JP2009170337A - Fuel cell system and control method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing re-freezing of produced water in the starting at below-zero temperature; and to provide its control method. <P>SOLUTION: The fuel cell system 300 includes a fuel cell 100 in which a cathode and oxidant gas passages 48, 49 for supplying oxidant gas to the cathode are installed; and temperature adjusting means 230, 240 for adjusting so that the downstream temperature of the oxidant gas passage is higher than the upstream temperature in the staring at below-zero temperature of the fuel cell. By this constitution, the re-freezing of the produced water can be suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a fuel cell control method.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of environment and can realize high energy efficiency, it has been widely developed as a future energy supply system. In particular, since the polymer electrolyte fuel cell operates at a relatively low temperature among various types of fuel cells, it has a good startability. For this reason, research has been actively conducted for practical application in various fields.

  A polymer electrolyte fuel cell has a membrane-electrode assembly (MEA) in which an anode and a cathode are provided on both sides of an electrolyte membrane made of a solid polymer electrolyte having proton conductivity, respectively, by means of a separator. It has a sandwiched structure.

  When this fuel cell is started below freezing point, the water generated at the cathode may freeze, reducing the effective power generation area. Therefore, a technique has been disclosed in which a second cooling water passage provided with a heater is provided to supply the fuel cell with a coolant heated by the heater at the time of low temperature startup (see, for example, Patent Document 1).

JP 2002-313392 A

  However, in the technique of Patent Document 1, the generated water may be re-iced on the outlet side of the oxidant gas flow path. In this case, the power generation performance may be reduced.

  An object of the present invention is to provide a fuel cell system capable of suppressing re-freezing of generated water at the time of starting below freezing point and a control method thereof.

  The fuel cell system according to the present invention includes a fuel cell provided with a cathode and an oxidant gas channel for supplying an oxidant gas to the cathode, and a downstream side of the oxidant gas channel when the fuel cell is started below freezing point. Temperature adjusting means for adjusting the temperature to be higher than the temperature on the upstream side. In the fuel cell system according to the present invention, re-freezing of power generation product water on the downstream side of the oxidant gas is suppressed at the time of starting below freezing point. Thereby, a power generation performance fall is suppressed.

  The temperature adjusting means includes a first cooling medium flow path formed on the upstream side of the oxidant gas flow path, a second cooling medium flow path formed on the downstream side of the oxidant gas flow path, and the first cooling medium flow. And a flow rate control means for controlling the flow rate of the cooling medium flowing through the passage and the flow rate of the cooling medium flowing through the second cooling medium flow path. The flow rate control means opens the second cooling medium flow path when the fuel cell is started below freezing point. The cooling medium flow rate may be controlled such that the flowing cooling medium flow rate is less than the cooling medium flow rate flowing through the first cooling medium flow path. In this case, the temperature increase on the downstream side of the oxidant gas is promoted compared to the upstream side of the oxidant gas. Thereby, re-freezing of the power generation product water on the downstream side of the oxidant gas is suppressed.

  The flow rate control means may stop supplying the coolant to the second coolant flow path when the fuel cell is started below freezing point. In this case, the temperature rise on the downstream side of the oxidant gas can be promoted. Thereby, re-freezing of the power generation product water on the downstream side of the oxidant gas is further suppressed.

  The temperature adjusting means includes a first cooling medium flow path formed on the upstream side of the oxidant gas flow path and a second cooling medium flow path formed on the downstream side of the oxidant gas flow path. The cross-sectional area of the medium flow path may be smaller than the cross-sectional area of the first cooling medium flow path. In this case, the flow rate of the cooling medium flowing through the second cooling medium is smaller than the flow rate of the cooling medium flowing through the first cooling medium flow path. Thereby, re-freezing of the power generation product water on the downstream side of the oxidant gas is suppressed.

  A control method for a fuel cell according to the present invention is a control method for a fuel cell provided with a cathode and an oxidant gas flow path for supplying an oxidant gas to the cathode. It includes a temperature adjustment step for adjusting the temperature on the downstream side of the agent gas flow path higher than the temperature on the upstream side. In the fuel cell control method according to the present invention, re-freezing of the power generation product water on the downstream side of the oxidant gas is suppressed at the time of starting below freezing point. Thereby, a power generation performance fall is suppressed.

  The fuel cell includes a first cooling medium flow path formed on the upstream side of the oxidant gas flow path and a second cooling medium flow path formed on the downstream side of the oxidant gas flow path. The step of controlling the coolant flow rate so that the coolant flow rate flowing through the second coolant flow path is smaller than the coolant flow rate flowing through the first coolant flow path when the fuel cell starts below freezing point. Good. In this case, the temperature increase on the downstream side of the oxidant gas is promoted compared to the upstream side of the oxidant gas. Thereby, re-freezing of the power generation product water on the downstream side of the oxidant gas is suppressed.

  The temperature adjustment step may be a step of stopping the supply of the cooling medium to the second cooling medium flow path when the fuel cell is started below the freezing point. In this case, the temperature rise on the downstream side of the oxidant gas can be promoted. Thereby, re-freezing of the power generation product water on the downstream side of the oxidant gas is further suppressed.

  According to the present invention, re-freezing of generated water can be suppressed at the time of starting below freezing.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic diagram showing an outline of a fuel cell system 300 according to a first embodiment of the present invention. As shown in FIG. 1, the fuel cell system 300 includes a fuel cell stack 100, a fuel gas supply unit 210, an oxidant gas supply unit 220, a cooling medium supply unit 230, and a control unit 240.

  The fuel cell stack 100 has a structure in which the stack 110 is sandwiched between an end plate 120a and an end plate 120b. The stacked body 110 has a structure in which a plurality of single cells 130 are stacked. The fuel gas supply unit 210 is a unit that supplies a fuel gas containing hydrogen to the fuel cell stack 100 in accordance with an instruction from the control unit 240. The oxidant gas supply means 220 is a means for supplying an oxidant gas containing oxygen to the fuel cell stack 100 in accordance with an instruction from the controller 240.

  The cooling medium supply unit 230 is a unit that supplies a cooling medium such as ethylene glycol to the fuel cell stack 100 in accordance with an instruction from the control unit 240. Details of the cooling medium supply means 230 will be described later. The control unit 240 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and includes a fuel gas supply unit 210, an oxidant gas supply unit 220, and a cooling medium supply unit 230. It is a means to control.

  Next, details of the single cell 130 will be described. FIG. 2 is a schematic cross-sectional view of the single cell 130. FIG. 2 shows a case where a plurality of single cells 130 are stacked. As shown in FIG. 2, the single cell 130 has a structure in which a seal gasket-integrated MEA (membrane electrode assembly) 20 is sandwiched between two separators 10. The separator 10 has a structure in which an intermediate plate 12 is sandwiched between a cathode facing plate 11 and an anode facing plate 13. These three plates constituting the separator 10 are joined by hot pressing or the like.

  The seal gasket-integrated MEA 20 includes an MEA 21 and a seal gasket 22. The MEA 21 has a structure in which a catalyst layer and a gas diffusion layer are sequentially formed on both surfaces of an electrolyte membrane having proton conductivity. The catalyst layer is made of a conductive material that supports a catalyst, such as platinum-supported carbon. The gas diffusion layer is made of a conductive material having gas permeability, for example, carbon cloth, carbon paper or the like. In this embodiment, the upper surface side (left side in the figure) of the MEA 21 functions as an anode, and the lower surface side (right side in the figure) of the MEA 21 functions as a cathode.

  On the upper surface side (left side in the figure) of the MEA 21, a porous body channel 23 is disposed. On the lower surface side (right side in the figure) of the MEA 21, a porous body flow path 24 is disposed. The porous body channels 23 and 24 are made of a conductive material harder than the gas diffusion layer, and are made of a metal porous body such as a foam metal made of titanium or the like, a metal mesh, or a metal three-dimensional structure. It is preferable that the porous channels 23 and 24 have such strength that the thickness is substantially constant regardless of the presence or absence of dimples in the separator 10. In this case, the porosity hardly changes regardless of the presence or absence of dimples. Further, the surface pressure on the diffusion layer can be made substantially constant in the surface regardless of the presence or absence of dimples. Therefore, since the local compression in the diffusion layer can be reduced, the drainage performance is improved.

  FIG. 3 is a diagram for explaining the details of the separator 10 and the seal gasket-integrated MEA 20. 3A is a schematic plan view of the cathode facing plate 11, FIG. 3B is a schematic plan view of the anode facing plate 13, and FIG. 3C is a schematic plan view of the intermediate plate 12. FIG. 3D is a schematic plan view of the seal gasket-integrated MEA 20.

  The cathode facing plate 11 is a rectangular metal plate. As the metal plate, a plate made of titanium, titanium alloy, stainless steel, or the like that has been subjected to plating treatment for corrosion prevention can be used.

  As shown in FIG. 3A, a portion of the cathode facing plate 11 facing the MEA 21 (hereinafter referred to as a power generation region X) is a plane. At the outer peripheral edge of the cathode facing plate 11, a fuel gas supply manifold 41a, a fuel gas discharge manifold 41b, oxidant gas supply manifolds 42a to 42c, oxidant gas discharge manifolds 42d to 42f, cooling medium supply manifolds 43a and 43b, and cooling are provided. Medium discharge manifolds 43c and 43d are formed.

  The oxidant gas supply manifolds 42 a to 42 c are formed in the vicinity of one side of the cathode facing plate 11 along the side direction. The oxidant gas discharge manifolds 42d to 42f are formed in the vicinity of opposite sides along the side direction. The cooling medium supply manifolds 43a and 43b are formed in the vicinity of one of the remaining two sides along the side direction. The cooling medium discharge manifolds 43c and 43d are formed in the vicinity of opposite sides along the side direction.

  In the present embodiment, the cooling medium supply manifold 43a is formed closer to the oxidizing gas supply manifolds 42a to 42c than the cooling medium supply manifold 43b. The cooling medium discharge manifold 43c is formed closer to the oxidant gas supply manifolds 42a to 42c than the cooling medium discharge manifold 43d. The cathode facing plate 11 has a plurality of oxidant gas supply holes 44a and a plurality of oxidant gas discharge holes 44b. The manifolds and the holes penetrate the cathode facing plate 11 in the thickness direction.

  As shown in FIG. 3B, the anode facing plate 13 is a rectangular metal plate having substantially the same shape as the cathode facing plate 11 and is made of the same material as the cathode facing plate 11. The power generation region X in the anode facing plate 13 is a plane.

  Similar to the cathode facing plate 11, the fuel gas supply manifold 41 a, the fuel gas discharge manifold 41 b, the oxidant gas supply manifolds 42 a to 42 c, the oxidant gas discharge manifolds 42 d to 42 f, Medium supply manifolds 43a and 43b and cooling medium discharge manifolds 43c and 43d are formed. The anode facing plate 13 is formed with a common rail 45a for supplying fuel gas and a common rail 45b for discharging fuel gas. The manifolds and the common rails penetrate the anode facing plate 13 in the thickness direction.

  As shown in FIG. 3C, the intermediate plate 12 is a rectangular metal plate having the same shape as the cathode facing plate 11 and is made of the same material as the cathode facing plate 11. Similar to the cathode facing plate 11, a fuel gas supply manifold 41a, a fuel gas discharge manifold 41b, oxidant gas supply manifolds 42a to 42c, and oxidant gas discharge manifolds 42d to 42f are formed on the outer peripheral edge of the intermediate plate 12. ing.

  The intermediate plate 12 is formed with a plurality of fuel gas supply passages 46a having one end communicating with the fuel gas supply manifold 41a and the other end communicating with the common rail 45a. Similarly, the intermediate plate 12 is formed with a plurality of fuel gas discharge passages 46b having one end communicating with the fuel gas discharge manifold 41b and the other end communicating with the common rail 45b.

  Further, the intermediate plate 12 is formed with a plurality of oxidant gas supply passages 47a having one end communicating with any of the oxidant gas supply manifolds 42a to 42c and the other end communicating with the oxidant gas supply hole 44a. Yes. Similarly, the intermediate plate 12 is formed with a plurality of oxidant gas discharge passages 47b with one end communicating with the oxidant gas discharge manifolds 42d to 42f and the other end communicating with the oxidant gas discharge hole 44b. Further, the intermediate plate 12 is formed with a plurality of first cooling medium flow paths 48 having one end communicating with the cooling medium supply manifold 43a and the other end communicating with the cooling medium discharge manifold 43c. Further, the intermediate plate 12 is formed with a plurality of second cooling medium flow paths 49 having one end communicating with the cooling medium supply manifold 43b and the other end communicating with the cooling medium discharge manifold 43d. Each flow path penetrates the intermediate plate 12 in the thickness direction.

  As shown in FIG. 3 (d), the seal gasket-integrated MEA 20 has a structure in which a seal gasket 22 is joined to the outer peripheral edge of the MEA 21. The seal gasket 22 is made of a resin material such as silicon rubber, butyl rubber, or fluorine rubber, for example. The seal gasket 22 is manufactured by injection-molding the resin material with the outer peripheral end of the MEA 21 facing the mold cavity. According to this method, the MEA 21 and the seal gasket 22 are joined without a gap. Thereby, leakage from the junction of the cooling medium, the oxidant gas, and the fuel gas can be prevented.

  Similar to the cathode facing plate 11, the seal gasket 22 includes a fuel gas supply manifold 41a, a fuel gas discharge manifold 41b, an oxidant gas supply manifold 42a to 42c, an oxidant gas discharge manifold 42d to 42f, a cooling medium supply manifold 43a, 43b and cooling medium discharge manifolds 43c and 43d are formed. The seal gasket 22 seals the two separators 10 in contact with the upper surface and the lower surface. The seal gasket 22 seals between the outer periphery of the MEA 21 and the outer periphery of each manifold.

  Next, an outline of the operation of the fuel cell system 300 during power generation by the fuel cell stack 100 will be described. First, the control unit 240 controls the fuel gas supply unit 210 so that the fuel gas containing hydrogen is supplied to the fuel gas supply manifold 41a. This fuel gas is supplied to the porous body flow path 23 via the fuel gas supply flow path 46a and the common rail 45a. Thereafter, the fuel gas is supplied to the anode side gas diffusion layer of the MEA 21 while flowing through the porous body flow path 23. Hydrogen in the fuel gas is converted into protons in the catalyst layer of the MEA 21. The converted protons conduct through the electrolyte membrane of MEA 21 and reach the cathode catalyst layer.

  On the other hand, the control unit 240 controls the oxidant gas supply means 220 so that the oxidant gas containing oxygen is supplied to the oxidant gas supply manifolds 42a to 42c. This oxidant gas is supplied to the porous body flow path 24 via the oxidant gas supply flow path 47a. Thereafter, the oxidant gas is supplied to the cathode side gas diffusion layer of the MEA 21 while flowing through the porous body flow path 24. In the cathode side catalyst layer of the MEA 21, water is generated and oxygen is generated from oxygen and protons in the oxidant gas. This chemical reaction generates heat. The generated electric power is collected through the separator 10.

  In addition, the control unit 240 controls the cooling medium supply unit 230 so that the cooling medium is supplied to the cooling medium supply manifolds 43a and 43b. The cooling medium supplied to the cooling medium supply manifold 43a flows through the first cooling medium flow path 48 and is discharged to the outside through the cooling medium discharge manifold 43c. The cooling medium supplied to the cooling medium supply manifold 43b flows through the second cooling medium flow path 49 and is discharged to the outside through the cooling medium discharge manifold 43d. Thereby, the fuel cell stack 100 is cooled. As a result, the temperature of the fuel cell stack 100 can be adjusted to an appropriate temperature.

  The fuel gas that has not been used for power generation is discharged to the outside through the common rail 45b, the fuel gas discharge passage 46b, and the fuel gas discharge manifold 41b. Further, the oxidant gas that has not been used for power generation is discharged to the outside through the oxidant gas discharge passage 47b and the oxidant gas discharge manifolds 42d to 42f.

  Here, the sub-freezing start-up of the fuel cell stack 100 will be considered. When the fuel cell stack 100 starts power generation below the freezing point, the temperature of the fuel cell stack 100 gradually increases due to heat generated by power generation. However, re-freezing may occur before the water generated by power generation is discharged. In this case, the effective power generation area decreases. As a result, power generation performance may be reduced.

  FIG. 4 is a diagram showing experimental results of power generation distribution at the time of low temperature startup. As shown in FIG. 4A, the power generation region X between the oxidant gas supply manifold 42c and the oxidant gas discharge manifold 42f was used as a test piece. The test piece was divided into 3 × 5, and the current density in each region was measured in a state where the test piece was kept constant at −10 ° C.

  FIG. 4B is a diagram showing changes in current density over time. As shown in FIG. 4B, at the start of power generation, power generation was performed almost uniformly over the entire surface. However, with the passage of time, the current density decreased on the downstream side of the oxidant gas. This is presumably because the moisture generated with power generation is re-freezing. As time passes, power generation occurs in only a part of the area.

  As described above, it was found that at the time of low temperature startup, the power generation performance decreases on the downstream side of the oxidant gas, and the overall power generation performance gradually decreases. Therefore, in this embodiment, the cooling medium flow rate is adjusted at the time of starting below freezing. Hereinafter, the operation of the fuel cell system 300 when the fuel cell stack 100 is activated below the freezing point will be described.

  FIG. 5 is a schematic diagram for explaining the operation of the fuel cell system 300 at the time of starting below freezing (for example, −35 ° C. to 0 ° C.). As shown in FIG. 5, the cooling medium supply means 230 includes a flow rate adjusting valve 231 for adjusting the flow rate of the cooling medium, and a temperature sensor 232 for detecting the temperature of the cooling medium. In the present embodiment, the temperature sensor 232 detects the temperature of the cooling medium downstream from the cooling medium discharge manifolds 43c and 43d. This is because the temperature of the fuel cell stack 100 can be detected with high accuracy.

  First, the control unit 240 controls the fuel gas supply unit 210 and the oxidant gas supply unit 220 to cause the fuel cell stack 100 to generate power. Next, the control unit 240 determines whether or not the temperature of the cooling medium is below freezing based on the detection result of the temperature sensor 232. When the temperature of the cooling medium is below the freezing point, the control unit 240 causes the cooling medium supply amount to the second cooling medium flow path 49 to be smaller than the cooling medium supply amount to the first cooling medium flow path 48. The flow rate adjusting valve 231 is controlled.

  In this case, the flow rate of the cooling medium on the downstream side of the oxidant gas is smaller than that on the upstream side of the oxidant gas. As a result, the flow rate of the cooling medium below the freezing point flowing on the downstream side of the oxidant gas is reduced, and the temperature increase on the downstream side of the oxidant gas due to heat generated by power generation is promoted. As a result, re-freezing on the downstream side of the oxidant gas of the power generation generated water contained in the oxidant gas is suppressed. From the above, it is possible to suppress a decrease in the effective power generation area.

  In the present embodiment, the flow rate of the cooling medium flowing through the second cooling medium flow path 49 is reduced, but the supply of the cooling medium to the second cooling medium flow path 49 may be stopped. In this case, since the cooling medium below freezing point does not flow on the downstream side of the oxidant gas, the temperature increase on the downstream side of the oxidant gas is promoted.

  Here, it is also conceivable to stop the supply of the cooling medium to the first cooling medium flow path 48 and the second cooling medium flow path 49 at the time of starting below the freezing point. This is because the temperature rise of the fuel cell stack 100 is promoted by heat generated by power generation. However, in this case, since it becomes difficult to detect the average temperature of the fuel cell stack 100, the control of the fuel cell stack 100 may be difficult. When the circulation of the cooling medium is stopped, the temperature locally rises in the cathode catalyst layer. In this case, each part of the fuel cell stack 100 may be damaged. Therefore, the cooling medium is preferably circulated as much as possible. In the present embodiment, since the circulation of the cooling medium is only partially stopped or suppressed, the fuel cell stack 100 can be efficiently started up while suppressing damage to each part of the fuel cell stack 100 and the like. .

  FIG. 6 shows an example of a flowchart when starting below freezing. When this flowchart is executed, power generation is started in the fuel cell stack 100. As shown in FIG. 6, the control unit 240 receives the detection result of the temperature sensor 232 and acquires the temperature T of the cooling medium (step S1). Next, the control unit 240 determines whether or not the temperature T of the cooling medium is less than 0 ° C. (step S2).

  If it is not determined in step S2 that the temperature T of the cooling medium is less than 0 ° C., the control unit 240 ends the execution of the flowchart. When it is determined in step S <b> 2 that the temperature T of the cooling medium is less than 0 ° C., the control unit 240 flows through the second cooling medium flow path 49 rather than the flow rate of the cooling medium flowing through the first cooling medium flow path 48. The flow rate adjusting valve 231 is controlled so that the flow rate of the cooling medium to be reduced is reduced (step S3).

  Next, the control unit 240 receives the detection result of the temperature sensor 232 and acquires the temperature T of the cooling medium again (step S4). Next, the control unit 240 determines whether or not the temperature T of the cooling medium is 0 ° C. or higher (step S5). When it is not determined in step S5 that the temperature T of the cooling medium is 0 ° C. or higher, the control unit 240 executes step S4 again. When it is determined in step S5 that the temperature T of the cooling medium is 0 ° C. or higher, the control unit 240 has the same flow rate of the cooling medium flowing through the first cooling medium flow path 48 and the second cooling medium flow path 49. Thus, the flow rate adjusting valve 231 is controlled (step S6). Thereafter, the control unit 240 ends the execution of the flowchart.

  By executing this flowchart, the flow rate of the coolant on the downstream side of the oxidant gas becomes smaller than that on the upstream side of the oxidant gas until the temperature of the coolant reaches 0 ° C. from below freezing point. Thereby, re-freezing on the downstream side of the oxidant gas of the power generation generated water contained in the oxidant gas is suppressed. As a result, a reduction in effective power generation area can be suppressed.

  FIG. 7A is a diagram illustrating an example of the flow rate of the cooling medium flowing through the first cooling medium flow path 48 and the second cooling medium flow path 49 at the time of starting below the freezing point. As shown in FIG. 7A, at the time of starting below freezing, the supply of the cooling medium to the second cooling medium flow path 49 is stopped, and the cooling medium is supplied only to the first cooling medium flow path 48. Thereafter, when the cooling medium flow rate to the second cooling medium flow path 49 is gradually or stepwise increased and the temperature of the cooling medium becomes 0 ° C. or higher, the first cooling medium flow path 48 and the second cooling medium The supply amount of the cooling medium to the flow path 49 is made equal. By controlling the coolant flow rate in this way, it is possible to efficiently suppress re-freezing of moisture on the oxidant gas outlet side.

  FIG. 7B shows a temperature distribution when the supply of the cooling medium to the second cooling medium flow path 49 is stopped. As shown in FIG. 7B, by stopping the supply of the cooling medium to the second cooling medium flow path 49, the temperature on the oxidant gas outlet side becomes higher than that on the oxidant gas inlet side.

  Further, when the temperature is high (for example, the cooling medium temperature is 80 ° C. or higher), the electrolyte membrane may be dried and power generation performance may be reduced. Therefore, as shown in FIG. 8A, at a high temperature, the flow rate of the cooling medium flowing in the second cooling medium flow path 49 is larger than the flow rate of the cooling medium flowing in the first cooling medium flow path 48. The flow rate adjustment valve 231 may be controlled. In this case, when the temperature on the outlet side of the oxidant gas is lowered, the discharge of moisture from the oxidant gas outlet side is suppressed. Thereby, drying of the electrolyte membrane is suppressed. In addition, if a cooling water pump is disposed instead of the flow rate adjusting valve and the flow rate of the second cooling medium flow path 49 is increased without changing the flow rate of the first cooling medium flow path 48, a further great effect can be obtained.

  FIG. 8B shows the temperature distribution when the coolant flow rate to the second coolant flow path 49 is increased. Here, originally, the region on the outlet side of the oxidant gas and the outlet side of the cooling medium becomes high temperature. However, as shown in FIG. 8B, by increasing the coolant flow rate to the second coolant flow path 49, the temperature increase in the region on the oxidant gas outlet side and the outlet side of the coolant is suppressed. . Thereby, the uniformity of the in-plane temperature can be measured.

  In this embodiment, the cooling medium supply unit 230 and the control unit 240 correspond to the temperature adjustment unit, and the flow rate adjustment valve 231 corresponds to the flow rate control unit.

  FIG. 9 is a schematic diagram for explaining a fuel cell system 300a according to a second embodiment of the present invention. In the present embodiment, as shown in FIG. 9, the cross-sectional area of the second cooling medium flow path 49 is set smaller than the cross-sectional area of the first cooling medium flow path 48. In this case, the coolant flow rate flowing through the second coolant flow path 49 is smaller than the coolant flow rate flowing through the first coolant flow path 48. Therefore, re-freezing of power generation generated water at the time of low temperature startup can be suppressed. Thereby, a power generation performance fall can be controlled.

  In each of the above embodiments, the cooling medium is divided into two types of flow paths and the flow rate of each flow path is adjusted, but the present invention is not limited to this. Even in the case of dividing into three or more types of flow paths, the effect of the present invention can be obtained by reducing the flow rate of the cooling medium flowing downstream of the oxidant gas compared to the upstream side of the oxidant gas when starting below freezing. Moreover, in each said Example, although temperature is adjusted using a cooling medium, it is not restricted to it. For example, you may provide the heater etc. which raise the temperature of oxidant gas downstream compared with oxidant gas upstream.

1 is a schematic diagram showing an outline of a fuel cell system according to a first embodiment of the present invention. It is typical sectional drawing of a single cell. It is a figure for demonstrating the detail of a separator and seal gasket integrated MEA. It is a figure which shows the experimental result of the electric power generation distribution at the time of low temperature starting. It is a schematic diagram for demonstrating operation | movement of the fuel cell system at the time of starting below freezing point. It is a figure which shows an example of the flowchart at the time of starting below freezing point. It is a figure which shows an example of the coolant flow rate which flows through the 1st and 2nd coolant flow path at the time of starting below freezing point. It is a figure which shows an example of the cooling medium flow volume which flows through the 1st and 2nd cooling medium flow path at the time of high temperature operation. It is a schematic diagram for demonstrating the fuel cell system which concerns on 2nd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Fuel cell stack 130 Single cell 230 Cooling medium supply means 240 Control part 42a-42c Oxidant gas supply manifold 42d-42f Oxidant gas discharge manifold 43a, 43b Cooling medium supply manifold 43c, 43d Cooling medium discharge manifold 48 1st cooling medium Flow path 49 Second cooling medium flow path 231 Flow rate adjustment valve 232 Temperature sensor 300 Fuel cell system

Claims (7)

A fuel cell provided with a cathode and an oxidant gas flow path for supplying an oxidant gas to the cathode;
A fuel cell system comprising: temperature adjusting means for adjusting the temperature on the downstream side of the oxidant gas flow path to be higher than the temperature on the upstream side when the fuel cell is started below freezing point. The temperature adjusting means includes a first coolant flow path formed on the upstream side of the oxidant gas flow path, a second coolant flow path formed on the downstream side of the oxidant gas flow path, and the first A flow rate control means for controlling a cooling medium flow rate flowing through the first cooling medium flow path and a cooling medium flow rate flowing through the second cooling medium flow path,
The flow rate control means is configured to reduce the coolant flow rate so that the coolant flow rate flowing through the second coolant flow path is smaller than the coolant flow rate flowing through the first coolant flow path when the fuel cell is started below freezing point. The fuel cell system according to claim 1, wherein the fuel cell system is controlled.   3. The fuel cell system according to claim 2, wherein the flow rate control unit stops supplying the cooling medium to the second cooling medium flow path when the fuel cell is started below freezing point. 4. The temperature adjusting means includes a first coolant flow path formed on the upstream side of the oxidant gas flow path and a second coolant flow path formed on the downstream side of the oxidant gas flow path,
2. The fuel cell system according to claim 1, wherein a cross-sectional area of the second coolant flow path is smaller than a cross-sectional area of the first coolant flow path. A control method of a fuel cell provided with a cathode and an oxidant gas flow path for supplying an oxidant gas to the cathode,
A fuel cell control method comprising a temperature adjustment step of adjusting a temperature on the downstream side of the oxidant gas flow path higher than a temperature on the upstream side when the fuel cell is started below freezing point. The fuel cell includes a first coolant flow path formed on the upstream side of the oxidant gas flow path and a second coolant flow path formed on the downstream side of the oxidant gas flow path,
In the temperature adjustment step, the coolant flow rate is such that the coolant flow rate flowing through the second coolant flow path is less than the coolant flow rate flowing through the first coolant flow path when the fuel cell is started below freezing point. 6. The method of controlling a fuel cell according to claim 5, wherein the method is a step of controlling the fuel cell.   The fuel cell control method according to claim 6, wherein the temperature adjusting step is a step of stopping supply of a cooling medium to the second cooling medium flow path when the fuel cell is started below freezing point.

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