Patent Publication Number: US-2021194024-A1

Title: Fuel cell system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2019-231269 filed on Dec. 23, 2019, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a fuel cell system. 
     2. Description of Related Art 
     For example, when operation of a fuel cell system is stopped in a below-freezing environment, moisture generated by electric power generation can freeze to become ice near an off gas outlet port of a fuel cell stack and the ice can block the off gas outlet port. Therefore, at the time of restart of the fuel cell system, a warm-up operation for melting the ice using heat generated by electric power generation is performed in order to restrain decrease in electric power generation performance due to the block of the off gas outlet port. 
     However, in a fuel cell system including a cyclic path for an off gas and an ejector, hydrogen gas is supplied from a tank through the ejector to the fuel cell stack, and further the off gas is also supplied from the cyclic path through the ejector to the fuel cell stack (see Japanese Patent Application Publication No. 2013-134882, for example). Therefore, another gas (referred to as an “impurity gas” hereinafter) in the off gas remaining in the cyclic path and the ejector, for example, nitrogen gas, is mixed with the hydrogen gas, so that the concentration of the hydrogen gas decreases. Therefore, because of the block of the off gas outlet port, the fuel cell stack is filled with the impurity gas, and the supply amount of the hydrogen gas becomes insufficient, so that there is a fear that it is not possible to continue the electric power generation until the ice sufficiently melts. 
     SUMMARY 
     In response, it is possible to continue the electric power generation by continuously supplying a high-concentration hydrogen gas to the fuel cell from a linear solenoid valve connected to the tank, while bypassing the ejector. However, in the case of supplying the hydrogen gas through the path that bypasses the ejector, the hydrogen gas can reversely flow into the ejector and the supply amount of the hydrogen gas can decrease, because the pressure in the cyclic path from the off gas outlet port to the ejector is lower than the pressure in the fuel cell stack. 
     It is possible to restrain the reverse flow by adding another ejector (referred to as an “additional ejector” hereinafter) connected to the ejector in parallel and another linear solenoid valve (referred to as an “additional valve” hereinafter) connected to the additional ejector and supplying a small amount of hydrogen gas from the additional valve through the additional ejector. However, the hydrogen gas flowing from the additional valve does not pulsate the pressure of an anode system. Therefore, liquid water sucked into the additional ejector together with the off gas or liquid water generated by condensation of water vapor due to a low-temperature hydrogen gas is hard to be discharged from the additional ejector. Accordingly, the liquid water can remain in the additional ejector even after the warm-up operation, can freeze when the ambient temperature becomes a below-freezing temperature, and can obstruct the injection of the hydrogen gas. 
     The disclosure provides a fuel cell system that can easily discharge the liquid water that remains in the ejector after the warm-up operation of the fuel cell. 
     A fuel cell system in the disclosure includes: a fuel cell that includes an installation port and a discharge port for a reactant gas that is used for electric power generation; a first injection device that intermittently injects the reactant gas; a second injection device and a third injection device that continuously inject the reactant gas; an ejector that includes an ejection port from which the reactant gas discharged from the discharge port is ejected together with the reactant gas injected from the first injection device or the second injection device; a first flow passage that connects the installation port and the ejection port; a second flow passage through which the reactant gas injected from the third injection device is led to the first flow passage without the ejector; and a control device configured to control an injection of the first injection device, the second injection device and the third injection device, in which: the ejector includes a common third flow passage through which the reactant gas discharged from the discharge port and the reactant gas injected from the first injection device and the second injection device flow to the ejection port; and the control device is configured to perform a warm-up operation of the fuel cell by executing an injection of the third injection device, restrains a reverse flow of the reactant gas by executing an injection of the second injection device, the reverse flow being a reverse flow by which the reactant gas flows from the third injection device to the third flow passage through the second flow passage, the first flow passage and the ejection port, and executes the injection of the first injection device after completion of the warm-up operation of the fuel cell. 
     With the above configuration, the control device is configured to perform the warm-up operation of the fuel cell by executing the injection of the third injection device, and restrains the reverse flow of the reactant gas by which the reactant gas flows from the third injection device to the third flow passage through the second flow passage, the first flow passage and the ejection port, by executing the injection of the second injection device. Since the second injection device and the third injection device continuously inject the reactant gas, the reverse flow of the reactant gas to the ejector is restrained. Further, it is possible to perform the warm-up operation, while continuously supplying the reactant gas that does not contain an impurity gas in the ejector and that has a high concentration from the third injection device to the fuel cell. 
     Further, the control device may be configured to execute the injection of the first injection device after the completion of the warm-up operation of the fuel cell. The first injection device intermittently injects the reactant gas, and the fuel cell uses the reactant gas for the electric power generation. Therefore, the pressure in the ejector pulsates due to the intermittent injection of the first injection device. 
     Further, the ejector includes the common third flow passage through which the reactant gas discharged from the discharge port and the reactant gas injected from the first injection device and the second injection device flow to the ejection port. Therefore, liquid water generated in the third flow passage by the injection of the second injection device is discharged from the discharge port by the pulsation of the pressure due to the intermittent injection of the first injection device. 
     Accordingly, the fuel cell system in the disclosure can easily discharge the liquid water that remains in the ejector after the warm-up operation of the fuel cell. 
     In the above configuration, the control device may be configured to stop the injection of the second injection device and the third injection device after the completion of the warm-up operation of the fuel cell. 
     In the above configuration, the control device may be configured to stop the injection of the first injection device until the completion of the warm-up operation of the fuel cell. 
     In the above configuration, the control device may be configured to execute the injection of the second injection device at a flow rate depending on the temperature of the fuel cell at a time of start of the warm-up operation of the fuel cell. 
     In the above configuration, the ejector may include a first nozzle from which the reactant gas injected from the first injection device is injected to the third flow passage, and a second nozzle from which the reactant gas injected from the second injection device is injected to the third flow passage. 
     In the above configuration, the ejector may include a common third nozzle from which the reactant gas injected from the first injection device and the reactant gas injected from the second injection device are injected to the third flow passage. 
     In the above configuration, the control device may be configured to perform the warm-up operation of the fuel cell until the temperature of the fuel cell exceeds a freezing point. 
     In the above configuration, the first injection device may include an injector, and each of the second injection device and the third injection device may include a linear solenoid valve. 
     With the disclosure, it is possible to easily discharge the liquid water that remains in the ejector after the warm-up operation of the fuel cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a configuration diagram showing an exemplary fuel cell system; 
         FIG. 2  is a diagram showing an exemplary flow of an anode gas and an anode off gas at the time of a warm-up operation of a fuel cell; 
         FIG. 3  is a diagram showing an exemplary flow of the anode gas and the anode off gas at the time of a normal operation of the fuel cell; 
         FIG. 4  is a diagram showing an exemplary temporal change in flow rates of anode gases injected from a bypass linear solenoid valve, an auxiliary linear solenoid valve and an injector; 
         FIG. 5  is a diagram showing a result of performance comparison between an injector and a linear solenoid valve; 
         FIG. 6  is a flowchart showing an exemplary process by an electronic control unit (ECU); 
         FIG. 7  is a configuration diagram showing another exemplary fuel cell system; and 
         FIG. 8  is a configuration diagram showing a fuel cell system in a comparative example. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Configuration of Fuel Cell System  100   
       FIG. 1  is a configuration diagram showing an exemplary fuel cell system  100 . The fuel cell system  100  is mounted on a fuel cell vehicle, for example, and includes a fuel cell (FC)  1 , a motor M, a cathode system  2 , an anode system  3 , and a control system  7 . The electric configuration of connecting the FC  1  and the motor M is not illustrated. 
     The FC  1  includes a laminated body constituted by a plurality of unit cells each of which has a solid polymer electrolyte. The FC  1  receives supply of a cathode gas and an anode gas, and generates electric power by a chemical reaction of the cathode gas and the anode gas. In the embodiment, air containing oxygen is used as the cathode gas, and hydrogen gas is used as the anode gas. The anode gas is an exemplary reactant gas that is used for electric power generation. The electric power generated by the FC  1  is supplied to the motor M. 
     The FC  1  includes an inlet port  11  and an outlet port  12  for the anode gas and an inlet port  13  and an outlet port  14  for the cathode gas. The inlet port  11  and the outlet port  12  for the anode gas are connected through an anode-gas flow passage L 31 , and the inlet port  13  and the outlet port  14  for the cathode gas are connected through a cathode-gas flow passage L 21 . Each of the anode-gas flow passage L 31  and the cathode-gas flow passage L 21  includes a manifold that passes through the laminated body constituted by the unit cells, grooves that are formed on separators of the unit cells, and the like. The inlet port  11  and the outlet port  12  for the anode gas are an exemplary installation port and an exemplary discharge port for the reactant gas, respectively. 
     The cathode system  2  supplies the air containing oxygen, as the cathode gas, to the FC  1 . For example, the cathode system  2  includes a cathode supply pipe L 20 , a cathode discharge pipe L 22 , and an air compressor  20 . 
     A downstream-side end portion of the cathode supply pipe L 20  is connected to the inlet port  13  of the FC  1  for the cathode gas. The air compressor (ACP)  20  is provided on the cathode supply pipe L 20 . The air compressor  20  compresses the cathode gas. The cathode gas flows through the cathode supply pipe L 20 , and is supplied to the FC  1 , as shown by an arrow R 20 . The cathode gas in the FC  1  flows through the cathode-gas flow passage L 21  from the inlet port  13 , as shown by an arrow R 21 , and is used for the electric power generation by the chemical reaction with the anode gas. 
     An upstream-side end portion of the cathode discharge pipe L 22  is connected to the outlet port  14  of the FC  1  for a cathode off gas. The FC  1  discharges the cathode gas used for the electric power generation, as the cathode off gas, from the outlet port  14  to the cathode discharge pipe L 22 . The cathode off gas flows through the cathode discharge pipe L 22 , and is discharged to the exterior, as shown by an arrow R 22 . 
     The anode system  3  supplies the anode gas to the FC  1 . The anode system  3  includes an anode supply pipe L 30 , an anode discharge pipe L 32 , a return pipe L 33 , a bypass pipe L 34 , a gas-liquid discharge pipe L 35 , a fuel tank  30 , an injector (INJ)  31 , an auxiliary linear solenoid valve (LS)  32 , a bypass linear solenoid valve (bypass LS)  33 , an ejector  4 , a gas-liquid separator  5 , and an anode discharge valve  6 . 
     In the fuel tank  30 , the anode gas is stored at a high pressure. The fuel tank  30  supplies the anode gas to the INJ  31 , the auxiliary LS  32  and the bypass LS  33 . The INJ  31  intermittently injects the anode gas. For example, at regular time intervals, the INJ  31  injects the anode gas at a predetermined flow rate. The auxiliary LS  32  and the bypass LS  33  continuously injects the anode gas. Further, the auxiliary LS  32  and the bypass LS  33  can inject the anode gas at arbitrary flow rates. 
     The bypass LS  33  and the auxiliary LS  32  inject the anode gas in a warm-up operation of the FC  1 , and the INJ  31  injects the anode gas in a normal operation after the warm-up operation of the FC  1 . The INJ  31  is an exemplary first injection device, the auxiliary LS  32  is an exemplary second injection device, and the bypass LS  33  is an exemplary third injection device. 
     The INJ  31  and the auxiliary LS  32  are connected to the ejector  4 . The bypass LS  33  is connected to the anode supply pipe L 30  through the bypass pipe L 34 . 
       FIG. 1  shows a cross section of the ejector  4  along a direction in which the anode gas flows. The ejector  4  includes a plate-like fixing part  40 , a large-diameter nozzle  41 , a small-diameter nozzle  42 , and a diffuser  43 . The material of the ejector  4  is steel use stainless (SUS), for example, but is not limited to SUS. 
     The fixing part  40  fixes the large-diameter nozzle  41  and the small-diameter nozzle  42 . An inlet port  410  of the large-diameter nozzle  41  is connected to the INJ  31 , and an inlet port  420  of the small-diameter nozzle  42  is connected to the auxiliary LS  32 . The large-diameter nozzle  41  injects the anode gas from the INJ  31 , from an injection port to the diffuser  43 , and the small-diameter nozzle  42  injects the anode gas from the auxiliary LS  32 , from an injection port to the diffuser  43 . The diameter of the injection port of the large-diameter nozzle  41  is larger than the diameter of the injection port of the small-diameter nozzle  42 . The large-diameter nozzle  41  is an exemplary first nozzle, and the small-diameter nozzle  42  is an exemplary second nozzle. 
     The diffuser  43  includes an ejector flow passage  44  through which the anode gas flows, and an outflow port  46  that is connected to the anode supply pipe L 30 . The anode gas injected from the large-diameter nozzle  41  and the small-diameter nozzle  42  flows through the ejector flow passage  44 . The anode gas flows through the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30 . 
     An inflow port  45  connected to the return pipe L 33  is provided on a side surface of the diffuser  43 . The return pipe L 33  connects the inflow port  45  and the gas-liquid separator  5 . An anode off gas that flows from the gas-liquid separator  5  to the return pipe L 33  is sucked from the inflow port  45  into the ejector flow passage  44 , because the anode gas injected from the large-diameter nozzle  41  or the small-diameter nozzle  42  acts as a drive fluid. The anode off gas flows from the gas-liquid separator  5  into the inflow port  45 . 
     The anode off gas flows from the inflow port  45  to the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30 , together with the anode gas. The ejector flow passage  44  is an exemplary common third flow passage through which the anode off gas and the reactant gas injected from the INJ  31  and the auxiliary LS  32  flow to the outflow port  46 , and the anode off gas is an exemplary reactant gas discharged from the FC  1 . 
     One end of the anode supply pipe L 30  is connected to the outflow port  46  of the ejector  4 , and the other end of the anode supply pipe L 30  is connected to the inlet port  11  of the FC  1  for the anode gas. The anode supply pipe L 30  is an exemplary first flow passage that connects the inlet port  11  and the inflow port  45 . One end of the bypass pipe L 34  extending from the bypass LS  33  is connected to the middle (see reference character P) of the anode supply pipe L 30 . The bypass pipe L 34  is an exemplary second flow passage through which the anode gas injected from the bypass LS  33  is led to the anode supply pipe L 30  without the ejector  4 . 
     One end of the anode discharge pipe L 32  is connected to the outlet port  12  of the FC  1  for the anode off gas, and the other end of the anode discharge pipe L 32  is connected to the gas-liquid separator  5 . The anode off gas flows through the anode discharge pipe L 32  from the outlet port  12 , and enters the gas-liquid separator  5 . 
     The gas-liquid separator  5  separates liquid water from the anode off gas discharged from the outlet port  12 . One end of the gas-liquid discharge pipe L 35  is connected to the gas-liquid separator  5 , and the other end of the gas-liquid discharge pipe L 35  is connected to the cathode discharge pipe L 22 . The anode discharge valve  6  is provided in the gas-liquid discharge pipe L 35 . When the anode discharge valve  6  is opened, the liquid water and some of the anode off gas that flow out of the gas-liquid separator  5  flows to the cathode discharge pipe L 22  through the gas-liquid discharge pipe L 35 , and is discharged to the exterior together with the cathode off gas, as shown by an arrow R 34 . 
     One end of the return pipe L 33  is connected to the gas-liquid separator  5 , and the other end of the return pipe L 33  is connected to the inflow port  45  of the ejector  4 . The anode off gas flows through the return pipe L 33  from the gas-liquid separator  5 , and enters the inflow port  45  of the ejector  4 . 
     The control system  7  includes an ECU  70 , an ignition switch  71 , an accelerator operation amount sensor  72 , and a temperature sensor  73 . The ignition switch  71  gives instructions of start and stop of the fuel cell vehicle, to the ECU  70 . The accelerator operation amount sensor  72  detects the operation amount of an accelerator (not illustrated) of the fuel cell vehicle, and gives information of the operation amount of the accelerator, to the ECU  70 . The temperature sensor  73  detects the temperature of coolant of the FC  1 , and gives information of the temperature of the coolant, to the ECU  70 . The ECU  70  processes the temperature measured by the temperature sensor  73 , as the temperature of the FC  1 . 
     The ECU  70  includes a central processing unit (CPU), a read-only memory (ROM), and a random-access memory (RAM). The ECU  70  is electrically connected to the ignition switch  71 , the accelerator operation amount sensor  72 , the temperature sensor  73 , the air compressor  20 , the INJ  31 , the auxiliary LS  32 , the bypass LS  33 , and the anode discharge valve  6 . The ECU  70  controls the actuation of the air compressor  20  and the injection of the INJ  31 , the auxiliary LS  32  and the bypass LS  33 . 
     The ECU  70  starts the electric power generation of the FC  1  when the ignition switch  71  is turned on, and stops the electric power generation of the FC  1  when the ignition switch  71  is turned off. When the ignition switch  71  is turned on, the ECU  70  actuates the air compressor  20 . At the start of the electric power generation of the FC  1 , in the case where the temperature of the FC  1  is equal to or lower than a predetermined reference temperature TH, the ECU  70  performs the warm-up operation of the FC  1 , and then performs the normal operation of the FC  1  after the temperature of the FC  1  exceeds to the predetermined reference temperature TH. During the warm-up operation, the ECU  70  promotes the heat generation and temperature rise of the FC  1 , by decreasing the stoichiometric ratio of the cathode gas compared to the normal operation. Furthermore, during the warm-up operation, the ECU  70  may promote the heat generation and temperature rise, by stopping the action of an unillustrated cooling system. In the following, the supply of the anode gas during the warm-up operation and the supply of the anode gas during the normal operation will be described. 
     Warm-Up Operation of FC  1   
       FIG. 2  is a diagram showing an exemplary flow of the anode gas and the anode off gas at the time of the warm-up operation of the FC  1 . In  FIG. 2 , constituents in common with  FIG. 1  are denoted by identical reference characters, and descriptions for the constituents are omitted. 
     The ECU  70  performs the warm-up operation of the FC  1  by executing the injection of the bypass LS  33 . The anode gas injected from the bypass LS  33  is introduced into the anode supply pipe L 30  without the ejector  4 , as shown by an arrow R 3 . On this occasion, some of the anode gas injected from the bypass LS  33  reversely flows to the ejector  4  through the anode supply pipe L 30 , as shown by an arrow R 30   r . The reversely flowing anode gas flows through the bypass pipe L 34  and the anode supply pipe L 30 , and flows from the outflow port  46  to the ejector flow passage  44 . 
     In response, the ECU  70  causes the auxiliary LS  32  to inject the anode gas, such that the reverse flow of the anode gas from the bypass LS  33  is restrained. The anode gas injected from the auxiliary LS  32  flows through the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30 , as shown by an arrow R 2 . 
     Since the auxiliary LS  32  and the bypass LS  33  continuously inject the reactant gas, the reverse flow of the reactant gas to the ejector  4  is restrained. Further, it is possible to perform the warm-up operation, while continuously supplying the reactant gas that does not contain an impurity gas in the ejector  4  and that has a high concentration, from the bypass LS  33  to the FC  1  through the anode supply pipe L 30 , as shown by an arrow R 30   f.    
     For example, the ECU  70  causes the bypass LS  33  to inject the anode gas at a flow rate depending on the temperature of the temperature sensor  73 . Therefore, it is possible to quickly perform the warm-up operation depending on the temperature of the FC  1 . 
     The anode gas flows through the anode gas flow passage L 31  from the inlet port  11 , as shown by an arrow R 31 , and is used for the electric power generation by the chemical reaction with the cathode gas. The FC  1  discharges the anode gas used for the electric power generation, from the outlet port  12  to the anode discharge pipe L 32  as the anode off gas. The anode off gas flows through the anode discharge pipe L 32  from the outlet port  12  of the FC  1 , and enters the gas-liquid separator  5 , as shown by an arrow R 32 . 
     The anode off gas flows through the return pipe L 33  from the gas-liquid separator  5 , and flows through the ejector flow passage  44  from the inflow port  45  of the ejector flow passage  44 , as shown by an arrow R 33 . That is, when the auxiliary LS  32  injects the anode gas, the anode off gas is sucked from the gas-liquid separator  5  into the ejector  4  through the return pipe L 33 . The anode off gas discharged from the FC  1  contains moisture that is generated by the electric power generation in the FC  1 . Therefore, during the warm-up operation, in the ejector flow passage  44 , a liquid water m that has not been separated by the gas-liquid separator  5  is generated, and a liquid water m due to condensation of water vapor is generated by cooling with the anode gas having a low temperature. 
     For example, when the liquid water m remains in the ejector flow passage  44 , there is a fear that the liquid water freezes at a below-freezing temperature to block the ejector flow passage  44 , and that the anode gas cannot be supplied to the FC  1  at a sufficient flow rate, at the time of restart of the fuel cell system  100 . 
     Therefore, the ECU  70  discharges the liquid water remaining in the ejector flow passage  44 , by executing the injection of the INJ  31  in the normal operation after the completion of the warm-up operation. 
     Normal Operation of FC  1   
       FIG. 3  is a diagram showing an exemplary flow of the anode gas and the anode off gas at the time of the normal operation of the FC  1 . In  FIG. 3 , constituents in common with  FIG. 1  are denoted by identical reference characters, and descriptions for the constituents are omitted. 
     After the completion of the warm-up operation of the FC  1 , the ECU  70  executes the injection of the INJ  31 . The anode gas injected from the INJ  31  flows through the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30 , as shown by an arrow RE Further, the anode off gas in the return pipe L 33  is sucked from the inflow port  45  into the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30 . 
     The anode gas and the anode off gas enter the anode gas flow passage L 31  of the FC  1  from the anode supply pipe L 30  through the inlet port  11 , as shown by an arrow R 30 . The anode gas and some of the anode off gas are used for the electric power generation. 
     The INJ  31  intermittently injects the anode gas, and the FC  1  uses the anode gas for the electric power generation. Therefore, the pressure in the ejector  4  pulsates due to the intermittent injection of the INJ  31 . The anode off gas sucked from the inflow port  45 , the anode gas injected from the auxiliary LS  32  and the anode gas injected from the INJ  31  flow through the ejector flow passage  44 . Therefore, the liquid water m generated in the ejector flow passage  44  by the injection of the auxiliary LS  32  is discharged from the outflow port  46  by the pulsation of the pressure due to the intermittent injection of the INJ  31 . 
     The liquid water m in the ejector flow passage  44  flows through the anode supply pipe L 30 , the anode gas flow passage L 31  and the anode discharge pipe L 32 , and is retained in the gas-liquid separator  5 . The liquid water in the gas-liquid separator  5  is discharged from the cathode discharge pipe L 22  at the time of opening of the anode discharge valve  6 . 
     In the normal operation of the FC  1 , the ECU  70  calculates a current value that the FC  1  is required to output, for example, depending on the accelerator operation amount detected by the accelerator operation amount sensor  72 . The ECU  70  gives an instruction of the flow rate of the cathode gas, to the air compressor  20 , and gives an instruction of the flow rate of the anode gas, to the INJ  31 . 
     Change in Anode Gas Flow Rate 
       FIG. 4  is a diagram showing an exemplary temporal change in flow rates of anode gases injected from the bypass LS  33 , the auxiliary LS  32  and the INJ  31 . Reference character Ga denotes an exemplary change in the anode gas flow rate of the bypass LS  33  with respect to time, reference character Gb denotes an exemplary change in the anode gas flow rate of the auxiliary LS  32  with respect to time, and reference character Gc denotes an exemplary change in the anode gas flow rate of the INJ  31  with respect to time. Further, reference character Gd denotes an exemplary change in the temperature of the FC  1  with respect to time. 
     The ECU  70  performs the warm-up operation of the FC  1  during a period from time  0  to time Tc, and performs the normal operation of the FC  1  after time Tc. The ECU  70  switches the operation of the FC  1  depending on the temperature detected by the temperature sensor  73 . As an example, the temperature of the FC  1  rises from a temperature Tm in proportion to time, and exceeds a reference temperature TH at time Tc. 
     During the warm-up operation, the ECU  70  executes the injection of the bypass LS  33  at a flow rate Vd depending on the temperature Tm of the FC  1  at time  0 . Thereby, the anode gas is supplied to the FC  1  at an appropriate flow rate Vd, and therefore the temperature of the FC  1  quickly rises. 
     Further, during the warm-up operation, the ECU  70  executes the injection of the auxiliary LS  32  at a flow rate Vr, such that the anode gas injected from the bypass LS  33  is restrained from reversely flowing to the ejector flow passage  44 . The ECU  70  calculates an appropriate flow rate Vr from the flow rate Vd of the anode gas that is injected from the bypass LS  33 . Based on the setting of the opening degrees of the auxiliary LS  32  and the bypass LS  33 , the ECU  70  controls the anode gas flow rates. 
     The ECU  70  stops the injection of the INJ  31  until the completion of the warm-up operation of the FC  1 . Since the INJ  31  intermittently injects the anode gas, the pressure of the anode gas pulsates, and the circulation amount of the anode off gas that is sucked from the return pipe L 33  into the ejector flow passage  44  increases. When the circulation amount of the anode off gas increases, the amount of the liquid water that is generated in the ejector flow passage  44  also increases. Therefore, it is preferable that the ECU  70  stop the injection of the INJ  31 , but without being limited to this, the ECU  70  may execute the injection of the INJ  31  at such a flow rate that the anode gas for restraining the reverse flow is compensated. 
     When the temperature of the FC  1  exceeds the reference temperature TH, the ECU  70  performs the normal operation of the FC  1  by executing the injection of the INJ  31 . The reference temperature TH is equal to or higher than 0° C., which is the freezing point. That is, the ECU  70  performs the warm-up operation until the temperature of the FC  1  exceeds the freezing point. This restrains the freezing of the liquid water generated in the ejector flow passage  44  during the warm-up operation, and therefore the liquid water is more easily discharged from the ejector flow passage  44  by the injection of the INJ  31 , compared to the case where there is ice. 
     The ECU  70  causes the INJ  31  to intermittently inject the anode gas by turning the INJ  31  on and off with a period f, for example. The ECU  70  decides an on-time Δt of the INJ  31  and the period f depending on the required current value of the FC  1 . Further, a flow rate Vn of the anode gas that is injected from the INJ  31  is constant. 
     When the INJ  31  injects the anode gas, the amount of the anode gas in the anode system  3  temporarily rises, and thereby the pressure of the anode gas rises. However, the amount of the anode gas decreases because of the use for the electric power generation of the FC  1 , and therefore the pressure of the anode gas decreases immediately after the injection. Accordingly, when the INJ  31  intermittently injects the anode gas, the pressure of the anode gas in the anode system  3  pulsates. On this occasion, the pressure in the ejector flow passage  44  also pulsates, and therefore the liquid water in the ejector flow passage  44  is easily discharged from the outflow port  46 . 
     The INJ  31  is higher in the responsiveness to the instruction from the ECU  70 , than the auxiliary LS  32  and the bypass LS  33 , and therefore the liquid water can be more effectively discharged by the injection of the INJ  31 . 
       FIG. 5  is a diagram showing a result of performance comparison between the injector and the linear solenoid valve. A solid line indicates the performance of the injector (the INJ  31 ), and a dotted line indicates the performance of the linear solenoid valve (the auxiliary LS  32  and the bypass LS  33 ). The injector is an electromagnetic valve, for example, and the valve is opened or closed by an electric on-off control (the opening degree is 100% or 0%). Unlike the injector, the linear solenoid valve allows flow rate adjustment, and therefore the opening degree can be electrically controlled to an arbitrary opening degree (0% to 100%). 
     Reference character Ha denotes an exemplary change in the anode gas flow rate with respect to time. Time Ts is a timing when the ECU  70  gives the instruction of the injection to the injector and the linear solenoid valve. A time necessary for the flow rate of the injector to reach a peak flow rate Vp from the instruction time Ts is shorter than a time necessary for the flow rate of the linear solenoid valve to reach the peak flow rate Vp from the instruction time Ts. That is, the responsiveness of the injector is higher than that of the linear solenoid valve. 
     Reference character Hb denotes an exemplary change in a pressure difference Δp between an upstream side and a downstream side of a water droplet fit in the flow passage with respect to time in the case of the injection of the injector and the linear solenoid valve. Because of the above difference in responsiveness, a time necessary for the pressure difference Δp in the injector to reach a maximum value p 1  is shorter than a time necessary for the pressure difference Δp in the linear solenoid valve to reach a maximum value p 2 . Further, the maximum value p 1  of the pressure difference Δp at the time of the injection of the injector is larger than the maximum value p 2  of the pressure difference Δp at the time of the injection of the linear solenoid valve. Therefore, when the ECU  70  executes the injection of the INJ  31 , the liquid water is more effectively discharged than when the ECU  70  executes the injection of the auxiliary LS  32  and the bypass LS  33 . 
     Back to  FIG. 4 , the ECU  70  stops the injection of the auxiliary LS  32  and the bypass LS  33  in the normal operation after the completion of the warm-up operation. This restrains the consumption of the anode gas that is generated by the injection of the auxiliary LS  32  and the bypass LS  33 . For example, in the case where it is predicted that the amount of the anode gas is insufficient because the required current value of the FC  1  is large, the ECU  70  may execute the injection of the auxiliary LS  32  and the bypass LS  33  in the normal operation. 
     Process by ECU  70   
       FIG. 6  is a flowchart showing an exemplary process by the ECU  70 . The process is executed while the ignition switch  71  is in the off-state and the fuel cell system  100  is in the stop state. 
     The ECU  70  determines whether the ignition switch  71  has been turned on (step St 1 ). In the case where the ignition switch  71  is in the off-state (No in step St 1 ), step St 1  is executed again. In the case where the ignition switch  71  has been turned on (Yes in step St 1 ), the ECU  70  actuates the air compressor  20  for the electric power generation of the FC  1  (step St 2 ). Thereby, the cathode gas starts to be supplied from the air compressor  20  to the FC  1 . 
     Next, the ECU  70  measures the temperature of the coolant as the temperature of the FC  1 , with the temperature sensor  73  (step St 3 ). In the case where the temperature of the FC  1  is equal to or lower than the reference temperature TH (Yes in step St 4 ), the ECU  70  performs the warm-up operation of the FC  1  (step St 5  to step St 8 ). In the case where the temperature of the FC  1  is higher than the reference temperature TH (No in step St 4 ), the ECU  70  performs the normal operation of the FC  1  (step St 11  to step St 13 ). 
     First, the warm-up operation will be described. The ECU  70  turns the INJ  31  off (step St 5 ). Therefore, the supply of the anode gas from the INJ  31  to the FC  1  is not performed. 
     Next, the ECU  70  calculates the opening degree of the bypass LS  33  based on the temperature of the FC  1  (step St 6 ). Thereby, the ECU  70  decides the flow rate of the anode gas that is injected from the bypass LS  33 , depending on the temperature of the FC  1  at the time of the start of the warm-up operation. 
     Next, the ECU  70  calculates the opening degree of the auxiliary LS  32  based on the opening degree of the bypass LS  33 , such that the reverse flow of the anode gas from the bypass LS  33  to the ejector flow passage  44  is restrained (step St 7 ). For example, the ECU  70  calculates the opening degree of the auxiliary LS  32 , such that the anode gas is injected at a flow rate that allows the reverse flow of the anode gas to be offset. 
     Next, the ECU  70  sets the opening degree of the bypass LS  33  and the opening degree of the auxiliary LS  32  (step St 8 ). Thereby, the bypass LS  33  and the auxiliary LS  32  start the injection of the anode gas at flow rates depending on the set opening degrees (step St 8 ). In this way, the ECU  70  executes the injection of the bypass LS  33  at a flow rate depending on the temperature of the FC  1  at the time of the start of the warm-up operation of the FC  1 , and therefore can quickly raise the temperature of the FC  1 . 
     Next, the ECU  70  measures the temperature of the FC  1  with the temperature sensor  73  (step St 9 ). In the case where the temperature of the FC  1  is equal to or lower than the reference temperature TH (Yes in step St 10 ), the ECU  70  measures the temperature of the FC  1  again (step St 9 ). In the case where the temperature of the FC  1  is higher than the reference temperature TH (No in step St 10 ), the ECU  70  performs the normal operation of the FC  1  (step St 11  to step St 13 ). 
     Next, the normal operation will be described. The ECU  70  closes the bypass LS  33  and the auxiliary LS  32  (step St 11 ). Thereby, the anode gas injection from the bypass LS  33  and the auxiliary LS  32  is stopped. 
     Next, the ECU  70  decides the required current value of the FC  1  based on the detection value of the accelerator operation amount sensor  72 , for example, and calculates the on-time of the INJ  31  and the period of on-off (Δt and f in  FIG. 4 ) based on the required current value (step St 12 ). Next, the ECU  70  performs the on-off control of the INJ  31  in accordance with the on-time and the period of on-off (step St 13 ). Thereby, the anode gas is supplied to the FC  1 , at a flow rate depending on the required current value. 
     Next, the ECU  70  determines whether the ignition switch  71  has been turned off (step St 14 ). In the case where the ignition switch  71  is in the on-state (No in step St 14 ), step St 12  to step St 14  are executed again. In the case where the ignition switch  71  has been turned off (Yes in step St 14 ), the ECU  70  turns the INJ  31  off (step St 15 ), and stops the air compressor  20  (step St 16 ). Thereby, the electric power generation of the FC  1  is stopped. 
     Another Fuel Cell System 
     In the above-described fuel cell system  100 , the ejector  4  includes the large-diameter nozzle  41  and the small-diameter nozzle  42  that are separately provided and that are connected to the INJ  31  and the auxiliary LS  32  respectively. That is, the ejector  4  includes the large-diameter nozzle  41  from which the anode gas injected from the INJ  31  is injected to the ejector flow passage  44 , and the small-diameter nozzle  42  from which the anode gas injected from the auxiliary LS  32  is injected to the ejector flow passage  44 . Therefore, it is possible to adopt appropriately different injection amounts, as the injection amount of the large-diameter nozzle  41  and the injection amount of the small-diameter nozzle  42 . However, without being limited to this, the INJ  31  and the auxiliary LS  32  may be connected to a common nozzle. 
       FIG. 7  is a configuration diagram showing another exemplary fuel cell system  100   a . In  FIG. 7 , constituents in common with  FIG. 2  are denoted by identical reference characters, and descriptions for the constituents are omitted. 
     The fuel cell system  100   a  includes an ejector  4   a  including a single nozzle  41   a , instead of the ejector  4 . The INJ  31  and the auxiliary LS  32  are connected to an inlet port  410   a  of the nozzle  41   a  through a bifurcated connecting pipe L 4 . Therefore, the anode gas injected from the INJ  31  or the auxiliary LS  32  flows from the nozzle  41   a  to the ejector flow passage  44 , as shown by an arrow R 4 . The nozzle  41   a  is an exemplary third nozzle. 
     In this way, the ejector  4   a  includes the common nozzle  41   a  from which the anode gas injected from the INJ  31  and the anode gas injected from the auxiliary LS  32  are injected to the ejector flow passage  44 . Therefore, the size of the ejector  4   a  is smaller than the size of the ejector  4  including the large-diameter nozzle  41  and the small-diameter nozzle  42 . 
     Fuel Cell System in Comparative Example 
       FIG. 8  is a configuration diagram showing a fuel cell system  100   x  in a comparative example. In  FIG. 8 , constituents in common with  FIG. 1  are denoted by identical reference characters, and descriptions for the constituents are omitted. 
     The fuel cell system  100   x  includes ejectors  4   j ,  4   k  connected to the INJ  31  and the auxiliary LS  32  respectively, instead of the ejector  4 . Each of the ejectors  4   j ,  4   k  has the same structure as the ejector  4   a  shown in  FIG. 7 . 
     Outflow ports  46  of the ejectors  4   j ,  4   k  are connected to the inlet port  11  of the FC  1  through a bifurcated anode supply pipe L 30   x . Further, inflow ports  45  of the ejectors  4   j ,  4   k  are connected to the gas-liquid separator  5  through a bifurcated return pipe L 33   x.    
     When the INJ  31  injects the anode gas, the anode off gas flows through the return pipe L 33   x  from the gas-liquid separator  5 , and is sucked from the inflow port  45  into the ejector  4   j , as shown by an arrow R 33   j . The anode gas injected from the INJ  31  flows through the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30   x , together with the anode off gas sucked from the inflow port  45 . 
     When the auxiliary LS  32  and the INJ  31  inject the anode gas, the anode off gas flows through the return pipe L 33   x  from the gas-liquid separator  5 , and is sucked from the inflow port  45  into the ejector  4   k , as shown by an arrow R 33   k . The anode gas injected from the INJ  31  flows through the ejector flow passage  44 , and is ejected from the outflow port  46  to the anode supply pipe L 30   x , together with the anode off gas sucked from the inflow port  45 . 
     The ECU  70  performs the warm-up operation of the FC  1 , by continuously executing the injection of the bypass LS  33  and the auxiliary LS  32 . On this occasion, the anode gas injected from the bypass LS  33  reversely flows to the ejectors  4   j ,  4   k  as shown by an arrow R 30   r.    
     The ECU  70  executes the injection of the auxiliary LS  32  such that the reverse flow of the anode gas is restrained. Thereby, the anode gas injected from the bypass LS  33  flows to the inlet port  11  of the FC  1  as shown by an arrow R 30   f.    
     On this occasion, the anode off gas flows from the inflow port  45  into the ejector  4   k . Therefore, when the ECU  70  stops the injection of the auxiliary LS  32  at the time of the completion of the warm-up operation, the liquid water contained in the anode off gas remains in the ejector flow passage  44  of the ejector  4   k.    
     After the completion of the warm-up operation, the ECU  70  performs the normal operation of the FC  1  by intermittently executing the injection of the INJ  31 . On this occasion, the anode off gas flows from the inflow port  45  into the ejector  4   j , and the liquid water is generated in the ejector flow passage  44 . However, since the injection of the INJ  31  is intermittently executed, the pressure of the anode gas pulsates, and the liquid water in the ejector flow passage  44  is easily discharged from the outflow port  46 . 
     In the comparative example, the ejector  4   j  connected to the INJ  31  and the ejector  4   k  connected to the auxiliary LS  32  are separately provided. Therefore, the liquid water remains in the ejector  4   k  after the stop of the injection of the auxiliary LS  32 . Even if the injection of the auxiliary LS  32  is continued in the normal operation, the injection is continuously performed. Therefore, the pressure of the anode gas does not pulsate, unlike the INJ  31 . Therefore, it is hard to discharge the liquid water in the ejector  4   k.    
     In response, the above-described fuel cell systems  100 ,  100   a  are provided with the common ejectors  4 ,  4   a  connected to the INJ  31  and the auxiliary LS  32 . Although the ECU  70  continuously executes the injection of the auxiliary LS  32  during the warm-up operation, the ECU  70  intermittently executes the injection of the INJ  31  after the warm-up operation. Therefore, unlike the comparative example, the liquid water in the ejectors  4 ,  4   a  is easily discharged by the pulsation of the pressure of the anode gas due to the injection of the INJ  31 . 
     As described above, the ECU  70  performs the warm-up operation of the FC  1  by executing the injection of the bypass LS  33 , and executes the injection of the auxiliary LS  32  such that the reserve flow of the anode gas from the bypass LS  33  to the ejectors  4 ,  4   a  is restrained. Since the auxiliary LS  32  and the bypass LS  33  continuously inject the anode gas, the reverse flow of the anode gas to the ejectors  4 ,  4   a  is restrained. Further, it is possible to perform the warm-up operation, while continuously supplying the anode gas that does not contain the impurity gas in the ejectors  4 ,  4   a  and that has a high concentration, from the bypass LS  33  to the FC  1 . 
     Further, the ECU  70  executes the injection of the INJ  31  after the completion of the warm-up operation of the FC  1 . The INJ  31  intermittently injects the anode gas, and the FC  1  uses the anode gas for the electric power generation. Therefore, the pressure in the ejectors  4 ,  4   a  pulsate due to the intermittent injection of the INJ  31 . 
     Further, the ejectors  4 ,  4   a  include the common ejector flow passage  44  through which the anode off gas discharged from the outlet port  12  of the FC  1  and the anode gas injected from the INJ  31  and the auxiliary LS  32  flow to the outflow port  46 . Therefore, the liquid water generated in the ejector flow passage  44  by the injection of the auxiliary LS  32  is discharged from the outflow port  46  by the pulsation of the pressure due to the intermittent injection of the INJ  31 . 
     Accordingly, the fuel cell systems  100 ,  100   a  in the embodiment can easily discharge the liquid water that remains in the ejectors  4 ,  4   a  after the warm-up operation of the FC  1 . 
     The above-described embodiment is an exemplary preferred embodiment of the disclosure. The disclosure is not limited to this embodiment, and various modifications can be made without departing from the spirit of the disclosure.