JP5200643B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  Conventionally, as disclosed in, for example, the following Patent Document 1, a fuel cell system that generates power while closing an exhaust mechanism provided downstream of a gas flow path of a fuel cell (or narrowing its opening) It has been known. According to such a fuel cell system, operation is performed with the downstream of the fuel gas passage blocked (hereinafter also referred to as “dead end operation”), or the amount of gas discharged from the downstream of the fuel gas passage is reduced. It is possible to operate with a minute amount (hereinafter also referred to as “small amount exhaust operation”). According to the dead end operation or the small amount exhaust operation, the fuel gas utilization efficiency can be increased in generating power.

JP 9-31167 A JP 2007-188665 A

  It is important to detect various abnormalities that occur inside the fuel cell. In a fuel cell system that performs a dead-end operation or a small amount of exhaust operation, impurities are accumulated in the gas flow path as time elapses. If the impurity is partially depleted of fuel gas on the downstream side of the gas flow path of the fuel cell (hereinafter, also referred to as “fuel depletion abnormality”), the catalyst inside the fuel cell may be deteriorated. Also, when an abnormality such as dry-up or flooding occurs inside the fuel cell, good power generation of the fuel cell is hindered. There is a high demand for detecting these abnormalities at an early stage and taking appropriate measures.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel cell system capable of detecting an abnormality in the fuel cell at an early stage.

In order to achieve the above object, the first invention provides
A fuel cell having a power generation body that receives power from the supply of fuel gas, and a fuel gas passage that extends along the surface of the power generation body while being in contact with the power generation body;
A fuel gas supply mechanism for supplying fuel gas to the fuel gas flow path,
The dead-end operation state in which the operation is performed by closing the downstream side of the fuel gas flow path, and the amount of gas discharged from the downstream side of the fuel gas flow path is set to the amount of gas flowing into the fuel gas flow path. A fuel cell system capable of realizing at least one operation state among a small amount exhaust operation state in which operation is performed with a minute amount compared to the above,
further,
Measuring means capable of measuring the difference between the pressure of the gas upstream of the fuel gas flow path and the pressure of the gas downstream of the fuel gas flow path;
Detecting means for detecting an abnormality of the fuel cell based on the pressure difference measured by the measuring means;
With
When the magnitude of the pressure difference measured by the measuring means is below a predetermined lower limit value, the detecting means determines that an abnormality in which fuel is deficient has occurred downstream of the fuel gas flow path. Including fuel deficiency detection means,
The detection means includes dry-up detection means for detecting the occurrence of dry-up in the fuel cell based on a comparison between the magnitude of the pressure difference measured by the measurement means and a predetermined dry-up determination value. It is characterized by.

In addition, the second aspect of the present invention, Oite in the first inventions,
The detection means includes flooding detection means for detecting the occurrence of flooding in the fuel cell based on a comparison between the magnitude of the pressure difference measured by the measurement means and a predetermined flooding judgment value. To do.

The third invention is the first or second invention, wherein
further,
Concentration detection means for detecting the fuel concentration in the gas downstream of the fuel gas flow path,
The detection means determines whether or not an abnormality in which the fuel is deficient has occurred downstream of the fuel gas flow path based on the fuel concentration detected by the concentration detection means.

  In a fourth aspect based on any one of the first to third aspects, the predetermined lower limit value is a flow rate per unit time of gas supplied from the fuel gas supply mechanism to the fuel gas flow path. It is characterized in that it is determined to take a larger value as there are more.
  In a fifth aspect based on the second aspect, the flooding determination value takes a larger value as the flow rate per unit time of gas supplied from the fuel gas supply mechanism to the fuel gas flow path increases. It is characterized by that.
  According to a sixth invention, in any one of the first to fifth inventions, the dry-up determination value is a flow rate per unit time of gas supplied from the fuel gas supply mechanism to the fuel gas flow path. It is characterized in that it is determined to take a larger value as there are more.

According to the first invention, the following effects can be obtained. The difference in pressure between the gas upstream of the fuel gas flow path and the gas downstream (hereinafter also referred to as “pressure difference”) increases or decreases according to the change in the power generation state of the power generation body. If attention is paid to the change in the pressure difference, information on the change in the power generation state of the power generator can be obtained at an early stage. According to the first invention, by utilizing this point and performing abnormality detection based on the pressure difference between the gas upstream and downstream of the fuel gas flow path, the abnormality inside the fuel cell can be detected at an early stage. . Further, based on the pressure difference between the gas upstream and downstream of the fuel gas flow path, it is possible to detect the bias in the power generation distribution caused by the lack of fuel at an early stage. Therefore, the fuel deficiency abnormality downstream of the fuel gas passage can be detected at an early stage. Furthermore, when dry-up occurs, the tendency of gas consumption inside the fuel cell changes, and the change is reflected in the pressure difference between the gas upstream and downstream of the fuel gas flow path. Using this point, it is possible to detect the occurrence of dry-up inside the fuel cell at an early stage.

According to the second invention, the following effects can be obtained. When flooding occurs, the tendency of gas consumption inside the fuel cell changes, and this change is reflected in the pressure difference between the gas upstream and downstream of the fuel gas flow path. According to the second invention, it is possible to detect the occurrence of flooding in the fuel cell at an early stage by utilizing this point.

According to the third aspect of the present invention, it is possible to accurately detect and detect a situation where a fuel deficiency abnormality occurs downstream of the fuel gas flow path from dry-up and flooding.

According to the fourth to sixth inventions, the influence of the change in the flow rate of the fuel gas flowing into the fuel gas flow path is reflected in various values for detecting an abnormality (lower limit value, flooding determination value, dry-up determination value). In addition, abnormality detection based on the pressure difference between the gas upstream and downstream of the fuel gas flow path can be performed. As a result, the abnormality determination can be performed with high accuracy under a situation where the flow rate of the fuel gas flowing into the fuel gas flow path varies.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram schematically showing the configuration of the fuel cell system according to Embodiment 1 of the present invention. The fuel cell system of Embodiment 1 includes a fuel cell 10. Usually, the fuel cell 10 is used as a fuel cell stack formed by stacking a plurality of unit cells 2. The unit cell 2 has a configuration in which a membrane electrode assembly is sandwiched between a pair of current collector plates. In the membrane / electrode assembly, a catalyst is integrated on both sides of a solid polymer electrolyte membrane, and a gas diffusion layer made of a carbon sheet or the like is further integrated on each side. The current collector plate also functions as a separator that partitions between two adjacent membrane electrode assemblies. Each unit cell 2 receives the supply of hydrogen as a fuel gas at the anode and the supply of air at the cathode to generate power.

  A supply pipe 14 for supplying hydrogen from the hydrogen tank 12 to the fuel cell 10 is connected to the fuel cell 10. A hydrogen pressure regulating valve 16 is disposed in the middle of the supply pipe 14. Hydrogen is supplied to the fuel cell 10 after being depressurized by the hydrogen pressure regulating valve 8 and adjusted to a desired pressure. Hydrogen supplied to the fuel cell 10 is distributed to the anode of each unit cell 2 by a supply manifold (not shown) formed in the fuel cell 10.

  The fuel cell system of the present embodiment includes an exhaust pipe 20 for extracting anode off gas from the fuel cell 10. The exhaust pipe 20 is connected to the downstream end of the anode side gas flow path of each unit cell 2 via an exhaust manifold (not shown) formed in the fuel cell 10. The gas (anode gas) in the anode gas passage is collected in the exhaust manifold and discharged to the exhaust pipe 20. The tip of the exhaust pipe 20 is open to the atmosphere or connected to a diluter.

  The exhaust pipe 20 is provided with an electromagnetic exhaust valve 22 capable of duty control as an exhaust mechanism for switching the communication state of the exhaust pipe 20. The exhaust valve 22 is preferably an injector type having excellent flow rate controllability. The operation of the exhaust valve 22 can be alternatively selected from a closed mode in which the exhaust valve 22 is completely closed (that is, the duty ratio is zero) and an exhaust mode in which opening control is performed at a predetermined duty ratio.

  When the blocking mode is selected, the communication between the anode-side gas flow path of the fuel cell 10 and the outside of the system is blocked. On the other hand, when the exhaust mode is selected, communication between the anode-side gas flow path and the outside of the system is realized, and the anode gas can be exhausted outside the system. However, the duty ratio in the exhaust mode is small, and the flow rate of the anode gas exhausted outside the system is adjusted to a very small value as compared with the amount of hydrogen consumed in the anode side gas flow path. Preferably, the exhaust amount in the exhaust mode is set to be approximately the same amount (or an amount corresponding to this amount of movement) as the amount of movement of the gas moving from the force sword to the anode through the electrolyte membrane per unit time. The amount of gas movement through the electrolyte membrane may be determined experimentally in advance, taking into account changes due to pressure, temperature, or the degree of deterioration of the electrolyte membrane.

  Hereinafter, the operation of the fuel cell system when the closed mode is selected is referred to as “dead end operation”, and the operation of the fuel cell system when the exhaust mode is selected is referred to as “small amount exhaust operation”. In the following description, the amount of gas discharged from the exhaust valve 22 to the outside of the system per unit time is also referred to as “exhaust flow rate”.

  Further, the system of the first embodiment has a cathode system for supplying air to the cathode of the fuel cell 10. The cathode system includes an air supply pipe 32 for supplying air to the fuel cell 10 and an air compressor 34 provided in the air supply pipe 32. The cathode system also includes a cathode exhaust pipe 36 that communicates with the downstream side of the cathode of the fuel cell 10. Air is taken into the air supply pipe 32 by the operation of the air compressor 34, and this air is supplied to the fuel cell 10. Air supplied to the fuel cell 10 is distributed to the cathodes of the individual unit cells 2 through a supply manifold formed in the fuel cell 10. The air that has passed through the cathodes of the individual unit cells 2 is collected in an exhaust manifold formed in the fuel cell 10 and discharged to the cathode exhaust pipe 36.

  The fuel cell system of Embodiment 1 includes a differential pressure gauge 24. As shown in FIG. 1, the differential pressure gauge 24 is connected between the supply pipe 14 and the exhaust pipe 20. Using the differential pressure gauge 24, a difference ΔP between the pressure of the gas in the supply pipe 14 upstream of the fuel cell 10 and the pressure of the gas in the exhaust pipe 20 downstream of the fuel cell 10 (hereinafter simply referred to as “pressure difference ΔP”). Can also be measured.

  In addition, the fuel cell system of Embodiment 1 includes an ammeter 26 that measures an output current when the fuel cell 10 generates power.

  The fuel cell system of Embodiment 1 includes an ECU (Electronic Control Unit) 30. A differential pressure gauge 24 and an ammeter 26 are connected to the ECU 30, and output values of these instruments are input. Further, the ECU 30 is connected to the hydrogen pressure regulating valve 16 and the exhaust valve 22, and sets the opening degree or the duty ratio to a desired value. The ECU 30 is connected to the air compressor 34 and controls the operation of the air compressor 34.

  FIG. 2 is a diagram showing the internal structure of the unit cell 2 constituting the fuel cell 10. In FIG. 2, the phenomenon occurring inside the unit cell 2 is schematically shown along with the structure of the unit cell 2. In FIG. 2, the part which concerns on the characteristic of this invention is shown, and illustration is abbreviate | omitted about parts, such as a collector and a manifold. Hereinafter, description will be made with reference to FIG. 2 together with FIG.

  As shown in FIG. 2, a fuel gas channel 42 and an oxidizing gas channel 44 are formed along each surface of the membrane electrode assembly 40. In the first embodiment, hydrogen is supplied to the fuel gas passage 42 as the fuel gas. In the first embodiment, air is supplied to the oxidizing gas channel 44 as the oxidizing gas. In the first embodiment, the gas flow direction in the fuel gas flow path 42 and the gas flow direction in the oxidizing gas flow path 44 are opposite to each other. Thus, the unit cell 2 has a so-called gas flow channel structure called a counter flow channel.

  In addition, there is no limitation in the shape and structure of these gas flow paths. For example, a groove may be formed on the surface of the current collector (separator), and the groove may be used as the fuel gas channel 42 or the oxidizing gas channel 44. Also, a porous layer made of a conductive material is provided between the current collector and the membrane electrode assembly 40, and a fuel gas channel 42 and an oxidizing gas channel 44 are formed by continuous pores in the porous layer. Also good.

Here, a phenomenon occurring inside the unit cell 2 during power generation will be described. The air supplied to the oxidizing gas passage 44 contains nitrogen (N ₂ ) in addition to oxygen (O ₂ ) used for power generation. Nitrogen is an inert gas and is not used for power generation, but is directly exhausted from the system through the oxidizing gas flow path 44. However, a part of the nitrogen permeates through the membrane electrode assembly 40 and enters the fuel gas passage 42 as schematically shown by arrows in FIG. At this time, the driving force for moving nitrogen toward the fuel gas flow path 42 is a partial pressure difference of nitrogen between the oxidizing gas flow path 44 and the fuel gas flow path 42. Nitrogen (N ₂ ) that has passed through the membrane electrode assembly 40 flows downstream of the fuel gas passage 42 as schematically shown by arrows in FIG. 2 due to the flow of hydrogen (H ₂ ) in the fuel gas passage 42. Will be washed away.

  In addition to nitrogen, air contains impurities such as water vapor and carbon dioxide that are not used for power generation. However, since the concentration in air is extremely small compared to nitrogen, in the following description, there may be a case where only nitrogen is considered as an impurity. However, it does not mean that substances other than nitrogen are excluded from the impurity assumed by the present invention.

  Note that the fuel cell system of Embodiment 1 also includes the following features (i) and (ii).

(I) The supply gas is high-concentration (pure) hydrogen In the first embodiment, the hydrogen supplied to the fuel cell 10 is a hydrogen tank (in a broader sense, a hydrogen supply source without being mixed with off-gas). ) Directly supplied. Therefore, compared to a so-called circulation type fuel cell system, a high concentration of hydrogen is supplied. Compared to the system configuration that employs a reformer as the hydrogen supply source, the system configuration that employs a hydrogen storage device that stores high-purity wastewater such as high-pressure tanks and hydrogen storage materials as the hydrogen supply source , Become even more prominent.

(Ii) Point where the hydrogen concentration of the exhaust gas is low In the first embodiment, the hydrogen concentration of the anode off-gas discharged from the fuel cell 10 is lowered to such an extent that the anode off-gas may be released into the atmosphere as it is. However, it may be discharged through a device that further reduces the hydrogen concentration, such as a diluter or a combustor. In any case, a fuel cell system that uses hydrogen energy in the offgas to improve efficiency, such as a system that uses anode offgas as a heating raw material for the reformer or a circulation type system that supplies anode offgas to the fuel cell again. In comparison, in the fuel cell system according to Embodiment 1, the hydrogen concentration in the anode off-gas is controlled to be lower.

[Abnormality detection in the first embodiment]
Hereinafter, abnormality detection performed by the fuel cell system of Embodiment 1 will be described.

  As schematically shown in FIG. 2, when the dead end operation or the small amount exhaust operation is performed, nitrogen is gradually accumulated in the downstream end portion of the fuel gas passage 42. If nitrogen covers the surface of the membrane electrode assembly 40, the reaction in the catalyst is hindered, leading to a decrease in voltage or deterioration of the membrane electrode assembly 40 due to an abnormal potential. There is a high demand for detecting such an abnormality (hereinafter also referred to as “fuel deficiency abnormality”) as early as possible and taking appropriate measures.

  In view of this point, the inventor of the present application has conducted extensive research and has come up with an abnormality detection technique described below.

  Hydrogen is consumed by the power generation reaction in the unit cell 2 in the process of flowing in the fuel gas flow path 42. Further, pressure loss occurs in the process in which hydrogen flows through the fuel gas passage 42. As described above, two phenomena occur in the fuel gas flow path 42, that is, a decrease in the amount of hydrogen accompanying power generation and generation of pressure loss due to the circulation of hydrogen.

  When the above-described fuel deficiency abnormality occurs, power generation in the downstream portion of the fuel gas passage 42 in the unit cell 2 is hindered. As a result, the distribution of the power generation amount of the unit cell 2 becomes non-uniform, and the hydrogen amount in the fuel gas passage 42 decreases when viewed along the gas flow direction of the fuel gas passage 42 (hereinafter, "Hydrogen consumption trend") changes. If the hydrogen consumption tendency changes, the distribution of the hydrogen flow rate in the fuel gas channel 42 changes. Under the influence, the sum of pressure losses generated in the fuel gas flow paths 42 of the individual unit cells 2 changes, and finally, the pressure difference ΔP measured by the differential pressure gauge 24 increases or decreases.

  3 and 4 are diagrams showing details of the contents of abnormality detection according to the first embodiment. 3 shows the current density distribution (FIG. 3 (a)), the hydrogen flow rate distribution (FIG. 3 (b)), and the unit cell 2 when the inlet-outlet direction of the fuel gas channel 42 is taken along the horizontal axis. A gas pressure distribution (FIG. 3C) in the fuel gas flow path 42 is schematically shown. FIG. 4 is a flow chart summarizing the content of the inventor's consideration of the state change process in the fuel gas flow path 42.

  3A to 3C, distributions indicated by solid lines correspond to each other in current density, hydrogen flow rate, and pressure. That is, in the state where the solid line current density distribution in FIG. 3A is shown, the hydrogen flow rate and pressure are the solid line distributions in FIGS. 3B and 3C, respectively. Similarly, the distributions indicated by the broken lines in FIGS. 3A to 3C correspond to each other.

  The current density distribution indicated by a solid line in FIG. 3A shows a uniform current density from the inlet to the outlet of the fuel gas flow path 42. This state is a state in which the power generation reaction occurs uniformly in the plane of the unit cell 2 (membrane electrode assembly 40).

  From this state, when nitrogen is accumulated on the outlet side (downstream side) of the fuel gas passage 42, the power generation reaction in this region is inhibited (step 50 in FIG. 4). As a result, the power generation capacity on the downstream side of the fuel gas channel 42 in the unit cell 2 is reduced.

  In order to satisfy the required output for the fuel cell 10 in accordance with the decrease in the power generation capacity on the downstream side, as shown by the broken line in FIG. The current will be generated. That is, the current density distribution changes from a flat distribution to a distribution in which the current density is biased to the upstream side of the fuel gas passage 42 as schematically shown in FIG. 3A (step 52 in FIG. 4). ).

  As the current density distribution changes, the hydrogen flow rate in the fuel gas passage 42 is affected as described below.

  FIG. 3B is a diagram showing a hydrogen flow rate distribution in the fuel gas flow channel 42. As described above, the fuel cell system of Embodiment 1 can perform a dead end operation or a small amount of exhaust operation. Under such an operation mode, basically, the hydrogen that has flowed into the fuel gas flow path 42 is almost entirely consumed by power generation. Therefore, as shown by the solid line in FIG. 3B, the hydrogen flow rate at the outlet side of the fuel gas flow path 42 becomes zero. Further, if the power generation reaction occurs uniformly in the plane of the membrane electrode assembly 40, it is considered that the consumption of hydrogen per unit area of the membrane electrode assembly 40 is substantially the same in the entire plane. Accordingly, as indicated by the solid line in FIG. 3B, the flow rate of hydrogen decreases linearly (proportionally) from the inlet to the outlet of the fuel gas passage 42.

  However, when the current density is biased to the upstream side of the fuel gas passage 42 as shown by the broken line in FIG. 3A, the hydrogen consumption on the upstream side of the fuel gas passage 42 is increased, resulting in a hydrogen flow distribution. Is as shown by the broken line in FIG. That is, power generation is performed in a state where hydrogen is completely consumed by Δl before the outlet position of the fuel gas passage 42.

Before and after the change of the hydrogen flow rate, the distance (in other words, the substantial gas flow path length) in which hydrogen substantially flows in the fuel gas flow path 42 will be compared. That is, the solid line and the broken line in FIG. Then, the gas flow path length (step 54 in FIG. 4) from the length l ₀ of the time of solid, which when the broken line is in a Δl as short becomes long l _1.

As the substantial gas flow path length is shortened, the pressure drop amount of the gas flowing through the fuel gas flow path 42 is reduced under the influence. FIG. 3C schematically shows such a change in the pressure drop amount. As the actual gas flow path length becomes shorter, the pressure drop tendency changes from a solid line to a broken line, and the gas pressure difference at the inlet / outlet position of the fuel gas flow path 42 changes from ΔP ₀ to ΔP _er1 . To do. That is, the gas pressure at the outlet position of each unit cell 2 increases. Eventually, the pressure difference ΔP of the fuel cell 10 decreases (step 56 in FIG. 4).

  As described above, the pressure difference between the gas upstream and downstream of the fuel gas flow path 42 decreases with the bias of the current density distribution accompanying the occurrence of the fuel deficiency abnormality. As a result, the pressure difference ΔP measured by the differential pressure gauge 26 also decreases. Therefore, in the first embodiment, it is determined whether or not a fuel deficiency abnormality has occurred downstream of the fuel cell 10 based on the decrease width of the pressure difference ΔP.

  Specifically, first, the range in which the value of the pressure difference ΔP can be shown during normal power generation (more specifically, when the power distribution in the plane of the unit cell 2 is substantially uniform) is experimentally or simulated. Specify in advance. Based on the specified range, a lower limit value of the pressure difference ΔP is determined. During the power generation of the fuel cell 10, the lower limit value is compared with the pressure difference ΔP measured by the differential pressure gauge 24. When the pressure difference ΔP decreases so as to fall below the lower limit value, it can be determined that a fuel deficiency abnormality has occurred inside the fuel cell 10.

  According to the first embodiment described above, by focusing on the pressure difference ΔP, the fuel deficiency abnormality inside the fuel cell 10 is detected when the current density distribution is biased due to the accumulation of the impurity gas. Is possible. Therefore, the fuel deficiency abnormality can be detected at an early stage.

  Note that when a fuel deficiency abnormality occurs, the power generation reaction in the catalyst is hindered, and the voltage of the unit cell 2 decreases. Focusing on this point, unlike the first embodiment, a method of detecting the occurrence of fuel deficiency abnormality by monitoring the voltage of the unit cell 2 is also conceivable. However, when measuring the voltage, the average voltage of the entire fuel cell is monitored. In this case, it is difficult to detect the situation where the fuel is partially deficient inside the fuel cell at an early stage. There is a possibility that various adverse effects such as catalyst deterioration have already started to occur inside the fuel cell when the voltage drop is detected. In order to prevent catalyst deterioration and the like with as little damage as possible (more preferably, in advance), it is desirable to detect an abnormality in fuel deficiency at an earlier stage.

  In this regard, in the first embodiment, by monitoring the pressure difference ΔP, it is possible to detect the fuel deficiency abnormality inside the fuel cell 10 when the current density distribution is biased inside the unit cell 2. Therefore, according to the first embodiment, it is possible to detect the fuel deficiency abnormality earlier than when the abnormality detection is performed based on the average voltage.

[Specific Processing in First Embodiment]
Hereinafter, specific processing executed by the fuel cell system of Embodiment 1 will be described. FIG. 5 is a flowchart of specific processing executed by the fuel cell system according to Embodiment 1. In the routine shown in FIG. 5, first, the output of the fuel cell 10 (the output current value in the present embodiment) is detected (step S100). In this step, specifically, the ECU 30 acquires the current output current value based on the output of the ammeter 26.

  Next, a routine for obtaining the pressure difference ΔP is executed (step S102). In this step, the ECU 30 acquires the current value of the pressure difference ΔP based on the output of the differential pressure gauge 24.

Next, it is determined whether or not the pressure difference ΔP is below a predetermined lower limit value (step S104). In this step, first, the ECU 30 _refers to a predetermined map of the lower limit value ΔP th — _l and acquires the lower limit value ΔP th — _l corresponding to the current output current value detected in step S100.

FIG. 6 is a map that defines the relationship between the lower limit value ΔP th — _l and the output current value. As shown in FIG. 6, ΔP th — _l (I ₁ ) is acquired according to the current output current value I ₁ .

The map of the lower limit value ΔP th — _l can be created by the following procedure, for example. First, in advance, the value of the pressure difference ΔP in the normal power generation state is ascertained through experiments and simulations, and the allowable range of the pressure difference ΔP is determined. The lower limit value of the allowable range may be set to ΔP th — _l . In the first embodiment, as shown in FIG. 6, as the output current value I of the fuel cell 10 is large, the lower limit value [Delta] P _{th - L} is to take a large value, to create a map of the lower limit value [Delta] P _{th - L.}

The larger the output current value I, the larger the flow rate per unit time of the gas flowing into the fuel gas passage 42. As the flow rate of hydrogen flowing into the fuel gas passage 42 increases, the pressure loss increases on average. In the first embodiment, in consideration of such points, the lower the lower limit value is, the larger the output current value I of the fuel cell 10 is, so that it can cope with a plurality of situations in which the flow rate of hydrogen (hydrogen supply amount) is different. ΔP th — _l is set large. As a result, the abnormality determination can be performed with high accuracy.

Note that the dotted line shown in FIG. 6 schematically illustrates ΔP _std which is a reference pressure difference value. Here, ΔP _std is a value indicated by the pressure difference ΔP when power generation occurs uniformly in the plane of the unit cell 2.

If the condition in step S104 is negative, it is determined that the pressure difference ΔP indicates a value within the allowable range, and the current routine ends. In this case, ΔP exists in a region above the paper surface with _{respect to} the straight line ΔP th — _l if described using the map of FIG. 6.

If the condition of step S104 is satisfied, it is determined that a fuel deficiency abnormality has occurred in the fuel cell 10 (step S106). In this case, ΔP exists in a region below the plane of the paper with _{respect to} the straight line ΔP th — _l , using the map of FIG. In this step, a determination is made that a fuel deficiency abnormality has occurred. In addition, according to this step S106, you may perform the process of switching the output signal for abnormality detection emitted outside. Thereby, the occurrence of abnormality can be transmitted to the outside.

  Subsequent to step S106, processing for increasing the exhaust flow rate of the exhaust valve 22 is executed (step S108). In this step, specifically, the ECU 30 changes the duty ratio of the exhaust valve 22 so as to increase from the current exhaust flow rate by a predetermined amount. As a result, more anode off gas flows out from the exhaust pipe 20 and the impurity gas accumulated downstream of the fuel gas flow path 42 is discharged. Thereafter, the current routine ends.

  According to the above processing, it is possible to detect the occurrence of the fuel deficiency abnormality of the fuel cell 10 based on the value of the pressure difference ΔP. It is possible to increase the displacement for the detected abnormality and take appropriate measures for the abnormality.

  In the first embodiment described above, the fuel cell 10 is a “fuel cell” in the first invention, the fuel gas passage 42 is a hydrogen tank in the “fuel gas passage” in the first invention. 12, the supply pipe 14 and the hydrogen pressure regulating valve 16 respectively correspond to the “fuel gas supply mechanism” in the first invention. Further, in the first embodiment, the differential pressure gauge 24 corresponds to the “measuring means” in the first invention, and the routine of step S104 and step S106 in the flowchart of FIG. The “detection means” in the invention is realized.

[Modification of Embodiment 1]
(First modification)
The fuel cell system according to Embodiment 1 includes an exhaust valve 22 and is a system that can realize a small amount of exhaust operation. However, the present invention is not limited to this. The present invention can also be applied to a fuel cell system (hereinafter also referred to as a “complete dead-end system”) in which the exhaust valve is not provided and the anode downstream of the fuel cell is completely blocked. .

  In the complete dead-end system, power generation of the fuel cell is continuously performed in a state where the partial pressure of the impurity gas in the anode and the impurity gas in the cathode are substantially balanced. In other words, the complete dead-end system continuously generates power in a state where the partial pressure of the impurity gas of the anode is increased to the partial pressure of the impurity gas of the cathode. The electrolyte membrane has a property of transmitting gas. When there is a gas partial pressure difference between the cathode and the anode, the gas moves through the electrolyte membrane so that the partial pressure difference is reduced. As a result of such a phenomenon, the partial pressure of the impurity gas at the anode and the cathode eventually stabilizes in a substantially balanced state. A complete dead-end system is a system that generates power in such a state.

  In the first modification, the same abnormality detection as that of the first embodiment is performed on the complete dead end system. Here, for simplification of description, in the fuel cell system of Embodiment 1, the downstream of the fuel gas flow path 42 of each unit cell 2 is blocked, and the exhaust pipe 20 and the downstream configuration thereof are removed. This is the fuel cell system of the first modification.

  By executing the routine of FIG. 5 for this first modification, it is possible to detect an abnormality as in the first embodiment. However, in the first modification, the routine of step S108 after the abnormality is detected is replaced with the routine described below.

  In the first modification, when a fuel deficiency abnormality is detected, the ECU 30 controls the air compressor 34 so that the cathode side pressure of the fuel cell 10 decreases by a predetermined amount. Thereby, the permeation of the impurity gas from the fuel gas channel 42 side toward the oxidizing gas channel 44 side becomes active. As a result, the amount of impurity gas in the fuel gas passage 42 can be reduced, and fuel deficiency can be alleviated. Alternatively, the hydrogen partial pressure in the fuel gas passage 42 may be increased by increasing the opening of the hydrogen pressure regulating valve 16. Thereby, hydrogen is spread to the downstream side of the fuel gas flow path 42, and fuel deficiency can be alleviated.

  According to the first modification described above, it is possible to detect the occurrence of the fuel depletion abnormality of the fuel cell based on the value of the pressure difference ΔP for the complete dead-end system. Appropriate measures such as a decrease in impurity gas and an increase in hydrogen partial pressure can be taken for the detected abnormality.

  In the first embodiment and the complete dead end system, substantially all of the fuel (hydrogen in the first embodiment) supplied to the anode of the fuel cell is consumed by the power generation reaction. The almost all fuels referred to here are preferably all the fuels supplied except for the fuel that has leaked out of the anode electrode via the seal structure or the electrolyte membrane.

(Second modification)
In the first embodiment, the pressure difference ΔP is measured using the differential pressure gauge 24. However, the present invention is not limited to this. One pressure gauge may be attached to each of the supply pipe 14 and the exhaust pipe 20, and the ECU 30 may calculate the difference between the pressure values indicated by these two pressure gauges.

(Third Modification)
In the first embodiment, the unit cell 2 includes a counter flow channel. However, the present invention is not limited to this. Even when the unit cell 2 is provided with a co-flow channel, it is possible to detect abnormality based on the pressure difference ΔP.

  The co-flow channel is a channel configured such that the gas flow in the fuel gas channel and the gas flow in the oxidizing gas channel are in the same direction. The co-flow channel is the same as the counter-flow channel in that impurities tend to accumulate downstream of the fuel gas channel.

  In addition to the counter flow channel and the co-flow channel, for example, the fuel gas channel and the oxidizing gas channel cross each other with the membrane electrode assembly 40 sandwiched between the unit cells 2. There is a gas flow path that is configured (also referred to as a cross flow flow path). The cross-flow channel is the same as the counter-flow channel in that impurities tend to accumulate downstream of the fuel gas channel. Even for such a cross flow channel, abnormality detection based on the pressure difference ΔP is possible.

Embodiment 2. FIG.
When flooding occurs, the power generation state in the unit cell 2 changes, and the gas consumption tendency in the surface of the unit cell 2 changes. As a result, the pressure difference ΔP changes. In the second embodiment, using this point, flooding inside the fuel cell 10 is detected based on the pressure difference ΔP.

[Configuration of Embodiment 2]
FIG. 7 is a diagram illustrating a configuration of the unit cell 202 according to the second embodiment. Similar to the first embodiment, the fuel cell system according to the second embodiment includes a unit cell 202 having a counterflow channel. Similar to the unit cell 2, the unit cell 202 includes a membrane electrode assembly 240, a fuel gas channel 242, and an oxidizing gas channel 244.

  The fuel cell system according to the second embodiment has the same configuration as that of the first embodiment except that the unit cell 2 is replaced with the unit cell 202. For this reason, the illustration of the system configuration of the second embodiment is omitted, and description will be made with reference to FIG. 1 as necessary.

[Abnormality detection of the second embodiment]
In the second embodiment, flooding inside a fuel cell is detected for a fuel cell having a counter flow channel. Details of the abnormality detection according to the second embodiment will be described below with reference to FIGS.

  8 shows the current density distribution (FIG. 8 (a)), hydrogen flow rate distribution (FIG. 8 (b)), and unit cell 2 when the inlet-outlet direction of the fuel gas passage 242 is taken along the horizontal axis. The gas pressure distribution in the fuel gas flow path 242 (FIG. 8C) is schematically shown. A solid line indicates a normal state, and a broken line indicates a state when flooding occurs. FIG. 9 is a flow diagram showing the results of the inventor's consideration regarding the process of state change in the fuel gas flow path 242.

  In the unit cell 202 having a counter flow channel, the outlet of the oxidizing gas channel 244 faces the inlet of the fuel gas channel 242 as shown in FIG. On the cathode side, air flows while containing power generation product water. For this reason, the outlet side of the oxidizing gas channel 244 is in a relatively high humidity state. Due to the influence of the movement of moisture through the membrane electrode assembly 240, the inlet portion of the fuel gas flow path 242 also has a lot of moisture. As described above, in the unit cell 202 including the counter flow channel, flooding is likely to occur at the inlet portion of the fuel gas channel 242.

  When flooding occurs at the inlet portion of the fuel gas flow channel 242, the power generation reaction of the membrane electrode assembly 240 at the inlet portion of the fuel gas flow channel 242 is inhibited (step 250 in FIG. 9). As a result, as shown by the broken line in FIG. 8A, the current density increases in the downstream portion of the fuel gas flow path 242 (step 252 in FIG. 9). That is, the current density is biased to the downstream side of the fuel gas flow path 242, contrary to the case of the first embodiment.

If power generation is hindered, the amount of hydrogen consumed also decreases, so that the amount of consumed hydrogen becomes minute or zero at the inlet portion of the fuel gas flow path 242. For this reason, as shown by the broken line in FIG. 8B, in the normal case where no flooding occurs in the inlet portion of the fuel gas flow path 242 (specifically, the region having a length of Δl ₂ from the inlet). In comparison, the flow rate of hydrogen is maintained at a large value (step 254 in FIG. 9).

The pressure loss experienced during the flow of hydrogen through the fuel gas flow path increases as the hydrogen flow rate increases. For this reason, when flooding occurs, the tendency of hydrogen pressure drop becomes more prominent as compared to the normal state (solid line) before the occurrence of flooding, as schematically shown by a broken line in FIG. As a result, when flooding occurs at the inlet portion of the fuel gas flow path 242, as schematically shown in FIG. 8C, the pressure difference at the inlet / outlet of the unit cell 2 is greater than ΔP ₀ before the occurrence of flooding. _{Becomes a} large _ΔPer2 . Accordingly, the pressure difference ΔP between the upstream and downstream sides of the fuel cell 10 increases (step 256 in FIG. 9).

  As described above, the pressure difference between the gas upstream and downstream of the fuel gas flow path 242 increases with the bias in the current density distribution accompanying the occurrence of flooding. Therefore, in the second embodiment, flooding is detected based on the increase width of the pressure difference ΔP.

  Specifically, first, a numerical range that can be indicated by the value of the pressure difference ΔP in a situation where it is determined that flooding has not occurred is specified in advance by experiment or simulation, and the upper limit value of the pressure difference ΔP is determined based on this range. Decide. This upper limit value is used as a determination value (flooding determination value) for use in determining flooding. During the power generation of the fuel cell 10, the flooding judgment value is compared with the pressure difference ΔP measured by the differential pressure gauge 24. When the pressure difference ΔP increases to exceed the flooding determination value, it can be determined that flooding has occurred inside the fuel cell 10.

  As described above, according to the second embodiment, by focusing on the pressure difference ΔP, the flooding in the fuel cell 10 can be detected when the current density distribution is biased. Therefore, flooding can be detected at an early stage.

[Specific Processing of Embodiment 2]
FIG. 10 is a flowchart of a routine executed in the fuel cell system of the second embodiment. In the routine shown in FIG. 10, first, similarly to the routine of the first embodiment shown in FIG. 5, the processes of step S100 and step S102 are sequentially executed.

Next, it is determined whether or not the pressure difference ΔP exceeds the flooding determination value (step S274). In this step, first, ECU 30 refers to the map of the flooding decision value _{[Delta] P Th_f} predetermined acquires flooding determination value _{[Delta] P Th_f} (I) according to the current output current value I is detected in step S100 . Hereinafter, for the sake of simplicity, the flooding determination value is also simply referred to as “determination value”.

FIG. 11 is a map that defines the relationship between the determination value ΔP _{th_f} and the output current value, which is used in the specific processing of the second embodiment. As shown in FIG. 11, a determination value ΔP _{th_f} (I ₂ ) is acquired according to the current output current value I ₂ .

The map of the determination value ΔP _{th_f} can be created by the following procedure, for example. First, in advance, the value of the pressure difference ΔP at the time of occurrence of flooding is grasped by experiments and simulations, and the allowable range of the pressure difference ΔP is determined. The upper limit value of the allowable range is set as a determination value ΔP _{th_f} . In the second embodiment, as shown in FIG. 11, the map is created so that the determination value ΔP _{th_f} takes a larger value as the output current value I of the fuel cell 10 is larger.

As described in the first embodiment, as the output current value I increases, the flow rate of hydrogen flowing into the fuel gas passage 242 per unit time increases. In the second embodiment, considering this point as in the first embodiment, the determination value ΔP _{th_f} is set to be larger as the output current value I of the fuel cell 10 is larger. As a result, the abnormality determination can be performed with high accuracy. In addition, the dotted line shown in FIG. 11 schematically illustrates ΔP _std which is a reference pressure difference value.

If the condition in step S274 is negative, it is determined that the pressure difference ΔP indicates a value within the allowable range, and the current routine ends. In this case, ΔP exists in a region below the plane of the paper with _{respect to} the straight line ΔP _{th_f} as described using the map of FIG.

When the condition of step S274 is satisfied, it is determined that flooding has occurred in the fuel cell 10 (step S276). In this case, ΔP exists in a region above the paper surface with _{respect to} the straight line ΔP _{th_f} as described using the map of FIG. In this step, as in step S106 of the first embodiment, the determination that flooding is occurring at the present time is determined. That is, an abnormality in the fuel cell 10 is detected.

  Subsequent to step S276, processing for increasing the air stoichiometric ratio is executed (step S278). In this step, the air compressor 34 is raised to a predetermined rotational speed to sufficiently increase the amount of air flowing into the cathode. This increases the stoichiometric ratio of the cathode and reduces the amount of diffusion water from the cathode to the anode. As a result, flooding can be reduced or eliminated. Thereafter, the current routine ends.

  According to the above processing, occurrence of flooding of the fuel cell 10 can be detected based on the value of the pressure difference ΔP. Flooding mitigation control is performed for the detected abnormality, and appropriate measures can be taken for the abnormality.

[Modification of Embodiment 2]
(First modification)
The second embodiment can be applied to a complete dead-end system as in the first embodiment.

(Second modification)
In the second embodiment, flooding is detected for a fuel cell having a counter flow channel. On the other hand, in the second modification, flooding is detected for a fuel cell having a coflow channel.

  FIG. 12 shows a unit cell 280 having a coflow channel. The fuel cell system according to the second modification is obtained by replacing the unit cell 2 with the unit cell 280 in the fuel cell system according to the second embodiment. Therefore, the system configuration diagram is omitted, and the unit cell 280 will be mainly described below. Similar to the unit cell 202, the unit cell 280 includes a membrane electrode assembly 240, a fuel gas channel 282, and an oxidizing gas channel 284.

  In the co-flow channel, the outlet of the oxidizing gas channel 284 faces the outlet of the fuel gas channel 282. For this reason, both the outlet side of the oxidizing gas channel 284 and the outlet side of the fuel gas channel 282 are in a relatively high humidity state. As a result, unlike the case of the counter flow channel, in the case of the co-flow channel, flooding is likely to occur at the outlet portion of the fuel gas channel 282.

  If flooding occurs at the outlet portion of the fuel gas channel 282, the power generation reaction at the outlet portion is hindered. As a result, the current density increases in the downstream portion of the fuel gas flow path 242. Such a bias in the current density distribution causes the same phenomenon as described with reference to FIG. 3 in the first embodiment. As a result, the pressure difference ΔP decreases.

  Therefore, in the case of the co-flow channel, the lower limit value of the numerical value range that can be indicated by the pressure difference ΔP under the condition that the flooding is not generated is set as the flooding determination value. Instead of step S274 in FIG. 10, it may be determined whether or not the pressure difference ΔP is less than the flooding determination value.

  As described above, according to the second modification, flooding inside the fuel cell can be detected for the co-flow type fuel cell. When flooding is detected, control for mitigating or eliminating flooding is executed as in the second embodiment.

Embodiment 3 FIG.
When a part of the membrane electrode assembly 40 is excessively dried, the resistance value of the part becomes large and power generation is inhibited. Such a phenomenon is called dry-up. When dry-up occurs, the power generation distribution inside the fuel cell is different from the normal state, and as a result, the gas consumption tendency inside the fuel cell changes. As a result, the pressure difference changes. Therefore, Embodiment 3 uses this point to detect dry-up inside the fuel cell based on the pressure difference ΔP.

  The configuration of the third embodiment is the same as that of the second embodiment. Therefore, the description is omitted.

  In the third embodiment, the dry-up inside the fuel cell is detected for a fuel cell having a counter flow channel. In the unit cell 202 having a counter flow channel (see FIG. 7), the inlet of the oxidizing gas channel 244 faces the outlet of the fuel gas channel 242. The inlet of the oxidizing gas channel 244 is relatively easy to dry. For this reason, the part sandwiched between the oxidizing gas flow path 244 inlet side and the fuel gas flow path 242 outlet side of the membrane electrode assembly 40 is in a relatively easy state to dry.

  When a part of the membrane electrode assembly 40 is excessively dried to increase the resistance value, the power generation in that part is hindered (dry up). As described above, in the unit cell 202 including the counter flow channel, dry-up easily occurs at the outlet portion of the fuel gas channel 242.

  If dry-up occurs at the outlet portion of the fuel gas channel 242, the power generation reaction at the outlet portion is hindered. As a result, the current density increases in the upstream portion of the fuel gas passage 242. Such a bias in the current density distribution causes the same phenomenon as described with reference to FIG. 3 in the first embodiment. As a result, the pressure difference ΔP decreases.

  Therefore, in the third embodiment, first, a numerical range that can be indicated by the value of the pressure difference ΔP in a situation where it is determined that dry-up has not occurred is specified in advance by experiment or simulation, and the pressure difference is determined based on this range. A lower limit value of ΔP is determined in advance. This lower limit is set as a determination value (dry-up determination value) for use in dry-up detection. During the power generation of the fuel cell 10, the dry-up determination value is compared with the pressure difference ΔP measured by the differential pressure gauge 24. When the pressure difference ΔP decreases to be lower than the dry-up determination value, it can be determined that dry-up has occurred inside the fuel cell 10.

  As described above, according to the third embodiment, by paying attention to the pressure difference ΔP, it is possible to detect the dry-up in the fuel cell 10 when the current density distribution is biased. Therefore, dry-up can be detected at an early stage.

[Specific Processing of Embodiment 3]
FIG. 13 is a flowchart of a routine executed in the fuel cell system according to the third embodiment. In the routine shown in FIG. 13, first, similarly to the routine of the first embodiment shown in FIG. 5, the processes of step S100 and step S102 are sequentially executed.

Next, it is determined whether or not the pressure difference ΔP is below the dry-up determination value (step S304). In this step, first, ECU 30 refers to the map of the dry-up determination value _{[Delta] P Th_d} predetermined, acquires the dry-up determination value _{ΔP th_d} (I) according to the current output current value detected in step S100 To do. Hereinafter, for simplicity, the dry-up determination value is also simply referred to as “determination value”. _{Similar to} the map of the lower limit value ΔP th — _l shown in FIG. 6, the map of the determination value ΔP th — _d can be determined so as to take a larger value as the output current value I increases.

  If the condition in step S304 is negative, it is determined that the pressure difference ΔP indicates a value within the allowable range, and the current routine ends.

  If the condition in step S304 is satisfied, it is determined that dry-up has occurred in the fuel cell 10 (step S306). In this step, as in step S106 of the first embodiment, the determination that dry-up is occurring at the present time is determined.

  Subsequent to step S306, dry-up mitigation control is executed (step S308). In the third embodiment, the opening degree of the hydrogen pressure regulating valve 8 is adjusted to be tight. This lowers the total hydrogen pressure to increase the flow rate and promotes water movement. As a result, dry-up can be reduced or eliminated. In this step, for example, a target value of the anode pressure that can sufficiently promote water movement is grasped in advance, and the opening degree of the hydrogen pressure control valve 8 is feedback-controlled so as to be the target value. Also good. After step S308 is executed, the current routine ends.

  According to the above processing, the occurrence of dry-up of the fuel cell 10 can be detected based on the value of the pressure difference ΔP. It is possible to perform dry-up mitigation control for the detected abnormality and take appropriate measures for the abnormality.

[Modification of Embodiment 3]
(First modification)
The third embodiment can be applied to a fuel cell having a coflow channel. Here, description will be made on the assumption that the unit cell 280 of FIG. In the case of the co-flow channel, the opposite relationship is established as in the case of the counter-flow channel. That is, in the case of the co-flow channel, the inlet portion of the fuel gas channel is easily dried.

  If the inlet portion of the fuel gas channel 282 is excessively dried and dry-up occurs, the current density is relatively increased at the position on the outlet side of the fuel gas channel 282 accordingly. Such a bias in the current density distribution causes the same phenomenon as described with reference to FIG. 8 in the second embodiment. As a result, the pressure difference ΔP increases.

  Therefore, in the case of the co-flow channel, the upper limit value in the numerical range that can be indicated by the pressure difference ΔP under the condition where dry-up has not occurred is set as the flooding determination value. Instead of step S304 in FIG. 13, a comparison process between the dry-up determination value and the pressure difference ΔP may be executed. As described above, according to the second modification, it is possible to determine whether or not dry-up has occurred inside the fuel cell for the fuel cell having the co-flow channel. When the occurrence of dry-up is detected, control for mitigating or eliminating dry-up is executed as in the third embodiment.

Embodiment 4 FIG.
The fourth embodiment can distinguish and detect a fuel deficiency abnormality that occurs downstream of the fuel gas flow path and other abnormalities such as dry-up and flooding.

[Configuration of Embodiment 4]
FIG. 14 is a diagram showing a configuration of the fuel cell system according to the fourth embodiment. The fuel cell system of the fourth embodiment has the same configuration as that of the first embodiment except that the exhaust pipe 20 is provided with a hydrogen concentration sensor 350. Therefore, the unit cell 2 of Embodiment 4 has a counterflow channel.

  The hydrogen concentration sensor 350 is connected to the ECU 30. ECU 30 detects the hydrogen concentration of the anode off-gas discharged from fuel cell 10 based on the output of hydrogen concentration sensor 350.

[Abnormality detection of the fourth embodiment]
As described in the first embodiment, when an impurity accumulates on the downstream side of the fuel gas passage 42 and a fuel deficiency abnormality occurs, the tendency of hydrogen consumption changes and the pressure difference ΔP finally decreases. .

  By the way, as described in the third embodiment, in the case of the counter flow channel, dry-up is likely to occur at the outlet portion of the fuel gas channel 42. When dry-up occurs at the outlet portion of the fuel gas passage 42, the current density in the upstream portion of the fuel gas passage 42 increases, and the pressure difference ΔP decreases due to the influence.

  Thus, in the case of the counterflow channel, both the fuel deficiency abnormality and the dry-up work to reduce the pressure difference ΔP. For this reason, when abnormality detection is performed based only on the decrease width of the pressure difference ΔP, it is difficult to distinguish between the fuel deficiency abnormality and the dry-up.

  In the exhaust pipe 20, anode off-gas exhausted from the anode of the fuel cell 10 exists. The anode off gas in the exhaust pipe 20 contains hydrogen although it is a very small amount. When the fuel deficiency abnormality occurs, the downstream side of the fuel gas passage 42 is occupied by nitrogen or the like, so that the hydrogen concentration of the anode off gas further decreases (hereinafter, the hydrogen concentration of the anode off gas is also referred to as “exhaust hydrogen concentration”).

  Therefore, in the fourth embodiment, when the exhaust hydrogen concentration is significantly decreased, it is determined that a fuel deficiency abnormality has occurred. Thereby, it is possible to distinguish and detect the fuel deficiency abnormality and the dry-up.

[Specific processing of the fourth embodiment]
Hereinafter, specific processing executed by the fuel cell system according to Embodiment 4 will be described. FIG. 15 is a flowchart of specific processing executed by the fuel cell system according to Embodiment 4. In the routine shown in FIG. 15, first, similarly to the routine of the first embodiment shown in FIG. 5, the processes of step S100 and step S102 are sequentially executed.

  Next, in the routine of FIG. 15, processing for detecting the exhaust hydrogen concentration is executed (step S380). In this step, the ECU 30 acquires the current exhaust hydrogen concentration based on the output of the hydrogen concentration sensor 350.

  Next, it is determined whether or not the exhaust hydrogen concentration is below a predetermined value (step S382). This predetermined value is determined based on a value obtained by measuring the exhaust hydrogen concentration in a situation where a fuel deficiency abnormality has occurred in advance through experiments or the like, and by obtaining this measurement.

  If the condition of step S382 is satisfied, it is determined that a fuel deficiency abnormality has occurred (step S384), and the exhaust gas flow rate is increased (step S386). As a result, similar to steps S106 and S108 in the specific processing of the first embodiment, the abnormality is detected and the abnormality is dealt with. Thereafter, the current routine ends.

  If the condition in step S382 is negative, it is then determined whether or not the pressure difference ΔP is below the dry-up determination value (step S304). Subsequent to this step, the routine is the same as that described in the third embodiment.

  According to the above processing, when performing abnormality detection based on the pressure difference ΔP for a unit cell having a counterflow channel, it is possible to distinguish between fuel deficiency abnormality and dry-up.

  In the first embodiment, the exhaust hydrogen concentration is first detected, and then the pressure difference ΔP is determined. However, the present invention is not limited to this. The order may be reversed. That is, the pressure difference ΔP may be determined first, and then the exhaust hydrogen concentration may be determined to distinguish the fuel deficiency abnormality from the dry-up.

[Modification of Embodiment 4]
(First modification)
The contents of Embodiment 4 can be applied to a fuel cell having a co-flow channel. As described in the first modification of the second embodiment, in the case of a coflow channel, when flooding occurs, the pressure difference ΔP decreases. For this reason, in the case of the coflow channel, both the fuel deficiency abnormality and the flooding work to reduce the pressure difference ΔP. Therefore, in the first modification, under such circumstances, the fuel deficiency abnormality is detected separately from flooding.

  Specifically, in the configuration shown in FIG. 14, unit cell 2 is replaced with unit cell 280. After changing steps S304, S306 and S308 for this system, the routine of FIG. 15 is executed. The content of step S304 is replaced with a determination process for determining whether or not the pressure difference ΔP is below a predetermined flooding determination value. Step S306 is replaced with a process for determining flooding, and step S308 is replaced with a process for increasing the air stoichiometric ratio.

  According to the above processing, when performing abnormality detection based on the pressure difference ΔP for a unit cell having a coflow channel, it is possible to distinguish between fuel deficiency abnormality and flooding. Furthermore, it is possible to take appropriate measures for the detected abnormality.

Embodiment 5 FIG.
Embodiment 5 relates to control at the time of startup of a fuel cell system. The fifth embodiment has the same configuration as the first embodiment. For this reason, illustration is abbreviate | omitted.

  In the fuel cell system, the cathode side gas enters the anode through the electrolyte membrane. Such gas intrusion can occur even when the fuel cell system is stopped. For this reason, in a fuel cell system, an impurity gas such as nitrogen may be filled in the anode when the system is started. In order for the fuel cell to generate electric power satisfactorily, hydrogen needs to be sufficiently distributed in the anode. For this reason, at the time of starting the fuel cell system, an operation of replacing the impurity gas in the anode with hydrogen is performed (hereinafter, this operation is also referred to as “gas replacement”).

  In the fifth embodiment, this gas replacement is performed as follows. First, when the system is started, power generation is performed with the power generation amount suppressed to a low level, and the pressure difference ΔP is monitored. Further, when the system is started, exhaust by the exhaust valve 22 is performed at a predetermined exhaust flow rate.

  Here, the exhaust flow rate at the time of starting the system can be determined as follows. FIG. 16 is a diagram schematically showing the gas distribution state in the fuel cell 10 at the time of system startup. In FIG. 16, for the sake of convenience, the anode space in the fuel cell 10 is regarded as one flow path, and the most upstream position of the anode is described as 0 and the most downstream position of the anode is described as 1. Immediately after the system is started, as shown in FIG. 16, there is sufficient hydrogen upstream of the anode, and nitrogen occupies a large volume (hereinafter referred to as “nitrogen amount V (L)”) on the downstream side of the anode. The exhaust flow rate may be determined so as to discharge the sum of the nitrogen amount V (L) and the nitrogen permeation amount from the cathode.

  As described in the first embodiment, as the amount of the impurity gas remaining in the downstream of the fuel gas flow path 42 increases, the current density distribution in the unit cell 2 is biased toward the upstream side. The difference ΔP is reduced. On the other hand, if the amount of the impurity gas decreases due to the exhaust of the exhaust valve 22 after startup, the current density distribution is less biased, and the pressure difference ΔP increases accordingly.

In the fifth embodiment, when the pressure difference ΔP exceeds a predetermined value ΔP _{th_start} preset as a threshold value, it is determined that hydrogen has sufficiently spread to the anode of the fuel cell 10. That is, it is determined that the gas replacement is completed. The value of ΔP _{th_start} may be set in advance by, for example, measuring a pressure difference ΔP when hydrogen sufficiently reaches the anode downstream side of the fuel cell 10. After the determination of gas replacement completion is made, the fuel cell system of Embodiment 5 starts power generation in earnest. That is, it shifts to a normal power generation state. The exhaust flow rate of the exhaust valve 22 thereafter can be set to the exhaust flow rate in the exhaust mode described in the first embodiment, for example.

  According to the fifth embodiment described above, the completion timing of gas replacement can be grasped, and the exhaust by the exhaust valve 22 can be performed in an appropriate amount when the system is activated. Therefore, gas replacement at the time of starting the system can be performed while suppressing wasteful discharge of hydrogen.

Note that Embodiments 1 to 4 described above may be used in combination. For example, when the first embodiment and the second embodiment are combined, the pressure difference ΔP falls within a predetermined numerical range defined by the flooding determination value and the lower limit value set for detecting the fuel deficiency abnormality. What is necessary is just to determine whether it exists. That is, it may be determined whether or not the pressure difference ΔP is within a specific range defined by ΔP _{th — 1 in} FIG. 6 and ΔP th — _f in FIG.

It is a figure which shows typically the structure of the fuel cell system of Embodiment 1 of this invention. 2 is a diagram showing an internal structure of a unit cell 2 constituting the fuel cell 10. FIG. FIG. 6 is a diagram for explaining details of abnormality detection according to the first embodiment; FIG. 6 is a diagram for explaining details of abnormality detection according to the first embodiment; 3 is a flowchart of specific processing executed by the fuel cell system according to Embodiment 1. ₆ is a map that defines the relationship between the lower limit value ΔP th — _l and the output current value, which is used in the specific processing of the first embodiment. 6 is a diagram illustrating a configuration of a unit cell 202 according to Embodiment 2. FIG. FIG. 9 is a diagram for explaining details of abnormality detection according to the second embodiment. FIG. 9 is a diagram for explaining details of abnormality detection according to the second embodiment. 5 is a flowchart of a routine that is executed in the fuel cell system according to the second embodiment. ₇ is a map that defines the relationship between a determination value ΔP _{th_f} and an output current value, which is used in specific processing according to the second embodiment. It is a figure which shows the unit cell 280 which has a coflow channel. 10 is a flowchart of a routine that is executed in the fuel cell system according to the third embodiment. FIG. 6 is a diagram showing a configuration of a fuel cell system according to a fourth embodiment. 10 is a flowchart of specific processing executed by the fuel cell system according to Embodiment 4. It is the figure which represented typically the gas distribution state in the fuel cell 10 at the time of system starting.

Explanation of symbols

2, 202, 280 Unit cell 8 Pressure regulating valve 10 Fuel cell 12 Hydrogen tank 14 Supply pipe 16 Hydrogen pressure regulating valve 20 Exhaust pipe 22 Exhaust valve 24 Differential pressure gauge 26 Ammeter 32 Air supply pipe 34 Air compressor 36 Cathode exhaust pipe 40, 240 Membrane Electrode assembly 42, 242 and 282 Fuel gas flow path 44, 244 and 284 Oxidation gas flow path 350 Hydrogen concentration sensor ΔP Pressure difference ΔP _{th_l} lower limit value ΔP _{th_d} dry-up determination value ΔP _{th_f} flooding determination value

Claims (6)

A fuel cell having a power generation body that receives power from the supply of fuel gas, and a fuel gas passage that extends along the surface of the power generation body while being in contact with the power generation body;
A fuel gas supply mechanism for supplying fuel gas to the fuel gas flow path,
The dead-end operation state in which the operation is performed by closing the downstream side of the fuel gas flow path, and the amount of gas discharged from the downstream side of the fuel gas flow path is set to the amount of gas flowing into the fuel gas flow path. A fuel cell system capable of realizing at least one operation state among a small amount exhaust operation state in which operation is performed with a minute amount compared to the above,
further,
Measuring means capable of measuring the difference between the pressure of the gas upstream of the fuel gas flow path and the pressure of the gas downstream of the fuel gas flow path;
Detecting means for detecting an abnormality of the fuel cell based on the pressure difference measured by the measuring means;
With
When the magnitude of the pressure difference measured by the measuring means is below a predetermined lower limit value, the detecting means determines that an abnormality in which fuel is deficient has occurred downstream of the fuel gas flow path. Including fuel deficiency detection means,
The detection means includes dry-up detection means for detecting the occurrence of dry-up in the fuel cell based on a comparison between the magnitude of the pressure difference measured by the measurement means and a predetermined dry-up determination value. A fuel cell system. The detection means includes flooding detection means for detecting the occurrence of flooding in the fuel cell based on a comparison between the magnitude of the pressure difference measured by the measurement means and a predetermined flooding judgment value. The fuel cell system according to claim 1 . The fuel cell system according to claim 1 or 2 ,
further,
Concentration detection means for detecting the fuel concentration in the gas downstream of the fuel gas flow path,
The fuel cell system, wherein the detection means determines whether or not an abnormality in which fuel is deficient has occurred downstream of the fuel gas flow path, based on the fuel concentration detected by the concentration detection means. Claim 1, wherein the predetermined lower limit value, characterized in that it is determined from the fuel gas supply mechanism to take the larger the value flow rate is high per unit time of the gas supplied to the fuel gas flow passage 4. The fuel cell system according to any one of items 1 to 3 . The flooding determination value, to claim 2, characterized in that are determined from the fuel gas supply mechanism to take the larger the value flow rate is high per unit time of the gas supplied to the fuel gas flow passage The fuel cell system described. Claim 1, wherein the dry-up determination value, characterized in that it is determined from the fuel gas supply mechanism to take the larger the value flow rate is high per unit time of the gas supplied to the fuel gas flow passage The fuel cell system according to any one of 1 to 5 .

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