in the stack of fuel cells of the fuel cell system such that heat generated in the fuel cell stack is transferred to the coolant, which then flows out of the fuel cell stack. The heat transferred to the coolant in the fuel cell stack is then removed from the cooling circuit, for example via a heat exchanger (HEX) which acts as a radiator to release heat to the surrounding air. In such a system, the air supply to the fuel cells used in the fuel cell reaction is a separate circuit, which flows into a separate flow path of the fuel cell stack.

[0004] When evaporative cooling is used for the thermal management of the fuel cell, the cooling water and air supplies for the fuel cell reaction are fed into the same flow path of the fuel cell stack. The fuel cell stack is cooled by transferring thermal energy from the fuel cell stack to the water, resulting in evaporation. The ratio of water to air fed into the fuel cell stack is such that the air leaving the fuel cell stack is saturated with water vapor and contains entrained water droplets. For example, the water vapor contained in the fuel cell stack outlet is condensed and the moisture is removed by connecting the fuel cell stack outlet to a coolant-air heat exchanger (i.e., a radiator).

[0005] A major problem with any method for managing fuel cell heat is the need to dissipate low-quality heat from the coolant to the surroundings.

[0006] This problem becomes even more severe when the fuel cell system is used in flight. The heat generated by the fuel cell stack is proportional to the operating current (and therefore power) of the fuel cell stack. The power demand and therefore heat generation for a fuel cell stack used in an aircraft is greatest during takeoff and initial climb, e.g., when the aircraft is at its maximum takeoff weight (MTOW). As the aircraft gains altitude, the ambient air temperature to which the aircraft is exposed decreases. However, since the times when high power is required generally coincide with the times when the aircraft is at altitudes lower than its cruising altitude, the heat generated by the fuel cell stack is highest when the ambient air temperature is relatively higher than the average temperature during the aircraft's flight. This occurs especially when the aircraft takes off when the ambient air temperature on the ground is high (high air temperature).

[0007] Typically, in a closed circuit cooling subsystem, the above problems are solved by providing a large heat transfer area to the heat exchanger, thus providing a high heat load to sufficiently cool the coolant, and / or by providing a large amount of coolant in the cooling subsystem such that the hot coolant leaving the fuel cell stack matches the negligible thermal mass of the coolant subsystem.

[0008] The heat load across a heat exchanger depends heavily on the temperature difference between the fluids on either side of the heat exchanger; the greater the temperature difference, the greater the heat load. Therefore, an aircraft fuel cell system having a cooling subsystem that lowers the temperature of the coolant with a heat exchanger that transfers heat from the coolant to the surroundings (i.e., as a radiator) must base the heat exchanger and coolant volumes on maximum takeoff weight at high temperatures to ensure that the cooling subsystem can keep the fuel cell stack adequately cool. As a result, the sizing criteria, for example, the heat exchanger and coolant volumes are significantly larger than in the case of maximum takeoff weight but not high ambient temperatures, which is the average for aircraft use.

[0009] Aircraft fuel cell systems with cooling subsystems equipped with large heat exchangers are problematic because such heat exchangers are heavy, expensive, and create significant resistance. Similarly, the use of a large volume of coolant obviously means that the coolant occupies more space inside the aircraft, potentially requiring larger aircraft dimensions, which increases the aircraft's mass. These problems become more severe as aircraft power increases, requiring larger heat exchanger dimensions and coolant volumes.

[0010] An additional problem with evaporative cooling systems is that the amount of water that can evaporate within the fuel cell stack per unit of air is limited based on the water saturation point of the air. The humidity and pressure of the incoming air are ideally set low to maximize the amount of water that can evaporate. However, low air pressure is undesirable because it slows down the reaction rates within the fuel cells, adversely affecting the efficiency and performance of the fuel cell system.

[0011] The present invention has been devised with these considerations in mind. Summary of the Invention [Means for solving the problem]

[0012] It is desirable to provide a fuel cell system having a cooling subsystem in which a heat exchanger of the cooling subsystem used to reject heat transferred to the coolant to the surrounding air is sized regardless of maximum ambient air temperature and maximum fuel cell power (e.g., maximum takeoff weight at high temperatures).

[0013] Thus, in a first aspect, the invention provides a fuel cell comprising: A fuel cell stack; a cooling subsystem, The cooling subsystem includes: A coolant tank; a stack supply line extending from the coolant tank to the fuel cell stack, the stack supply line having a pump disposed thereon for pumping coolant from the tank through the stack supply line to the fuel cell stack; a valve network including a first multi-outlet valve arrangement having a first valve inlet, a first valve outlet, and a second valve outlet; A coolant heat exchanger; A coolant exhaust system; a stack exhaust line extending from the fuel cell stack to the first valve inlet for removing coolant from the fuel cell stack; a first recirculation line extending from the first valve outlet to the coolant tank, a first side of the coolant heat exchanger being disposed in the first recirculation line, and heat being removed from the coolant recirculated through the first recirculation line; a exhaust line extending from the second valve outlet to the coolant exhaust device; The first multi-outlet valve device comprises: a first state in which a first valve outlet is open and the second valve outlet is closed, thereby providing a closed circuit cooling subsystem in which a coolant passageway is opened from the first multi-valve arrangement through the coolant heat exchanger to the coolant tank and a coolant passageway is closed from the first multi-valve arrangement to the coolant exhaust arrangement; a second state in which the first valve outlet is closed and the second valve outlet is open, thereby providing an open-ventilation cooling subsystem in which a coolant passageway is open from the first multi-valve arrangement to the coolant exhaust arrangement and a coolant passageway is closed from the first multi-valve arrangement through the coolant heat exchanger to the coolant tank; The fuel cell, wherein the cooling subsystem further comprises a computer-based controller that controls the valve network and switches the first multi-outlet valve device between the first state and the second state based on a balance between the cooling subsystem's required heat load across the fuel cell stack and the cooling subsystem's available heat load across the coolant heat exchanger.

[0014] This configuration of the fuel cell system, and in particular the cooling subsystem, allows the coolant heat exchanger to be sized for operating conditions that do not take into account maximum take-off weight at high temperatures, by having an exhaust line and a first multi-outlet valve arrangement that allows the cooling system to operate as a closed circuit system or an open-ventilation subsystem. Thus, for operating conditions such as maximum take-off weight at high temperatures or similar conditions where the coolant heat exchanger may be too small for the cooling subsystem to operate as a closed circuit, but still provide the cooling required for the fuel cell stack, the cooling subsystem can be operated as an open-ventilation subsystem where the coolant exiting the fuel cell stack is exhausted from the cooling subsystem and no load is placed on the coolant heat exchanger. Also, for operating conditions such as maximum take-off weight at high temperatures or similar conditions where the coolant heat exchanger is large enough for the cooling subsystem to operate as a closed circuit subsystem and provide the cooling required by the fuel cell stack, the first multi-outlet valve arrangement can be set to recirculate the coolant exiting the fuel cell stack through the coolant heat exchanger. Thus, the minimum heat transfer area of ​​the coolant heat exchanger required to provide the required cooling to the fuel cell stack so that it does not overheat is less than the minimum heat transfer area in a conventional cooling subsystem that does not have the ability to operate as an open-ventilation cooling subsystem.

[0015] Several optional features herein are described below, which may be applied alone or in any combination with the aspects herein, except where such combinations are expressly unacceptable or expressly avoided.

[0016] Typically, the cooling subsystem controller is also configured to switch the first multi-outlet valve arrangement from the first state to the second state in response to an increase in the cooling subsystem required heat load across the fuel cell stack and / or a decrease in the cooling subsystem available heat load across the coolant heat exchanger. Additionally, the controller is also typically configured to switch the first multi-outlet valve arrangement from the second state to the first state in response to a decrease in the cooling subsystem required heat load across the fuel cell stack and / or an increase in the cooling subsystem available heat load across the coolant heat exchanger. A controller configured in this manner assists the cooling subsystem in providing the required heat load to the entire fuel cell stack while at the same time reducing the amount of coolant exhausted from the cooling subsystem via the exhaust device by avoiding unnecessarily operating with the first multi-outlet valve arrangement in the second state.

[0017] The first multi-outlet valve arrangement may be configured to have a third state providing a cooling subsystem in which the first and second valve outlets are both open and a coolant passageway is open from the first multi-valve arrangement through the coolant heat exchanger to the coolant tank. Such a first multi-outlet valve arrangement having a third state is advantageous because it can reduce the amount of coolant discharged from the cooling subsystem during operation of the fuel cell system because, when transitioning from an open-ventilation cooling subsystem to a closed-circuit cooling subsystem, recirculation of some of the coolant can begin before the available heat load across the coolant heat exchanger is large enough for all of the coolant to be recirculated and still meet the required heat load of the cooling subsystem across the fuel cell stack. The controller may be configured to switch the first multi-outlet valve arrangement between three states, including the first state, the second state and the third state, depending on a balance between the required heat load of the cooling subsystem across the fuel cell stack and the available heat load of the cooling subsystem across the coolant heat exchanger. The controller configured in this manner can reduce the amount of coolant discharged from the cooling subsystem during operation of the fuel cell system, as described above, and can provide an additional control variable to the cooling subsystem by setting the first multi-outlet valve arrangement to a third state.

[0018] Typically, the cooling subsystem is configured to use water as the coolant, which is practical if the system is configured to exhaust the coolant from the cooling subsystem to the environment via an exhaust device.

[0019] The fuel cell system may further include a cathode subsystem having an air supply line for supplying air to the fuel cell stack and an air exhaust line for removing air from the fuel cell stack, and an anode subsystem having a fuel supply line for supplying fuel to the fuel cell stack. Such a fuel cell system may provide reactants for the fuel cell reaction to the fuel cell stack.

[0020] The cooling subsystem of the fuel cell system may further include a moisture separator disposed in the air exhaust line to recover moisture from the air removed from the fuel cell stack, and a second recirculation line extending from the moisture separator to the coolant tank. Such a fuel cell system may allow separation of water from the air exhaust line and recirculate the water to the cooling subsystem. The cooling subsystem may be doped with water to compensate for water discharged from the system through the discharge device when operating with the first multi-outlet valve arrangement in the second state, and the size of the coolant tank and the initial amount of coolant in the system may be smaller than without the dosing of water.

[0021] Optionally, the fuel cell system may be configured such that the valve network further comprises a second multi-outlet valve arrangement having a second valve inlet, a third valve outlet, and a fourth valve outlet, the second valve inlet and the fourth valve outlet being disposed in a stack supply line, and a first multi-inlet valve arrangement having a third valve inlet, a fourth valve inlet, and a fifth valve outlet, the third valve inlet and the fifth valve outlet being disposed in a stack exhaust line. Correspondingly, the cooling subsystem may further comprise a gas pre-treatment line extending from the third valve outlet to the fourth valve inlet. The controller may be configured to control the valve network to switch the second multi-outlet valve arrangement and the first multi-inlet valve arrangement between an open state in which the third valve outlet and the fourth valve inlet are opened to open the coolant passage through the gas pre-treatment line, and a closed state in which the third valve outlet and the fourth valve inlet are closed to close the coolant passage through the gas pre-treatment line. The cathode side subsystem may further include a cathode side heat exchanger, a first side of which is disposed in the air supply line, and a second side of which is disposed in the gas pre-treatment line between the third valve outlet and the fourth valve inlet. Similarly, the anode side subsystem may further include an anode side heat exchanger, a first side of which is disposed in the fuel supply line, and a second side of which is disposed in the gas pre-treatment line between the third valve outlet and the fourth valve inlet. The controller may be configured to open or close the gas pre-treatment line based on a balance of any two or more of the required heat load of the cooling subsystem (300) across the fuel cell stack, the available heat load of the cooling subsystem (300) across the coolant heat exchanger, and the desired adjustment of the compressed air and / or fuel flow. Advantageously, such a fuel cell system allows the cooling subsystem to pre-cool and adjust the humidity of the air entering the fuel cell stack via the air supply line, and / or pre-adjust the temperature of the fuel entering the fuel cell stack via the fuel supply line, thereby improving performance and control of the fuel cell stack.

[0022] Typically, the cooling subsystem includes a deionizer for the coolant, which may be located in the stack supply line. The deionizer serves to reduce the concentration of certain ions in the coolant entering the coolant flow passages of the fuel cell stack, thereby reducing damage to the fuel cell stack, for example by minimizing short circuits and electrical leakage. In particular, when water is sent from the water separator to the cooling subsystem, the deionizer is preferably located in the stack supply line so that the coolant is deionized just before it enters the fuel cell stack.

[0023] The cooling subsystem of the fuel cell system may further comprise a heat exchanger bypass line extending from the stack exhaust or exhaust line to a location on the first recirculation line downstream of the coolant heat exchanger. The controller may also be configured to open or close the heat exchanger bypass line based on a balance between the required heat load of the cooling subsystem across the fuel cell stack and the available heat load of the cooling subsystem across the coolant heat exchanger. Typically, the controller is configured to close the heat exchanger bypass line when the first multi-outlet valve arrangement is switched to the second state. Thus, an additional control variable of the cooling subsystem is provided by facilitating bypass of the coolant heat exchanger while allowing the cooling subsystem to operate as a closed circuit cooling subsystem. Optionally, the controller may be configured to allow the heat exchanger bypass line to be partially opened such that the coolant passages through the coolant heat exchanger and the coolant passages through the heat exchanger bypass line are simultaneously open. In this manner, additional control over the fuel cell system is facilitated.

[0024] Optionally, the cooling subsystem may further include an anti-icing coolant circuit extending from and returning to the first recirculation line. The anti-icing coolant circuit delivers coolant heated by the fuel cell stack to the aircraft's anti-icing system where the heated coolant loses heat before returning to the first recirculation line to anti-icing the aircraft. Advantageously, in conjunction with the cooling heat exchanger, the anti-icing coolant circuit provides the cooling subsystem with another method of rejecting heat to the environment while reducing the amount of energy input to the anti-icing system, improving the efficiency of the vehicle. Typically, the anti-icing coolant circuit is connected to the first recirculation line in parallel with the coolant heat exchanger, providing an additional control variable for the cooling subsystem.

[0025] Typically, the coolant exhaust system includes an exhaust nozzle that assists the cooling subsystem in ensuring that the coolant flowing through the exhaust line is expelled from the cooling subsystem.

[0026] The fuel cell stack may comprise a plurality of proton exchange membrane fuel cells (PEMFCs). Fuel cell stacks with proton exchange membrane fuel cells are advantageous because they are lighter and have a higher energy density than fuel cell stacks with other types of fuel cells.

[0027] Typically, a fuel cell system may include a fuel cell stack that is a hydrogen fuel cell stack. Fuel cell systems having a fuel cell stack that uses hydrogen as a fuel source are advantageous in that the only chemical species produced by the reaction in the fuel cell stack is water.

[0028] Typically, the coolant heat exchanger is an air-cooled heat exchanger with a second side exposed to an outside air stream (e.g., an aircraft's outside air stream) that receives heat from the coolant, thereby simplifying the cooling subsystem compared to using other types of heat exchangers as the coolant heat exchanger.

[0029] In a second aspect, there is provided a propulsion device comprising the fuel cell system of the first aspect and an electric propulsion device, the fuel cell system further comprising a power subsystem for harvesting power generated by the fuel cell stack, the power subsystem being electrically connected to the propulsion device and for supplying the generated power to the propulsion device. Advantageously, such a propulsion device can be made lighter and smaller than a fuel cell powered propulsion device that does not have a cooling subsystem that can operate as an open-ventilation cooling subsystem, because the coolant heat exchanger of the propulsion device of the second aspect can be made lighter and smaller.

[0030] Such a propulsion device can be used as an aircraft thruster. Indeed, in a third aspect, there is provided an aircraft equipped with a second propulsion device.

[0031] In a fourth aspect, there is provided a method of operating the fuel cell system of the first aspect, the method comprising: operating the cooling subsystem as a closed circuit cooling subsystem by switching the first multi-valve arrangement to a first state such that a coolant passageway is open from the first multi-valve arrangement through the coolant heat exchanger to the coolant tank and a coolant passageway is closed from the first multi-valve arrangement to the coolant exhaust arrangement; and switching the first multi-outlet valve arrangement to a second state to operate the cooling subsystem as an open-vent cooling subsystem in which a coolant passageway from the first multi-valve arrangement to the coolant exhaust arrangement is open and a coolant passageway from the first multi-valve arrangement through the coolant heat exchanger to the coolant tank is closed; Switching of the first multi-outlet valve arrangement between the first and second states is performed in response to a required cooling subsystem heat load across the fuel cell stack and an available cooling subsystem heat load across the coolant heat exchanger, thereby advantageously providing the fuel cell stack with the cooling it requires during operation while simultaneously sizing the coolant heat exchanger of the cooling subsystem independent of maximum takeoff weight requirements at high temperatures.

[0032] Optionally, the method may further comprise operating the cooling subsystem in a third state by switching the first multi-valve arrangement to an open coolant passage from the first multi-valve arrangement to the coolant exhaust arrangement and also to a coolant passage from the first multi-valve arrangement to a coolant tank via the coolant heat exchanger. Switching the first multi-outlet valve arrangement to and from the third state is performed in response to the required heat load of the cooling subsystem across the fuel cell stack and the available heat load of the cooling subsystem across the coolant heat exchanger. Operating the cooling subsystem of the first multi-outlet valve arrangement in the third state may advantageously reduce the amount of coolant discharged from the cooling subsystem during operation of the fuel cell system because, during the transition from an open-ventilation cooling subsystem to a closed circuit subsystem, recirculation of a portion of the coolant may begin before the available heat load across the coolant heat exchanger is large enough to recirculate all the coolant while simultaneously satisfying the required heat load of the cooling subsystem across the fuel cell stack.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments and experiments illustrating the principles of the present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a process flow diagram including a fuel cell system. [Diagram 2] FIG. 1 is a process flow diagram including another fuel cell system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Aspects and embodiments of the present invention will be described with reference to the accompanying drawings. Other aspects and embodiments will be readily apparent to those skilled in the art. All documents cited herein are incorporated by reference.

[0036] The features disclosed in the above, claims, or accompanying drawings, which may be described in a specific form or in terms of means for performing a disclosed function or methods or steps for obtaining a disclosed result, may be used, individually or in any combination as appropriate, to realise the invention in diverse forms thereof.

[0037] FIG. 1 is a process flow diagram including a fuel cell system 1. The fuel cell system 1 includes a fuel cell stack 100 and four subsystems, including a cathode side subsystem 200, a cooling subsystem 300, an anode side subsystem 400, and a power subsystem 500. The fuel cell stack 100 itself includes a number of fuel cells, each of which has an anode side and a cathode side. Typically, the fuel cells forming the fuel cell stack 100 are proton exchange membrane fuel cells (PEMFCs). The cathode and anode inlets of each fuel cell, which can supply reactants for the fuel cell reaction, may be connected to a common anode inlet and cathode inlet, respectively, of the fuel cell stack 100. Thus, the fuel cell stack 100 itself essentially has a cathode side 102 and an anode side 104.

[0038] The cathode side subsystem 200 and the anode side subsystem 400 interact with the cathode side 102 and the anode side 104 of the fuel cell stack 100, respectively. The cooling subsystem 300 is configured to manage heat generated in the fuel cell stack 100 by the fuel cell reaction. Specifically, the cooling subsystem 300 passes the coolant through the fuel cell stack 100, transferring heat from the fuel cell stack 100 to the coolant, which then flows out of the fuel cell stack 100. The power subsystem 500 is configured to provide a circuit connected to the cathode and anode of each fuel cell, such that a voltage generated by the fuel cell reaction causes a current to flow through the circuit for harvesting power generated by the fuel cell stack.

[0039] The fuel cell system 1 is configured to perform a fuel cell reaction of a fuel, such as hydrogen or oxygen. Accordingly, the cathode subsystem 200 is configured to deliver air to the cathode side 102 of the fuel cell stack 100 for the fuel cell reaction via an air supply line 216. The air entering the cathode subsystem 200 first passes through a filter 205 to remove any contaminants in the incoming air before being compressed to a higher pressure by the compressor 210. Compressing the air prior to the fuel cell stack 100 can improve the reaction rate of the fuel cell reaction, thereby improving the efficiency and performance of the fuel cell stack 100. The compressed air leaving the compressor 210 travels to a humidifier 215 before entering the cathode side 102 of the fuel cell stack 100 via the air supply line 216. The humidifier 215 humidifies the compressed air flowing through the air supply line 216 before the compressed air enters the fuel cell stack 100. A purge line is also provided extending from the humidifier 215.

[0040] The airflow leaving the cathode side 102 of the fuel cell stack 100 in an air exhaust line 217 passes through a humidifier 215 arranged in the air exhaust line 217 so that the compressed air in the air supply line 216 can be humidified by water formed in the fuel cell stack 100. The airflow then enters a turbine 220 arranged in the air exhaust line 217. The airflow in the air exhaust line 217 expands in the turbine 220. Advantageously, the mechanical action of this expansion powers, in part, the compressor 210 via a turbocharger arrangement in which the turbine 220 is mechanically connected to the compressor 210. A motor 225 is also provided in the turbocharger arrangement to make up the difference between the power provided by the turbine 220 and the power consumed by the compressor 210. The expanded airflow then leaves the fuel cell system 1 via the air exhaust line 217.

[0041] A humidifier typically includes a small water circuit and / or membrane that can deliver water from the air exhaust line 217 into the air supply line 216 .

[0042] The anode side subsystem 400 delivers fuel to the anode side 104 of the fuel cell stack 100 for fuel cell reaction. The fuel stream entering the fuel cell system 1 through the fuel supply line 401 is sent to an ejector 405 before entering the anode side 104. The fuel stream flows through the anode side 104 and exits the fuel cell stack 100 in an anode side exhaust stream. Typically, excess fuel is provided at the anode 104 of the fuel cell stack to improve reaction operation during transient operation. Therefore, the anode side exhaust stream, consisting of a mixture of unreacted fuel and reaction products, is recirculated to the anode inlet to allow optimal reactant flow. The fuel cell reaction typically produces water (potentially together with other reaction products). Thus, the anode side exhaust stream is sent to a water trap 410 to separate the water from the contents of the remaining fuel exhaust stream. The water captured in the water trap 410 is sent to a purge line together with a portion of the anode side exhaust stream, and the remaining anode side exhaust stream is recirculated to the ejector 405 in the fuel recycle stream. It can thus be seen that the ejector 405 takes the place of a pressure regulator for the fuel recycle flow and the fuel flow to the anode inlet.

[0043] The power subsystem 500 includes a direct current to high voltage direct current (HV DC / DC) converter 505 and a direct current to low voltage direct current (LV DC / DC) converter 510, which convert the direct current generated in the power subsystem 500 by the fuel cell reaction into a high voltage direct current and a low voltage direct current, respectively. This allows the fuel cell system 1 to provide both high voltage and low voltage direct current power outputs. The power subsystem 500 further includes a low voltage bus 515 and a DC / AC inverter 510, which converts the direct current generated in the power subsystem into an alternating current source. This alternating current source is sent from the inverter 510 to the motor 225 of the cathode side subsystem 200, which drives the compressor 210.

[0044] Heat is a by-product of the fuel cell reaction, and the cooling subsystem 300 is configured to manage heat generated in the fuel cell stack 100 by the fuel cell reaction. Specifically, the cooling subsystem 300 is configured to allow coolant to flow through the fuel cell stack 100, exchange heat from the fuel cell stack 100 to the coolant, and then allow the coolant to exit the fuel cell stack 100. The cooling subsystem includes a coolant tank 305 that contains a reservoir of coolant, typically water. A stack supply line 340 extends from the coolant tank 305 to the fuel cell stack 100. A pump 310 is disposed in the stack supply line 340 and pumps the coolant from the tank 305 to the fuel cell stack 100 via the stack supply line 340. As shown in FIG. 1, the pump 310 may be powered using low voltage power directed to the pump from a LV DC / DC converter 510 by a low voltage bus 515 of the power subsystem 500. The coolant exiting the pump then circulates through one or more coolant flow paths within the fuel cell stack 100 such that heat generated in the fuel cell stack 100 is transferred to the coolant before it exits the fuel cell stack 100 and reaches a stack exhaust line 345 that extends between the fuel cell stack 100 and the first valve inlet 316 of the first multi-outlet valve arrangement 315. Thus, heat is transferred out of the fuel cell stack 100 to the cooling subsystem 300.

[0045] The first multi-outlet valve arrangement 315 forms part of a valve network and includes a first valve outlet 317 and a second valve outlet 318 in addition to a first valve inlet 316. Although the first multi-outlet valve arrangement 315 depicted in FIG. 1 takes the form of a three-port valve, those skilled in the art will appreciate that the first multi-outlet valve arrangement 315 may be provided with any valve layout. A first recirculation line 330 extends from the first valve outlet 317 to the coolant tank 305 and defines a closed circuit within the cooling subsystem 300 that allows coolant pumped around the system from the coolant tank 305 to be recirculated back to the coolant tank 305. A first side of a coolant heat exchanger (HEX) 320 is disposed in the first recirculation line 330 to remove heat from the coolant recirculating through the first recirculation line 330.

[0046] The coolant heat exchanger 320 releases low quality heat transferred to the coolant in the fuel cell stack 100 to the surroundings so that the coolant passing through the first recirculation line 330 downstream of the coolant heat exchanger 320 is at a lower temperature than when it passed from the fuel cell stack 100 to the stack discharge line 345. As a result, the coolant recirculates around the closed circuit back to the fuel cell stack 100, transferring more heat from the fuel cell stack 100. Typically, the coolant heat exchanger 320 is an air-cooled heat exchanger, and the second side of the coolant heat exchanger is exposed to an external air flow that receives heat from the coolant (i.e., the heat exchanger is a radiator). Thus, the fuel cell system 1 may be ventilated to maintain a large temperature difference between the air around the coolant heat exchanger 320 and the coolant passing through the coolant heat exchanger 320, and to increase the heat transfer coefficient of the coolant heat exchanger 320, thereby increasing the obtainable heat load across the coolant heat exchanger 320.

[0047] The available heat load across the coolant heat exchanger 320 depends largely on the heat transfer area of ​​the coolant heat exchanger 320 and the temperature difference between the fluids on either side of the coolant heat exchanger 320. In the context of an aircraft, and in a cooling subsystem configured only to operate as a closed-loop cooling subsystem, the heat transfer area of ​​the coolant heat exchanger must be large enough to provide a heat load across the coolant heat exchanger that reduces the temperature of the coolant enough that the cooling subsystem can provide the required cooling to the fuel cell stack when the fuel cell system is operating under conditions of maximum takeoff weight at high air temperature. However, for the majority of the operating time of the fuel cell system, the fuel cell stack will operate without regard to these conditions. Thus, the coolant heat exchangers of conventional cooling subsystems are typically much larger, heavier, and more expensive than necessary to meet the average operating conditions of the fuel cell system in which they are included.

[0048] According to the fuel cell system 1 of the present invention, the problem of sizing the coolant heat exchanger 320 is solved by providing a coolant exhaust device 325 and an exhaust line 340 extending from the second valve outlet 318 to the coolant exhaust device 325, so that the cooling subsystem 300 discharges the coolant as a discharge fluid from the cooling subsystem 300. Thus, in addition to the closed circuit configuration, the cooling subsystem 300 of the present invention is also provided with an open-vent configuration. In such a fuel cell system 1, it is advantageous to use water as a coolant, since discharging water as a discharge fluid is less harmful to the environment than discharging other possible coolants, such as petroleum-based fluids and fluorocarbons. The first multi-outlet valve device 315 can be set to various states to control whether the cooling subsystem 300 operates only as a closed circuit cooling subsystem, only as an open-vent cooling subsystem, or as a combination of the two. The first multi-outlet valve arrangement 315 has a first state in which the first valve outlet 317 is open and the second valve outlet 318 is closed, thereby providing a closed circuit cooling subsystem 300 in which a coolant passageway is open from the first multi-outlet valve arrangement 315 through the coolant heat exchanger 320 to the coolant tank 305 and a coolant passageway is closed from the first multi-outlet valve arrangement 315 to the coolant exhaust arrangement 325. The first multi-outlet valve arrangement 315 also has a second state in which the first valve outlet 317 is closed and the second valve outlet 318 is open, thereby providing an open-ventilation cooling subsystem in which a coolant passageway is open from the first multi-outlet valve arrangement 315 to the coolant exhaust arrangement 325 and a coolant passageway is closed from the first multi-outlet valve arrangement 315 through the coolant heat exchanger 320 to the coolant tank 305.

[0049] As can be seen from the above description, for the first multi-outlet valve arrangement 315 to operate the cooling subsystem 300 in a first state, the temperature of the coolant across the coolant heat exchanger 320 must be sufficiently reduced such that the available heat load across the coolant heat exchanger 320 is large enough that the required heat load can be applied by the cooling subsystem 300 to the fuel cell stack 100. In contrast, for the first multi-outlet valve arrangement 315 to operate the cooling subsystem 300 in a second state, the coolant heat exchanger 320 is bypassed and the coolant exiting the fuel cell stack 100 is not recirculated to the coolant tank 305. Because the coolant exiting the fuel cell stack 100 is discharged from the cooling subsystem 300, low-quality heat that such coolant may have absorbed from the fuel cell stack 100 does not have to be discharged to the surroundings via the coolant heat exchanger 320.

[0050] The cooling subsystem 300 further comprises a computer-based controller 395 configured to control the valve network to switch the first multi-outlet valve arrangement 315 between a first state and a second state. The controller 395 is configured to perform the switching based on a balance between the required heat load of the cooling subsystem 300 across the fuel cell stack 100 and the available heat load of the cooling subsystem 300 across the coolant heat exchanger 320.

[0051] Thus, the cooling subsystem 300 may have a coolant heat exchanger 320 sized regardless of the high temperature maximum takeoff weight condition, and may provide the required cooling thermal load to the fuel cell stack 100 under conditions at or near the high temperature maximum takeoff weight condition by operating the first multi-outlet valve arrangement in a second state in which coolant exiting the fuel cell stack 100 is discharged from the cooling system 300 via the coolant exhaust arrangement 325. When the conditions are such that the coolant heat exchanger 320 is capable of providing a thermal load to the coolant heat exchanger 320 that allows the cooling subsystem 300 to operate as a closed circuit cooling subsystem (i.e., conditions sufficiently removed from the high temperature maximum takeoff weight condition based on the available thermal load across the coolant heat exchanger 320 and the required thermal load across the fuel cell stack 100), the controller 395 may switch the first multi-outlet valve arrangement 315 to the first state to stop discharging coolant from the cooling subsystem 300.

[0052] Switching the first multi-outlet valve arrangement 315 from the second state to the first state based on a balance between the required heat load of the cooling subsystem 300 across the fuel cell stack 100 and the available heat load of the cooling subsystem 300 across the coolant heat exchanger 320 beneficially reduces the amount of coolant discharged from the cooling subsystem 300. This may be particularly important when the amount of coolant in the coolant tank 305 cannot be easily replenished during operation of the fuel cell system 1 and / or when there is only enough coolant in the coolant tank 305 to allow the cooling subsystem 300 to operate as an open-ventilated cooling subsystem for only a limited period of time before there is insufficient coolant in the cooling subsystem 300 to provide sufficient cooling heat load to the fuel cell stack 100.

[0053] The controller 395 is typically configured to switch the first multi-outlet valve arrangement 315 from the first state to the second state in response to an increase in the required heat load of the cooling subsystem 300 across the fuel cell stack 100 and / or a decrease in the available heat load of the cooling subsystem 300 across the coolant heat exchanger 320. For example, the controller 395 may switch the first multi-outlet valve arrangement 315 from the first state to the second state if the power of the fuel cell stack 100 increases, or the ambient air temperature increases, or the amount of air ventilating the fuel cell system 1 decreases. Similarly, the controller 395 is typically configured to switch the first multi-outlet valve arrangement 315 from the second state to the first state in response to a decrease in the required heat load of the cooling subsystem 300 across the fuel cell stack 100 and / or an increase in the available heat load of the cooling subsystem 300 across the coolant heat exchanger 320. For example, if the power of the fuel cell stack 100 decreases, or the ambient air temperature decreases, or the amount of air ventilating the fuel cell system 1 increases, the controller 395 may switch the first multi-outlet valve device 315 from the second state to the first state.

[0054] It can be seen that it is desirable to operate the cooling subsystem 300 under operating conditions where a portion of the coolant entering the first multi-outlet valve arrangement 315 is recirculated via the coolant heat exchanger 320 to the coolant tank 305 in the first recirculation line 330, and the remaining coolant is discharged from the cooling subsystem 300 through the exhaust line 340. Accordingly, the controller 395 may be configured to set the first multi-outlet valve arrangement 315 to a third state in which both the first valve outlet 317 and the second valve outlet 318 are open. The ability to set the first multi-outlet valve arrangement 315 to the above state is desirable since it reduces the amount of coolant discharged from the cooling subsystem 300. This is because, when transitioning from an open-ventilation cooling subsystem to a closed circuit cooling subsystem, the available heat load across the coolant heat exchanger 320 is large enough to recirculate all of the coolant and can begin to recirculate a portion of the coolant before meeting the required heat load of the cooling subsystem 300 across the fuel cell stack 100.

[0055] Such a fuel cell system 1 can have a coolant heat exchanger 320 that is significantly smaller and lighter than if the cooling subsystem 300 did not have the ability to switch between a closed-circuit cooling subsystem and an open-ventilation cooling subsystem. The reduced size, weight and cost of the coolant heat exchanger 320 is particularly beneficial when the fuel cell system 1 forms part of a propulsion system that uses the power generated by the fuel cell stack 100 to supply electric propulsors 800 via a high voltage power output typically provided by an HV DC / DC converter 505. In this case, the power to weight and power to CdA ratios of the vehicle in which such a propulsor is used can be increased, thereby improving the fuel efficiency of the vehicle. Increasing these ratios is particularly beneficial when the propulsors are used in aircraft.

[0056] 1 typically further comprises a gas pre-treatment line 370 that can be used to pre-cool compressed air and / or pre-treat the fuel stream entering the fuel cell stack 100. The valve network further comprises a second multi-outlet valve arrangement 360 having a second valve inlet 361 and a fourth valve outlet 363 disposed in the stack supply line 340, and a first multi-inlet valve arrangement 365 having a third valve inlet 366 and a fifth valve outlet 368 disposed in the stack exhaust line 345. Thus, the gas pre-treatment line 370 extends from the third valve outlet 362 of the second multi-outlet valve arrangement 360 to the fourth valve inlet 367 of the first multi-inlet valve arrangement 365.

[0057] Although the second multi-outlet valve arrangement 360 and the first multi-inlet valve arrangement 365 shown in FIG. 1 each take the form of a three-port valve, those skilled in the art will appreciate that the second multi-outlet valve arrangement 360 and the first multi-inlet valve arrangement 365 may be provided by any valve layout.

[0058] A first side of the cathode heat exchanger 230 is disposed in the air supply line 216, and a second side of the cathode heat exchanger 230 is disposed in the gas pre-treatment line 370 between the third valve outlet 362 and the fourth valve inlet 367, so that the compressed air entering the fuel cell stack 100 can be pre-cooled by the coolant flowing through the gas pre-treatment line 370. Typically, the cathode heat exchanger is located between the outlet of the compressor 210 and the humidifier 215, as shown in Figure 1, and the cathode heat exchanger regulates the temperature of the air supply. The cathode heat exchanger also helps to maintain an appropriate humidity level in the air supply.

[0059] Similarly, a first side of the anode side heat exchanger 415 is disposed in the fuel supply line 401 and a second side of the anode side heat exchanger 415 is disposed in the gas pre-treatment line 370 so that the fuel stream entering the fuel cell stack 100 is pre-treated by a coolant passing through the gas pre-treatment line 370.

[0060] The controller 395 is configured to control the second multi-outlet valve arrangement 360 and the first multi-inlet valve arrangement 365 to switch the second multi-outlet valve arrangement 360 and the first multi-inlet valve arrangement 365 between an open state in which the third valve outlet 362 and the fourth valve inlet 367 are open and the coolant passage is open through the gas pre-treatment line 370, and a closed state in which the third valve outlet 362 and the fourth valve inlet 367 are closed and the coolant passage is closed through the gas pre-treatment line 370.

[0061] The controller 395 may be configured to control the opening of the third valve outlet 362 and / or the fourth valve inlet 367, which in turn varies the flow rate of coolant through the gas pre-treatment line 370 and thus the degree of pre-cooling of the compressed air and fuel streams. The controller 395 is configured to vary the state of the second multi-outlet valve arrangement 360 and the first multi-inlet valve arrangement 365 based on a balance of two or more of the following: the required heat load of the cooling subsystem (300) across the fuel cell stack (100); the available heat load of the cooling subsystem (300) across the coolant heat exchanger (320); The desired degree of pre-treatment of the compressed air and fuel streams.

[0062] Although both the cathode heat exchanger 230 and the anode heat exchanger 415 are shown in Figure 2, it will be understood that either may be provided without the other, and only the compressed air and fuel streams may be pre-cooled with coolant via the gas pre-treatment line 370. It may be desirable to independently control the flow rate of coolant through each of the cathode heat exchanger 230 and the anode heat exchanger 415 so that the degree of pre-cooling of the compressed air and fuel streams may be individually controlled. Thus, the cathode heat exchanger 230 and the anode heat exchanger 415 may be provided in separate gas pre-treatment lines, for example, or bypasses to the heat exchangers 230 and 415 may be provided, each of which may be independently operable.

[0063] The cooling subsystem 300 of FIG. 1 typically also includes a deionizer 390 for deionizing the coolant entering the fuel cell stack 100. The deionizer 390 is located in the stack supply line 340 of the cooling subsystem 300 of FIG. 1, but may be located elsewhere in the cooling subsystem 300 (e.g., in other lines in the closed circuit or in the second recirculation line 350, if any). Locating the deionizer 390 in the stack supply line 340 is beneficial in that the coolant necessarily passes through the deionizer 390 before entering the fuel cell stack 100, thereby reducing the concentration of ions in the coolant that may have formed in the cooling subsystem 300 (e.g., through filtration, decomposition corrosion, etc.) before the coolant enters the fuel cell stack 100. It is desirable to deionize the coolant to reduce the risk of leakage current or short circuits in the fuel cell stack 100.

[0064] FIG. 2 is another process flow diagram illustrating a fuel cell system 2 which is optionally modified in several respects from the fuel cell system 1 described above in FIG.

[0065] The fuel cell system 2 of Figure 2 operates in generally the same manner as the fuel cell system of Figure 1. Therefore, the following description will mainly focus on various modifications of the fuel cell system 2.

[0066] First, the cooling subsystem 300 of FIG. 2 is configured to recover water from the exhaust gas of the cathode subsystem 200 and recirculate the recovered water to the cooling subsystem 300. For example, a water separator 355 is disposed in an air exhaust line extending from the turbine 225 of the cathode subsystem 200, which removes air from the fuel cell stack 100. The water separator 355 is configured to collect water from the air removed from the fuel cell stack 100. A second recirculation line 350 extends from the water separator 355 to the coolant tank 305 and delivers the collected water to the coolant tank 305. Such a cooling subsystem 300 (ideally using water as a coolant) is advantageous because it can supplement at least a portion of the amount of coolant discharged from the cooling subsystem 300 when the cooling subsystem operates as an open-ventilation cooling subsystem with the first multi-outlet valve device in the second state by replenishing the coolant in the cooling subsystem 300 with water via the second recirculation line 350. The ability to replenish coolant during operation of the fuel cell system 2 is beneficial when it is anticipated that the cooling subsystem 300 will have to operate as an open-ventilation cooling subsystem. The ability to replenish coolant allows the cooling subsystem 300 to begin operation of the fuel cell system 2 with less coolant than would otherwise be required to accommodate operation as an open-ventilation cooling subsystem. The coolant tank 305 can also be made smaller since it does not need to contain as much coolant as it would otherwise need. This allows the cooling subsystem 300, and the fuel cell system 2 as a whole, to be smaller and lighter, thereby reducing the size, mass, and cost of the coolant tank 305.

[0067] The cooling subsystem 300 of FIG. 2 also includes a deionizer 390 for deionizing the coolant entering the fuel cell stack 100. The deionizer 390 is particularly useful when the fuel cell system 2 includes the water separator 355 and the second recirculation line 350, since the water introduced into the cooling subsystem 300 by the second recirculation line 350 tends to have a high concentration of ions that should not be introduced into the coolant flow paths of the fuel cell stack 100. The deionizer 390 is located in the stack supply line 340 of the cooling subsystem 300 of FIG. 2, but may be located elsewhere in the cooling subsystem 300 (e.g., in other lines in the closed circuit, if any, or in the second recirculation line 350). The location of the deionizer 390 in the stack supply line 340 is beneficial in that the water collected from the water separator 355 and introduced into the cooling subsystem 300 necessarily passes through the deionizer 390 before entering the fuel cell stack 100, ensuring that the water is deionized before entering the fuel cell stack 100. It is desirable to deionize the coolant to reduce the risk of electrical leakage or short circuits within the fuel cell stack 100 .

[0068] Another modification in the cooling subsystem 300 of FIG. 2 is the provision of a heat exchanger bypass line 379 that allows the coolant to flow around the closed circuit of the cooling subsystem 300 while bypassing the coolant heat exchanger 320. The heat exchanger bypass line 379 in FIG. 2 extends from the stack discharge line 345 to a position on the first recirculation line 330 downstream of the coolant heat exchanger 320, but may also extend from the exhaust line 340 to a position on the first recirculation line 330 downstream of the coolant heat exchanger 320. Furthermore, the controller 395 is configured to open and close the heat exchanger bypass line based on a balance between the required heat load of the cooling subsystem 300 across the fuel cell stack 100 and the available heat load of the cooling subsystem 300 across the coolant heat exchanger 320. Typically, the controller 395 is also configured to close the heat exchanger bypass line 379 when the first multi-outlet valve device 315 is switched to the second state.

[0069] 2, the coolant subsystem 300 further includes a third multi-outlet valve arrangement 375 having a fifth valve inlet 376, a sixth valve outlet 377, and a seventh valve outlet 378, and a second multi-inlet valve arrangement 380 having a sixth valve inlet 381, a seventh valve inlet 382, ​​and an eighth valve outlet 383, thereby providing a heat exchanger bypass line 379. The fifth valve inlet 376 and the seventh valve outlet 378 are disposed in the stack discharge line 345, and the sixth valve inlet 381 and the eighth valve outlet 383 are disposed in the first recirculation line 330. The heat exchanger bypass line 379 extends from the sixth valve outlet 377 to the seventh valve inlet 382. 2 are in the form of three-port valves, those skilled in the art will appreciate that the third multi-outlet valve arrangement 375 and the second multi-inlet valve arrangement 380 may be provided with any valve layout. While the cooling subsystem 300 operates as a closed circuit cooling subsystem, the controller 395 is configured to switch the third multi-outlet valve arrangement 375 and the second multi-inlet valve arrangement 380 between a bypass state in which the heat exchanger bypass line 379 is open to prevent coolant from flowing from the first multi-outlet valve arrangement through the coolant heat exchanger 320 via the first recirculation line to the coolant tank 305, and a non-bypass state in which the heat exchanger bypass line 379 is closed to allow coolant to flow from the first multi-outlet valve arrangement through the coolant heat exchanger 320 via the first recirculation line to the coolant tank 305.

[0070] In the device of FIG. 2, the bypass state is The fifth valve inlet 376, the sixth valve outlet 377, the seventh valve inlet 382, ​​and the eighth valve outlet 383 are opened; Provided by closing any one of the seventh valve outlet 378, the first valve inlet 316, the first valve outlet 317, and the sixth valve inlet 381; The non-bypass state is open the fifth valve inlet 376, the seventh valve outlet 378, the first valve inlet 316, the first valve outlet 317, the sixth valve inlet 318, and the eighth valve outlet 383; Close either the sixth valve outlet 377 or the seventh valve outlet 382 This can be provided by:

[0071] When the fifth valve inlet 376 and the seventh valve outlet 378 are positioned in the exhaust line 340 such that the heat exchanger bypass line 379 extends from the exhaust line 340, the bypass condition is: opening the first valve inlet 316, the second valve outlet 318, the fifth valve inlet 376, the sixth valve outlet 377, the seventh valve inlet 382, ​​and the eighth valve outlet 383; Either the first valve outlet 317 or the sixth valve inlet 381 is closed.

[0023] The non-bypass state is The first valve inlet 316, the first valve outlet 317, the sixth valve inlet 381, and the eighth valve outlet 383 are opened; Close any one of the fifth valve inlet 376, the sixth valve outlet 377, and the seventh valve inlet 382. This can be provided by:

[0072] It will be appreciated that it may also be desirable to operate the cooling subsystem 300 such that a portion of the coolant entering the third multi-outlet valve arrangement 375 enters the heat exchanger bypass line 379, with the remaining coolant entering the coolant heat exchanger 320. Accordingly, the controller 395 may be configured to set the third multi-outlet valve arrangement 375 and the second multi-inlet valve arrangement 380 such that both the coolant passage through the heat exchanger bypass line 379 and the coolant passage through the coolant heat exchanger 320 are open.

[0073] While the cooling subsystem is operating as an open-ventilation cooling subsystem 300, the controller is configured to set the third multi-outlet valve arrangement 375 and the second multi-inlet valve arrangement 380 such that the bypass line 379 is closed between the first multi-outlet valve arrangement 315 and the exhaust arrangement 325 while the exhaust line is open.

[0074] 2 includes an exhaust 325 having an exhaust nozzle 326 such that under a second operating condition, coolant is discharged from the cooling subsystem 300 through the exhaust 325. This assists the cooling subsystem 300 in ensuring that the coolant flowing through the exhaust line 340 is discharged from the cooling subsystem 300.

[0075] Another modification in the cooling subsystem 300 of FIG. 2 is the anti-icing cooling circuits 395a, 395b extending from and returning to the first recirculation line 330. The anti-icing cooling circuits are configured to transport the coolant heated by the fuel cell stack 100 to an aircraft anti-icing device 700 via the output portion of the circuit 395a, so that the heated coolant can dissipate heat and thereby de-icing the aircraft. The coolant then returns from the anti-icing device 700 to the first recirculation line 330 via the input portion of the circuit 395b. The anti-icing device 700 is essentially an additional heat exchanger connected in parallel with the coolant heat exchanger 320. Such a device can provide coolant cooling power to the coolant subsystem 300 in excess of that provided by the coolant heat exchanger 320, and can utilize heat extracted from the coolant flowing through the anti-icing device 700 rather than simply dissipating it to the surroundings. Vehicles such as aircraft typically include an anti-icing device 700 to melt ice on their exterior surfaces and / or to prevent ice from forming on their exterior surfaces. Thus, the efficiency of a vehicle having a fuel cell system 2 with an anti-icing cooling circuit is improved by utilizing heat transferred to the coolant as described above. Although Fig. 2 illustrates the anti-icing device 700 connected in parallel with the coolant heat exchanger 320, it will be appreciated that similar benefits may be achieved with other connection arrangements of the anti-icing device 700, such as connecting the anti-icing device 700 in series with the coolant heat exchanger 320.

[0076] 2 illustrates an electric propulsion device 800 that includes an inverter 805, a motor 810, and an aircraft propeller 815. High voltage DC power is applied from the HV DC / DC converter 515 to the inverter 805, which then applies AC power to the motor 810 to drive the propeller 815.

[0077] Although the present invention has been described in conjunction with the above exemplary embodiments, those skilled in the art who have read this specification will readily recognize that there are various equivalent modifications and variations. Therefore, the above exemplary embodiments of the present invention are illustrative examples of the present invention, and are not limiting. Various modifications can be made to the above embodiments without departing from the spirit and scope of the present invention.

[0078] For the avoidance of doubt, the theoretical explanations set forth herein are presented for the sake of clarity of understanding of the reader, and the inventors of the present invention do not wish to be limited by any of these theoretical explanations.

[0079] Any headings provided herein are for organizational purposes only and are not meant to limit the subject matter described.

[0080] Throughout this specification, including the claims which follow, unless the context requires otherwise, the words "comprise" and "include", as well as variations thereof such as "comprises", "comprising", "including" and the like, will be understood to mean the inclusion of a stated integer or step or collection of integers or steps, but not to the exclusion of any other stated integer or step or collection of integers or steps.

[0081] As used herein and in the appended claims, it should be noted that the singular forms "a," "an," and "the" include plural referents unless the context clearly indicates otherwise. As used herein, ranges may be expressed as from "about" one particular value, and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations by the antecedent "about," it will be understood that the particular value forms another embodiment. The word "about" associated with numerical values ​​is optional and may mean, for example, + / - 10%.

[0082] This application claims the benefit of priority from UK Patent Application No. 2205780.6, filed April 21, 2022, the entire contents of which are incorporated by reference as if fully set forth herein.

Claims

1. a fuel cell stack (100); a cooling subsystem (300); A fuel cell system (1, 2) comprising: The cooling subsystem (300) comprises: a coolant tank (305); a stack supply line (340) extending from the coolant tank (305) to the fuel cell stack (100), wherein a pump (310) is disposed in the stack supply line (340) to pump coolant from the tank (305) to the fuel cell stack (100) via the stack supply line (340); a valve network including a first multi-outlet valve device (315) having a first valve inlet (316), a first valve outlet (317), and a second valve outlet (318); a coolant heat exchanger (320); a coolant exhaust system (325); a stack exhaust line (345) extending from the fuel cell stack (100) to the first valve inlet (316) for removing coolant from the fuel cell stack (100); a first recirculation line (330) extending from the first valve outlet (317) to the coolant tank (305), wherein a first side of the coolant heat exchanger (320) is disposed in the first recirculation line (330), and heat is removed from the coolant recirculated through the first recirculation line (330); an exhaust line (340) extending from the second valve outlet (318) to the coolant exhaust system (325); The first multi-outlet valve device (315) comprises: a first state providing a closed-circuit cooling subsystem in which the first valve outlet (317) is open and the second valve outlet (318) is closed, thereby opening a coolant passage from the first multi-valve device (315) through the coolant heat exchanger (320) to the coolant tank (305) and closing a coolant passage from the first multi-valve device (315) to the coolant exhaust device (325); a second state providing an open-vent cooling subsystem in which the first valve outlet (317) is closed and the second valve outlet (318) is open, thereby opening a coolant passage from the first multi-valve device (315) to the coolant exhaust device (325) and closing a coolant passage from the first multi-valve device (315) to the coolant tank (305) through the coolant heat exchanger (325); The cooling subsystem (300) further comprises a computer-based controller (395) configured to control the valve network and switch the first multi-outlet valve arrangement (315) between the first state and the second state based on a balance between the cooling subsystem's required heat load across the fuel cell stack (100) and the cooling subsystem's available heat load across the coolant heat exchanger (320). Fuel cell system (1, 2).

2. The controller (395) further switching the first multi-outlet valve device (315) from the first state to the second state in response to an increase in the required heat load of the cooling subsystem (300) across the fuel cell stack (100) and / or a decrease in the available heat load of the cooling subsystem (300) across the coolant heat exchanger (320); configured to switch the first multi-outlet valve device (315) from the second state to the first state in response to a decrease in the required heat load of the cooling subsystem (300) across the fuel cell stack (100) and / or an increase in the available heat load of the cooling subsystem (300) across the coolant heat exchanger (320). A fuel cell system (1, 2) according to claim 1.

3. The fuel cell system (1, 2) of claim 1, wherein the cooling subsystem (300) is configured to use water as a coolant.

4. a cathode subsystem (200) including an air supply line (216) for supplying air to the fuel cell stack (100) and an air exhaust line (217) for removing air from the fuel cell stack (100); an anode-side subsystem (400) including a fuel supply line (401) for supplying fuel to the fuel cell stack (100); 2. The fuel cell system (1, 2) according to claim 1, comprising:

5. the cooling subsystem (300) further comprises a second recirculation line (350) and a water separator (355) disposed in the air exhaust line (217) to collect water from the air removed from the fuel cell stack (100); the second recirculation line (350) extends from the water separator (355) to the coolant tank (305) and delivers the collected water to the coolant tank (305); A fuel cell system (1, 2) according to claim 4.

6. (i) the valve network comprises: a second multi-outlet valve arrangement (360) having a second valve inlet (361), a third valve outlet (362), and a fourth valve outlet (363), the second valve inlet (361) and the fourth valve outlet (363) being disposed in the stack supply line (340); a first multi-inlet valve arrangement (365) having a third valve inlet (366), a fourth valve inlet (367), and a fifth valve outlet (368), the third valve inlet (366) and the fifth valve outlet (368) being disposed in the stack discharge line (345); (ii) the cooling subsystem (300) further comprises a gas pre-treatment line (370) extending from the third valve outlet (362) to the fourth valve inlet (367); the controller (395) is further configured to control the valve network to switch the second multi-outlet valve arrangement (360) and the first multi-inlet valve arrangement (365) between an open state in which the third valve outlet (362) and the fourth valve inlet (367) are opened to open a coolant passage through the gas pre-treatment line (370), and a closed state in which the third valve outlet (362) and the fourth valve inlet (367) are closed to close the coolant passage through the gas pre-treatment line (370); (iii) (A) the cathode side subsystem (200) further comprises a cathode side heat exchanger (230), a first side of which is disposed in the air supply line (216) and a second side of which is disposed in the gas pre-treatment line (370) between the third valve outlet (362) and the fourth valve inlet (367); and / or (B) the anode side subsystem (400) further comprises an anode side heat exchanger (415), a first side of which is disposed in the fuel supply line (401) and a second side of which is disposed in the gas pre-treatment line (370) between the third valve outlet (362) and the fourth valve inlet (367); (iv) the controller (395) further comprises: (a) the required heat load of the cooling subsystem (300) across the fuel cell stack (100); and (b) the available heat load of the cooling subsystem (300) across the coolant heat exchanger (320); and (c) a desired adjustment of compressed air and / or fuel flow. A fuel cell system (1, 2) according to claim 4.

7. 7. The fuel cell system (1, 2) of claim 1, wherein the cooling subsystem (300) further comprises a deionizer (390) for the coolant, optionally the deionizer (390) being disposed in the stack supply line (340).

8. (a) the cooling subsystem (300) further comprises a heat exchanger bypass line (379) extending from the stack discharge line (345) or the exhaust line (340) to a location on the first recirculation line (330) downstream of the coolant heat exchanger (320); (b) the controller (395) is configured to open or close the heat exchanger bypass line (379) based on a balance between a required heat load of the cooling subsystem (300) across the fuel cell stack (100) and an available heat load of the cooling subsystem (300) across the coolant heat exchanger (320), and optionally (c) the controller (395) is further configured to close the heat exchanger bypass line (379) when the first multi-outlet valve device (315) is switched to the second state. A fuel cell system (1, 2) according to any one of claims 1 to 6.

9. 7. The fuel cell system of claim 1, wherein the cooling subsystem further comprises an anti-icing coolant circuit extending from and returning to the first recirculation line, the anti-icing coolant circuit configured to transport coolant heated by the fuel cell stack to an aircraft anti-icing system, whereby the heated coolant loses heat before returning to the first recirculation line to de-ice the aircraft, and optionally the anti-icing coolant circuit is connected to the first recirculation line so as to be in parallel with the coolant heat exchanger.

10. 7. The fuel cell system (1, 2) according to any one of claims 1 to 6, wherein the coolant exhaust device (325) comprises an exhaust nozzle (326).

11. (a) the fuel cell stack (100) comprises a plurality of proton exchange membrane fuel cells; or (b) the fuel cell stack (100) is a hydrogen fuel cell stack; A fuel cell system (1, 2) according to any one of claims 1 to 6.

12. 7. A fuel cell system (1, 2) as described in any one of claims 1 to 6, wherein the coolant heat exchanger (320) is an air-cooled heat exchanger, and a second side of the coolant heat exchanger is exposed to an outside air flow that receives heat from the coolant.

13. A propulsion device comprising the fuel cell system according to any one of claims 1 to 6 and an electric propulsion device (800), (a) the fuel cell system further comprises a power subsystem (500) that harvests power generated by the fuel cell stack (100); (b) the power subsystem (500) is electrically connected to the thruster (800) and supplies the generated power to the thruster (800); Propulsion device.

14. An aircraft comprising a propulsion device according to claim 13.

15. A method for operating a fuel cell system (1, 2) according to any one of claims 1 to 6, comprising the steps of: (a) switching the first multi-valve device (315) to a first state to operate the cooling subsystem (300) as a closed-circuit cooling subsystem in which a coolant passage from the first multi-valve device (315) through the coolant heat exchanger (320) to the coolant tank (305) is open and a coolant passage from the first multi-valve device (315) to the coolant exhaust device (325) is closed; (b) switching the first multi-outlet valve device (315) to a second state, thereby operating the cooling subsystem (300) as an open-vent cooling subsystem in which a coolant passage from the first multi-valve device (315) to the coolant exhaust device (325) is open and a coolant passage from the first multi-valve device (315) to the coolant tank (305) through the coolant heat exchanger (320) is closed; the first multi-outlet valve device (315) is switched between the first state and the second state based on a required heat load of the cooling subsystem (300) across the fuel cell stack (100) and an available heat load of the cooling subsystem (300) across the coolant heat exchanger (320); method.

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