JP2008190336A - Ejector and fuel cell system including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ejector and a fuel cell system capable of stabilizing flow control when a flow rate is low. <P>SOLUTION: This ejector is provided with a nozzle injecting a first fluid and generating a vacuum for sucking a second fluid, and a diffuser in which the injected first fluid and the sucked second fluid join to each other is arranged downstream of the nozzle. In this configuration, an injector for adjusting the flow rate of the first fluid injected from the nozzle is arranged upstream of the nozzle. The injector intermittently supplies the first fluid to the nozzle, thereby adjusting the flow rate of the first fluid injected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a variable flow rate ejector and a fuel cell system including the ejector.

  The fuel cell system includes a fuel cell that generates electric power by receiving supply of fuel gas and oxygen gas (hereinafter collectively referred to as “reaction gas”). The fuel off-gas and oxidation off-gas (hereinafter collectively referred to as “reaction off-gas”) discharged from the fuel cell may contain reaction gas that has not contributed to power generation of the fuel cell. In order to reuse this unreacted reaction gas for power generation, there is also a fuel cell system in which a fuel off-gas is circulated to the fuel cell by an ejector.

The fuel cell system described in Patent Document 1 circulates fuel off-gas using a variable flow rate ejector. The ejector includes a nozzle and a movable needle. Due to the injection of the fuel gas from the nozzle, the fuel off-gas is sucked into the ejector, merged with the fuel gas, and supplied to the fuel cell. The needle is moved by a motor or the like to change the opening area of the nozzle defined by the outer peripheral surface of the needle and the inner peripheral surface of the nozzle. By changing the opening area of the nozzle so as to satisfy the output requirement of the fuel cell, the injection flow rate of the fuel gas from the nozzle and the suction flow rate of the fuel off gas are controlled.
JP 2004-95528 A

  According to this ejector, it is considered that the flow rate of the reaction gas can be controlled in a wide range from a small flow rate to a large flow rate. However, in the configuration in which the nozzle opening area is variable as described above, it is difficult to stably control the nozzle opening area corresponding to a small flow rate. Because it is necessary to reduce the opening area of the nozzle in order to cope with a small flow rate, in order to control the opening area defined by the two members (nozzle and needle) having a variation in size within a small range, the needle This is because it is necessary to control this with high accuracy.

  An object of the present invention is to provide an ejector in which flow control at a small flow rate is stable. Another object of the present invention is to provide a fuel cell system capable of stably supplying a wide range of flow rates of reaction gas to the fuel cell.

  In order to achieve the above object, an ejector of the present invention includes a nozzle that generates a negative pressure for injecting a first fluid and sucking the second fluid, and a first fluid that is provided and injected downstream of the nozzle. And a diffuser in which the sucked second fluid merges. The ejector further includes an injector for adjusting the injection flow rate of the first fluid from the nozzle on the upstream side of the nozzle.

  Thus, by providing the injector, the injection flow rate of the first fluid from the nozzle can be adjusted without changing the opening area of the nozzle. Thereby, compared with the type which changes the opening area of a nozzle, the flow control at the time of a small flow rate can be stabilized not only at the time of a large flow rate.

  According to a preferred aspect of the present invention, the injector adjusts the injection flow rate of the first fluid by intermittently supplying the first fluid to the nozzle or by controlling the opening / closing operation by duty control. Good.

  According to such a configuration, the flow control at a small flow rate can be easily stabilized as compared with the type in which the opening area of the nozzle is variable.

  According to another preferable aspect of the present invention, the injector may be configured to be able to shut off the supply of the first fluid to the nozzle.

  According to this configuration, when the supply destination of the first fluid and the second fluid does not require the first fluid, it is not necessary to supply the first fluid.

  A fuel cell system for achieving the above object includes a supply channel for supplying a new reaction gas to the fuel cell, a circulation channel for circulating the reaction off gas discharged from the fuel cell to the supply channel, and a supply channel. And the ejector of the present invention provided at a connection portion between the gas flow path and the circulation channel. One of the first fluid and the second fluid is a new reaction gas, and the other is a reaction off gas.

  According to this configuration, the reaction gas or the reaction off-gas can be circulated to the fuel cell by the ejector of the present invention suitably corresponding to a small flow rate.

  According to a preferred aspect of the fuel cell system of the present invention, the first fluid may be a fuel gas as a new reaction gas, and the second fluid may be a fuel off gas as a reaction off gas.

  More preferably, the fuel cell system of the present invention includes a control device that controls the injector. The control device may control the injector so that the circulation flow rate of the fuel off gas with respect to the injection flow rate of the fuel gas is maximized when the fuel cell system is activated.

  According to this configuration, discharge of impurities such as nitrogen gas that can accumulate in the fuel cell when the fuel cell system is stopped can be favorably promoted when the system is started.

  According to another preferable aspect of the fuel cell system of the present invention, the control device may control the injector so as to cut off the flow of the fuel gas to the nozzle when the fuel cell system is stopped.

  According to this configuration, the supply of new reaction gas to the fuel cell can be cut off when power generation is stopped without consuming the reaction gas in the fuel cell. Thereby, the pressure rise in a fuel cell can be suppressed appropriately.

  According to the ejector and fuel cell system of the present invention described above, flow control at a small flow rate is stable.

  Hereinafter, an example in which an ejector according to a preferred embodiment of the present invention is applied to a fuel cell system will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 2, an oxygen gas piping system 3, a fuel gas piping system 4, and a control device 5.

  The fuel cell 2 is made of, for example, a solid polymer electrolyte type and has a stack structure in which a large number of cells are stacked. The fuel cell 2 generates electric power upon receiving supply of oxygen gas and fuel gas. Supply and discharge of oxygen gas and fuel gas to and from the fuel cell 2 are performed by an oxygen gas piping system 3 and a fuel gas piping system 4.

  Oxygen gas and fuel gas are collectively referred to as reaction gas. In particular, oxygen gas and fuel gas discharged from the fuel cell 2 are referred to as oxygen off gas and fuel off gas, respectively, and these are collectively referred to as reaction off gas. Hereinafter, air will be described as an example of oxygen gas, and hydrogen gas will be described as an example of fuel gas.

  The oxygen gas piping system 3 includes a humidifier 11, a supply flow path 12, a discharge flow path 13, an exhaust flow path 14, and a compressor 15. The compressor 15 is provided at the upstream end of the supply flow path 12. Air in the atmosphere (oxygen gas) taken in by the compressor 15 flows through the supply flow path 12, is pumped to the humidifier 11, is humidified by the humidifier 11, and is supplied to the fuel cell 2. The oxygen off-gas discharged from the fuel cell 2 flows through the discharge flow path 13 and is introduced into the humidifier 11, and then flows through the exhaust flow path 14 and is discharged to the outside.

  The fuel gas piping system 4 includes a hydrogen tank 21, a supply flow path 22, a circulation flow path 23, and an ejector 24. The hydrogen tank 21 is a hydrogen supply source that stores high-pressure hydrogen gas. The supply channel 22 supplies the hydrogen gas in the hydrogen tank 21 to the fuel cell 2. The supply flow path 22 includes a main flow flow path 22a and a mixing flow path 22b. The main flow channel 22 a is located on the upstream side of the ejector 24, and introduces new hydrogen gas (unused hydrogen gas) to the ejector 24. The mixing channel 22 b is located on the downstream side of the ejector 24.

  The main flow path 22a is provided with a shut valve 31, a regulator 32, and a pressure sensor P1. The shut valve 31 functions as a main valve of the hydrogen tank 21. The regulator 32 decompresses the hydrogen gas, and the pressure of the decompressed hydrogen gas is detected by the pressure sensor P1. Note that the pressure of the hydrogen gas that has passed through the regulator 32 is higher than the hydrogen gas pressure in the fuel cell 2. The mixing channel 22 b guides the mixed hydrogen gas discharged from the ejector 24 to the fuel cell 2. A pressure sensor P2 that detects a hydrogen supply pressure to the fuel cell 2 is provided in the mixing channel 22b.

  The circulation channel 23 returns the hydrogen off gas discharged from the hydrogen gas outlet of the fuel cell 2 to the supply channel 22. A check valve 34 and a gas-liquid separator 35 are interposed in the circulation channel 23. The check valve 34 blocks the flow of fluid from the ejector 24 to the gas-liquid separator 35. The gas-liquid separator 35 separates the hydrogen off gas into a liquid and a gas. The separated liquid is water generated by the electrochemical reaction of the fuel cell 2, and is discharged to the outside through the drainage channel 37 by opening the drain valve 36. The separated gas in the hydrogen off-gas is sucked into the ejector 24 through the check valve 34. Further, the gas in the separated hydrogen off-gas can be exhausted downstream of the purge path 38 by periodically opening the purge valve 38. Thereby, the fall of the hydrogen concentration of the hydrogen gas circulated and supplied to the fuel cell 2 can be suppressed.

  The ejector 24 is provided at a connection portion between the supply flow path 22 and the circulation flow path 23. The ejector 24 injects new hydrogen gas from the hydrogen tank 21 and sucks the hydrogen off gas. Then, the ejector 24 merges new hydrogen gas and hydrogen off-gas, and supplies the mixed hydrogen gas after the merge to the fuel cell 2. The ejector 24 is configured so that the flow rate of the hydrogen gas supplied to the fuel cell 2 can be varied. In the following description, the new hydrogen gas supplied from the hydrogen tank 21 is referred to as “mainstream gas”, the drawn off hydrogen gas is referred to as “circulation gas”, and the respective flow rates are “mainstream flow rate” and “circulation flow rate”. May be called.

  As shown in FIG. 2, the ejector 24 has a housing 41. The housing 41 includes a primary side main inlet 42, a secondary side outlet 43, and a suction port 44. The main flow inlet 42 is formed in the injector 50 attached to the housing 41, and is connected to the downstream side of the main flow channel 22a. The discharge port 43 is connected to the upstream side of the mixing channel 22b. The suction port 44 is connected to the downstream side of the circulation channel 23.

  The housing 41 has a nozzle 51 and a diffuser 52 inside. The nozzle 51 injects the mainstream gas toward the downstream side. The nozzle 51 has a tip ejection portion 61 that opens to the diffuser 51 side. In the ejector 24, the diameter of the nozzle 51 is designed so that new hydrogen gas has a maximum flow velocity at the tip ejection portion 61. Due to the injection of the mainstream gas from the nozzle 51, a negative pressure for sucking the hydrogen off gas is generated, and the circulating gas is sucked into the diffuser 48 through the suction port 44.

  The diffuser 52 is formed coaxially with the nozzle 51 on the downstream side of the nozzle 51. A space between the diffuser 52 and the nozzle 51 communicates with the suction port 44. In the diffuser 52, the circulating gas sucked from the suction port 44 and the mainstream gas jetted from the nozzle 51 merge to mix them. The mixed hydrogen gas flows downstream of the diffuser 52 and is discharged from the discharge port 43 to the mixing flow path 22b. However, when the flow of the mainstream gas is blocked by the injector 50, only the circulating gas flows through the diffuser 52.

  The injector 50 is located on the upstream side of the nozzle 51. The injector 50 controls the supply of the mainstream gas to the nozzle 51 and thereby adjusts the injection flow rate of the mainstream gas from the nozzle 51. The injector 50 is electrically connected to the control device 5 and its drive is controlled by an output signal from the control device 5. The injector 50 adjusts the flow rate and pressure of the mainstream gas to the secondary side (nozzle 51 side), for example, by driving the valve body directly at a predetermined driving cycle with an electromagnetic driving force and separating it from the valve seat. It is a possible electromagnetically driven on-off valve. Therefore, by controlling the injector 50, the supply of the mainstream gas to the nozzle 51 can be shut off, and the mainstream gas can be intermittently supplied to the nozzle 51.

  Although details are not illustrated, the injector 50 includes, for example, a main valve portion including a valve body and a valve seat, and a solenoid portion having a coil, an iron core, and a plunger. The axial direction of the valve body is preferably coaxial with the nozzle 51. The distance between the valve seat and the nozzle 51 is preferably as short as possible in order to reduce the volume between the two and ensure the flow velocity of the mainstream gas. For example, the distance between the valve seat and the nozzle 51 is set shorter than the distance between the nozzle 51 and the diffuser 51. . In such a configuration, when the coil is energized, the magnetized iron core attracts the plunger and the valve body, and separates the valve body from the valve seat. Conversely, the valve element is brought into contact with the valve seat by stopping energization of the coil.

  The injector 50 can basically be used in two positions, “open” and “closed”, by turning on and off the current supplied to the coil. And by the opening and closing, the flow rate of the mainstream gas supplied from the injector 50 to the nozzle 51 can be changed stepwise. That is, the injector 50 controls the supply flow rate of the mainstream gas to the nozzle 51 by changing the opening time and the opening / closing timing. As this control method, it is preferable to use duty control that changes the duty ratio of the pulsed excitation current supplied to the coil of the injector 50. Here, the duty ratio is obtained by dividing the ON time of the pulsed excitation current by the switching period obtained by adding the ON time and the OFF time of the pulsed excitation current.

  FIG. 3 is a diagram showing the relationship between the duty ratio of the injector 50, the main flow rate and the circulation flow rate. The straight line L1 indicates the main flow rate ejected from the nozzle 51, that is, the ejection flow rate. A curve L2 indicates the circulation flow rate sucked by the ejector 24, that is, the suction flow rate.

  FIG. 4 is a diagram showing the relationship between the duty ratio of the injector 50 and the circulation ratio. Here, the circulation ratio is obtained by dividing the circulation flow rate sucked by the ejector 24 by the main flow rate injected from the nozzle 51. The curve M1 shown in FIG. 4 is derived from the relationship between the straight line L1 and the curve L2 shown in FIG. 3 and the duty ratio. The circulation ratio rapidly increases as the duty ratio increases up to a predetermined value D1 of the duty ratio, but gradually decreases as the duty ratio increases beyond this value D1.

  The injector 50 according to another embodiment may be configured such that the opening degree of the injector (opening degree of the valve seat) or the opening time can be switched between multistage, continuous (no stage), or linear. The opening / closing operation of the injector 50 may not be controlled by duty control.

  The control device 5 is configured as a microcomputer having a CPU, a ROM, and a RAM therein. The CPU executes a desired calculation according to the control program and performs various processes and controls such as control of the injector 50. The ROM stores control programs and control data processed by the CPU. The RAM is mainly used as various work areas for control processing. The control device 5 inputs detection signals such as pressure sensors P1 and P2 in the gas system (3, 4), and outputs a control signal to each component.

In the present embodiment, the control device 5 supplies hydrogen gas to the fuel cell 2 so as to realize hydrogen gas control according to the required output of the fuel cell 2 (hereinafter referred to as “supply flow F ₁ ”). To control. Here, the required output of the fuel cell 2 is detected by the accelerator opening when the fuel cell system 1 is mounted on a vehicle.

For example, the control device 5 detects the required output of the fuel cell 2 and controls the opening time and opening / closing timing of the injector 50 so that the supply flow rate F ₁ satisfies the required output. As a result, the main flow rate injected from the nozzle 51 is adjusted, and the circulating flow rate sucked by this injection is adjusted, so that the supply flow rate F ₁ obtained by adding these satisfies the required output of the fuel cell 2. To come.

Therefore, according to this embodiment, the injection flow rate of the hydrogen gas from the nozzle 51 can be adjusted by the injector 50 without providing the nozzle 51 or the diffuser 52 with a mechanism for changing the diameter thereof, and a desired supply to the fuel cell 2 can be achieved. A flow rate F ₁ can be supplied.

In the present embodiment, it is further preferable that the control device 5 measures the supply flow rate F ₁ based on the opening times of the pressure sensor P1, the pressure sensor P2, and the injector 50. And the control apparatus 5 is good to control the opening-closing timing and opening time of the injector 50 based on this measurement result. In this way, by executing the feedback control for the supply flow rate F _1, the supply flow rate F ₁ corresponding to the required output and the state of the fuel cell 2 (consumption state of the hydrogen gas) can be accurately supplied to the fuel cell 2.

Further, the control device 5 may control the suction flow rate (circulation flow rate) of the ejector 24 based on the hydrogen gas supply flow rate F ₂ from the injector 50 to the nozzle 51 and the opening / closing timing of the injector 50. This control also makes it possible to control the pressure of the hydrogen gas circulation system. Here, the pressure control of the hydrogen gas circulation system means the control of the pressure of the hydrogen gas at the discharge port 43, the hydrogen gas inlet and the hydrogen gas outlet of the fuel cell 2. The supply flow rate F ₂ can be calculated from the pressure sensor P1 and the open time of the injector 50.

Further, the control device 5 may positively control the pressure of the hydrogen gas circulation system by the control of the injector 50. Specifically, when the power generation in the fuel cell 2 increases, the amount of hydrogen consumption increases, so the hydrogen gas pressure at the hydrogen gas inlet and the hydrogen gas outlet of the fuel cell 2 decreases. Therefore, in order to increase these pressures, the control device 5 may control the opening / closing timing and opening time of the injector 50 so that the supply flow rate F ₂ is larger than the hydrogen consumption in the fuel cell 2. Conversely, when the power generation in the fuel cell 2 decreases, the pressure of the hydrogen gas at the hydrogen gas inlet and the hydrogen gas outlet of the fuel cell 2 increases. Therefore, in this case, in order to reduce these pressures, the control device 5 controls the opening / closing timing and opening time of the injector 50 so that the supply flow rate F ₂ is less than the hydrogen consumption in the fuel cell 2. Good.

  As described above, according to the fuel cell system 1 including the ejector 24 of the present embodiment, the injection flow rate of new hydrogen gas from the nozzle 50 can be adjusted without changing the opening area of the nozzle 50. Thereby, the flow rate of the hydrogen gas to the fuel cell 2 can be controlled in a wide range, and in particular, the minute flow rate of the hydrogen gas to the fuel cell 2 can be stably controlled.

  Further, when the consumption amount of hydrogen gas in the fuel cell 2 is zero, the inflow of new hydrogen gas into the fuel cell 2 can be prevented by closing the injector 50. Thereby, the pressure rise in the fuel cell 2 can be suppressed. Here, the case where the fuel cell 2 does not consume hydrogen gas during operation of the fuel cell system 1 means, for example, when the fuel cell 2 stops generating power or when it is idle. From the viewpoint of the fuel cell vehicle, the fuel cell vehicle When idling or during regenerative braking.

  The ejector 24 having a high suction capability can be mounted on the fuel cell system 1 due to the effect that new hydrogen gas can be prevented from flowing into the fuel cell 2. Further, by using the ejector 24 having a high suction capability, the system efficiency such as improvement of drainage of water generated by the power generation reaction can be improved.

<Other control examples>
Next, an example of control of the injector 50 when the fuel cell system 1 is stopped and started will be described.

  First, when the fuel cell system 1 is stopped, the control device 5 closes the injector 50. In this way, when the system is stopped, the ejector 24 itself can also function as a pressure reducing valve, and supply of new hydrogen gas to the fuel cell 2 can be shut off. Further, the hydrogen circulation system (consisting of the mixing flow path 22b, the flow path in the fuel cell 2 and the circulation flow path 23) can be set to a closed system.

  In general, it is known that fuel gas and oxygen gas in the fuel cell 2 cross-leak when the system is stopped. Due to this cross leak, oxygen gas in the oxygen gas piping system 3 leaks to the fuel electrode side of the fuel cell 2, and hydrogen gas in the fuel gas piping system 4 leaks to the air electrode side of the fuel cell 2. When a predetermined time has elapsed, the fuel cell 2 is in an equilibrium state. Since the oxygen gas leaked to the fuel electrode side contains nitrogen gas in the air, the fuel electrode side flow passage in the fuel cell 2 contains impurities such as nitrogen gas. .

  Next, when the fuel cell system 1 is started, the control device 5 opens the injector 50 and supplies hydrogen gas to the hydrogen circulation system. At this time, the control device 5 controls the injector 50 so that the circulation ratio of hydrogen gas is maximized. For example, the control device 5 controls the opening and closing of the injector 50 with a duty ratio within a range included in the dotted frame line in FIG. By so doing, the circulation of hydrogen gas in the hydrogen circulation system can be suitably ensured, and the discharge of impurities such as nitrogen gas accumulated in the fuel cell 2 is promoted. Thereby, the shortage of hydrogen gas in the fuel cell 2 after system startup can be suppressed, and power generation of the fuel cell 2 after system startup can be started quickly. Further, by supplying hydrogen gas until the hydrogen gas pressure in the fuel cell 2 becomes higher than that during normal operation at the time of starting the system, the circulation time can be extended and the discharge of indivisible matter can be promoted.

<Modification>
Although the main flow gas (injection gas) of the ejector 24 is a new hydrogen gas and the side flow gas (suction gas) is a hydrogen off gas, the reverse configuration may be used. That is, the ejector 24 may suck new hydrogen gas from the hydrogen tank 21 when injecting hydrogen off-gas from the nozzle 50.

  Further, the ejector 24 may be disposed in the oxygen gas piping system 3. For example, the oxygen off-gas in the discharge flow path 13 may be merged with new oxygen gas from the compressor 15 by the ejector 24, and the mixed oxygen gas after the merge may be supplied to the fuel cell 2.

  The above-described ejector 24 of the present invention can be applied not only to the fuel cell system 1 but also to other systems that need to supply fluids by joining them. In particular, it can be suitably used when the device to which the fluid is supplied by the ejector 24 requires a wide range of flow rates.

  The above-described fuel cell system 1 of the present invention can be mounted on a train other than a two-wheeled or four-wheeled vehicle, an aircraft, a ship, a self-propelled robot, or other moving objects. Further, the fuel cell system 1 can be used for stationary use and can be incorporated into a cogeneration system.

It is a block diagram which shows the principal part of the fuel cell system which concerns on embodiment. It is a figure which shows the ejector which concerns on embodiment, and is the figure which made a part of ejector into sectional drawing. It is a figure which shows the relationship between the duty ratio of the injector which concerns on embodiment, the injection flow volume from a nozzle, and the suction | inhalation flow volume to a nozzle. It is a figure which shows the relationship between the duty ratio of the injector which concerns on embodiment, and the circulation ratio of a reactive gas.

Explanation of symbols

  1: fuel cell system, 2: fuel cell, 3: oxygen gas piping system, 4: hydrogen gas piping system, 5: control device, 22: supply channel, 23: circulation channel, 24: ejector, 50: injector, 51: Nozzle, 52: Diffuser

Claims (8)

A nozzle that generates a negative pressure for ejecting the first fluid and sucking the second fluid;
In an ejector provided on the downstream side of the nozzle, and comprising a diffuser in which the ejected first fluid and the sucked second fluid merge.
An ejector comprising an injector for adjusting an injection flow rate of the first fluid from the nozzle on the upstream side of the nozzle.   The ejector according to claim 1, wherein the injector adjusts an injection flow rate of the first fluid by intermittently supplying the first fluid to the nozzle.   The ejector according to claim 1, wherein the injector adjusts an injection flow rate of the first fluid by controlling an opening / closing operation by duty control.   The ejector according to claim 1, wherein the injector is configured to be able to block supply of the first fluid to the nozzle. A supply channel for supplying new reaction gas to the fuel cell;
A circulation channel for circulating the reaction off-gas discharged from the fuel cell to the supply channel;
The ejector according to any one of claims 1 to 4, provided at a connection portion between the supply flow path and the circulation flow path,
A fuel cell system comprising:
One of the first fluid and the second fluid is the new reaction gas, and the other is the reaction off gas. The first fluid is a fuel gas as the new reaction gas,
The fuel cell system according to claim 5, wherein the second fluid is a fuel off-gas as the reaction off-gas. A control device for controlling the injector;
The fuel cell system according to claim 6, wherein the control device controls the injector so that a circulation flow rate of the fuel off-gas with respect to an injection flow rate of the fuel gas is maximized when the fuel cell system is activated. A control device for controlling the injector;
The fuel cell system according to claim 6, wherein the control device controls the injector so as to cut off the flow of the fuel gas to the nozzle when the fuel cell system is stopped.

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