Cooling system for fuel cells

Abstract

A cooling system 250 for a fuel cell system 200 of a vehicle (Fig. 1, 1), comprising a water source, a pump 255 and at least one sprayer 259A connected to the pump and configured to spray water from t

Description

TECHNICAL FIELD The present disclosure relates to a cooling system for fuel cells. Aspects of the invention relate to a cooling system, to a fuel cell system, to a vehicle, and to a method. BACKGROUND In a fuel cell, such as a hydrogen fuel cell, an electrochemical reaction occurs between gaseous hydrogen and oxygen, forthe purpose of generating electrical energy. Heat and water are generated as by-products. In some fuel cells, each kilogram of gaseous hydrogen consumed produces around several kilograms of water which is expelled through an exhaust port. The heat of the reaction is dissipated by a cooling system. It is an aim of the present invention to address one or more disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a cooling system, a fuel cell system, a vehicle, and a method as claimed in the appended claims. According to an aspect of the present invention there is provided a cooling system (water spray cooling system) for a fuel cell system of a vehicle, the system comprising a water source, a pump, and at least one sprayer connected to the pump and being configured to spray water from the water source onto at least one heat exchanger associated with the fuel cell system. An advantage is improved thermal management of the fuel cell, due to the cooling effect of the water on the heat exchanger. This is useful in thermally-demanding use cases such as high fuel cell power outputs, and high ambient temperatures or altitudes. This can prolong the duration for which the fuel cell is operated at a high power output before any thermal degradation occurs, such as limiting power output. Optionally, the water source comprises a condenser positioned in the path of at least some fuel cell exhaust gases, and a receptacle configured to collect water condensed in the condenser, wherein the pump is configured to pump condensed water from the receptacle, wherein the at least one sprayer is connected to the pump and is configured to spray the condensed water pumped from the receptacle onto the at least one heat exchanger. An advantage is improved thermal management because the water supply is self-replenishing. The fuel cell generates a large mass of water which can be used for water cooling. The condenser cools the water from a vapour phase to a liquid phase, so that the water can be stored in the receptacle. Furthermore, the rate of water production increases with the power output of the fuel cell and therefore with the cooling demand. Optionally, the pump is operable at pump pressure selected from the range 500kPa to 800kPa. This advantageously improves cooling efficiency by ensuring that the water is atomised and adequately evaporates from the heat exchanger. Optionally, the condenser is fluidly connected along an exhaust gas passage between an outlet of a humidifier of the fuel cell system, and an exhaust gas vent of the fuel cell system for exhausting fuel cell byproducts. Optionally, the exhaust gas passage is branched from a main exhaust gas duct, the main exhaust gas duct extending between the outlet of the humidifier and the exhaust gas vent. Optionally, the main exhaust gas duct connects the outlet of the humidifier to the exhaust gas vent. An advantage is improved thermal management because the gases downstream of the humidifier are more humid so more water is available. Optionally, the cooling system further comprises a pH corrector to at least partially neutralise a water pH upstream of the at least one sprayer. Optionally, the pH corrector is located upstream of the pump. Optionally, the pH corrector is located upstream of the condenser. An advantage is improved durability because the pH corrector neutralises any nitric acid or other acids from the fuel cell waste water, and therefore prevents corrosion of the sprayed surfaces. Locating the pH corrector further upstream protects the pump, or pump and receptacle, or pump and receptacle and condenser, from corrosion. Optionally, the at least one heat exchanger comprises a first heat exchanger, and wherein the cooling system comprises a plurality of the sprayers arranged to spray the water onto the first heat exchanger. Optionally, the plurality of the sprayers are arranged to simultaneously spray the water onto different areas of the first heat exchanger that are mostly or entirely non-overlapping. An advantage is enabling a greater spray coverage area of the surface of the first heat exchanger. Optionally, the at least one heat exchanger comprises an intake gas intercooler for cooling fuel cell intake gas. An advantage is an efficient means of improving the air charge density for the fuel cell. By spray-cooling the intake gas intercooler, other systems such as an intake air compressor do not have to consume as much electrical power, to achieve a desirable air charge density. Furthermore, the maximum air charge density is increased, when the sprayer is operating simultaneously to the intake air compressor operating at high power. Optionally, the at least one heat exchanger comprises a coolant radiator of a coolant circuit of the fuel cell system. An advantage is an efficient means of improving the thermal management of the fuel cell. The temperature loss of the coolant through the coolant radiator is improved, without other systems such as a radiator fan or a 2 coolant pump having to consume as much electrical power. Furthermore, the maximum possible rate of cooling is increased, when the sprayer is operating simultaneously to the radiator fan and coolant pump operating at high power. Optionally, the cooling system comprises a plurality of the sprayers, including a first subset configured to spray the intake gas intercooler, and a second subset configured to spray the coolant radiator. Optionally, the subsets are fluidly connected to the same pump, or one of the subsets is fluidly connected to the pump (first pump) and the other subset is fluidly connected to a second pump, wherein the first and second pumps are configured to receive water from the receptacle. This provides both advantages described above. The large amount of water generated by a fuel cell means that there is enough for both the intake gas intercooler and the coolant radiator. According to another aspect of the invention, there is provided a fuel cell cooling system for a fuel cell of a vehicle, the fuel cell cooling system comprising a condenser positioned in the path of at least some fuel cell exhaust gases, a receptacle configured to collect water condensed in the condenser, and a pump configured to pump condensed water from the receptacle, and at least one sprayer connected to the pump. According to a further aspect of the invention, there is provided a cooling system fora fuel cell powered vehicle, the system comprising a water source, a pump, and at least one sprayer connected to the pump and being configured to spray water from the water source onto at least one cooling device (e.g., heat exchanger). According to a further aspect of the invention, there is provided a fuel cell system comprising the cooling system and a fuel cell. Optionally, the fuel cell is a hydrogen fuel cell. According to a further aspect of the invention, there is provided a vehicle comprising the cooling system or the fuel cell system. According to a further aspect of the invention, there is provided a method of cooling a fuel cell system of a vehicle, the method comprising: operating a pump to pump water from a water source through at least one sprayer, wherein the at least one sprayer is connected to the pump; and spraying, by the at least one sprayer, water from the water source onto at least one heat exchanger associated with the fuel cell system. Optionally, the method comprises: condensing, using a condenser, water from fuel cell exhaust gases; collecting the condensed water in a receptacle, the receptable and condenser defining the water source; and operating the pump to pump the condensed water from the receptacle to the at least one sprayer. According to a further aspect of the invention, there is provided a control system comprising one or more processors collectively configured to perform the method. The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to operate the pump to pump the water through the at least one sprayer to spray the water onto the at least one heat exchanger. According to a further aspect of the invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform any one or more of the methods described herein. According to a further aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out any one or more of the methods described herein. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination that falls within the scope of the appended claims. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination that falls within the scope of the appended claims, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 illustrates a perspective view illustrating an example of a vehicle; FIG. 2 illustrates a schematic view illustrating an example of a fuel cell system and a vehicle electrical system; FIG. 3 illustrates a schematic view illustrating an example of a control system; FIG. 4 illustrates a schematic view illustrating an example of a non-transitory computer-readable medium; and FIG. 5 illustrates a flowchart illustrating an example of a method. DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying FIG. 1. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles. FIG. 2 illustrates a fuel cell system 200 of the vehicle 1, as well as an electric drive system 20. The fuel cell system 200 comprises a fuel cell 202. In a non-limiting example, the fuel cell 202 is a hydrogen fuel cell. The fuel cell 202 is connected to at least one fuel tank 242 storing a chemical fuel such as gaseous hydrogen. The fuel cell 202 is configured to convert the chemical energy of the fuel into electrical energy through an electrochemical reaction. The fuel cell 202 is also connected to an electrical bus 28 of the vehicle 1 via a voltage converter 22 such as a DC-DC (direct current to direct current) converter for converting between a bus voltage and a fuel cell output voltage. The fuel cell 202 is configured to generate electrical energy and output the electrical energy to the electrical bus 28 via the voltage converter 22. The peak electrical power output of the fuel cell 202 may be greaterthan 50 kilowatt hours (peak power >50kW) or greater than 80 kilowatt hours (peak power >80kW). The fuel cell system 200 may comprise a stack of a plurality of fuel cells 202, to achieve this peak power. The stack of fuel cells 202, or single fuel cell 202, may optionally be housed within an enclosure having various ports for liquids and gases, and electrical interfaces. The electric drive system 20 comprises the voltage converter 22, the electrical bus 28, an electric drive unit 26, and an electrical energy storage means such as a traction battery 24. The traction battery 24 is electrically connected to the electrical bus 28. When discharging, the traction battery 24 is configured to output electrical energy to the electrical bus 28. When charging, the traction battery 24 is configured to receive and store electrical energy from the electrical bus 28. The traction battery 24 may have a peak electrical energy storage capacity of greaterthan 5 kilowatt-hours, or greater than 10 kilowatt-hours. The traction battery 24 has a high enough capacity to provide assistive electrical power over a long or challenging drive cycle. Assistive electrical power may be required, for example when power demand exceeds the peak electrical energy of the fuel cell 202. As will be described, the fuel cell 202 is cooled by a water spray cooling system 250. This is useful for the above implementation in which the fuel cell 202 has a higher peak power output than the traction battery 24, such that the fuel cell 202 is a primary source of tractive electrical power whereas the traction battery 24 is a secondary (assistive) source. This is because the fuel cell 202 generates high thermal energy when operating at high power outputs. However, it would be appreciated that aspects of the present invention could be implemented in vehicles where the fuel cell 202 or stack of fuel cells 202 has a lower peak electrical power output than the traction battery 24. One or more electric drive units 26 are connected to the electrical bus 28. Each electric drive unit 26 comprises an inverter electrically connected to a corresponding electric machine, such as an electric motor. One electric drive unit 26 is shown. However, a four-wheeled vehicle 1 could comprise two, three, or even four electric drive units 26, fordriving different wheels of the vehicle 1. The electric drive units 26 may be configured to exchange electrical energy with the same electrical bus 28. The fuel cell system 200 further comprises various fluid systems operably coupled to the fuel cell 202, including an intake air system 210, an exhaust gas system 220, a coolant loop 230, a hydrogen supply system, and a cooling system 250 in the form of a water spray cooling system. These are each described, in turn. The intake air system 210 comprises an ambient air inlet 212 configured to receive ambient air from outside the vehicle 1. This may take the form of a port configured to receive ambient air from an opening located in a bumper assembly of the vehicle 1, or elsewhere. If the vehicle 1 comprises forced air induction, the ambient air inlet 212 is connected by air ducting to an intake air compressor 214 and an intake gas intercooler 216. Without forced air induction, the intake air compressor 214 and intake gas intercooler 216 may be omitted. The intake air compressor 214 may comprise an electric motor coupled to a rotary impeller, collectively configured to compress and therefore increase the air pressure and density of the ambient air. Since the intake air compressor 214 increases the temperature of the air, an intake gas intercooler 216 is provided downstream of the intake aircompressor214, to dissipate heat from the compressed airto an external environment. The intake gas intercooler 216 may comprise an air-to-liquid heat exchanger since liquid (e.g., water) has a high convective heat transfer coefficient compared to air. The heat exchanger may be fanless or fan-cooled. The intake air system 210 further comprises an optional humidifier 218. The purpose of the humidifier 218 is to increase or maintain a high humidity of the intake air, to maintain a high protonic conductivity of a polymer electrolyte membrane of the fuel cell 202 and therefore maintain high fuel cell performance. The humidifier218 comprises an intake air inlet fluidly connected to an outlet of the intake gas intercooler 216, and an intake air outlet fluidly connected to an air inlet of the fuel cell 202. An intake gas stream flows from the intake air inlet to the intake air outlet of the humidifier 218. The humidifier 218 also comprises an exhaust gas inlet fluidly connected to an air outlet of the fuel cell 202, and an exhaust gas outlet fluidly connected to an exhaust gas vent 224. An exhaust gas stream flows from the exhaust gas inlet to the exhaust gas outlet of the humidifier 218. The humidifier 218 comprises a water-permeable membrane configured to allow water to pass from the exhaust gas stream to the inlet gas stream, while keeping the gases separate. In other implementations, the humidifier 218 may receive water from a water source other than the fuel cell’s exhaust gases, such as a water tank. The exhaust gas system 220 comprises an elongate main exhaust gas duct 222 having an inlet connected to the exhaust gas outlet of the humidifier 218, and an outlet in the form of an exhaust gas vent 224. Exhaust gases from the fuel cell 202 comprise water, nitrogen, unreacted air, small amounts of unreacted hydrogen, and various other fuel cell by-products, for example. The main exhaust gas duct 222 transports the exhaust gases to a desirable location for emitting the exhaust gases into the ambient environment outside the vehicle 1. For example, the exhaust gas vent 224 may be located in a rear region of the vehicle 1. The coolant loop 230 comprises a closed fluid circuit comprising a coolant fluid. The fluid circuit passes through the fuel cell 202, to receive thermal energy from the fuel cell 202. The coolant loop 230 further comprises a coolant pump 232 configured to pump the coolant around the fluid circuit. The coolant loop 230 may further comprise a coolant heater 234, such as a resistive heater, to increase a temperature of the coolant. The coolant loop 230 further comprises a coolant radiator 236 downstream of the fuel cell 202, configured to reduce a temperature of the heated coolant. The coolant radiator 236 may comprise a liquid-to-air or liquid-to-liquid heat exchanger, for example. In the illustrated example, the coolant radiator 236 comprises a liquid-to-air heat exchanger. Furthermore, a radiator fan 238 is located proximal to the coolant radiator 236 and faces the coolant radiator 236. When active, the radiator fan 238 drives forced airflow through the coolant radiator 236. The fuel supply system 240 comprises the at least one pressurised gaseous hydrogen fuel tank 242 and a fuel processing system 244 configured to supply fuel from the fuel tank 242 to the fuel cell 202. The fuel supply system 240 may comprise multiple gaseous hydrogen tanks 242, for example. The fuel processing system 244 may comprise a fuel filter, for example. The water spray cooling system 250 comprises an exhaust gas passage 251 having an inlet connected at a branch to the main exhaust gas duct 222, between the humidifier 218 and the exhaust gas vent 224. The exhaust gas passage 251 is configured to receive a portion of the exhaust gases flowing along the main exhaust gas duct 222. For example, the exhaust gas system 220 may comprise a T-connection orY-connection branching a single main exhaust gas duct 222 into a pair of ducts including a continued main exhaust gas duct 222 leading to the exhaust gas vent 224 and a second duct (exhaust gas passage 251) leading to components of the water spray cooling system 250. The exhaust gases from the exhaust gas passage 251 pass through a pH corrector 252 to a condenser 253. The condenser 253 is configured to cool the water in the exhaust gases from a vapour phase to a liquid phase. The condenser 253 may comprise a housing comprising an inlet, an outlet, and a plurality of internal baffles preventing direct line of sight from the inlet to the outlet. The internal baffles may be formed from a thermally conductive material such as metal (e.g., aluminium). The internal baffles of the condenser 253 are at a colder temperature than the warm exhaust gases, therefore, moisture in the exhaust gases condense on the internal baffles of the condenser 253. Optionally, the internal baffles are thermally coupled to a cooling device such as a heatsink or fan. The water spray cooling system 250 further comprises a receptacle 254 (accumulator) configured to receive the condensed water from the internal baffles of the condenser 253. For example, the receptacle 254 may be located beneath or downstream of the condenser 253, and configured to receive dripping water from the internal baffles of the condenser 253. The receptacle 254 is a water tank having a capacity sufficient to provide water for a long hot drive cycle. For example, the capacity may be in the order of 3 to 300 or 50 to 300 litres. The large capacity (volume) of the receptacle 254 avoids a situation in which the receptacle 254 becomes full and overflows. The receptacle 254 comprises an outlet connected to a plurality of sprayers 259A, 259B (water injectors) via a water pump 255 and water lines 257A, 257B. The water pump 255 can comprise an electrically powered impeller, for example, to pump water to the sprayers 259A, 259B. An operating pump pressure of200kPa to 1000kPa improves efficiency by ensuring that the water is atomised and adequately evaporates. FIG. 2 illustrates that the water spray cooling system 250 can comprise a pair of first sprayers 259A, and additionally or alternatively can comprise a pair of second sprayers 259B. The first sprayers 259A are arranged to spray water from the water pump 255 onto a cooling surface of the intake gas intercooler 216. For example, the intake gas intercooler 216 may comprise a plurality of cooling fins thermally coupled to intake air pipes, wherein the first sprayers 259A are configured to spray an atomised mist or atomised spray of water droplets onto the cooling fins of the intake gas intercooler 216. Nozzles of the second sprayers 259B point towards the cooling fins of the intake gas intercooler 216. An advantage is an efficient means of improving the air charge density for the fuel cell 202. By spray-cooling the intake gas intercooler 216, other systems such as an intake air compressor 214 do not have to consume as much electrical power, to achieve a desirable air charge density. Furthermore, the maximum air charge density is increased, when the sprayer 259A, 259B is operating simultaneously to the intake air compressor 214 operating at high power with adverse ambient conditions such as high altitude. The pair of first sprayers 259A are offset from each other and face in different non-parallel directions than each other, so that their spray patterns are mostly or entirely non-overlapping thereby covering a large contact surface area. Alternatively, a single sprayer with a large spray pattern may be used. Or, if the cooling surface is particularly large, more than two sprayers may be provided. To supply the pair of first sprayers 259A, a first water line 257A extends from an outlet of the water pump 255 to a water manifold 258A. The water manifold 258A has one inlet and a number of outlets corresponding to the number of first sprayers 259A. Alternatively, each sprayer 259A may be fed by separate pumps and water lines. The second sprayers 259B are arranged to spray water from the water pump 255 onto a cooling surface of the coolant radiator 236 of the coolant loop 230. For example, the coolant radiator 236 may comprise a plurality of cooling fins thermally coupled to coolant pipes, wherein the second sprayers 259B are configured to spray an atomised mist or atomised spray of water droplets onto the cooling fins of the coolant radiator 236. Nozzles of the second sprayers 259B point towards the cooling fins of the coolant radiator 236. An advantage is an efficient means of improving the thermal management of the fuel cell 202. The temperature loss of the coolant through the coolant radiator 236 is improved, without other systems such as the radiator fan 238 or the coolant pump 232 having to consume as much electrical power. Furthermore, the maximum possible rate of cooling is increased, when the sprayer 259B is operating simultaneously to the radiator fan 238 and coolant pump 232 operating at high power. The second sprayers 259B may be arranged so that the radiator fan 238 is outside a spray pattern of the second sprayers 259B. Therefore, the radiator fan 238 remains dry. For example, nozzles of the second sprayers may be located between the radiator fan 238 and the coolant radiator 236. The pair of second sprayers 259B are offset from each other and face in different non-parallel directions than each other, so that their spray patterns are mostly or entirely non-overlapping. Alternatively, a single sprayer with a large spray pattern may be used. Or, if the cooling surface is particularly large, more than two sprayers may be provided. To supply the pair of second sprayers 259B, a second water line 257B extends from an outlet of the water pump 255 to a water manifold 258B. The water manifold 258B has one inlet and two outlets, one for each of the second sprayers 259B. Alternatively, each sprayer 259B may be fed by separate pumps and water lines. In some examples, the first and second sprayers 259B are coupled to the outlet of the same pump 255. Alternatively, separate pumps 255 may be provided for the first and second sprayers 259B. It is not essential to spray water onto both the intake air compressor 214 and the coolant radiator 236. For example, the pair of second sprayers 259B could be omitted so that only the intake air compressor 214 is water cooled. Alternatively, the pair of first sprayers 259A could be omitted so that only the coolant radiator 236 is water cooled. The illustrated pH corrector 252 is configured to neutralise a pH of the exhaust gases prior to entering the condenser 253. The pH corrector 252 may be configured to maintain the water within a pH range of 6.8 to 7, or 6 to 8. This protects the components of the water spray cooling system 250, as well as the heat exchangers 216, 236 from corrosion by nitric acids and similar corrosives in the exhaust gases. For example, the pH corrector 252 may comprise mineral pH buffers (e.g., zeolites or limestone) in a gas path leading to the condenser 253, or catalytic coatings, or a chemical dosing system configured to spray a pH neutralising chemical into the exhaust gases to neutralise the exhaust gases. In other examples, the pH corrector 252 in another location such as between the condenser 253 and the accumulator, or between the receptacle 254 and the pump 255, or between the pump 255 and the sprayers 259A, 259B. In some examples, the water spray cooling system 250 may be supplied as a module. The module may be supplied with a housing 256 enclosing any two or more of the pH corrector 252, condenser 253, receptacle 254, and pump 255. With reference to FIG. 3, there is illustrated a control system 300 for a vehicle 1. The control system 300 comprises one or more controllers 301. For air cooling, the control system 300 may be configured to receive air temperature data from a temperature sensor 314 (e.g., thermistor) and determine if water injection is required to cool inducted air within the air intake gas intercooler 216. The control system 300 may then output a control signal to control the water pump 255 of the cooling system 250, to activate water injection, for example in dependence on the air temperature being greater than a threshold. The threshold may be selected from the range 30 to 45 Celsius. For coolant cooling, the control system 300 may be configured to receive coolant temperature data from a coolant temperature sensor 316 and determine if water injection is required to cool the coolant within the coolant radiator 236. The control system 300 may then output a control signal to control the water pump 255 of the cooling system 250, to activate water injection, for example in dependence on the coolant temperature being greater than a threshold. The control system 300 as illustrated in FIG. 3 comprises one controller 301, although it will be appreciated that this is merely illustrative. The controller 301 comprises processing means 304 and memory means 306. The processing means 304 may be one or more electronic processing device 304 which operably execute computer-readable instructions. The memory means 306 may be one or more memory device 306. The memory means 306 is electrically coupled to the processing means 304. The memory means 306 is configured to store instructions, and the processing means 304 is configured to access the memory means 306 and execute the instructions stored thereon. The controller 301 comprises an input means 310 and an output means 312. The input means 310 may comprise an electrical input 310 of the controller 301. The output means 312 may comprise an electrical output 312 of the controller 301. The controller 301 may have an interface 302 comprising an electrical input / output I / O 310, 312, or an electrical input 310, or an electrical output 312, for receiving information and interacting with external components. The input 310 is arranged to receive an air temperature signal from an air temperature sensor 314, and / or a coolant temperature signal from a coolant temperature sensor 316. The signal is an electrical signal which is indicative of an air temperature of air in the intake air system 210, or coolant temperature of the coolant in the coolant loop 230. The output 312 is arranged to output a pump control signal, indicative of a requested pump speed or activation state, for controlling the speed or activation state of the pump. FIG. 4 illustrates a non-transitory computer-readable storage medium 400 comprising the instructions (computer software). FIG. 5 illustrates a method 500 according to an embodiment of the invention. The method 500 is a method of cooling a fuel cell system 200 of a vehicle 1, such as the vehicle 1 illustrated in FIG. 1. In particular, the method 500 is a method of water spray cooling a fuel cell system 200 of a vehicle 1. At least part of the method 500 may be performed by the control system 300 illustrated in FIG. 3. In particular, the memory 306 may comprise computer-readable instructions 308 which, when executed by the processor 304, perform at least part of the method 500. Block 502 comprises condensing, using the condenser 253, water from fuel cell exhaust gases. If the internal baffles of the condenser 253 are actively cooled, for example by an active cooling device such as a fan, the method may comprise activating the active cooling device to cool the internal baffles of the condenser 253. Block 504 comprises collecting the condensed water in the receptacle 254, the receptacle 254 and condenser 253 defining a water source. If the receptacle 254 has an active entrance valve, the method may comprise opening the entrance valve to allow the receptacle 254 to fill. If the receptacle 254 or the pump has an active water exchange valve, the method may comprise closing the valve to allow the receptacle 254 to fill. Block 506 comprises operating the pump to pump water from the water source through at least one sprayer, wherein the at least one sprayer is connected to the pump. The at least one sprayer may be at one or more of the four sprayer locations shown in FIG. 2. For example, the control signal may be output to the pump to activate the pump. The activation of the pump may be executed in dependence on satisfaction of a suitable entry condition. For example, an air temperature signal from an air temperature sensor 314 may trigger activation ofthe pump 255, when the air temperature signal is greater than a threshold as described above. A similar condition may be applied for coolant, as described above. In some examples, an above-threshold air temperature will activate the sprayers 259A, 259B to cool both the air and coolant, and / or an above-threshold coolant temperature will activate the sprayers 259A, 259B to cool both the air and coolant. Alternatively, the sprayers 259A, 259B are controlled separately, based on a respective air temperature threshold and coolant temperature threshold. Block 508 comprises spraying, by the at least one sprayer, water from the water source onto the at least one heat exchanger 216, 236 associated with the fuel cell system 200. This may occur automatically as a result of operation ofthe pump. If a valve is positioned between the pump and the sprayer, block 508 may comprise outputting a control signal to open the valve. The method may be performed via closed loop control, for example to minimise a temperature error relative to a setpoint, such as the sensed temperature ofthe coolant and / or the intake air. If both the first and second pairs of sprayers 259A, 259B are implemented, they may or may not be operated at the same time as each other. For example, they may be connected to separate pumps 255, and / or may have individually controllable valves downstream of the pump(s) 255. For example, the condition for initiating blocks 506 and 508 (pumping and spraying) may differ for the different pairs of sprayers 259A, 259B. For instance, the activation of the pair of first sprayers 259A may depend on sensed air temperature from an air temperature sensor, whereas the activation of the pair of second sprayers 259B may depend on sensed coolant temperature from a coolant temperature sensor. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. For example, the source of the water for the sprayers 259A, 259B may from a water tank that is periodically manually re-filled, rather than being continuously replenished by water from exhaust gases from the fuel cell 202. It is to be understood that the or each controller 301 can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller 301 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 301 to implement the control techniques described herein (including some or all of the functionality required for the method(s) described herein). The set of instructions 308 could be embedded in said one or more electronic processors 304 of the controller 301; or alternatively, the set of instructions 308 could be provided as software to be executed in the controller 301. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful. The, or each, electronic processor 304 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions 308. The, or each, electronic memory device 306 may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and / or instructions therein or thereon. In an embodiment, the memory device 306 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor 304 may access the memory device 306 and execute and / or use that orthose instructions and information to carry out or perform some or all of the functionality and methodology described herein. The at least one memory device 306 may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors / computational devices. Examples of the form include, without limitation: 12 a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information / instructions. It will be appreciated that embodiments of the present invention can be realised in any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc. The blocks illustrated in FIG. 5 may represent steps in a method and / or sections of code in the computer program 308. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Claims

1. A cooling system for a fuel cell system of a vehicle 1, the cooling system comprising a water source a pump and at least one sprayer connected to the pump and being configured to spray water from the water source onto at least one heat exchanger associated with the fuel cell system.

2. The cooling system of claim 1, the water source comprising a condenser positioned in the path of at least some fuel cell exhaust gases, and a receptacle configured to collect water condensed in the condenser, wherein the pump is configured to pump condensed water from the receptacle, wherein the at least one sprayer is connected to the pump and is configured to spray the condensed water pumped from the receptacle onto the at least one heat exchanger.

3. The cooling system of claim 2, wherein the condenser is fluidly connected along an exhaust gas passage between an outlet of a humidifier of the fuel cell system and an exhaust gas vent of the fuel cell system for exhausting fuel cell byproducts.

4. The cooling system of any preceding claim, further comprising a pH corrector to at least partially neutralise a water pH upstream of the at least one sprayer.

5. The cooling system of claim 2 or 3 and claim 4, wherein the pH corrector is located upstream of the condenser.

6. The cooling system of any preceding claim, wherein the at least one heat exchanger comprises a first heat exchanger and wherein the cooling system comprises a plurality of the sprayers arranged to spray the water onto the first heat exchanger.

7. The cooling system of claim 6, wherein the plurality of the sprayers are arranged to simultaneously spray the water onto different areas of the first heat exchanger that are mostly or entirely non-overlapping.

8. The cooling system of any preceding claim, wherein the at least one heat exchanger comprises an intake gas intercooler for cooling fuel cell intake gas.

9. The cooling system of any preceding claim, wherein the at least one heat exchanger comprises a coolant radiator of a coolant circuit of the fuel cell system.

10. The cooling system of claim 8 and 9, comprising a plurality of the sprayers including a first subset configured to spray the intake gas intercooler and a second subset configured to spray the coolant radiator.

11. A fuel cell system comprising the cooling system of any one of the preceding claims, and a fuel cell.

12. The fuel cell system of claim 11, wherein the fuel cell is a hydrogen fuel cell.

13. A vehicle 1 comprising the cooling system of any one of claims 1 to 10, or the fuel cell system of claim11 or12.5 14. A method of cooling a fuel cell system of a vehicle 1, the method comprising:operating a pump to pump water from a water source, through at least one sprayer wherein the at least one sprayer is connected to the pump; andspraying by the at least one sprayer water from the water source onto at least one heat exchanger associated with the fuel cell system.1015. The method of claim 14, comprising:condensing, using a condenser, water from fuel cell exhaust gases;collecting the condensed water in a receptacle, the receptable and condenser defining the water source; and operating the pump to pump the condensed water from the receptacle to the at least one sprayer.15s

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