Fuel cell system

Abstract

fuel cell system, featuring a fuel cell stack an ejector, an injector set comprising a first injector that supplies fuel gas to the ejector, and a second injector arranged parallel to the first injector, which has a smaller fuel gas injection quantity than the first injector, and which supplies the fuel gas to the ejector, a third injector that supplies the fuel gas to the fuel electrodes of the fuel cell stack, a fuel gas supply device that supplies the fuel gas to the first, second and third injectors, a first supply flow path that connects the fuel gas supply device, the injector set, the ejector and the fuel cell stack in that order, a second supply flow path, which branches off in an area between the fuel gas supply device and the injector set of the first supply flow path, bypasses the injector set and the ejector, and joins the first supply flow path at a downstream position of the ejector to enable the supply of fuel gas from the third injector to the fuel electrodes of the fuel cell stack, a circulation flow path that recovers the fuel exhaust gas emitted from the fuel electrodes of the fuel cell stack and returns the fuel exhaust gas to the ejector as circulation gas, a temperature detector that measures the temperature of the fuel cell stack, and a controller wherein the ejector supplies mixed gas, containing the fuel gas and the circulating gas, to the fuel electrodes of the fuel cell stack, and wherein, in the event that the temperature of the fuel cell stack detected by the temperature detector exceeds a predetermined threshold, the controller switches from the first injector to the second injector and supplies the fuel gas to the ejector, and the controller supplies the fuel gas from the third injector to the fuel electrodes of the fuel cell stack.

Description

TECHNICAL AREA

[0001] The invention relates to a fuel cell system. BACKGROUND

[0002] A fuel cell (FC) is a power generation device that produces electrical power, or current, through an electrochemical reaction between hydrogen (H₂), which serves as the fuel gas, and oxygen (O₂), which serves as the oxidizer gas, in a fuel cell stack (hereinafter also referred to simply as a "stack") consisting of stacked unit fuel cells (hereinafter also referred to as cells). Hereinafter, the fuel gas and oxidizer gas can be referred to collectively and simply as the "reaction gas" or "gas".

[0003] In general, unit fuel cells consist of a membrane electrode assembly (MEA) and, if required, two separators that sandwich the membrane electrode assembly.

[0004] The membrane electrode arrangement has such a structure that a catalyst layer and a gas diffusion layer are formed in that order on both surfaces of a solid polymer electrolyte membrane with proton (H+) conductivity (hereinafter simply referred to as the "electrolyte membrane").

[0005] In general, the separators have a structure such that a groove is formed on a surface in contact with the gas diffusion layer, serving as a flow path for the reaction gases. The separators act as a collector for the generated current or electricity.

[0006] In the fuel cell's anode, hydrogen supplied from the gas flow path and the gas diffusion layer is protonated by the catalytic activity of the catalyst layer. The protonated hydrogen then passes through the electrolyte membrane to the cathode. Simultaneously, an electron is generated, which travels through an external circuit, performs work, and then travels to the cathode. The oxygen supplied to the cathode reacts with the proton and the electron at the cathode, producing water.

[0007] The generated water supplies the electrolyte membrane with the necessary moisture. The excess water permeates the gas diffusion layer and is then drained to the outside.

[0008] It is required that a fuel cell system includes a fuel cell in which fuel exhaust, containing redundant fuel from a fuel electrode, circulates on a fuel supply side and excellent fuel circulation is ensured over an overall operating range from low load to high load.

[0009] For example, patent literature 1 discloses a fuel cell system that is equipped with an ejector bypass line and a controller for controlling the opening and controlling it depending on an operating load condition.

[0010] Patent literature 2 discloses a fuel cell system with a bypass line and a buffer storage arranged in the bypass line. Patent Literature 1: Japanese Patent Application JP 2003-151593A Patent Literature 2: Japanese Patent Application JP 2007-242476A

[0011] During high-temperature operation of the stack, the amount of water vapor contained in the anode exhaust (water vapor removed from the stack) increases. During high-temperature operation, it is necessary to reduce the drying out of the stack interior.

[0012] Accordingly, during high-temperature operation, the flow rate of anode exhaust gas discharged from the stack to the outside of the system must be reduced. Even in the case of a fuel cell system with a recirculation path for the anode exhaust gas, water vapor is drawn from the stack and condenses in a gas-liquid separator installed in the recirculation path, at a lower temperature than the temperature inside the stack, and so on. Consequently, not all of the water vapor contained in the anode exhaust gas can return to the stack as recirculation gas. As a result, the interior of the stack tends to dry out.

[0013] In the fuel cell system described in patent literature 1, the circulating gas flow rate can be reduced by introducing fuel gas from the ejector bypass line into the stack and utilizing a backflow phenomenon to the ejector resulting from a high pressure drop at the stack inlet. Accordingly, it is possible to reduce the amount of water vapor discharged from the stack. However, the flow velocity of the circulating gas supplied to the stack by the ejector is not taken into account, and it is sometimes difficult to reduce the amount of water vapor removed from the stack based on an increase in stack temperature associated with an increase in load.

[0014] The fuel cell system of patent specification 2 can reduce the pressure increase on the ejector outlet side. However, when using such a fuel cell system as a power source for a fuel cell vehicle (hereinafter also referred to as "vehicle"), etc., a response to the required power that depends on the vehicle's operating state may be insufficient. SUMMARY

[0015] The disclosed embodiments were achieved in consideration of the circumstances described above. One objective of the disclosed embodiments is to create a fuel cell system configured to reduce the drying out of the interior of the fuel cell stack and to increase the power generation output of the fuel cell stack by reducing the circulating gas flow rate (i.e., the amount of water vapor removed from the fuel cell stack) during high-temperature operation.

[0016] In a first embodiment, a fuel cell system is created which has: a fuel cell stack an ejector, an injector set comprising a first injector that supplies fuel gas to the ejector, and a second injector arranged parallel to the first injector, which has a smaller fuel gas injection quantity than the first injector, and which supplies the fuel gas to the ejector, a third injector that supplies the fuel gas to the fuel electrodes of the fuel cell stack, a fuel gas supply device that supplies the fuel gas to the first, second and third injectors, a first supply flow path that connects the fuel gas supply device, the injector set, the ejector and the fuel cell stack in that order, a second supply flow path, which branches off in an area between the fuel gas supply device and the injector set of the first supply flow path, bypasses the injector set and the ejector, and joins the first supply flow path at a downstream position of the ejector to enable the supply of fuel gas from the third injector to the fuel electrodes of the fuel cell stack, a circulation flow path that recovers the fuel exhaust gas emitted from the fuel electrodes of the fuel cell stack and returns the fuel exhaust gas to the ejector as circulation gas, a temperature detector that measures the temperature of the fuel cell stack, and a controller wherein the ejector supplies mixed gas, containing the fuel gas and the circulating gas, to the fuel electrodes of the fuel cell stack, and wherein, in the event that the temperature of the fuel cell stack detected by the temperature detector exceeds a predetermined threshold, the controller switches from the first injector to the second injector and supplies the fuel gas to the ejector, and the controller supplies the fuel gas from the third injector to the fuel electrodes of the fuel cell stack.

[0017] In the event that the temperature of the fuel cell stack detected by the temperature detector is the predetermined threshold or less, the controller can supply the fuel gas from the first injector to the ejector, and the controller can stop the supply of fuel gas from the second injector to the ejector and from the third injector to the fuel electrodes of the fuel cell stack.

[0018] According to the disclosed embodiments, the fuel cell system can be configured to reduce the drying out of the interior of the fuel cell stack and to increase the power generation output of the fuel cell stack by reducing the circulating gas flow rate during high-temperature operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The attached drawings show: Fig. 1 a schematic configuration diagram of an example of the fuel cell system according to the disclosed embodiments, and Fig. 2 a flowchart of an example of the method for controlling the fuel cell system according to the disclosed embodiments. DETAILED DESCRIPTION

[0020] The fuel cell system of the disclosed embodiments is a fuel cell system that comprises: a fuel cell stack an ejector, an injector set comprising a first injector that supplies fuel gas to the ejector, and a second injector arranged parallel to the first injector, which has a smaller fuel gas injection quantity than the first injector, and which supplies the fuel gas to the ejector, a third injector that supplies the fuel gas to the fuel electrodes of the fuel cell stack, a fuel gas supply device that supplies the fuel gas to the first, second and third injectors, a first supply flow path that connects the fuel gas supply device, the injector set, the ejector and the fuel cell stack in that order, a second supply flow path, which branches off in an area between the fuel gas supply device and the injector set of the first supply flow path, bypasses the injector set and the ejector, and joins the first supply flow path at a downstream position of the ejector to enable the supply of fuel gas from the third injector to the fuel electrodes of the fuel cell stack, a circulation flow path that recovers the fuel exhaust gas emitted from the fuel electrodes of the fuel cell stack and returns the fuel exhaust gas to the ejector as circulation gas, a temperature detector that measures the temperature of the fuel cell stack, and a controller wherein the ejector supplies mixed gas, containing the fuel gas and the circulating gas, to the fuel electrodes of the fuel cell stack, and wherein, in the event that the temperature of the fuel cell stack detected by the temperature detector exceeds a predetermined threshold, the controller switches from the first injector to the second injector and supplies the fuel gas to the ejector, and the controller supplies the fuel gas from the third injector to the fuel electrodes of the fuel cell stack.

[0021] The fuel cell system of the disclosed embodiments comprises the circulation flow path and the injectors, which differ in the amount of fuel gas injected. During high-temperature operation of the system, fuel gas is supplied to the stack from the second supply flow path (an ejector bypass flow path), and fuel gas is supplied to the ejector from the second injector with a small amount of fuel gas injected, thereby reducing the circulation gas flow rate, i.e., the amount of water vapor removed from the stack.

[0022] According to the disclosed embodiments, the use of both the ejector and the ejector bypass flow path during high-temperature operation provides the force that causes the fuel gas to flow back from the ejector bypass flow path to the recirculation gas injection nozzle side of the ejector. This allows the recirculation flow rate to be reduced.

[0023] If, during high-temperature operation, the flow rate of the fuel gas supplied to the ejector is reduced and the circulating gas flow rate is reduced without using the ejector bypass flow path, the stack's performance may be reduced by an increase in anode overvoltage.

[0024] By using the ejector bypass flow path, the flow rate of the circulating gas supplied to the stack can be reduced, while the flow rate of the fuel gas supplied to the stack is increased.

[0025] Examples of high-temperature operation include, but are not limited to, operating conditions that place more emphasis on safe power delivery than on fuel efficiency: driving uphill in a vehicle in which the fuel cell system of the disclosed embodiments is installed, and driving the vehicle while towing another vehicle.

[0026] Fig. Figure 1 is a schematic configuration diagram of an example of the fuel cell system according to the disclosed embodiments.

[0027] A in Fig. The fuel cell system 100 shown in Figure 1 comprises the following: a fuel cell stack 11; a temperature detector 12; a first feed flow path 13; a circulation flow path 14; a second feed flow path 15; an injector set 20 comprising a first injector 21 and a second injector 22 in parallel; a third injector 23; an ejector 24; a fuel gas supply device 30; an oxidation gas supply device 40; an oxidation gas supply flow path 41; an oxidation gas discharge flow path 42; and a controller 50.

[0028] The temperature detector 12, the first injector 21, the second injector 22, and the third injector 23 are electrically connected to the controller 50. The controller 50 receives the temperature of the fuel cell stack 11 as detected by the temperature detector 12. Based on this temperature, the controller 50 controls the first injector 21, the second injector 22, and the third injector 23.

[0029] The fuel cell system of the disclosed embodiments comprises at least the fuel cell stack, the temperature detector, the first feed flow path, the circulation flow path, the second feed flow path, the injector set comprising the first and second injectors in parallel, the third injector, the ejector, the fuel gas supply device, and the controller. In general, the fuel cell system further comprises an oxidation gas supply device, an oxidation gas supply flow path, an oxidation gas discharge flow path, a cooling water supply device, a cooling water circulation flow path, etc.

[0030] In general, the fuel cell system of the disclosed embodiments is installed and used in a fuel cell vehicle that uses an engine as a power source.

[0031] The motor is not particularly limited. It can be a conventionally known electric motor.

[0032] The fuel cell stack can supply the engine with electricity.

[0033] The fuel cell stack is made up of stacked unit fuel cells.

[0034] The number of stacked unit fuel cells is not particularly limited. For example, two to several hundred unit fuel cells can be stacked, or two to 200 unit fuel cells can be stacked.

[0035] The fuel cell stack can contain an end plate at both ends of the unit fuel cells located in the stacking direction.

[0036] Each standard fuel cell contains at least one membrane electrode assembly with an oxidation electrode, an electrolyte membrane, and a fuel electrode. Depending on requirements, it may include two separators that sandwich the membrane electrode assembly.

[0037] The separators can have a reaction gas flow path on a surface in contact with a gas diffusion layer. Additionally, the separators can have a cooling water flow path on a surface opposite the surface in contact with the gas diffusion layer to maintain the temperature of the fuel cell stack at a constant level.

[0038] The separators can have inlet and outlet openings for supplying reaction gas and cooling water towards the fuel cell stack.

[0039] Examples of the supply opening include, but are not limited to, a fuel gas supply opening, an oxidation gas supply opening, and a cooling water supply opening.

[0040] Examples of the outlet opening include, but are not limited to, a fuel gas outlet opening, an oxidation gas outlet opening, and a cooling water outlet opening.

[0041] The separators can be gas-tight, electrically conductive, etc. Examples of electrically conductive elements include, but are not limited to, gas-tight, dense carbon obtained by carbon compaction, and a metal plate (such as an iron plate, an aluminum plate, or a stainless steel plate) obtained by pressing. The separators can also have a current-collecting function.

[0042] The fuel cell stack can have a distributor, such as an inlet distributor that communicates between inlet ports, and an outlet distributor that communicates between outlet ports.

[0043] Examples of inlet distributors include, but are not limited to, an anode inlet distributor, a cathode inlet distributor, and a cooling water inlet distributor.

[0044] Examples of outlet distributors include, but are not limited to, an anode outlet distributor, a cathode outlet distributor, and a cooling water outlet distributor.

[0045] The oxidation electrode comprises an oxidation electrode catalyst layer and a gas diffusion layer.

[0046] The fuel electrode comprises a fuel electrode catalyst layer and a gas diffusion layer.

[0047] The oxidation electrode catalyst layer and the fuel electrode catalyst layer can contain, for example, a catalyst metal to accelerate an electrochemical reaction, a proton-conducting electrolyte, or electron-conducting carbon particles.

[0048] Platinum (Pt) or an alloy of Pt and another metal (e.g. a Pt alloy mixed with cobalt, nickel, etc.) can be used as the catalyst metal.

[0049] The electrolyte can be a fluorinated resin or similar substance. For example, a Nafion solution can be used as a fluorinated resin.

[0050] The catalyst metal is carried by carbon particles. In each catalyst layer, the carbon particles carrying the catalyst metal (i.e., the catalyst particles) and the electrolyte can be mixed.

[0051] For example, water-repellent carbon particles can be used as the carbon particles for carrying the catalyst metal (i.e., carrying carbon particles), which are obtained by enhancing the water-repellent properties of commercially available carbon particles (carbon powder) through heating.

[0052] The gas diffusion layer can be a gas-permeable, electrically conductive element or something similar.

[0053] Examples of the electrically conductive element include, but are not limited to, a porous carbon material, such as carbon fabric and carbon paper, and a porous metal material, such as metal fabric and metal foam.

[0054] The electrolyte membrane can be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include, but are not limited to, hydrocarbon electrolyte membranes and fluorine electrolyte membranes, such as a moisture-containing, thin perfluorosulfonic acid membrane. The electrolyte membrane can be, for example, a Nafion membrane (manufactured by DuPont).

[0055] The temperature detector detects the temperature of the fuel cell stack. The temperature of the fuel cell stack can be the temperature of the cooling water circulating in and out of the fuel cell stack. It can also be the temperature of the cooling water flowing around the fuel cell stack's cooling water inlet, or it can be the temperature of the cooling water flowing around the fuel cell stack's cooling water outlet.

[0056] Examples of temperature detectors include, but are not limited to, a temperature sensor.

[0057] The first supply flow path connects the fuel gas supply device, the injector set, the ejector and the fuel cell stack in that order.

[0058] The first supply flow path connects the fuel gas supply unit and the injector assembly to allow the supply of fuel gas from the fuel gas supply unit to the first and second injectors of the injector assembly. The first supply flow path also connects the injector assembly and the ejector to allow the supply of fuel gas from the injector assembly to the ejector. Furthermore, the first supply flow path connects the ejector and a fuel-based gas inlet (e.g., the anode inlet manifold) of the fuel cell stack to allow the supply of the mixed gas from the ejector to the fuel electrodes of the fuel cell stack. The fuel-based gas comprises fuel gas and a mixed gas containing fuel gas and recirculation gas.

[0059] The second supply flow path branches off downstream of the fuel gas supply device of the first supply flow path, i.e., in the area between the fuel gas supply device and the injector assembly of the first supply flow path. It bypasses the injector assembly and the ejector and merges into the first supply flow path downstream of the ejector to enable the supply of fuel gas from the third injector to the fuel electrodes of the fuel cell stack. Accordingly, the second supply flow path connects the fuel gas supply device and the third injector to enable the supply of fuel gas from the fuel gas supply device to the third injector.

[0060] The second supply flow path is an ejector bypass flow path that bypasses the ejector to allow the direct supply of fuel gas to the fuel cell stack.

[0061] The circulation flow path enables the connection of the fuel exhaust outlet (e.g., the anode outlet distributor) of the fuel cell stack to the ejector, the recovery of the fuel exhaust emitted by the fuel electrodes of the fuel cell stack, and the supply of the fuel exhaust as circulation gas to the ejector.

[0062] The fuel exhaust gas mainly contains fuel gas that has passed through the fuel electrodes without reacting, and moisture, which is water that was generated at the oxidation electrodes and transferred to the fuel electrodes.

[0063] A gas-liquid separator can be installed in the circulation flow path to remove condensed water formed by the cooling of the fuel exhaust gas's water vapor within the flow path. Additionally, a drain flow path can be installed in the circulation flow path, branching off from the circulation flow path through the gas-liquid separator, and a drain valve can be installed in the drain flow path.

[0064] In the gas-liquid separator, the removed condensate can be drained by opening the drain valve of the drain path branching off from the circulation flow path.

[0065] The circulation flow path can also be equipped with a circulation pump for the efficient supply of the circulating gas to the ejector.

[0066] The ejector delivers the mixed gas, containing the fuel gas and the circulation gas, to the fuel electrodes of the fuel cell stack. A commercially available ejector can be used.

[0067] The injector set includes the first injector and the second injector in parallel.

[0068] The first injector delivers the fuel gas to the ejector.

[0069] The second injector is arranged parallel to the first injector, has a smaller amount of fuel gas injection than the first injector, and supplies the fuel gas to the ejector.

[0070] The amount of fuel gas injected by the second injector is not particularly limited, as long as it is smaller than that of the first injector.

[0071] The injectors of the injector set are electrically connected to the controller. Any one of the injectors in the set can be activated by a signal from the controller. To switch the injector in use, the injector set can be equipped with an injector switching valve. This switching valve can be electrically connected to the controller, and the injector in use can be switched by controlling the valve via a signal from the controller.

[0072] The third injector is located on the second supply flow path, separate from the injector set, and it delivers the fuel gas directly to the fuel electrodes of the fuel cell stack.

[0073] The fuel gas injection quantity of the third injector is not particularly limited and can be smaller than that of the first injector. The fuel gas injection quantity of the third injector can also be greater, less, or equal to the fuel gas injection quantity of the second injector. From the perspective of reducing the circulation flow rate, the fuel gas injection quantity of the third injector can be greater than that of the second injector.

[0074] Generally, the second feed path merges into the first feed path at a downstream position of the ejector, and the pressure drop around the fuel-based gas inlet (e.g., the anode inlet manifold) of the stack is greater than the pressure drop of the first feed path. Consequently, some of the fuel gas supplied to the fuel cell stack by the third injector flows back through the first feed path, reducing the supply of the mixed gas from the ejector to the fuel cell stack. This reduces the recirculating gas flow rate and the amount of water vapor removed from the fuel cell stack by the anode exhaust.

[0075] By using the third injector in combination with the second injector, which has a lower fuel gas injection quantity than the first injector, the increase in anode overvoltage is reduced and the decrease in stack power is lessened.

[0076] The third injector can be electrically connected to the controller in order to switch the start switch of the third injector on and off via the controller.

[0077] The fuel gas supply device delivers the fuel gas to the first, second, and third injectors.

[0078] The fuel gas is a gas that mainly contains hydrogen. It could, for example, be hydrogen gas.

[0079] Examples of fuel gas supply equipment include, but are not limited to, a fuel tank such as a liquid hydrogen tank and a pressurized hydrogen tank.

[0080] The fuel gas supply device can be electrically connected to the controller to control the fuel gas supply injectors via a signal from the controller. Additionally, a control valve for controlling the fuel gas supply to the third injector can be located upstream of the third injector on the second supply flow path. The control valve can be electrically connected to the controller to control the fuel gas supply from the fuel gas supply device to the third injector by controlling the opening and closing of the control valve via a signal from the controller.

[0081] The fuel cell system can include the oxidation gas supply device, the oxidation gas supply flow path, and the oxidation gas discharge flow path.

[0082] The oxidation gas supply device provides at least the oxidation electrodes of the fuel cell stack with oxidation gas.

[0083] Examples of oxidation gas supply devices include, but are not limited to, an air compressor. The air compressor is driven by a control signal from the controller and supplies the oxidation gas to the cathode side (e.g., the oxidation electrode and the cathode inlet manifold) of the fuel cell.

[0084] The oxidation gas supply flow path enables the connection of the oxidation gas supply device to the fuel cell stack and the supply of oxidation gas from the oxidation gas supply device to the oxidation electrodes of the fuel cell stack.

[0085] The oxidizing gas is an oxygen-containing gas. It can be air, dry air, pure oxygen, or something similar.

[0086] The oxidation gas discharge flow path allows the oxidation gas to flow away from the oxidation electrodes of the fuel cell stack.

[0087] The fuel cell system may include a cooling water supply device and a cooling water circulation flow path.

[0088] The cooling water circulation flow path enables the connection between the cooling water inlet manifold and the cooling water outlet manifold installed in the fuel cell stack, the circulation of the cooling water supplied by the cooling water supply device into and out of the fuel cell stack, and the cooling of the fuel cell stack.

[0089] Examples of cooling water supply equipment include, but are not limited to, a cooling water pump.

[0090] A mixed solution of ethylene glycol and water can be used as cooling water (refrigerant) to prevent freezing at low temperatures.

[0091] The fuel cell system may include a fuel exhaust gas separator.

[0092] The fuel gas separator can discharge the fuel gas, in which the concentration of the fuel gas is at or below the predetermined concentration, to the outside. "Outside" refers to the exterior of the fuel cell system.

[0093] The fuel exhaust separator may include a fuel exhaust drain valve. Depending on requirements, it may also include a fuel exhaust flow path.

[0094] The fuel exhaust gas drain valve controls the amount of fuel exhaust gas being discharged.

[0095] The fuel exhaust gas discharge flow path can branch off from the circulation flow path.

[0096] The fuel exhaust gas separator can discharge the fuel exhaust gas to the outside when, for example, the concentration of the fuel gas, such as hydrogen, in the fuel exhaust gas is at or below the predetermined concentration. The predetermined concentration of the fuel gas is not particularly limited and can be appropriately determined, for example, by taking into account the fuel efficiency of the fuel cell system.

[0097] The method for determining the concentration of the fuel gas in the fuel exhaust is not particularly restrictive. For example, a conventionally known concentration sensor can be used.

[0098] The controller manages the fuel cell system.

[0099] The controller can be connected via an input / output interface to the temperature detector, the injector set, the third injector, the fuel gas supply device, the fuel exhaust gas separator, the oxidation gas supply device, and so on.

[0100] The controller decides whether the temperature of the fuel cell stack, as detected by the temperature sensor, exceeds the predetermined threshold. The controller also switches the injector used in the injector set, controls the on / off switching of the start switch of the third injector, etc.

[0101] The controller physically comprises a processing unit, such as a central processing unit (CPU), a storage device, such as read-only memory (ROM) and random-access memory (RAM), and the input / output interface. The ROM is used to store a control program processed by the CPU, control data, etc., and the RAM is primarily used as various workspaces for control processes. The controller can also be a control unit, such as an engine control unit (ECU).

[0102] Fig. Figure 2 is a flowchart of an example of the method for controlling the fuel cell system according to the disclosed embodiments. The disclosed embodiments are not limited to this typical example.

[0103] In the Fig. In the control methods shown in Figure 2, the controller first supplies the fuel gas from the first injector to the ejector at the time of the start-up of the fuel cell stack or during normal operation of the fuel cell stack, and it supplies the mixed gas to the fuel electrodes of the fuel cell stack using the ejector.

[0104] Next, the temperature detector measures the temperature of the fuel cell stack.

[0105] If the detected temperature of the fuel cell stack is at or below the predetermined threshold, the controller terminates the control process.

[0106] Conversely, if the measured temperature of the fuel cell stack exceeds the predetermined threshold, the controller switches from the first injector to the second injector and delivers the fuel gas to the ejector, and the controller starts the third injector and delivers the fuel gas from the third injector to the fuel electrodes of the fuel cell stack. The controller then terminates the control process. (1) Detection of the temperature of the fuel cell stack

[0107] The temperature detector records the temperature of the fuel cell stack at predetermined times.

[0108] The method for measuring the temperature of the fuel cell stack is not particularly restricted. It can be achieved, for example, by installing a conventionally known temperature sensor in the fuel cell system and measuring the temperature of the fuel cell stack (e.g., the temperature of the cooling water around the cooling water inlet (such as the cooling water inlet manifold) of the fuel cell stack) using the temperature sensor.

[0109] The timing for recording the temperature of the fuel cell stack is not particularly limited. The temperature can be recorded every time a predetermined time elapses after the fuel cell stack has started operating; it can be recorded when the fuel cell stack starts operating; or it can be recorded continuously. The recording time can be set appropriately. (2) Assessment of whether the temperature of the fuel cell stack exceeds the predetermined threshold or not

[0110] The controller assesses whether the temperature of the fuel cell stack detected by the temperature detector exceeds the predetermined threshold or not.

[0111] The temperature threshold of the fuel cell stack can be determined, for example, as follows: A data set showing a correlation between the temperature of the fuel cell stack and the power generation output of the fuel cell stack is prepared in advance by an experiment, etc., and the temperature threshold of the fuel cell stack is appropriately determined by the power output, etc., of the fuel cell stack obtained from the data set. (3) Control of the circulating gas flow rate (3-1) The case where the temperature of the fuel cell stack exceeds the predetermined threshold

[0112] If the temperature of the fuel cell stack, as detected by the temperature sensor, exceeds the predetermined threshold, the controller switches from the first injector to the second injector and delivers the fuel gas to the ejector; using the ejector, the controller delivers the mixed gas to the fuel electrodes of the fuel cell stack; and the controller starts the third injector and delivers the fuel gas from the third injector to the fuel electrodes of the fuel cell stack. The controller then terminates the control process.

[0113] Accordingly, the circulating gas flow rate can be reduced during high-temperature operation of the fuel cell stack. This can reduce the drying out of the interior of the fuel cell stack and increase its power generation output. (3-2) The case in which the temperature of the fuel cell stack is the predetermined threshold or less

[0114] At the time of starting operation of the fuel cell stack and during normal operation of the fuel cell stack, the controller supplies the fuel gas from the first injector to the ejector, and the controller does not supply the fuel gas from the second injector to the ejector and from the third injector to the fuel electrodes of the fuel cell stack.

[0115] Accordingly, the controller can terminate control if the temperature of the fuel cell stack is at or below the predetermined threshold, and if the controller is supplying the fuel gas from the first injector to the ejector.

[0116] The controller also switches from the second injector to the first injector and delivers fuel gas to the ejector and from the third injector to the fuel electrodes of the fuel cell stack if the temperature of the fuel cell stack is at or below the predetermined threshold. At this point, the controller stops the third injector to terminate the fuel gas supply to the fuel electrodes of the fuel cell stack. The controller can then end the control process.

[0117] The timing at which the second and subsequent control cycles are started after the first control cycle has been completed by the controller is not particularly limited. They can be carried out at a predetermined time interval, the timing of which can be set accordingly. REFERENCE MARK LIST 11 fuel cell stacks 12 Temperature detector 13 First feed flow path 14 Circulation flow path 15 Second feed flow path 20 injector sets 21 First injector 22 Second injector 23 Third injector 24 ejector 30 Fuel gas supply device 40 Oxidation gas supply device 41 Oxidation gas supply flow path 42 Oxidation gas removal flow path 50 controllers 100 fuel cell systems

Claims

[1] Fuel cell system comprising a fuel cell stack an ejector, an injector set comprising a first injector that supplies fuel gas to the ejector, and a second injector arranged parallel to the first injector, which has a smaller fuel gas injection quantity than the first injector, and which supplies the fuel gas to the ejector, a third injector that supplies the fuel gas to the fuel electrodes of the fuel cell stack, a fuel gas supply device that supplies the fuel gas to the first, second and third injectors, a first supply flow path that connects the fuel gas supply device, the injector set, the ejector and the fuel cell stack in that order, a second supply flow path, which branches off in an area between the fuel gas supply device and the injector set of the first supply flow path, bypasses the injector set and the ejector, and joins the first supply flow path at a downstream position of the ejector to enable the supply of fuel gas from the third injector to the fuel electrodes of the fuel cell stack, a circulation flow path that recovers the fuel exhaust gas emitted from the fuel electrodes of the fuel cell stack and returns the fuel exhaust gas to the ejector as circulation gas, a temperature detector that measures the temperature of the fuel cell stack, and a controller wherein the ejector supplies mixed gas, containing the fuel gas and the circulating gas, to the fuel electrodes of the fuel cell stack, and wherein, in the event that the temperature of the fuel cell stack detected by the temperature detector exceeds a predetermined threshold, the controller switches from the first injector to the second injector and supplies the fuel gas to the ejector, and the controller supplies the fuel gas from the third injector to the fuel electrodes of the fuel cell stack. [2] Fuel cell system according to claim 1, wherein in the case where the temperature of the fuel cell stack detected by the temperature detector is the predetermined threshold or less, the controller supplies the fuel gas from the first injector to the ejector and the controller stops the supply of the fuel gas from the second injector to the ejector and from the third injector to the fuel electrodes of the fuel cell stack.

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