Fuel Cell Systems

Abstract

To execute wastewater treatment while suppressing pressure rise inside a fuel cell.SOLUTION: A fuel cell system includes a fuel cell, a fuel gas supply unit, and a control device, the fuel cell includes a fuel gas supply path and a fuel gas discharge path, the fuel gas supply unit includes a fuel gas supply device that changes the flow rate of fuel gas, a reflux path that refluxes the fuel gas discharged from the fuel gas discharge path, a gas-liquid separator provided in the reflux route, and a discharge valve that discharges the fuel gas and water from the gas-liquid separator. The control device executes normal processing of operating the fuel gas supply device with the discharge valve closed, and first wastewater processing of discharging water from the fuel gas discharge path by operating the fuel gas supply device at a flow rate higher than that in the normal processing with the discharge valve opened.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a fuel cell system.

[0002] The fuel cell system disclosed in Patent Document 1 generates electricity by supplying fuel gas to a fuel cell. When electricity is generated in the fuel cell, water is generated within the fuel cell. When the residual water in the fuel cell increases, this fuel cell system performs a drainage process to discharge the residual water from the fuel cell by increasing the supply flow rate of fuel gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-139910 A Summary of the Invention [Problem to be solved by the invention]

[0004] Increasing the flow rate of fuel gas during the drainage process increases the pressure inside the fuel cell. Therefore, it is necessary to end the drainage process before the pressure inside the fuel cell reaches an upper limit. For this reason, in conventional drainage processes, the flow rate of fuel gas during the drainage process cannot be increased very much, and the drainage process cannot be performed for a long period of time. This specification proposes a fuel cell system that can perform the drainage process while suppressing the pressure increase inside the fuel cell. [Means for solving the problem]

[0005] The fuel cell system of item 1 disclosed in this specification includes a fuel cell having a plurality of stacked cells, a fuel gas supply unit, and a control device. The fuel cell includes a fuel gas supply path that supplies fuel gas to the plurality of cells, and a fuel gas exhaust path that exhausts the fuel gas that has passed through the plurality of cells. The fuel gas supply unit includes a fuel gas supply device that changes the flow rate of the fuel gas supplied to the fuel gas supply path, a return path that returns the fuel gas exhausted from the fuel gas exhaust path to the fuel gas supply path, a gas-liquid separator provided in the return path, and an exhaust valve that exhausts the fuel gas and water from the gas-liquid separator. The control device executes a normal process in which the fuel gas supply device is operated with the exhaust valve closed, and a first drainage process in which water is discharged from the fuel gas exhaust path by operating the fuel gas supply device with the exhaust valve open and at a flow rate higher than that of the normal process.

[0006] In this fuel cell system, the control device operates the fuel gas supply device in a normal process with the exhaust valve closed. In the normal process, fuel gas is supplied from the fuel gas supply device to the fuel gas supply path and from the reflux path to the fuel gas supply path. In the normal operation, power is generated in the fuel cell and water is produced in the fuel cell. In addition, the control device operates the fuel gas supply device at a flow rate higher than that in the normal process in the first drainage process. Then, the fuel gas flows at a high flow rate in the fuel gas exhaust path, and water is discharged from the fuel gas exhaust path together with the fuel gas. In this way, in the first drainage process, the water in the fuel cell can be discharged to the outside of the fuel cell. In addition, the first drainage process is performed with the exhaust valve open. Therefore, a part of the fuel gas in the reflux path is discharged from the exhaust valve to the outside of the fuel gas supply unit. Therefore, the pressure rise in the fuel cell is suppressed. In this way, according to this fuel cell system, the drainage process can be performed while suppressing the pressure rise inside the fuel cell. [Brief description of the drawings]

[0007] [Figure 1] 1 is a block diagram of a fuel electronics system 100. [Diagram 2] FIG. [Diagram 3] 4 is a graph showing the relationship between the flow rate of fuel gas and the time required for residual water W to reach an anode discharge port 24a. [Figure 4] Graph showing changes in each value in the second wastewater treatment. [Diagram 5] Graph showing changes in each value in the first wastewater treatment in Example 1. [Figure 6] Graph showing changes in each value in the first wastewater treatment in Example 2. [Figure 7] 1 is a graph showing the changes in each value during the first wastewater treatment and the subsequent treatments in Example 3. [Figure 8] 1 is a graph showing the relationship between hydrogen concentration N and the flow rate V required to drain residual water W. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The configuration of the technology disclosed in this specification will be described below item by item, following item 1 above. do. (Item 2) The fuel cell system described in item 1, wherein the control device performs a second drainage process to discharge water from the fuel gas exhaust path by operating the fuel gas supply device at a flow rate higher than the normal process and lower than the first drainage process with the exhaust valve closed. (Item 3) 3. The fuel cell system according to item 1 or 2, wherein an output current of the fuel cell is increased in the first wastewater treatment compared to the normal treatment. (Item 4) The fuel cell system according to any one of items 1 to 3, wherein, when the control device performs the first drainage process, the control device alternately performs the first drainage process and a pressure reduction process in which the pressure in the fuel gas exhaust path is reduced by operating the fuel gas supply device at a flow rate lower than that of the first drainage process with the exhaust valve closed. (Item 5) 5. The fuel cell system according to item 4, wherein the frequency of opening the discharge valve is reduced when the number of times the first drainage process and the pressure reduction process are repeated exceeds a reference number.

[0009] According to the configuration of item 2 above, when discharging water from the fuel cell, the first drainage process is performed if a high flow rate of fuel gas is required, and the second drainage process is performed if a not so high flow rate of fuel gas is required. The second drainage process is performed with the discharge valve closed, but since the flow rate of fuel gas in the second drainage process is low, it is possible to suppress an increase in pressure inside the fuel cell. Furthermore, the second drainage process allows the fuel gas to be used efficiently.

[0010] According to the configuration of item 3 above, the fuel gas consumed in the fuel cell during the first drainage treatment increases, so that the increase in pressure in the fuel cell can be more effectively suppressed.

[0011] According to the configuration of item 4 above, the pressure inside the fuel cell that has increased in the first drainage process can be reduced by the pressure reduction process.

[0012] According to the configuration of item 5 above, it is possible to suppress an increase in the concentration of the fuel gas in the fuel cell, thereby suppressing the phenomenon in which it becomes difficult to discharge water in the fuel cell due to an increase in the concentration of the fuel gas. EXAMPLES

[0013] The fuel cell system 100 of the embodiment shown in Fig. 1 is mounted on an electric vehicle (not shown). The fuel cell system 100 includes a fuel cell 20. The fuel cell system 100 is a system for generating power using the fuel cell 20. The fuel cell system 100 supplies the generated power to a traction motor (not shown) of the electric vehicle. Alternatively, the fuel cell system 100 charges a battery (not shown) of the electric vehicle with the generated power.

[0014] The fuel cell 20 has an anode supply port 22a for taking in a fuel gas and a cathode supply port 22k for taking in an oxidizing gas. In this embodiment, the fuel gas is hydrogen and the oxidizing gas is air. The fuel cell 20 generates electricity by chemically reacting the hydrogen taken in from the anode supply port 22a with oxygen in the air taken in from the cathode supply port 22k.

[0015] The fuel cell system 100 includes a fuel gas supply unit 10, an oxidizing gas supply unit 30, and a control device 40.

[0016] The fuel gas supply unit 10 is a unit for supplying the fuel gas stored in the fuel gas tank 1 to the fuel cell 20. The fuel gas supply unit 10 includes a supply pipe 3. An upstream end of the supply pipe 3 is connected to the fuel gas tank 1. A downstream end of the supply pipe 3 is connected to the anode supply port 22a of the fuel cell 20. The fuel gas is supplied from the fuel gas tank 1 to the anode supply port 22a through the supply pipe 3. A pressure reducing valve 2, a medium pressure side pressure sensor 4, an injector 6, an ejector 8, and a low pressure side pressure sensor 12 are installed in the supply pipe 3. The pressure reducing valve 2 reduces the pressure of the high pressure fuel gas supplied from the fuel gas tank 1. The medium pressure side pressure sensor 4 is installed downstream of the pressure reducing valve 2. The medium pressure side pressure sensor 4 detects the pressure of the fuel gas reduced by the pressure reducing valve 2. An injector 6 is installed downstream of the medium pressure side pressure sensor 4, and an ejector 8 is installed downstream of the injector 6. The injector 6 is an electromagnetic valve that adjusts the flow rate of fuel gas supplied to the ejector 8. The wider the injector 6 opens, the greater the flow rate of fuel gas supplied to the ejector 8. The ejector 8 takes in fuel gas from the return pipe 5 by utilizing the pressure of the fuel gas supplied from the injector 6. The low-pressure side pressure sensor 12 detects the pressure of the fuel gas supplied from the ejector 8 to the fuel cell 20. The pressure detected by the low-pressure side pressure sensor 12 is approximately equal to the pressure inside the fuel cell 20.

[0017] As shown in FIG. 2, the fuel cell 20 has a case 21 and a plurality of cells 26. The plurality of cells 26 are stacked in the thickness direction. The stack of the plurality of cells 26 is housed inside the case 21. An anode supply port 22a and an anode discharge port 24a are provided on one end face of the case 21. A fuel gas supply channel 23 and a fuel gas discharge channel 27 are provided inside the fuel cell 20. The fuel gas supply channel 23 extends along the stacking direction of the plurality of cells 26. An upstream end of the fuel gas supply channel 23 is connected to the supply pipe 3 via the anode supply port 22a. A rear end 23a of the fuel gas supply channel 23 (i.e., an end opposite to the anode supply port 22a) is closed by the case 21. The fuel gas discharge channel 27 extends along the stacking direction of the plurality of cells 26. The fuel gas discharge channel 27 is disposed below the fuel gas supply channel 23. A downstream end of the fuel gas discharge channel 27 is connected to the anode discharge port 24a. The inner end 27a of the fuel gas discharge passage 27 (i.e., the end opposite to the anode discharge port 24a) is closed by the case 21. Fuel gas is supplied from the supply pipe 3 to the fuel gas supply passage 23. The fuel gas flows from the fuel gas supply passage 23 to each cell 26. The fuel gas (i.e., off-gas) that has passed through each cell 26 flows through the fuel gas discharge passage 27 to the anode discharge port 24a. The off-gas contains hydrogen gas, nitrogen gas, water, and the like. The hydrogen gas contained in the off-gas is hydrogen gas that has not been consumed in the fuel cell 20. The nitrogen gas contained in the off-gas is nitrogen contained in the air supplied to the cathode supply port 22k, which has passed through the electrolyte membranes (not shown) of the multiple cells 26 and reached the anode side. The water contained in the off-gas is water that is generated by the reaction of the fuel gas and the oxidizing gas in the fuel cell 20.

[0018] In each cell 26, the fuel gas reacts with the oxidizing gas to generate electricity. In each cell 26, the fuel gas reacts with the oxidizing gas to generate water. Because the fuel gas discharge channel 27 is disposed below the fuel gas supply channel 23, the water generated in each cell 26 flows into the fuel gas discharge channel 27. Therefore, residual water W accumulates in the fuel gas discharge channel 27.

[0019] As shown in FIG. 1, the fuel gas supply unit 10 has an exhaust pipe 7, a reflux pipe 5, and an exhaust pipe 9. The upstream end of the exhaust pipe 7 is connected to the anode exhaust port 24a of the fuel cell 20. The downstream end of the exhaust pipe 7 is connected to the gas-liquid separator 14. The fuel gas exhausted from the anode exhaust port 24a of the fuel cell 20 flows into the gas-liquid separator 14 through the exhaust pipe 7. The gas-liquid separator 14 is connected to the ejector 8 through the reflux pipe 5. A pump 18 is installed in the reflux pipe 5. The pump 18 sends the fuel gas in the reflux pipe 5 toward the ejector 8. The gas-liquid separator 14 separates impurities from the fuel gas flowing into the gas-liquid separator 14 from the exhaust pipe 7. For example, the gas-liquid separator 14 separates water from the fuel gas. The gas-liquid separator 14 temporarily stores the water separated from the fuel gas. The pump 18 supplies the fuel gas from which impurities have been separated in the gas-liquid separator 14 to the ejector 8 via the return pipe 5. As a result, the fuel gas in the return pipe 5 is supplied again to the anode supply port 22a of the fuel cell 20 via the ejector 8. In this manner, the fuel gas supply unit 10 returns the fuel gas. In addition, in a modified example, the fuel gas supply unit 10 may not include the pump 18. In that case, the fuel gas in the return pipe 5 is supplied to the ejector 8 by the negative pressure generated by the ejector 8. In addition, the gas-liquid separator 14 is connected to the discharge pipe 9 via the discharge valve 16. When the discharge valve 16 is opened, the gas and water in the gas-liquid separator 14 are discharged to the outside of the fuel cell system 100 via the discharge pipe 9.

[0020] The oxidizing gas supply unit 30 supplies air (oxygen) to the fuel cell 20. The oxidizing gas supply unit 30 includes a compressor 32, a supply pipe 33, a bypass pipe 35, an exhaust pipe 37, and valves 34, 36, and 38. The supply pipe 33 is connected to the cathode supply port 22k. The compressor 32 compresses outside air and supplies the air to the cathode supply port 22k of the fuel cell 20 via the supply pipe 33. The exhaust pipe 37 is connected to the cathode exhaust port 24k of the fuel cell 20. The bypass pipe 35 connects the supply pipe 33 and the exhaust pipe 37 via the valve 38. The valves 34 and 36 are so-called pressure adjusting valves. The pressure of the air supplied to the fuel cell 20 is adjusted by the valves 34 and 36.

[0021] The control device 40 is a computer having a CPU and a memory. The control device 40 controls the units 10, 30 based on driving information such as the accelerator opening and speed of the fuel cell vehicle. This causes the fuel cell 20 to generate electric power based on the driving information.

[0022] As shown in FIG. 2, the bypass tube 29 is installed inside the fuel gas discharge passage 27. The bypass tube 29 has a cylindrical shape and both ends are open. The bypass tube 29 is disposed on the bottom surface of the fuel gas discharge passage 27. The bypass tube 29 extends from a position near the rear end 27a of the fuel gas discharge passage 27 to a position near the anode discharge port 24a. The flow path cross-sectional area inside the bypass tube 29 is smaller than the flow path cross-sectional area of ​​the fuel gas discharge passage 27 outside the bypass tube 29. Therefore, the flow rate of the fuel gas passing through the bypass tube 29 is faster than the flow rate of the fuel gas passing through the fuel gas discharge passage 27 outside the bypass tube 29. As described above, the residual water W accumulates in the fuel gas discharge passage 27. Therefore, the residual water W flows into the bypass tube 29. A pressure difference occurs between the inlet and the outlet of the bypass tube 29 due to the manifold pressure loss and the dynamic pressure difference. This pressure difference causes the residual water W in the bypass tube 29 to flow downstream (i.e., toward the anode outlet 24a). In this manner, the bypass tube 29 transports the residual water W from the rear end 27a to the anode outlet 24a.

[0023] The inclination angle X in FIG. 2 indicates the inclination angle of the fuel cell 20 with respect to the ground GL. The inclination angle X is defined as a positive value when the rear end 27a is lower than the anode outlet 24a. If the inclination angle X is large, the residual water W accumulates near the rear end 27a in the fuel gas outlet 27, and the residual water W becomes difficult to discharge from the fuel cell 20. FIG. 3 shows the relationship between the flow rate of the fuel gas and the time required for the residual water W to reach the anode outlet 24a when the amount of the residual water W is constant. As shown in FIG. 3, the larger the inclination angle X, the more difficult it becomes for the residual water W to be discharged from the fuel cell 20.

[0024] Next, the process executed by the control device 40 will be described. The control device 40 generates power in the fuel cell 20 in response to an external power generation request. During power generation, the control device 40 calculates the amount of residual water W inside the fuel cell 20. The amount of residual water W is calculated based on the operating time of the fuel cell 20, the integrated value of the amount of power generation, and the like. The control device 40 also calculates the inclination angle X of the fuel cell 20 shown in FIG. 2. The inclination angle X is calculated based on, for example, the torque, rotation speed, and running speed of the motor. The inclination angle X may also be detected by a sensor (not shown). The control device 40 selectively executes a normal process, a first drainage process, or a second drainage process according to the amount of residual water W and the inclination angle X.

[0025] (Normal processing) The control device 40 executes the normal process when the amount of the residual water W is less than the reference value. That is, the control device 40 executes the normal process when the amount of the residual water W is small and there is no need to drain the residual water W from the fuel cell 20. In the normal process, the control device 40 operates the injector 6 and the pump 18 with the discharge valve 16 closed. When the injector 6 operates, the fuel gas is supplied to the fuel cell 20 from the supply pipe 3. The fuel gas that has passed through the fuel cell 20 flows into the gas-liquid separator 14, where impurities (i.e., water, etc.) are separated from the fuel gas. The fuel gas from which the impurities have been separated in the gas-liquid separator 14 is supplied to the ejector 8 via the pump 18, and is sent from the ejector 8 to the fuel cell 20 again. In this way, in the normal operation, the fuel gas circulates in a circulation path that passes through the ejector 8, the fuel cell 20, the gas-liquid separator 14, and the pump 18. In addition, the control device 40 supplies the oxidizing gas to the fuel cell 20 by the oxidizing gas supply unit 30. Therefore, hydrogen reacts with oxidation in the fuel cell 20 to generate electricity. In normal operation, the injector 6 is controlled so that it discharges approximately the same amount of hydrogen as the hydrogen consumed in the fuel cell 20. Therefore, in normal operation, the pressure inside the fuel cell 20 is kept approximately constant. Furthermore, when the amount of water in the gas-liquid separator 14 increases during normal operation, the control device 40 opens the discharge valve 16 to discharge the water inside the gas-liquid separator 14.

[0026] During normal operation, hydrogen and oxygen react in the fuel cell 20 to generate water. Therefore, the residual water W in the fuel cell 20 increases during normal operation. When the amount of the residual water W increases to or above a reference value, the control device 40 executes either a first drainage process or a second drainage process. The first drainage process and the second drainage process are processes for discharging the residual water W from the fuel cell 20 while continuing power generation in the fuel cell 20. That is, the first drainage process and the second drainage process are processes for discharging the residual water W from the fuel cell 20 while supplying fuel gas and oxidizing gas to the fuel cell 20. The second drainage process is a process for discharging the residual water W by flowing fuel gas into the fuel gas discharge path 27 at a flow rate higher than that of the normal process. The first drainage process is a process for discharging the residual water W by flowing fuel gas into the fuel gas discharge path 27 at an even higher flow rate than that of the second drainage process. The control device 40 executes the second drainage process when the tilt angle X is less than the reference value (i.e., when the situation is such that it is easy to drain the residual water W), and executes the first drainage process when the tilt angle X is equal to or greater than the reference value (i.e., when the situation is such that it is difficult to drain the residual water W).

[0027] (Second wastewater treatment) Fig. 4 shows the changes in each value in the second drainage process. In Fig. 4 and Figs. 5 to 7 described later, graph A shows the pressure P in the fuel cell 20 (i.e., the pressure detected by the low-pressure side pressure sensor 12). In graph A, the solid line shows the control target value of the pressure P, and the dashed line shows the actual pressure P. In Figs. 4 to 7, graph B shows the open / closed state of the exhaust valve 16, and graph C shows the flow rate V of the fuel gas flowing in the fuel gas exhaust passage 27. Furthermore, symbol S21 shows the second drainage process, and symbol S22 shows the pressure reduction process. The control device 40 alternately performs the second drainage process S21 and the pressure reduction process S22.

[0028] In the second drainage process S21, the control device 40 closes the discharge valve 16. In addition, in the second drainage process S21, the control target value of the pressure P is set to a control target value P2 higher than the control target value P1 in the normal control. Therefore, the control device 40 increases the opening amount of the injector 6 at the same time as the start of the second drainage process S21, and increases the flow rate of the fuel gas discharged from the injector 6. Therefore, during the second drainage process S21, the flow rate V of the fuel gas in the fuel gas discharge path 27 increases from the flow rate V1 in the normal process to the flow rate V2. In this way, the fuel gas flows at a high flow rate in the fuel gas discharge path 27, so that the residual water W in the fuel gas discharge path 27 flows downstream, and the residual water W is discharged from the fuel cell 20 to the discharge pipe 7. The water discharged from the fuel cell 20 to the discharge pipe 7 is stored in the gas-liquid separator 14. In the second drainage process S21, the exhaust valve 16 is closed, so that the fuel gas circulates through a circulation path that passes through the ejector 8, the fuel cell 20, the gas-liquid separator 14, and the pump 18. With the fuel gas circulating in this manner, the injector 6 supplies the fuel gas to the fuel cell 20 at a high flow rate, so that the pressure P in the fuel cell 20 increases during the second drainage process S21. When the pressure P reaches pressure P2, the control device 40 ends the second drainage process S21 and executes the pressure reduction process S22.

[0029] In the pressure reduction process S22, the control device 40 opens the exhaust valve 16. Therefore, during the pressure reduction process S22, water and excess gas are discharged from the gas-liquid separator 14. Also, in the pressure reduction process S22, the control target value of the pressure P is set to the same control target value P1 (i.e., a lower value) as the control target value in normal control. Therefore, the control device 40 reduces the opening amount of the injector 6 at the same time as the start of the pressure reduction process S22, and reduces the flow rate V of the fuel gas from flow rate V2 to flow rate V1. In this way, in the pressure reduction process S22, the exhaust valve 16 opens and the flow rate of the fuel gas discharged by the injector 6 decreases. Therefore, during the pressure reduction process S22, the pressure P in the fuel cell 20 decreases from pressure P2 to pressure P1.

[0030] The control device 40 alternately and repeatedly executes the second drainage process S21 and the pressure reduction process S22. In the second drainage process S21, the residual water W is discharged from the fuel cell 20 and the pressure P increases, and in the pressure reduction process S22, the pressure P decreases. In this way, the control device 40 alternately and repeatedly executes the second drainage process S21 and the pressure reduction process S22, thereby discharging the residual water W while preventing the pressure P from increasing excessively. The control device 40 alternately and repeatedly executes the second drainage process S21 and the pressure reduction process S22 until the amount of residual water W falls below a reference value.

[0031] (First wastewater treatment) 5 shows changes in each value during the first drainage process. Reference numeral S11 indicates the first drainage process, and reference numeral S12 indicates the pressure reduction process. The control device 40 alternately performs the first drainage process S11 and the pressure reduction process S12.

[0032] In the first drainage process S11, the control device 40 opens the discharge valve 16. In addition, in the first drainage process S11, the control target value of the pressure P is set to a control target value P2 higher than the control target value P1 in the normal control. Therefore, the control device 40 increases the opening amount of the injector 6 at the same time as the start of the first drainage process S11, and increases the flow rate of the fuel gas discharged from the injector 6. Therefore, during the first drainage process S11, the flow rate V of the fuel gas in the fuel gas discharge path 27 increases from the flow rate V1 during the normal process. In the first drainage process S11, the control device 40 controls the injector 6 so that the flow rate of the fuel gas discharged from the injector 6 is higher than the flow rate of the gas discharged from the discharge valve 16, thereby increasing the pressure P. Therefore, in the first drainage process S11, the flow rate V of the fuel gas in the fuel gas discharge path 27 increases to a flow rate V3 higher than the flow rate V2 in the second drainage process S21. In this way, in the first drainage process S11, the fuel gas flows in the fuel gas discharge passage 27 at a flow rate V3 higher than that in the second drainage process S21. Therefore, even in a situation where the inclination angle X is large and the residual water W is difficult to discharge, the residual water W is discharged from the fuel cell 20. Since the discharge valve 16 is open, the water discharged from the fuel cell 20 to the discharge pipe 7 is discharged to the outside together with the fuel gas via the gas-liquid separator 14 and the discharge valve 16. Also, in the first drainage process S11, the flow rate of the fuel gas discharged from the injector 6 is higher than the flow rate of the fuel gas discharged from the discharge valve 16, so the pressure P in the fuel cell 20 rises. However, since the discharge valve 16 is open, even if the flow rate of the fuel gas discharged from the injector 6 is high, the rising speed of the pressure P in the fuel cell 20 is not so fast. In this embodiment, in the first drainage process S11, the pressure P rises at approximately the same speed as that in the second drainage process S21. In this way, in the first drainage process, it is possible to suppress an increase in pressure P while flowing fuel gas at an extremely high flow rate V3 into the fuel gas discharge path 27. When the pressure P reaches pressure P2, the control device 40 ends the first drainage process S11 and executes the pressure reduction process S12.

[0033] In the pressure reduction process S12, the control target value of the pressure P is set to the same control target value P1 (i.e., a low value) as the control target value in normal control. Therefore, the control device 40 reduces the opening amount of the injector 6 at the same time as the start of the pressure reduction process S12, and reduces the flow rate V of the fuel gas from the flow rate V3 to the flow rate V1. In addition, in the initial stage of the pressure reduction process S12, the control device 40 maintains the exhaust valve 16 in an open state. Thus, in the initial stage of the pressure reduction process S12, the flow rate of the fuel gas discharged by the injector 6 decreases while the exhaust valve 16 is maintained in an open state, so that the pressure P in the fuel cell 20 decreases. When the pressure P in the fuel cell 20 decreases to a value close to the pressure P1, the control device 40 closes the exhaust valve 16. While the exhaust valve 16 is closed, the pressure P stabilizes at the pressure P1.

[0034] The control device 40 alternately and repeatedly executes the first drainage process S11 and the pressure reduction process S12. In the first drainage process S11, the residual water W is discharged from the fuel cell 20 and the pressure P increases, and in the pressure reduction process S12, the pressure P decreases. In this way, the control device 40 alternately and repeatedly executes the first drainage process S11 and the pressure reduction process S12, thereby discharging the residual water W while preventing the pressure P from increasing excessively. The control device 40 alternately and repeatedly executes the first drainage process S11 and the pressure reduction process S12 until the amount of residual water W falls below a reference value.

[0035] As described above, the fuel cell system 100 of the first embodiment executes the second drainage process S21 when the residual water W is easily discharged and executes the first drainage process S11 when the residual water W is difficult to discharge, when the drainage process is required. In the second drainage process S21, the discharge flow rate of the injector 6 is increased with the discharge valve 16 closed, so that most of the fuel gas discharged from the injector 6 repeatedly circulates through the circulation path passing through the ejector 8, the fuel cell 20, the gas-liquid separator 14, and the pump 18. Since hydrogen in the fuel gas is consumed every time the circulating fuel gas passes through the fuel cell 20, the hydrogen concentration in the fuel gas is unlikely to increase. Therefore, when the discharge valve 16 is opened in the pressure reduction process S22 after the second drainage process S21, the hydrogen concentration in the gas discharged from the discharge valve 16 is low. In this way, in the second drainage process S21, the hydrogen in the fuel gas can be effectively utilized, and the gas with a low hydrogen concentration is discharged from the discharge valve 16, so that the environmental load can be reduced. On the other hand, in the first drainage process, the discharge flow rate of the injector 6 is increased with the exhaust valve 16 open, so that most of the fuel gas that has passed through the fuel cell 20 is exhausted from the exhaust valve 16, and little fuel gas circulates through the circulation path. Therefore, in the first drainage process S11, the utilization efficiency of hydrogen in the fuel gas is low. In the above-mentioned embodiment, the first drainage process S11 is performed only when it is difficult to drain the residual water W, and the second drainage process S21 is performed when it is easy to drain the residual water W. This allows for effective utilization of hydrogen and reduces the environmental load. EXAMPLES

[0036] Fig. 6 shows the first drainage treatment S11 and the pressure reduction treatment S12 of the fuel cell system of Example 2. In the fuel cell system of Example 1 described above, the output current I of the fuel cell 20 is maintained at a constant value in the first drainage treatment S11 and the pressure reduction treatment S12. In contrast, in the fuel cell system of Example 2, as shown in graph D of Fig. 6, the output current I1 in the first drainage treatment S11 is higher than the output current I2 in the pressure reduction treatment S12. The other configurations of the fuel cell system of Example 2 are the same as those of the fuel cell system of Example 1.

[0037] 6, when the output current I in the first drainage treatment S11 becomes high, more hydrogen gas is consumed by the fuel cell 20 during the first drainage treatment S11. This makes it more difficult for the pressure P in the fuel cell 20 to increase during the first drainage treatment S11. Therefore, according to the fuel cell system of Example 2, in the first drainage treatment S11, the flow rate V of the fuel gas can be made larger than in Example 1, and the time for the first drainage treatment S11 can be made longer than in Example 1. Therefore, according to Example 2, the residual water W is easier to discharge.

[0038] In the second embodiment, in the first drainage treatment S11, the output current I may be increased as the tilt angle X increases (i.e., as the residual water W is more difficult to drain and the flow rate V required for drainage is higher). By adjusting the output current I in this manner, the residual water W can be more effectively drained. However, if the output current I is too large, the amount of water generated in the fuel cell 20 increases, and it may become difficult to reduce the residual water W. Therefore, when the tilt angle X exceeds a predetermined angle, the output current I may be maintained at a constant value without being increased any further. EXAMPLES

[0039] FIG. 7 shows the first drainage process of the fuel cell system of Example 3. Graph E of FIG. 7 shows the hydrogen concentration N in the fuel gas in the fuel cell 20. Graph F of FIG. 7 shows the amount of residual water W. The dashed line in graph E shows the hydrogen concentration N when the first drainage process S11 and the pressure reduction process S12 are repeatedly performed in the fuel cell system of Example 1. As described above, in the first drainage process S11, the utilization efficiency of hydrogen in the fuel gas is low. Therefore, the hydrogen concentration N increases during the first drainage process S11. Therefore, as shown by the dashed line, the hydrogen concentration N increases as the number of times the first drainage process S11 and the pressure reduction process S12 are repeated increases. When the hydrogen concentration N increases, the pressure loss in the fuel gas discharge passage 27 decreases, and a pressure difference is less likely to occur between the rear end 27a of the fuel gas discharge passage 27 and the anode discharge port 24a. Therefore, when the hydrogen concentration N increases, it becomes more difficult to discharge the residual water W. For example, Fig. 8 shows the relationship between the hydrogen concentration N in the fuel gas and the fuel gas flow rate V required to discharge the residual water W for each tilt angle X. As shown in Fig. 8, for any tilt angle X, the higher the hydrogen concentration N, the higher the fuel gas flow rate V required to discharge the residual water W. In this way, as the hydrogen concentration N in the fuel gas increases, it becomes more difficult to discharge the residual water W.

[0040] In contrast, the fuel cell system of the third embodiment repeatedly executes the first drainage process S11 and the pressure reduction process S12, and reduces the frequency of opening the exhaust valve 16 when the number of repetitions n of the first drainage process S11 and the pressure reduction process S12 exceeds a reference number. For example, in FIG. 7, the timing t1 is the timing when the number of repetitions n exceeds the reference number. Then, the control device 40 maintains the exhaust valve 16 in a closed state after the timing t1. Therefore, in the process S31 after the timing t1, the discharge flow rate of the injector 6 is increased with the exhaust valve 16 closed, and the flow rate V and the pressure P increase. In the process S32 after the process S31, the discharge flow rate of the injector 6 is decreased with the exhaust valve 16 closed, and the flow rate V and the pressure P decrease. The processes S31 and S32 are repeatedly executed until the residual water W falls below the reference value. In this way, when the number of repetitions n exceeds the reference number, the exhaust valve 16 is maintained in a closed state. Therefore, the increase in the hydrogen concentration N after the timing t1 is suppressed. This prevents the efficiency of draining the residual water W from decreasing.

[0041] In the above-described third embodiment, the discharge valve 16 was maintained in a closed state after the number of repetitions n exceeded the reference number (i.e., the frequency at which the discharge valve 16 was opened was set to zero). However, after the number of repetitions n exceeded the reference number, the discharge valve 16 may be opened at a frequency lower than the period during which the first drainage process S11 and the pressure reduction process S12 were repeated. Even with this configuration, the increase in the hydrogen concentration N can be suppressed after the number of repetitions n exceeded the reference number.

[0042] In addition, in the third embodiment, the frequency with which the discharge valve 16 is opened may be changed according to the inclination angle X. For example, in one modification, when the inclination angle X is less than a reference angle, the first drainage process S11 and the pressure reduction process S12 may be repeatedly executed even if the number of repetitions n exceeds the reference number, and when the inclination angle X is equal to or greater than the reference angle, the frequency with which the discharge valve 16 is opened may be reduced. In another modification, the frequency with which the discharge valve 16 is opened may be reduced as the inclination angle X increases.

[0043] In the above-mentioned Examples 1 to 3, the flow rates V2 and V3 were set so that the rate of increase of the pressure P in the first drainage treatment S11 and the second drainage treatment S21 was approximately equal. However, the flow rates V2 and V3 may be set so that the rate of increase of the pressure P in the first drainage treatment S11 is lower than that in the second drainage treatment S21. With this configuration, the first drainage treatment S11 can be performed for a longer period of time than the second drainage treatment S21. Therefore, when it is difficult to drain the residual water W, the residual water W can be drained by performing the first drainage treatment S11 for a longer period of time.

[0044] In the above-described Examples 1 to 3, the flow rate V was gradually increased during the first drainage treatment S11 and the second drainage treatment S21. However, in the second drainage treatment S21, the flow rate V may be controlled to a constant value of the flow rate V2 by controlling the injector 6, and in the first drainage treatment S11, the flow rate V may be controlled to a constant value of the flow rate V3 by controlling the injector 6.

[0045] In addition, in the above-mentioned first to third embodiments, a linear solenoid valve may be provided instead of the injector 6, and the flow rate of the fuel gas supplied to the fuel cell 20 may be controlled by the linear solenoid valve.

[0046] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings achieves multiple objectives simultaneously, and achieving one of the objectives itself has technical utility. [Explanation of symbols]

[0047] 1: fuel gas tank, 6: injector, 8: ejector, 14: gas-liquid separator, 16: exhaust valve, 20: fuel cell, 26: cell, 27: fuel gas exhaust path, 29: bypass tube

Claims

1. A fuel cell having a plurality of stacked cells; A fuel gas supply unit; Control device, having The fuel cell is a fuel gas supply channel for supplying a fuel gas to the plurality of cells; a fuel gas discharge passage for discharging the fuel gas that has passed through the plurality of cells; having The fuel gas supply unit, a fuel gas supply device that changes a flow rate of the fuel gas supplied to the fuel gas supply path; a return path for returning the fuel gas discharged from the fuel gas discharge path to the fuel gas supply path; a discharge valve for discharging the fuel gas and water from the reflux path; having The control device, a normal process of operating the fuel gas supply device with the exhaust valve closed; a first drainage process for discharging water from the fuel gas discharge passage by operating the fuel gas supply device at a flow rate higher than that of the normal process with the discharge valve open; Run In the first drainage process, an output current of the fuel cell is increased as compared with that of the normal process. Fuel cell system.

2. 2. The fuel cell system of claim 1, wherein the control device performs a second drainage process to discharge water from the fuel gas exhaust path by operating the fuel gas supply device with the exhaust valve closed and at a flow rate higher than the normal process and lower than the first drainage process.

3. The liquid-vapor separator further comprises a gas-liquid separator provided in the reflux path, the exhaust valve exhausts the fuel gas and water from the gas-liquid separator; 3. The fuel cell system according to claim 1 or 2.

4. A fuel cell having a plurality of stacked cells; A fuel gas supply unit; Control device, having The fuel cell is a fuel gas supply channel for supplying a fuel gas to the plurality of cells; a fuel gas discharge passage for discharging the fuel gas that has passed through the plurality of cells; having The fuel gas supply unit, a fuel gas supply device that changes a flow rate of the fuel gas supplied to the fuel gas supply path; a return path for returning the fuel gas discharged from the fuel gas discharge path to the fuel gas supply path; a discharge valve for discharging the fuel gas and water from the reflux path; having The control device, a normal process of operating the fuel gas supply device with the exhaust valve closed; a first drainage process for discharging water from the fuel gas discharge passage by operating the fuel gas supply device at a flow rate higher than that of the normal process with the discharge valve open; Run When the control device executes the first drainage process, the control device alternately executes the first drainage process and a pressure reduction process in which the pressure in the fuel gas discharge path is reduced by operating the fuel gas supply device at a flow rate lower than that of the first drainage process with the discharge valve closed. Fuel cell system.

5. 5. The fuel cell system according to claim 4, wherein the frequency of opening the discharge valve is reduced when the number of times the first drainage process and the pressure reduction process are repeated exceeds a reference number.

6. Further comprising a gas-liquid separator provided in the reflux path, the exhaust valve exhausts the fuel gas and water from the gas-liquid separator; 6. The fuel cell system according to claim 4 or 5.

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