JP2003168456A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system, which can maintain a high circulation rate within the wide range amount of the fuel gas supplying flow. <P>SOLUTION: It has a small ejector 104, which shows the high circulation rate when fuel gas has low flow amount by making off-gas from the fuel cell 108 circulate by making fuel gas as a driving flow, and a large ejector 105, which shows the high circulation rate when the fuel gas has except low flow amount by making the gas discharged from the small ejector 104 circulate by making the fuel gas as the driving flow. The introduction of the fuel gas to the small ejector 104 and the large ejector 105 is controlled according to the demand fuel gas flow amount of the fuel cell, so that an ejector circulation rate may become to a predetermined high circulation rate. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system, and more particularly to a fuel circulation system for reusing off gas of a fuel electrode.

[0002]

2. Description of the Related Art As a conventional system for reusing excess fuel discharged from the fuel electrode of a fuel cell, Japanese Patent Application Laid-Open No. 9-22
The one disclosed in Japanese Patent No. 714 is known. This is to provide an ejector in which the fuel gas newly supplied to the fuel cell system and the surplus fuel (off gas) are mixed, and the off gas from the fuel electrode is selectively provided between the ejector and the discharge part of the fuel electrode. There is a purge line that can be discharged to the outside.

Excessive off-gas is circulated by an ejector to reduce waste of fuel, and at the time of purging when the fuel cell is clogged with water, the purge line and the outside of the system are circulated to discharge gas into the atmosphere to clog the water. Has been resolved.

[0004]

[Problems to be solved by the invention] However,
In this fuel circulation system, it was difficult to secure a high circulation rate by the ejector in the entire operation area. This is because if the ejector nozzle is made smaller in diameter in order to obtain a sufficient circulation rate at low output, this small nozzle has a large resistance at high output, making it difficult to flow a large flow rate.
This is because if the diameter of the ejector nozzle is increased in order to obtain a sufficient circulation rate at the time of high output, the circulation rate of this large nozzle will decrease at the time of low output.

Further, when the cells of the fuel cell stack become clogged with water and need to be purged, surplus fuel gas must always be discharged to the outside, which causes a problem that fuel efficiency is deteriorated. .

[0006] Therefore, an object of the present invention is to provide a fuel cell system capable of obtaining a high circulation rate at both low output and high output.

[0007]

A first aspect of the present invention is directed to a large ejector which is interposed in a passage for feeding a fuel gas to a fuel cell and has a high circulation rate when the fuel gas serving as a driving flow has a high flow rate. , A small ejector which is interposed in a passage for circulating the off gas from the fuel cell to the suction side of the large ejector and has a high circulation rate when the fuel gas serving as a driving flow has a low flow rate, and an ejector circulation rate of a predetermined value. A means for controlling the introduction of the fuel gas into the small ejector and the large ejector according to the required fuel gas flow rate of the fuel cell so as to obtain a high circulation rate.

In a second aspect based on the first aspect, a variable throttle valve is provided upstream of a fuel gas supply section of the large ejector and upstream of a fuel gas supply section of the small ejector, and the required fuel gas is provided. The flow rate of the fuel gas supplied to the large ejector and the small ejector is controlled according to the flow rate.

In a third aspect based on the first aspect, a switching valve is provided upstream of the fuel gas supply section of the large ejector and upstream of the fuel gas supply section of the small ejector to adjust the required fuel gas flow rate. The fuel gas supplied to the large ejector and the small ejector is switched accordingly.

A fourth aspect of the present invention is the fuel cell system according to the second or third aspect, wherein the required fuel gas flow rate is within a range in which the circulation rates of the large ejector and the small ejector can both maintain a predetermined high circulation rate. Control to supply fuel gas to the ejector.

A fifth invention is the fuel cell system according to the second invention, further comprising a purge valve for discharging off-gas from the fuel cell to the outside, and means for judging whether or not the purge control of the fuel cell is necessary. When it is determined that the purge control needs to be performed, the control means opens the purge valve and
In addition to the variable throttle valve that is opened according to the required fuel gas flow rate at that time, the other variable throttle valve is also opened to increase the mixed gas flow rate of the fuel gas and the off gas flowing into the fuel cell.

According to a sixth aspect of the present invention, in the second or third aspect, a purge valve for discharging the off gas from the fuel cell to the outside and a means for determining whether or not the purge control of the fuel cell needs to be performed, When it is determined that the purge control needs to be performed, the control means keeps the purge valve closed, and the ejector for which the circulation rate of the mixed gas of the fuel gas and the off gas flowing into the fuel cell becomes large. The fuel gas is controlled to be supplied to.

According to a seventh aspect of the invention, in the second or third aspect, a purge valve for discharging the off gas from the fuel cell to the outside and a means for determining whether or not it is necessary to perform purge control of the fuel cell immediately after startup. And the control means opens the purge valve when it is determined that the purge control needs to be performed, and the ejector for which the circulation rate of the mixed gas of the fuel gas and the off-gas flowing into the fuel cell increases. The fuel gas is controlled to be supplied to.

[0014]

According to the first aspect of the invention, the ejector having the higher ejector circulation rate is selected depending on the required fuel gas flow rate, so that a good circulation rate can be maintained over a wide range of flow rates. it can. The ejector that is not selected flows an off gas or a mixed gas of the fuel gas and the off gas, but since these gases do not pass through the portion where the ejector driving flow flows, the flow path resistance does not increase, Energy loss in the fuel gas supply system can be reduced.

According to the second aspect of the present invention, by adjusting the flow rate of the fuel gas supplied to each of the large ejector and the small ejector so that the high circulation rate is always required, the flow rate can be increased over a wider range. The circulation rate can be maintained.

According to the third invention, by switching between the case of supplying the fuel gas through the large ejector and the case of supplying the fuel gas through the small ejector, the small ejector and the large ejector can be selectively used and wide range. A high circulation rate can be maintained for the flow rate of.

According to the fourth aspect of the invention, the fuel gas is supplied to the large ejector in a region where a high circulation rate can be obtained by either ejector, so that the fuel gas supply system can maintain a high circulation rate. Pressure loss can be reduced.

According to the fifth aspect of the invention, when it is determined that the purge control is required, both variable throttle valves are opened to discharge the off gas to the outside.
By temporarily increasing the flow rate supplied to the fuel cell,
The purge time can be shortened.

According to the sixth aspect of the present invention, when it is determined that the purge control is required, the fuel gas is supplied to the ejector having the higher circulation rate of the mixed gas flowing into the fuel cell. In addition, it is possible to efficiently perform the purging in a short time without discharging the off gas to the outside.

According to the seventh aspect of the invention, the purge control immediately after the fuel cell is started can be completed in a short time by supplying the fuel gas to the ejector so that the circulation rate of the mixed gas becomes large. it can.

[0021]

FIG. 1 shows the configuration of a fuel circulation system provided in the fuel cell system according to the first embodiment.

Hydrogen-rich fuel gas produced in the fuel reforming system or fuel gas from a hydrogen cylinder or the like is supplied from the supply unit 101 to the fuel circulation system. Supply unit 1
The fuel gas supplied from 01 is divided into two pipe lines 1
The flow is divided by 01a and 101b, one of which is the variable throttle valve 10
2 and the other is supplied to the variable throttle valve 103.
A small ejector 104 is provided downstream of the variable throttle valve 102.
Is arranged, and the large ejector 1 is provided downstream of the variable throttle valve 103.
05 is arranged.

A circulation path 115, which branches from the discharge side of the fuel electrode of the fuel cell 108, is connected to the recirculation gas inlet 104c, which is the suction side of the small ejector 104 which operates by using the fuel gas from the variable throttle valve 102 as a driving flow. Sucking in the excess off-gas, which is the reflux gas, discharged from the fuel cell 108,
Mix with fuel gas.

The large ejector 105 installed in the fuel supply passage 114 of the fuel cell 108 operates by using the fuel gas from the variable throttle valve 103 as a driving flow, and the recirculation gas inlet 105c on the suction side of the large ejector 105 from the small ejector 104. A mixed gas of the discharged fuel gas and reflux gas is introduced.

The small ejector 104 exhibits a high circulation rate when the supplied fuel gas has a low flow rate, while the large ejector 105 exhibits a high circulation rate when the flow rate is higher than that of the small ejector 104. So that the fuel gas supply port 10
The nozzle diameters between 4a and 105a and the mixed gas discharge ports 104b and 105b are set. Specifically, the nozzle diameter of the large ejector 105 is smaller than that of the small ejector 104.
It is set larger than the nozzle diameter of.

By opening and closing the variable throttle valves 102 and 103, the function of the small or large ejector 104 or 105 is controlled. That is, when the variable throttle valve 102 is opened, the small ejector 1 uses the fuel gas as a driving flow.
When the variable throttle valve 102 is not opened, the circulation gas is not sucked by the small ejector 104 and is supplied from the recirculation gas inlet 104c of the small ejector 104. If the variable throttle valve 103 has passed to the mixed gas discharge port 104b and the variable throttle valve 103 is open, the large ejector 105 sucks the mixed gas from the small ejector 104, imparts the energy required for circulation, and opens the variable throttle valve 103. If not, the circulating gas is not sucked by the large ejector 105, and the mixed gas exhaust port 10 is supplied from the reflux gas inlet 105c of the large ejector 105.
Pass 5b.

Regarding the opening and closing of the variable throttle valves 102 and 103, the control unit 11 which will be described later is set so that the ejector circulation rate becomes a predetermined high circulation rate according to the operating conditions.
Controlled by 2.

A large ejector 1 is installed in the fuel supply passage 114.
A mixed fuel gas of the fuel gas and the reflux gas from 05 is introduced, and this mixed gas is supplied to the fuel electrode of the fuel cell 108 after sufficiently containing moisture necessary for the electrochemical reaction in the humidifier 106. The fuel cell 108 generates electricity by an electrochemical reaction using hydrogen in the fuel gas and oxygen in the air supplied to an air electrode (not shown).

A purge line 116 branching from the circulation path 115 is connected to the downstream side of the fuel electrode of the fuel cell 108, and a purge valve 109 is provided in the purge line 116.
When water is accumulated in the fuel cell 108, it can be opened to discharge the off gas to the outside of the system.

On the other hand, the circulation path 115 is provided with a condenser 111 for removing water in the reflux gas, and the water removed by the condenser 111 is stored in a water tank (not shown) and used again in the fuel cell system.

Next, the relationship between the fuel gas supply amount and the circulation rate represented by the ratio of the supply amount of the fuel gas to the small ejector 104 and the large ejector 105 used in the fuel circulation system and the flow rate of the sucked recirculation gas. Is shown in FIG.

The small ejector 104 exhibits a high circulation rate in the region where the fuel gas supply amount is small, while the large ejector 1
Reference numeral 05 shows a high circulation rate in a region where the fuel gas supply amount is from a medium flow rate to a high flow rate, that is, a high flow rate region than the small ejector 104. Here, the large ejector 105 is shown.
Is a predetermined high circulation rate, the fuel gas flow rate Qa is a boundary between the low flow rate region and the medium flow rate region, and the fuel gas flow rate Qb is such that the circulation rate of the large ejector 105 is higher than that of the small ejector 104.
Is the boundary between the medium flow rate region and the high flow rate region.

The variable throttle control during normal operation in the fuel cell system performed by the control unit 112 is as follows.
First, when the fuel gas supply amount is small, that is, when the fuel gas flow rate in FIG. 2 is in the low flow rate region of Qa or less, the variable throttle valve 102 is opened to supply the fuel gas to the small ejector 104 in order to maintain the high circulation rate. To do.

On the other hand, the fuel gas flow rate is Qa to Qb.
The variable throttle valve 1 is used so that the large ejector 105 is used at the medium flow rate represented by
02 is closed and the variable throttle valve 103 is opened. In a part of the medium flow rate region and the high flow rate region, the small ejector 104 can maintain a high circulation rate, but it is better to supply fuel to the large ejector 105.
For example, since the pressure loss due to the nozzle, which is the fuel gas supply path in the ejector, is small, the fuel gas is supplied to the fuel cell 108.
It is possible to reduce the energy to be supplied to the.
Therefore, in a state in which the large ejector 105 can secure the required circulation rate, the fuel gas supply destination is immediately changed to the large ejector 105.
Energy consumption is reduced by switching to.

Further, in the low flow rate region, the humidifier 10
6 is installed between the fuel cell 108 and the fuel cell 108,
It is also possible to adjust the variable throttle valve 102 so that the measured pressure becomes the pressure required to supply the fuel gas to the fuel cell 108, and to supply the fuel gas from the small ejector 104. The opening of the variable throttle valve 102 may be feedback-controlled according to the difference between the command pressure and the pressure measured by the pressure sensor 107. At this time, when the fuel gas is supplied in an amount larger than the flow rate to be supplied to the small ejector 104 for obtaining the circulation pressure, the variable throttle valve 103 is opened, for example, fully opened to supply from the large ejector 105. Thus, pressure loss can be suppressed and energy efficiency can be improved.

Thus, during normal operation, the small ejector 1
By combining 04 and the large ejector 105, it becomes possible to realize a high ejector circulation rate in a wide range of the fuel gas supply amount from a low flow rate to a high flow rate.

By the way, when the large ejector 105 is operated, the reflux gas outlet 104c of the small ejector 104 and the reflux gas inlet 105c of the large ejector 105 communicate with each other, and the reflux gas does not pass through the nozzle of the small ejector 104. No pressure loss occurs and it is possible to suppress a decrease in the circulation flow rate. On the other hand, when the small ejector 104 is used, the recirculation gas inlet 10 of the large ejector 105 is
5c and the mixed gas outlet 105b are small ejectors 10.
Since the fuel gas flow rate of No. 4 can be made sufficiently large, it does not hinder the passage of the mixed gas of the fuel gas and the reflux gas from the small ejector 104, so that a sufficiently large circulation flow rate can be maintained.

On the other hand, in such a fuel cell system, for example, when the catalyst filled in the fuel cell 108 is clogged with water, the control unit 112 controls the fuel gas flowing through the fuel cell 108 in order to eliminate it. The water is purged by increasing the circulation rate.

In this embodiment, without discharging the fuel gas to the outside of the system, the internal purge for increasing the circulation rate of the mixed fuel gas supplied to the fuel cell 108 to purge the water content and the fuel gas to the outside of the system. 2 of external purge to discharge
By performing different types of purging separately, the amount of fuel gas discharged to the outside of the system is reduced.

First, when the fuel supply amount is in the medium flow rate region, that is, when the supply amount is from Qa to Qb in FIG.
Perform internal purging. In normal operation in this flow rate region, the variable throttle valve 102 is closed and the variable throttle valve 103 is opened, so that the fuel gas is supplied only to the large ejector 105.
When the output of the fuel cell 108 decreases due to the water clogging of the catalyst and a water purging command is issued from the control unit 112, the variable throttle valve 102 is opened and the variable throttle valve 103 is throttled or closed. To supply. As described above, by using the small ejector 104 instead of the large ejector 105, the energy loss of the fuel supply system increases, but the circulation rate improves, so that the flow rate of the mixed fuel gas supplied to the fuel cell 108 can be increased. The water in the fuel cell 108 can be purged to eliminate clogging. At this time, the purge valve 109 is kept closed.

A timing chart for such internal purging is shown in FIG. When it is determined that purging is necessary, the amount of recirculation gas is increased by supplying the fuel gas to the small ejector 104. Here, when the electric power taken out from the fuel cell 108 is constant, the small ejector 10 is used at the time of purging.
4 and the amount of fuel gas supplied to the large ejector 105 are made equal to the amount of fuel gas supplied to the large ejector 105 before purging, whereby stable operation can be realized.

Next, in the low flow rate region and the high flow rate region, that is, when the fuel gas supply amount is Qa or less in FIG.
The external purging in the case of b or more will be described.

In this external purging region, unlike the internal purging region described above, it is not possible to increase the amount of fuel gas supplied to the fuel cell 108 by simply switching from the large ejector 105 to the small ejector 104.

Therefore, while the purge valve 109 is opened, based on the fuel gas supply amount at that time, other variable throttle valves are opened in addition to the variable throttle valve opened at that time, and the system is temporarily operated. Increase the fuel gas flow rate to be supplied. Note that this increase amount corresponds to the amount of off-gas discharged from the opened purge valve 109 to the outside, so that the fuel cell 10
It is possible to prevent the output of No. 8 from decreasing.

For example, in the region where the fuel gas supply amount is Qb or more, at this time, the variable throttle valve 103 opened in advance so as to supply the required flow rate and the other variable throttle valve 10 are provided.
2 is opened by a predetermined opening and both the small ejector 104 and the large ejector 105 are used to increase the flow rate of the fuel gas flowing into the fuel cell and maintain a high circulation rate.
As a result, the flow rate of the fuel gas supplied to the fuel cell 108 is increased, so that the water clogging of the catalyst filled in the fuel cell 108 can be eliminated.

Here, while the variable throttle valves 102 and 103 are both opened to increase the flow rate to be supplied at the time of purging in the low / high flow rate range, the supply flow rate of the fuel gas and the circulation flow rate of the recirculation gas are increased. The openings of the variable throttle valves 102 and 103 may be controlled so that the total sum becomes maximum.

The control performed by the control unit 112 of such a fuel cell system is shown in the flow chart of FIG.

First, in step S401, the cell voltage is measured by the voltage sensor arranged in the fuel cell 108, and water clogging of the fuel cell 108 is detected by the cell voltage drop. In step S402, it is determined whether or not purging is required depending on the cell voltage drop level. How much the purge is to be performed may be appropriately determined in consideration of the required stability of the extraction output and the acceptable frequency of the purge.

If it is determined to purge, the process proceeds to step S403. In step S403, it is determined whether the fuel gas supply amount is in the medium flow rate region or in the low / high flow rate region.
If it is in the medium flow rate region, the process proceeds to step S404, and internal purging is performed. In this step S404, the variable throttle valve 1
02 is opened to supply the fuel gas to the small ejector 104, and the purge valve 109 is kept closed. At this time,
The variable throttle valve 103 may be fully closed or may be opened by the small ejector 104 to such an extent that the circulation pressure required for purging is obtained. By such internal purging, the consumption of fuel gas due to purging can be suppressed, so that the fuel utilization efficiency can be improved.

On the other hand, if it is determined in step S403 that the flow rate is in the low / high flow rate region, the flow proceeds to step S405, in which the other variable throttle valves 102 and 103 are opened together with the valve that has been opened so far, and the circulation rate and the fuel are temporarily increased. Battery 10
The fuel supply amount to be supplied to No. 8 is increased, and at the same time, the purge valve 109 is opened to perform external purging. At this time, if the mixed fuel gas supplied to the fuel cell 108 is increased by temporarily increasing the flow rate of the supplied fuel gas, the moisture can be purged in a short time.

If it is determined in step S402 that it is not necessary to perform purging, the process proceeds to step S406 and normal variable throttle control is performed. This variable aperture control will be described with reference to the flowchart shown in FIG.

In step S501, the flow rate Qs of the fuel gas supplied to the fuel cell 108 is calculated from the required output. Next, the process proceeds to step S502 and step S50.
The fuel gas flow rate Qs calculated in 1 is compared with the limit fuel gas flow rate Qa at which the large ejector exhibits a high circulation rate. As a result, if Qs ≧ Qa, the process proceeds to step S503, the variable throttle valve 102 is closed, and the fuel gas is supplied to the large ejector 105 to reduce the pressure loss. On the other hand, when Qs <Qa, in order to obtain a sufficient circulation rate, step S50
4, the variable throttle valve 102 is opened to supply the fuel gas only to the small ejector 104.

By controlling in this way, it is possible to maintain a high circulation rate at all times during normal operation and to suppress pressure loss. On the other hand, at the time of purging, in the internal purging, the fuel cell 108 is switched by switching the large ejector 105 and the small ejector 104 to the one having the highest fuel gas circulation rate in the current system operating state.
To improve the fuel efficiency of the fuel cell system by eliminating the clogging by eliminating the clogging by increasing the circulation rate of the mixed fuel gas that is supplied to the large ejector 105 and the small ejector 104. By opening
Purging can be performed efficiently in a short time.

FIG. 6 shows the structure of the fuel cell system according to the second embodiment, particularly the fuel circulation system.

As in the first embodiment, a pressure adjusting valve 202 is provided to adjust the pressure of the fuel gas supplied from the supply section 201. A switching valve 203 that selectively switches the supply of the fuel gas to the small ejector 104 and the large ejector 105 is installed downstream of the pressure adjusting valve 202.
In addition, in this way, the pressure regulating valve 20 is provided upstream of the switching valve 203.
By installing No. 2, the control can be performed without changing the reference pressure of the fuel cell supply system, so that more stable control is possible.

FIG. 7 shows the relationship between the fuel supply amount and the circulation rate of the ejector used in the second embodiment. The fuel gas supply amount Q is defined as the limit flow rate at which the large ejector 105 exhibits a predetermined high circulation rate.
c, the switching valve 203 in the region below the supply flow rate Qc
Is turned on, and the fuel gas is supplied only to the small ejector 104. On the other hand, in the region where the supply flow rate is Qc or higher, the large ejector 105 can also obtain a high circulation rate, so the switching valve 203 is turned off and the fuel gas is supplied only to the large ejector 105. By controlling in this way, a high circulation rate can be maintained in the operating range from low output to high output in the fuel cell 108.

The control performed by the control unit 112 in such a system will be described with reference to the flowchart shown in FIG. In addition, in order to purge the inert gas other than the fuel gas existing in the region where the fuel gas is supplied in the system at the time of starting the fuel cell system,
External purge for discharging the gas in the pipeline to the outside of the system will also be described.

In step S801, it is determined whether the fuel cell system is in a state immediately after starting. If the fuel cell system requires startup control immediately after startup, the process proceeds to step S802, and it is determined whether hydrogen replacement for expelling the inert gas is necessary. If the system is still filled with an inert gas such as air, hydrogen replacement is required from immediately after the start up until a predetermined time elapses, and therefore the process proceeds to step S803 and is purged with hydrogen gas. Here, in order to discharge the air and the like contained in the humidifier 106, the fuel cell 108, and the pipes to the outside of the system to fill the hydrogen gas while the system is stopped, the switching valve 203
OFF and open the purge valve 109 to remove the large ejector 1.
Hydrogen gas is supplied from 05. As a result, a large flow rate of hydrogen gas can be supplied, and the replacement time can be shortened.

Such control is repeated to repeat step S8.
In 02, when the predetermined replacement time has passed and hydrogen replacement is no longer necessary, the flow proceeds to step S804, and the switching valve 203 is turned on.
Then, the purge valve 109 is closed again. This allows
When the supplied fuel is small immediately after the start-up, the fuel gas is caused to flow to the small ejector 104 side, and the discharge of the fuel to the outside is stopped.

Returning to step S801 again, if it is determined that the fuel cell system does not require control immediately after startup,
In step S805, flow path switching valve control during normal operation is performed.

The normal flow path switching valve control will be described with reference to the flowchart of FIG.

In step S901, the fuel cell 10
The supply flow rate Qs of the fuel gas supplied to the fuel cell 108 is calculated from the output required for No. 8. In step S902, it is determined whether the supply amount Qs obtained in step S901 is larger than the circulatory lower limit flow rate Qc of the large ejector 105. If the supply amount Qs is equal to or higher than the circulatory lower limit flow rate Qc, the process proceeds to step S903, the switching valve 203 is turned off, and the fuel gas is supplied to the large ejector 105. Supply Q
If s is smaller than the circulatory lower limit flow rate Qc, it is impossible to circulate by the large ejector 105, so step S9
04, the switching valve 203 is turned on and the small ejector 10
4 is supplied with fuel gas.

By controlling in this manner, the off gas can be circulated regardless of the fuel supply amount, and the energy given to the fuel gas for forming the driving flow can be reduced, so that efficient power generation is possible. You can

The water purge control is described in the first embodiment, and the inert gas purge control at the time of starting the fuel cell system is described in the second embodiment. However, the inert gas purge control is performed in the first embodiment. In the second embodiment, the water purge control may be performed as in the first embodiment. However,
Since only one of the ejectors can be used in the second embodiment, the small ejector 10 is used in the low flow rate region of the normal operation.
4 and the large ejector 105 is used in the medium / high flow rate region. At the time of purging, the large ejector 105 performs external purging in the low / high flow rate region, and the internal purge is performed by the small ejector in the medium flow rate region.

As described above, it is needless to say that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the technical idea described in the claims.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a fuel circulation system according to a first embodiment.

FIG. 2 is a relationship diagram of a circulation rate and a supply flow rate of an ejector used in the first embodiment.

FIG. 3 is a timing chart at the time of internal purging according to the first embodiment.

FIG. 4 is a flowchart of control in the first embodiment.

FIG. 5 is a flowchart of normal variable aperture control in the first embodiment.

FIG. 6 is a configuration diagram of a fuel circulation system according to a second embodiment.

FIG. 7 is a relationship diagram of a circulation rate of an ejector used in the second embodiment and a provided flow rate.

FIG. 8 is a flow chart of control in the second embodiment.

FIG. 9 is a flowchart of normal variable aperture control in the second embodiment.

[Explanation of symbols]

101 Fuel supply unit 102 Variable throttle valve 103 Variable throttle valve 104 Small ejector 105 large ejector 108 Fuel cell 109 Purge valve 114 Fuel supply passage 115 circuit 203 switching valve

Claims (7)

[Claims] 1. A large ejector which is interposed in a passage for feeding the fuel gas to the fuel cell and has a high circulation rate when the fuel gas serving as a driving flow has a high flow rate, and an off gas from the fuel cell is supplied to the large ejector. A small ejector that is installed in the passage that circulates to the suction side and that has a high circulation rate when the fuel gas that is the driving flow has a low flow rate, and a requirement for the fuel cell that the ejector circulation rate has a predetermined high circulation rate. A fuel cell system comprising: a small ejector and a means for controlling the introduction of the fuel gas into the large ejector according to the flow rate of the fuel gas. 2. A variable throttle valve is provided on each of an upstream side of a fuel gas supply section of the large ejector and an upstream side of a fuel gas supply section of the small ejector, and the large ejector and the small ejector are provided in accordance with the required fuel gas flow rate. The fuel cell system according to claim 1, wherein the flow rate of the fuel gas supplied to the ejector is controlled. 3. A switching valve is provided on the upstream side of the fuel gas supply section of the large ejector and the upstream side of the fuel gas supply section of the small ejector, and the switching valve is provided on the large ejector and the small ejector according to the required fuel gas flow rate. The fuel cell system according to claim 1, wherein the fuel gas to be supplied is switched. 4. The required fuel gas flow rate is controlled so as to supply the fuel gas to the large ejector in a region where the circulation rates of the large ejector and the small ejector can both maintain a predetermined high circulation rate. 2. The fuel cell system according to 2 or 3. 5. A purge valve for discharging off-gas from the fuel cell to the outside, and a means for judging whether or not the purge control of the fuel cell is required, the control means being required to perform the purge control. When it is judged that there is, the purge valve is opened, and in addition to the variable throttle valve that is opened according to the required fuel gas flow rate at that time, the other variable throttle valve is also opened, and the fuel gas flowing into the fuel cell is The fuel cell system according to claim 2, wherein the flow rate of the mixed gas of off gas is increased. 6. A purge valve for discharging off-gas from a fuel cell to the outside, and a means for judging whether or not the purge control of the fuel cell is required, the control means being required to perform the purge control. 3. When it is determined that the fuel gas is present, the fuel gas is controlled to be supplied to the ejector having a higher circulation rate of the mixed gas of the fuel gas and the off gas flowing into the fuel cell while the purge valve is closed. Alternatively, the fuel cell system according to Item 3. 7. A purge valve for discharging off-gas from the fuel cell to the outside, and means for determining whether or not it is necessary to perform purge control of the fuel cell immediately after startup, wherein the control means performs purge control. When it is determined that it is necessary to perform, the purge valve is opened and the fuel gas is supplied to the ejector having a higher circulation rate of the mixed gas of the fuel gas and the off gas flowing into the fuel cell. 2. The fuel cell system according to 2 or 3.