JP4765290B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly, to a technique effective for preventing freezing of water existing inside a fuel cell.

  Inside the fuel cell, there is water generated by an electrochemical reaction accompanying power generation and water supplied for humidifying the electrolyte membrane. When the fuel cell is left in a state where water is present inside after the system is shut down, when the fuel cell is cooled due to a decrease in the outside air temperature, the water present inside the fuel cell eventually begins to freeze. When the system is restarted in such a state, the supply of reaction gas to the electrode is hindered by the ice formed by freezing, so it takes a long time for the system to start completely after the rise in the fuel cell voltage is delayed. Is required.

As measures against water freezing in a fuel cell system, for example, techniques described in Patent Documents 1 to 3 are known. In the fuel cell system described in Patent Document 1, the possibility of freezing is predicted from the outside air temperature, and when freezing is predicted, the water remaining in the exhaust gas path is removed using the high-temperature gas obtained from the reformer. It is designed to be dried. In the fuel cell system described in Patent Document 2, the possibility of freezing is predicted from the average air temperature, the outside air temperature, the date and time, navigation information, and the like. When freezing is predicted, The water is purged. Moreover, in the fuel cell system described in Patent Document 3, the fuel cell is covered with a heat insulating material layer to keep the fuel cell warm, and the internal water is prevented from freezing.
JP-A-10-223249 JP 2004-39527 A JP 2003-151595 A

  However, it is difficult for the conventional technique described in Patent Document 1 to obtain a high effect in a fuel cell system that does not have a reformer. The high temperature gas obtained from the reformer reaches several hundred degrees Celsius, whereas in the fuel cell system without the reformer, the temperature of the fuel cell stack is the highest, and the temperature of the obtained gas is about 100 degrees Celsius at most. Because there is only. Even in a fuel cell system having a reformer, when the inside of the fuel cell is dried, it is necessary to prevent deterioration of the electrolyte membrane, so that the temperature of the gas supplied to the fuel cell is not too high. Can not. On the other hand, when water is purged with air at room temperature as in the prior art described in Patent Document 2, the amount of water evaporation is small compared to high-temperature gas, and thus drying may be insufficient. . In order to sufficiently dry, it is necessary to supply a large amount of air, which consumes a lot of energy.

  The prior art described in Patent Document 3 cannot be expected to be effective when the system is down for a long time. Even if it is covered with a heat insulating material layer, there is a slow release of heat from the fuel cell. For this reason, if the outside temperature is below the freezing point and the stop time is extended for a long period of time, the temperature of the fuel cell will eventually drop below the freezing point and the water inside will freeze.

  The present invention has been made to solve the above-described problems, and provides a fuel cell system which can be quickly started even in a low temperature environment by preventing freezing of water in the fuel cell. With the goal.

In order to achieve the above object, a first invention provides a fuel cell having a heat insulating structure;
Outside air supply means for supplying outside air to the gas flow path of the fuel cell;
Measuring means for measuring the temperature of the outside air or the dew point;
After the power generation of the fuel cell is stopped, when the measured value of the measuring means falls below a predetermined reference value, the outside air supply means is operated to introduce outside air into the gas flow path, and the inside of the fuel cell is dried. Control means for causing
It is characterized by having.

  In a second aspect based on the first aspect described above, the control means determines whether or not the dew point temperature of the outside air is reduced from at least two combinations of time, calendar information, navigation information, and statistical information such as temperature and humidity of each place. The reference value is set based on the predicted dew point temperature decrease state.

  In the first invention, after the power generation of the fuel cell is stopped, when the measured value of the measuring means falls below the reference value due to a decrease in the outside air temperature, the outside air supplying means is activated and the outside air is introduced into the gas flow path of the fuel cell. Since the dew point temperature of the outside air decreases as the temperature decreases, the amount of water contained in the outside air introduced is extremely small. On the other hand, since the fuel cell is kept warm by the heat insulating structure, even when the outside air temperature decreases, the temperature decrease of the fuel cell is suppressed. For this reason, a large temperature difference occurs between the introduced outside air and the fuel cell. However, since the heat capacity of air is extremely low, the temperature of the air reaches the vicinity of the temperature of the fuel cell as soon as it is introduced into the fuel cell. To rise. As the temperature rises, the amount of water that can be contained in the air increases, the evaporation of the water in the fuel cell is promoted, and the drying in the fuel cell proceeds. Thus, according to the first invention, the inside of the fuel cell can be efficiently dried with less energy.

  In addition, according to the second invention, since the start time of the drying process is determined based on the decrease in the dew point temperature of the outside air predicted in advance from various information, the drying process can be executed more efficiently. .

Embodiment 1 FIG.
The first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a schematic configuration diagram of a fuel cell system as Embodiment 1 of the present invention. The fuel cell system can be configured as a vehicle fuel cell system mounted on an electric vehicle, for example.

  An electric vehicle has a motor as a prime mover, and a fuel cell 2 is mounted as a power source for driving the motor. The fuel cell 2 is configured as a stack in which a plurality of single cells are stacked. Although not shown, the single cell is configured such that both sides of the electrolyte membrane are sandwiched between an anode and a cathode as catalyst electrodes, and both sides are sandwiched between conductive separators. In each single cell, an anode gas flow path through which a fuel gas containing hydrogen flows is formed between the anode and the separator, and a cathode gas flow path through which an oxidizing gas containing oxygen flows between the cathode and the separator. Is formed. In addition, a cooling water passage through which cooling water as a coolant flows is formed between the separators of adjacent cells.

  Supply of the oxidizing gas to the fuel cell 2 is performed via the gas supply pipe 4. The air supply pipe 4 is connected to the inlet of the cathode gas flow path of the fuel cell 2, and an air pump 8 is disposed in the middle of the air supply pipe 4. Air (outside air) is taken into the air supply pipe 4 by the operation of the air pump 8, and the taken-in air is supplied as an oxidizing gas to the cathode gas flow path. An air discharge pipe 6 is connected to the outlet of the cathode gas flow path of the fuel cell 2, and the air flowing through the fuel cell 2 is released from the air discharge pipe 6 into the atmosphere again.

  The operation of the air pump 8 is controlled by a control device 20 that integrally controls the entire fuel cell system. A dew point meter 22 for measuring the dew point temperature of the outside air is connected to the control device 20. The control device 20 can control the operation of the air pump 8 based on measurement information from the dew point meter 22 as will be described later.

  In the present embodiment, the periphery of the fuel cell 2 is covered with the heat insulating material 10. FIG. 2 is a diagram showing a comparison between changes in the outside air temperature and dew point temperature after the system is stopped, and changes in the temperature of the fuel cell 2 (fuel cell temperature). By being covered with the heat insulating material 10, even when the outside air temperature decreases, the decrease in the fuel cell temperature is suppressed, and for a certain period after the system is stopped, it is maintained at a high temperature immediately after the system is stopped. However, if the system is stopped for a long time in an environment where the outside air temperature is below freezing point, the fuel cell temperature will eventually drop below freezing point. At this time, if the water remaining in the fuel cell 2 is frozen, there is a problem that the power generation of the fuel cell is hindered when the system is restarted and the startability is deteriorated.

  With respect to the above problem, in the present embodiment, the air pump 8 is operated and air is introduced after the system is stopped to dry the inside of the fuel cell 2. However, it cannot be efficiently dried simply by introducing air as it is. When drying with air is premised, in order to dry efficiently with a small air flow rate, the amount of water that can be evaporated by increasing the air temperature and the amount of water that can be evaporated by lowering the dew point temperature of the air It is possible to increase the However, the former method is difficult to adopt due to problems such as the necessity of a high-temperature heat source and the durability of the electrolyte membrane. Therefore, in this embodiment, the latter method, that is, a method of drying the inside of the fuel cell 2 by introducing air with a lowered dew point temperature is adopted. Hereinafter, a freeze prevention measure at the time of system stop executed in the present embodiment will be specifically described.

  A freeze prevention measure is required in the fuel cell system when the next start-up is below freezing. In such an environment, the dew point temperature is always lower than the air temperature, so the dew point temperature of the outside air has dropped to below freezing point. On the other hand, as shown in FIG. 2, even when the dew point temperature of the outside air drops below the freezing point, the fuel cell temperature does not drop immediately but is maintained at a temperature higher than the dew point temperature of the outside air. In the present embodiment, the air pump 8 is operated and the outside air is introduced into the fuel cell 2 in such a situation where the temperature difference between the fuel cell temperature and the dew point temperature of the outside air is large. Since the heat capacity of air is extremely low, the temperature of the air rises to near the temperature of the fuel cell 2 as soon as it is introduced into the fuel cell 2. As the temperature rises, the amount of water that the air can contain increases, so that the evaporation of water in the fuel cell 2 is promoted. As a result, the inside of the fuel cell 2 can be efficiently dried with a small air flow rate, and energy consumption for operating the air pump 8 can be suppressed.

  FIG. 3 is a flowchart showing a freeze prevention control routine executed by the control device 20 in the present embodiment. As shown in FIG. 3, in the first step 100, it is determined whether or not the power generation of the fuel cell 2 is stopped. When the power generation of the fuel cell 2 is stopped with the stop of the system, the processing of steps 102 to 106 is performed thereafter.

  In step 102, the dew point temperature of the outside air is measured by the dew point meter 22. The measured dew point temperature of the outside air is compared with a predetermined reference value in the next step 104. The reference value is set to a temperature lower than 0 ° C. As a result of the comparison, when the dew point temperature is lower than the reference value, the drying process in the fuel cell 2 by the operation of the air pump 8 is performed. Air whose dew point temperature is lowered by the operation of the air pump 8 is introduced into the fuel cell 2, and the evaporation of water remaining in the fuel cell 2 is promoted.

  Note that the lower the reference value used in the determination in step 104, the lower the dew point temperature of the air introduced into the fuel cell 2. The lower the outdoor temperature, the lower the moisture content, and the greater the drying effect due to the introduction of air. However, on the other hand, it is expected that the dew point temperature does not easily fall below the reference value depending on the dew point temperature drop condition. If it takes time for the dew point temperature to fall below the reference value, the temperature of the fuel cell 2 will decrease over time, and the drying effect at the time of air introduction may decrease. Therefore, it is desirable to set the reference value in consideration of the state of change in the dew point temperature in the usage environment of the fuel cell system.

  By executing the routine by the control device 20, it is possible to prevent water from freezing inside the fuel cell 2 when the system is stopped, and to quickly start the system in a low temperature environment. Further, according to the above routine, the drying process of the fuel cell 2 is not executed immediately after the system is stopped, but is executed after waiting until the dew point temperature of the outside air decreases. Therefore, when the system is restarted immediately after the system is stopped, that is, when there is no fear of freezing, unnecessary drying processing is performed and energy is not wasted.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG.
The present embodiment is characterized by a method for setting a reference value of dew point temperature that is a criterion for determining whether or not to perform a drying process. In the first embodiment described above, the reference value is a fixed value, but in this embodiment, the reference value can be variably set as described below.

  FIG. 4 illustrates the difference in dew point temperature change by region. In the example shown in FIG. 4, the dew point temperature is lowered to a lower temperature in the region B than in the region A. In such a case, in the region B, by setting the reference value lower than that in the region A, it is possible to introduce the air having a lower dew point temperature into the fuel cell 2 and perform the drying process. On the contrary, in the area A, by setting the reference value higher than that in the area B, the drying process can be surely performed even when the dew point temperature does not drop so much.

  In this embodiment, a dew point temperature decrease state for each region as shown in FIG. 4 is predicted from a combination of time, calendar information, navigation information, and statistical information such as temperature and humidity in each region. For example, when the navigation information determines that the current location is area A, statistical information such as temperature and humidity in area A is read from the database. The database may be included in the control device 20, and an external database may be accessed by information communication means such as the Internet. Then, by comparing the current date and time with the statistical information, it is possible to expect the future dew point temperature decrease, specifically, the expected value of dew point temperature (center value of the band in FIG. 4) and variation (FIG. 4). The width of the middle band) is calculated.

  The control device 20 sets a reference value for the dew point temperature that is a criterion for determining whether or not to perform the drying process based on the expected value and variation of the calculated dew point temperature. For example, as shown in FIG. 4, the upper limit value of the dew point temperature variation may be set as the reference value. By setting the reference value by such a method, the drying process can be executed more efficiently.

Others.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the above-described embodiment, the entire fuel cell 2 is covered with the heat insulating material 10, but it is sufficient that at least the portion of the fuel cell 2 where water is present can be kept warm. For example, the heat insulating layer may be provided limited to a portion where the heat radiation of the fuel cell 2 is large.

  In the above embodiment, the dew point temperature of the outside air is measured by the dew point meter 22, but the outside temperature may be measured by the thermometer and it may be determined whether or not to perform the drying process based on the outside air temperature. . Since the dew point temperature is always lower than the outside air temperature, the inside of the fuel cell 2 can be efficiently dried even when the drying process is executed when the outside air temperature falls below a reference value (for example, the freezing point).

  In the above embodiment, the time, calendar information, navigation information, and statistical information such as temperature / humidity of each place are combined to predict the dew point temperature drop state, but all of this information must be used for prediction. Also good. For example, when the area where the system is used is fixed, the dew point temperature can be predicted to be lowered from the time, calendar information, and statistical information such as the temperature and humidity of the area. In addition, when the season in which the system is used is determined, it is possible to predict a dew point temperature decrease state from navigation information and statistical information such as temperature and humidity of each place.

It is a figure which shows schematic structure of the fuel cell system as Embodiment 1 of this invention. It is a figure which shows the change of the external temperature after a system stop, dew point temperature, and fuel cell temperature. It is a flowchart of the freeze prevention control routine performed in Embodiment 1 of this invention. It is explanatory drawing for demonstrating the setting method of the reference value of the dew point temperature in Embodiment 2 of this invention.

Explanation of symbols

2 Fuel Cell 4 Air Supply Pipe 6 Air Discharge Pipe 8 Air Pump 10 Heat Insulating Material 20 Controller 22 Dew Point Meter

Claims (2)

A fuel cell having a heat insulating structure;
Outside air supply means for supplying outside air to the gas flow path of the fuel cell;
Measuring means for measuring the temperature of the outside air or the dew point;
In a situation where the temperature of the fuel cell after the power generation of the fuel cell is stopped is higher than the temperature of the outside air, when the measured value of the measuring means falls below a predetermined reference value, the outside air supply means is operated to operate the gas Control means for introducing outside air at a temperature lower than the temperature of the fuel cell into the flow path, and drying the inside of the fuel cell;
A fuel cell system comprising: The control means predicts a decrease in dew point temperature of the outside air from at least two combinations of time, calendar information, navigation information, and statistical information on temperature and humidity in each place, and based on the predicted decrease in dew point temperature, The fuel cell system according to claim 2, wherein a reference value is set.

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