阅读说明：本技术 燃料电池系统及液态水量预测方法 (Fuel cell system and liquid water amount prediction method ) 是由 小牧克哉 于 2019-06-03 设计创作，主要内容包括：本发明涉及一种燃料电池系统及液态水量预测方法。所述燃料电池系统具有：燃料电池堆,其通过氢与氧的化学反应而进行发电,并且使生成水及排气被排出；液态水量预测部,其基于燃料电池堆的发电电流量、向燃料电池堆供给的空气的量、该空气的温度及相对湿度、从燃料电池堆被排出的排气的温度、和该排气的压力,而对所述生成水中的液态水的量进行预测。(The present invention relates to a fuel cell system and a liquid water amount prediction method. The fuel cell system has: a fuel cell stack that generates electricity by a chemical reaction between hydrogen and oxygen, and discharges produced water and exhaust gas; and a liquid water amount prediction unit that predicts the amount of liquid water in the generated water based on the amount of generated current of the fuel cell stack, the amount of air supplied to the fuel cell stack, the temperature and relative humidity of the air, the temperature of exhaust gas discharged from the fuel cell stack, and the pressure of the exhaust gas.)

1. A fuel cell system having:

a fuel cell stack that generates electricity by a chemical reaction between hydrogen and oxygen, and discharges produced water and exhaust gas;

and a liquid water amount prediction unit that predicts an amount of liquid water in the generated water based on a generated current amount of the fuel cell stack, an amount of air supplied to the fuel cell stack, a temperature of the air, a relative humidity of the air, a temperature of exhaust gas discharged from the fuel cell stack, and a pressure of the exhaust gas.

2. The fuel cell system according to claim 1,

the disclosed device is provided with:

a water storage tank that stores liquid water discharged from the fuel cell stack;

a valve provided in a drain pipe connecting the fuel cell stack and the water storage tank;

a valve control unit that controls the opening of the valve,

the valve control unit increases the opening degree of the valve as the amount of liquid water predicted by the liquid water amount prediction unit increases, and decreases the opening degree of the valve as the amount of liquid water predicted by the liquid water amount prediction unit decreases.

3. The fuel cell system according to claim 2,

the water supply device is provided with an injection unit that injects the liquid water stored in the water storage tank to a heat exchanger of a vehicle.

4. A method for predicting the amount of liquid water is applied to a fuel cell system having a fuel cell stack that generates electric power by a chemical reaction between hydrogen and oxygen and discharges generated water and exhaust gas,

in the liquid water amount prediction method, the amount of water in the liquid state,

the amount of liquid water in the generated water is predicted based on the amount of generated current of the fuel cell stack, the amount of air supplied to the fuel cell stack, the temperature of the air, the relative humidity of the air, the temperature of exhaust gas discharged from the fuel cell stack, and the pressure of the exhaust gas.

Technical Field

The present disclosure relates to a fuel cell system and a liquid water amount prediction method.

Background

Jp 2010-153246 a discloses a fuel cell system that generates electricity by reacting a fuel gas with an oxidizing gas, and has a structure in which liquid water generated during the generation of electricity is stored in a collection tank. Further, japanese patent application laid-open No. 2010-153246 discloses a method of calculating a predicted generated water amount based on a generated current integrated value and opening a drain valve when it is determined that the generated water amount stored in a trap tank is equal to or more than a threshold value based on the prediction result.

However, when the generated water amount is predicted based on only the integrated value of the generated current as in japanese patent application laid-open No. 2010-153246, only the generated water amount in which the water vapor and the liquid water are mixed can be predicted. Therefore, from the viewpoint of predicting the amount of liquid water produced, there is still room for improvement.

Disclosure of Invention

In view of the above, the present disclosure obtains a fuel cell system and a liquid water amount prediction method that can predict the amount of liquid water in generated water.

Means for solving the problems

A fuel cell system of a first aspect includes: a fuel cell stack that generates electricity by a chemical reaction between hydrogen and oxygen, and discharges produced water and exhaust gas; and a liquid water amount prediction unit that predicts an amount of liquid water in the generated water based on a generated current amount of the fuel cell stack, an amount of air supplied to the fuel cell stack, a temperature of the air, a relative humidity of the air, a temperature of exhaust gas discharged from the fuel cell stack, and a pressure of the exhaust gas.

In the fuel cell system of the first aspect, the hydrogen and the oxygen are chemically reacted in the fuel cell stack to generate power, and the generated water and the exhaust gas are discharged. Here, the fuel cell system includes a liquid water amount prediction unit that predicts the amount of liquid water to be generated based on the amount of generated current of the fuel cell stack, the amount of supplied air, the temperature of the air, the relative humidity of the air, the exhaust temperature, and the exhaust pressure. In this way, by adding information on the supply side such as the amount and relative humidity of air supplied to the fuel cell stack and information on the exhaust side such as the temperature and exhaust pressure of exhaust gas discharged from the fuel cell stack to the amount of generated current of the fuel cell stack, it is possible to predict the amount of liquid water in the generated water.

A fuel cell system according to a second aspect is the first aspect, including: a water storage tank that stores liquid water discharged from the fuel cell stack; a valve provided in a drain pipe connecting the fuel cell stack and the water storage tank; and a valve control unit that controls an opening degree of the valve, wherein the valve control unit increases the opening degree of the valve as the amount of liquid water predicted by the liquid water amount prediction unit increases, and decreases the opening degree of the valve as the amount of liquid water predicted by the liquid water amount prediction unit decreases.

The fuel cell system according to the second aspect includes a water storage tank that stores liquid water discharged from the fuel cell stack. The fuel cell stack and the water storage tank are connected by a drain pipe, and the drain pipe is provided with a valve. The opening degree of the valve is controlled by a valve control unit, and the valve control unit increases the opening degree of the valve as the amount of liquid water predicted by the liquid water amount prediction unit increases. Accordingly, when the amount of liquid water to be generated is large, the flow path cross-sectional area of the drain pipe is increased by increasing the opening degree of the valve, and it is possible to suppress the generated liquid water from being discharged to the atmosphere without being stored in the water storage tank. In contrast, the valve control unit decreases the valve opening degree as the liquid water amount predicted by the liquid water amount prediction unit decreases. Thus, when the amount of liquid water to be generated is small, the flow path cross-sectional area of the drain pipe is reduced by reducing the opening degree of the valve, and the entry of gas other than the liquid water into the water storage tank can be suppressed.

A fuel cell system according to a third aspect is the fuel cell system according to the second aspect, wherein the fuel cell system includes an injection unit that injects the liquid water stored in the water storage tank to a heat exchanger of the vehicle.

In the fuel cell system according to the third aspect, the generated liquid water is injected into the heat exchanger of the vehicle, thereby facilitating heat exchange.

A liquid water amount prediction method according to a fourth aspect is a liquid water amount prediction method applied to a fuel cell system including a fuel cell stack that generates electricity by a chemical reaction between hydrogen and oxygen and discharges produced water and exhaust gas, and predicts an amount of liquid water in the produced water based on an amount of electricity generated by the fuel cell stack, an amount of air supplied to the fuel cell stack, a temperature of the air, a relative humidity of the air, a temperature of the exhaust gas discharged from the fuel cell stack, and a pressure of the exhaust gas.

In the liquid water amount prediction method of the fourth aspect, the amount of liquid water generated is predicted based on the amount of generated current of the fuel cell stack, the amount of air supplied, the temperature of the air, the relative humidity of the air, the exhaust temperature, and the exhaust pressure. In this way, by adding information on the supply side such as the amount and relative humidity of air supplied to the fuel cell stack and information on the exhaust side such as the temperature and exhaust pressure of exhaust gas discharged from the fuel cell stack to the amount of power generation current of the fuel cell stack, it is possible to predict the amount of liquid water in the generated water.

As described above, according to the fuel cell system of the first aspect and the liquid water amount prediction method of the fourth aspect, the amount of liquid water to be generated can be predicted.

According to the fuel cell system of the second aspect, liquid water can be efficiently stored in the water storage tank.

According to the fuel cell system of the third aspect, the performance of the heat exchanger can be improved.

Drawings

Exemplary embodiments of the present disclosure are described in detail based on the following drawings.

Fig. 1 is a schematic diagram schematically showing the overall configuration of a fuel cell system according to an embodiment.

Fig. 2 is a schematic diagram corresponding to fig. 1, showing a first modification of the fuel cell system according to the embodiment.

Fig. 3 is a schematic diagram corresponding to fig. 1, showing a second modification of the fuel cell system according to the embodiment.

Fig. 4 is a schematic diagram corresponding to fig. 1, showing a third modification of the fuel cell system according to the embodiment.

Fig. 5 is a graph showing an example of the relationship between the total pressure and the proportion of liquid water.

Fig. 6 is a schematic block diagram of the fuel cell system according to the embodiment.

Fig. 7 is a flowchart showing an example of the liquid water amount prediction method according to the embodiment.

Fig. 8 is a flowchart showing another example of the liquid water amount prediction method.

Detailed Description

(Overall Structure)

A fuel cell system 10 according to an embodiment will be described with reference to the drawings. As shown in fig. 1, a fuel cell system 10 according to the present embodiment is mounted on a vehicle and includes a fuel cell stack 12.

The fuel cell stack 12 of the present embodiment is a cell that generates electricity by being supplied with hydrogen and air. Specifically, the fuel cell stack 12 includes a plurality of cells, and hydrogen flows between the positive electrodes (anode and fuel electrode) of the cells and the separators on the positive electrode side, and air containing oxygen flows between the negative electrodes (cathode and air electrode) of the cells and the separators on the negative electrode side. Then, power generation is performed by a chemical reaction between the hydrogen and oxygen. Further, the motor is driven by supplying electric power from the fuel cell stack 12 to the motor.

At this time, since the fuel cell stack 12 generates heat, cooling water flows through the fuel cells to absorb the heat generated in the fuel cell stack 12. In addition, along with the power generation performed by the fuel cell stack 12, the exhaust gas containing oxygen and nitrogen and the generated water containing liquid water and water vapor are discharged.

A hydrogen supply pipe 14 for supplying hydrogen from a hydrogen tank, not shown, is connected to the fuel cell stack 12. An air supply pipe 16 for supplying air is connected to the fuel cell stack 12, and an air compressor, not shown, is provided in the air supply pipe 16. Then, the hydrogen gas supplied from the hydrogen supply pipe 14 to the fuel cell stack 12 is reacted with oxygen in the air supplied from the air supply pipe 16 to the fuel cell stack 12.

One end side of a first exhaust pipe 17 is connected to the fuel cell stack 12, and unreacted hydrogen gas flows through the first exhaust pipe 17. Further, since the other end portion of the first exhaust pipe 17 is open to the atmosphere, unreacted hydrogen gas is released to the atmosphere. In addition, the amount of unreacted hydrogen released is trace and does not reach the concentration required for combustion.

One end side of the second exhaust pipe 18 is connected to the fuel cell stack 12. The second exhaust pipe 18 is an exhaust pipe through which the generated exhaust gas such as oxygen and nitrogen is discharged, and the other end side of the second exhaust pipe 18 is connected to a gas-liquid separator 20. In addition to oxygen and nitrogen, the second exhaust pipe 18 also flows water containing water vapor and liquid water.

The gas-liquid separator 20 is connected to a third exhaust pipe 22 and a drain pipe 26. The third exhaust pipe 22 is an exhaust pipe through which the gas separated by the gas-liquid separator 20 flows, and is open to the atmosphere. Therefore, the gas flowing through the third exhaust pipe 22 is released to the atmosphere. A pressure regulating valve 24 is provided in the third exhaust pipe 22, and the third exhaust pipe 22 is opened and closed by operating the pressure regulating valve 24. Therefore, the gas can be released to the atmosphere at an arbitrary timing.

The liquid water separated by the gas-liquid separator 20 flows through the drain pipe 26, and the drain pipe 26 is connected to the water storage tank 30. The drain pipe 26 is provided with a drain valve 28, and the drain pipe 26 is opened and closed by operating the drain valve 28.

The water storage tank 30 is a tank that stores liquid water flowing through the drain pipe 26, and one end side of the liquid sending pipe 32 is connected to the water storage tank 30. The other end side of the liquid sending pipe 32 is located in the vicinity of a radiator 38 as a heat exchanger, and an ejection portion 36 is provided at the other end of the liquid sending pipe 32. The injection unit 36 is configured to include a nozzle or the like, and is configured to inject the liquid water stored in the water storage tank 30 from the injection unit 36 to the radiator 38 through the liquid delivery pipe 32. The liquid sending pump 34 is connected to the liquid sending pipe 32, and the liquid sending pump 34 is operated to send the liquid water in the liquid sending pipe 32 to the spraying section 36.

Next, an example of a control section in the fuel cell system 10 according to the present embodiment will be described. As shown in fig. 6, the fuel cell system 10 includes a computer 50. The computer 50 includes a CPU (central processing Unit), a ROM (Read only Memory) in which programs and the like for realizing the respective processing flows are stored, a RAM (Random Access Memory) in which data is temporarily stored, a Memory as a storage Unit, a network interface, and the like.

The computer 50 is functionally provided with an information acquisition unit 52, an information storage unit 54, a liquid water amount prediction unit 56, an information output unit 58, a pump control unit 60, and a valve control unit 62.

The information acquisition unit 52 acquires various information from the fuel cell stack 12. Specifically, the information acquiring unit 52 acquires the amount of power generation current of the fuel cell stack 12, the amount of air supplied to the fuel cell stack 12, the temperature of the air supplied to the fuel cell stack 12, the relative humidity of the air, the temperature of the exhaust gas discharged from the fuel cell stack 12, the pressure of the exhaust gas discharged from the fuel cell stack 12, and the like. These pieces of information are measured by a plurality of sensors not shown, and the information acquisition unit 52 acquires the measured values.

The information storage unit 54 stores the information acquired by the information acquisition unit 52. Further, information such as a mathematical expression is stored in the information storage unit 54. The liquid water amount prediction unit 56 predicts the amount of liquid water to be generated based on the information acquired by the information acquisition unit 52. The details of the predictive expression used at this time will be described later.

The information output unit 58 outputs the liquid water amount predicted by the liquid water amount prediction unit 56 to the pump control unit 60 and the valve control unit 62. Further, the output may be output to a display unit such as a display, not shown, disposed on an instrument panel of the vehicle.

The pump control unit 60 controls the liquid feeding pump 34. That is, the liquid-state water in the liquid-sending pipe 32 is carried to the jetting unit 36 by operating the liquid-sending pump 34 by the pump control unit 60, and the liquid-state water is jetted from the jetting unit 36 to the radiator 38.

The valve control unit 62 controls the pressure regulating valve 24 and the drain valve 28. That is, the valve control unit 62 opens the pressure regulating valve 24, thereby releasing the exhaust gas in the third exhaust pipe 22 to the atmosphere. The valve control unit 62 opens the drain valve 28, so that the liquid water in the drain pipe 26 is stored in the water storage tank 30. In the present embodiment, the opening degree of the water discharge valve 28 can be adjusted to any opening degree between the fully open state and the fully closed state by the valve control unit 62.

(method of predicting amount of liquid Water)

Next, a method of predicting the amount of liquid water generated by the fuel cell stack 12 will be described. First, the reaction formula of the fuel cell stack 12 is as follows. In this case, the hydrogen consumption is 100%, and the molar ratio of the oxygen to be absorbed to the hydrogen consumption is k.

1.88 in the above reaction formula is a coefficient indicating a molar ratio in air based on N in air₂And O₂About 0.79: 0.21 ratio.

Here, the molar flow rate of water vapor in the exhaust gas is represented by n_ST(mol/sec) and the molar flow rate of nitrogen in the exhaust gas is n_N2(mol/sec) and the molar flow rate of oxygen in the exhaust gas is n_O2(mol/sec), the pressure of the exhaust gas is P (kPa), and the saturated vapor pressure at the exhaust temperature T (. degree. C.) is P_ST(kPa), it can be determined according to the partial pressure in daltonsThe following equation (1) is derived.

[ mathematical formula 1]

Furthermore, according to the empirical formula of Tetens, the saturated vapor pressure P_ST(kPa) is expressed by the following equation (2).

[ mathematical formula 2]

Next, since the relative humidity of the intake air is set to Φ (%), the intake air temperature is set to T_HWater vapor pressure P of intake air at (DEG C)_H(kPa) is P_H＝P_STSince x Φ/100, it is represented by the following equation (3).

[ mathematical formula 3]

Further, let n be the molar flow rate of water vapor in the intake air_H(mol/sec) and the molar flow rate n of the steam when the hydrogen consumption flow rate is n (mol/sec)_HUsing the water vapour pressure P of the intake air_HAnd is expressed by the following equation (4). In addition, Pa in the following formula (4) is atmospheric pressure.

[ mathematical formula 4]

Here, the amount of liquid water n in the exhaust gas_LiqSince the generated water amount- (saturated water vapor amount-water vapor amount in intake air) is obtained, it can be expressed by the following equation (5).

[ math figure 5]

In addition, although k is 0.5 when an ideal chemical reaction between hydrogen and oxygen occurs in the molar ratio k of the oxygen to be taken in, actually, it varies depending on various conditions. For example, the variation occurs according to the performance, temperature, or degree of deterioration of the fuel cell stack 12. In addition, the output may vary depending on factors such as required output and ambient temperature. Therefore, for example, a method may be employed in which the characteristics of the cells and the fuel cell system 10 are grasped in advance, a map of the k value is created in advance, and the k value is read from the map in accordance with various conditions at the time of recovering the liquid water. As another method, the amount of hydrogen and oxygen taken in may be measured in advance, and the k value may be calculated based on the measurement result.

If it is assumed that the molar ratio k of the intake oxygen is 1 and the relative humidity Φ of the intake air is 0 (%), the following equation (6) is obtained if k is 1 and Φ is 0 and the above equation (5) is substituted.

[ mathematical formula 6]

From the contents of the above equation (6), the relationship between the proportion of liquid water and the total pressure when k is 1 and Φ is 0 is shown in fig. 5. In fig. 5, the relationship between the proportion of liquid water and the total pressure in a state where the exhaust temperature is 65 (deg.c) is indicated by a solid line L1, and the relationship between the proportion of liquid water and the total pressure in a state where the exhaust temperature is 75 (deg.c) is indicated by a dashed dotted line L2. The relationship between the proportion of liquid water and the total pressure in a state where the exhaust temperature is 85 (deg.c) is indicated by a two-dot chain line L3, and the relationship between the proportion of liquid water and the total pressure in a state where the exhaust temperature is 95 (deg.c) is indicated by a broken line L4. Therefore, as can be seen from the solid line L1, the proportion of liquid water is about 80 (%) when the total pressure is 250(kPa) at the exhaust gas temperature of 65 (deg.c), for example. By adopting the above method, the amount of liquid water generated by the fuel cell stack 12 can be predicted.

An example of a method for predicting the amount of generated liquid water will be described with reference to the flowchart of fig. 7. First, at step 102, the amount of generated current and the amount of intake air (the amount of air supplied to the fuel cell stack 12) are measured by a sensor or the like. Further, since the amount of generated current is proportional to the amount of hydrogen consumed, the amount of generated current can be determined from the amount of hydrogen consumed.

Next, in step 104, the temperature T of the air supplied to the fuel cell stack 12 by a sensor or the like_H(° c), the relative humidity Φ (%) of the air supplied to the fuel cell stack 12, the temperature T (° c) of the exhaust gas discharged from the fuel cell stack 12, and the pressure p (kpa) of the exhaust gas discharged from the fuel cell stack 12 were measured.

Next, in step 106, the k value is set. Here, as an example, the k value is set by reading the k value according to the condition from a map of the k value set in advance.

Finally, in step 108, the measured value is substituted into the above-described expressions (1) to (5), thereby calculating the generated predetermined amount of liquid water.

Here, the valve control unit 62 shown in fig. 6 controls the opening degree of the drain valve 28 based on the liquid water amount predicted by the liquid water amount prediction unit 56. Specifically, in fig. 1, the valve control unit 62 increases the opening degree of the drain valve 28 and increases the cross-sectional area of the flow path of the drain pipe 26 as the predicted amount of liquid water increases. On the other hand, the valve control unit 62 decreases the opening degree of the drain valve 28 and decreases the cross-sectional area of the flow path of the drain pipe 26 as the amount of liquid water predicted by the liquid water amount prediction unit 56 decreases.

On the other hand, the pump control unit 60 shown in fig. 6 controls the liquid feeding pump 34 to operate when the liquid water stored in the water storage tank 30 (see fig. 1) is a certain amount or more and a need arises to promote heat exchange in the radiator 38.

Here, the amount of liquid water stored in water storage tank 30 and the predetermined amount of liquid water stored in water storage tank 30 are grasped based on the amount of liquid water predicted by liquid water amount prediction unit 56 and the amount of liquid water delivered by operating liquid delivery pump 34.

(action)

Next, the operation of the present embodiment will be explained.

In the fuel cell system 10 of the present embodiment, the amount of liquid water to be generated is predicted based on the amount of generated current of the fuel cell stack 12, the amount of supplied air, the temperature of air, the relative humidity of air, the exhaust temperature, and the exhaust pressure. In this way, by adding the amount of air supplied to the fuel cell stack 12, information on the supply side such as the temperature and the relative humidity, and information on the exhaust side such as the temperature and the exhaust pressure of the exhaust gas discharged from the fuel cell stack 12 to the amount of generated current of the fuel cell stack 12, the amount of liquid water in the generated water can be accurately predicted, as compared with a method of predicting the amount of generated water based only on the amount of generated current.

As shown in fig. 1, the present embodiment includes a water storage tank 30 that stores liquid water discharged from the fuel cell stack 12. The fuel cell stack 12 and the water storage tank 30 are connected by a drain pipe 26, and a drain valve 28 is provided in the drain pipe 26. The opening degree of the drain valve 28 is controlled so that the larger the predicted liquid water amount, the larger the flow passage cross-sectional area of the drain pipe 26. Thus, when the amount of liquid water to be generated is large, the opening degree of the drain valve 28 is increased, whereby it is possible to suppress a situation in which a part of the generated liquid water is discharged to the atmosphere from the third exhaust pipe 22 without being stored in the water storage tank 30.

On the contrary, when the amount of liquid water to be generated is small, the opening degree of the drain valve 28 is reduced, whereby the entry of gas such as water vapor into the water storage tank 30 can be suppressed. That is, when the opening degree of the drain valve 28 is large, a part of the generated gas may flow from the second exhaust pipe 18 to the water storage tank 30. In contrast, in the present embodiment, the intake of gas into the water storage tank 30 can be suppressed by controlling the drain valve 28 in the above-described manner.

In the present embodiment, the generated liquid water is sprayed to the radiator 38, and therefore, heat exchange in the radiator 38 can be promoted. That is, in a situation where the load on the fuel cell stack 12 increases during traveling, the fuel cell stack 12 may become hot. In such a case, when the fuel cell stack 12 is cooled by the cooling water, it is necessary to efficiently perform heat exchange in the radiator 38. As in the present embodiment, by spraying liquid water to the radiator 38, the temperature of the radiator 38 can be lowered by using the heat of vaporization of the liquid water or the like, and heat exchange can be promoted.

The present disclosure is not limited to the configuration shown in fig. 1, and the modified configurations shown in fig. 2 to 4 may be adopted.

(first modification example)

As shown in fig. 2, the fuel cell system 70 according to the present modification has the same configuration as that of the embodiment, except that the position of the pressure regulating valve 24 is different.

The pressure regulating valve 24 of the present modification is provided in the second exhaust pipe 18 that connects the fuel cell stack 12 and the gas-liquid separator 20. Therefore, if the pressure regulating valve 24 is closed, the exhaust gas including the unreacted oxygen in the fuel cell stack 12 and the nitrogen having passed through the fuel cell stack 12 and the generated water generated by the fuel cell stack 12 can be prevented from flowing to the gas-liquid separator 20.

(second modification example)

As shown in fig. 3, a fuel cell system 80 according to this modified example has the same configuration as that of the embodiment, except that the connection position of the first exhaust pipe 17 is different.

One end side of the first exhaust pipe 17 of the present modification is connected to the fuel cell stack 12. On the other hand, the other end side of the first exhaust pipe 17 is connected to the third exhaust pipe 22. Specifically, the other end side of the first exhaust pipe 17 is connected to the third exhaust pipe 22 downstream of the pressure regulating valve 24.

Therefore, the hydrogen gas that has not reacted in the fuel cell stack 12 is released to the atmosphere together with the exhaust gas flowing through the third exhaust pipe 22 from the gas-liquid separator 20.

(third modification example)

As shown in fig. 4, the fuel cell system 90 according to the present modification has the same configuration as that of the embodiment except that the position of the pressure regulating valve 24 and the connection position of the first exhaust pipe 17 are different.

The pressure regulating valve 24 of the present modification is provided in the second exhaust pipe 18 that connects the fuel cell stack 12 and the gas-liquid separator 20. Further, the first exhaust pipe 17 is connected to a second exhaust pipe 18. Specifically, the first exhaust pipe 17 is connected to the second exhaust pipe 18 downstream of the pressure regulating valve 24.

Therefore, the hydrogen gas that has not reacted in the fuel cell stack 12 flows toward the gas-liquid separator 20 together with the exhaust gas flowing from the fuel cell stack 12 through the second exhaust pipe 18.

Although the embodiment and the modification have been described above, it is needless to say that the embodiment and the modification can be implemented in various ways. For example, in the above-described embodiment, the amount of liquid water generated during the traveling of the vehicle is predicted, but the present invention is not limited thereto, and the amount of liquid water generated may be predicted before the traveling of the vehicle. An example of this case will be described below.

A vehicle provided with an automatic driving function of setting a route to a predetermined destination and causing the vehicle to travel along the route is considered. In such a vehicle, information such as a distance to a destination and a gradient can be acquired by setting a route. Then, from this information, it is possible to grasp the point at which the load of the fuel cell stack 12 is predicted to be large. On the other hand, if the amount of liquid water generated during the traveling is predicted, the liquid water can be effectively injected to the radiator 38 at the point where the load on the fuel cell stack 12 is predicted to be large.

An example of a method of predicting the amount of liquid water generated before the vehicle travels will be described with reference to the flowchart of fig. 8. First, in step 202, a destination is set by an operation of the occupant. At this time, the computer 50 acquires the travel route based on the set destination. Here, the travel route may be acquired from map information stored in the vehicle in advance, or the travel route information may be acquired from an external server via the internet.

Next, at step 204, the amount of generated current and the amount of intake air are calculated based on the travel distance and the like. Then, in step 206, the temperature and relative humidity of the intake air, and the exhaust temperature and exhaust pressure are predicted. In this case, information such as outdoor temperature and humidity at an arbitrary point on the travel route may be referred to by accessing the external server via the internet.

Next, in step 208, the k value is set. Here, as an example, the k value is set by reading the k value according to the condition from a map of the k value set in advance.

Finally, in step 210, the measured values of the parameters obtained in steps 204 to 208 are substituted into the above-described expressions (1) to (5), thereby calculating the predetermined amount of liquid water to be generated.

As described above, the amount of liquid water generated during travel can be predicted at a stage before travel. By predicting the amount of liquid water to be generated, the drain valve 28 and the liquid feed pump 34 can be controlled so as to inject a sufficient amount of liquid water into the radiator 38 at a point where the load on the fuel cell stack 12 is large.

In the above-described embodiment and modification, the unreacted hydrogen gas is released into the atmosphere, but the present invention is not limited thereto. For example, unreacted hydrogen may be circulated and supplied again to the fuel cell stack 12.

In the above-described embodiment and modification, the configuration in which the fuel cell system is mounted on the vehicle has been described, but the present invention is not limited to this configuration. The same effect can be obtained as long as the fuel cell system is provided with a fuel cell stack that generates electric power by a chemical reaction between hydrogen and oxygen.

In the above-described embodiment and modification, the structure including the radiator has been described as an example of the heat exchanger, but the present invention is not limited to this. For example, the present invention can also be applied to a condenser or the like that performs heat exchange between a refrigerant circulating in an air conditioner of a vehicle and outside air.