JP2009211940A - Fuel cell in-plane state estimation system and fuel cell in-plane state estimation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply accurately estimate an in-plane state of a membrane electrode assembly in a fuel cell. <P>SOLUTION: The membrane electrode assembly is virtually divided into a plurality of small regions arranged in a line along the flow of reaction gas. The current density I in each small region (n region) is calculated based on the power generation environment in each region, and the reaction gas consumption and the water generation is calculated based on the current density I. The movement of each gas component from the n region to the downstream n+1 region dn_H2_An, dn_N2_An, dn_H2O_An and the liquid water movement dn_liqH2O_An are also calculated according to each movement characteristic. Power generation environment where the n region is placed is updated based on each gas component movement and liquid water movement from an upstream n-1 region to the n region, each gas component movement and liquid water movement from the n region to a downstream n+1 region, and the reaction gas consumption and water generation in the n region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell in-plane state estimation system and estimation method, and more particularly to an in-plane state estimation system and estimation method for accurately estimating a current distribution in a plane of a membrane electrode assembly constituting a fuel cell. .

  Japanese Unexamined Patent Application Publication No. 2005-347016 discloses a method for easily predicting the in-plane state of a membrane electrode assembly of a fuel cell. Specifically, the above publication discloses a method of creating a model obtained by reducing the prediction of a membrane electrode assembly to be predicted to 1 / n and predicting the in-plane state using this model.

  In the conventional prediction method, the in-plane state of the membrane electrode assembly is predicted by an existing calculation method. Since the calculation method used here should be developed with enormous adaptation work etc., the development requires a long period of time. If the prediction calculation is performed using the 1 / n reduced model, the development time of the calculation method can be remarkably reduced as compared with the case of performing the full size prediction. In this respect, the conventional prediction method is effective as a method for easily predicting the in-plane state of the membrane electrode assembly.

JP 2005-347016 A

  However, the phenomenon that occurs in the 1 / n reduction model does not exactly match the phenomenon that occurs in a full-size membrane electrode assembly. For this reason, the conventional prediction method cannot accurately predict the in-plane state that occurs in an actual membrane electrode assembly. That is, the above conventional method leaves room for improvement in terms of prediction accuracy.

  The present invention has been made to solve the above-described problems, and provides an in-plane state estimation system and an estimation method that can easily and accurately estimate the in-plane state of a membrane electrode assembly of a fuel cell. The purpose is to do.

In order to achieve the above object, a first invention is a system for estimating an in-plane state of a fuel cell,
A membrane electrode assembly of a fuel cell that generates power by receiving supply of a reaction gas to each of an anode and a cathode;
A power generation characteristic storage means for storing a power generation characteristic defining a relationship between a power generation amount of the membrane electrode assembly and a power generation environment;
Consumption generation characteristic storage means for storing consumption generation characteristics defining the relationship between the amount of reaction gas consumption and water generation amount of the membrane electrode assembly and the amount of power generation;
Gas movement characteristic storage means for storing movement characteristics of gas components along the flow of the reaction gas;
Liquid water movement characteristic storage means for storing liquid water movement characteristics along the flow of the reaction gas;
A small region defining means for virtually dividing the membrane electrode assembly into a plurality of small regions arranged along the flow of the reaction gas;
A power generation amount calculating means for calculating a power generation amount in each of the plurality of small regions based on the power generation characteristics based on a power generation environment in which the small region is placed;
A consumption generation amount calculating means for calculating a reaction gas consumption amount and a water generation amount in each of the plurality of small regions according to the consumption generation characteristic based on the power generation amount generated in the small region;
For each of the plurality of small areas, a gas movement amount calculating means for calculating the movement amount of each gas component from the small area to the small area located downstream of the flow of the reaction gas according to the gas movement characteristics;
For each of the plurality of small areas, a liquid water movement amount calculating means for calculating the movement amount of liquid water from the small area to the small area located downstream of the flow of the reaction gas according to the liquid water movement characteristics;
The power generation environment in which each of the plurality of small areas is placed is based on the movement amount of each gas component and the movement amount of liquid water between adjacent small areas, and the reaction gas consumption amount and the water generation amount in the small area. Power generation environment updating means for updating
It is characterized by having.

The second invention is the first invention, wherein
The power generation environment updating means adds the amount of liquid water existing in each of the plurality of small regions to the amount of liquid water transferred from the small region located upstream of the flow of the reaction gas to the amount of liquid water existing in the small region. Further, the present invention is characterized in that the liquid water transfer amount to a small area located downstream of the flow of the reaction gas is updated by subtracting from the liquid water amount existing in the small area.

The third invention is the second invention, wherein
Generation evaporation characteristic storage means for storing generation evaporation characteristics defining the relationship between the generation or evaporation amount of liquid water in the membrane electrode assembly and the power generation environment;
Liquid water generation evaporation amount calculating means for calculating the liquid water generation amount or liquid water evaporation amount in each of the plurality of small regions according to the generation evaporation characteristics based on the power generation environment in which the small region is placed. ,
The power generation environment updating means adds the amount of liquid water existing in each of the plurality of small regions, adds the amount of liquid water generated in the small regions to the amount of liquid water present in the small regions, or evaporates liquid water in the small regions. The quantity is updated by subtracting from the quantity of liquid water present in the small area.

In addition, a fourth invention is any one of the first to third inventions,
The liquid water transfer characteristic is characterized in that the amount of liquid water transferred from each small region to a small region located downstream of the flow of the reaction gas is related to the flow rate of the gas component in the small region.

The fifth invention is the invention according to any one of the first to fourth inventions,
The liquid water movement characteristic is characterized in that the movement amount of liquid water from each small region to the small region located downstream of the flow of the reaction gas is related to the pressure difference between the small regions.

Further, the sixth invention is the invention according to any one of the first to fifth inventions,
The liquid water movement characteristic is characterized in that the amount of liquid water transferred from each small region to a small region located downstream of the flow of the reaction gas is related to the amount of liquid water existing in the small region.

The seventh invention is the invention according to any one of the first to sixth inventions,
The liquid water movement characteristic is characterized in that the movement amount of liquid water from each small region to a small region located downstream of the flow of the reaction gas is associated with the flow path shape of the small region.

Further, an eighth invention is any one of the first to seventh inventions,
Water crossing movement characteristic storage means for storing water crossing movement characteristics that define the relationship between the amount of water that moves across the membrane electrode assembly from the cathode to the anode of the membrane electrode assembly and the power generation environment;
A water crossing movement amount calculating means for calculating a water crossing movement amount in each of the plurality of small areas based on the water crossing movement characteristic based on a power generation environment in which the small area is placed;
The power generation environment update means updates the power generation environment in which each of the plurality of small areas is placed, reflecting the amount of water crossing movement in the small area.

A ninth invention is a method for estimating an in-plane state of a fuel cell in order to achieve the above object,
Supplying a reactive gas to the anode and cathode of the membrane electrode assembly of the fuel cell,
A small region defining step of virtually dividing the membrane electrode assembly into a plurality of small regions arranged along the flow of the reaction gas;
Power generation amount for calculating the power generation amount in each of the plurality of small regions based on the power generation environment in which the small region is placed according to the power generation characteristics that define the relationship between the power generation amount of the membrane electrode assembly and the power generation environment A calculation step;
In accordance with the consumption generation characteristics that define the relationship between the reaction gas consumption amount and the water generation amount of the membrane electrode assembly and the power generation amount, the reaction gas consumption amount and the water generation amount in each of the plurality of small regions A consumption generation amount calculating step for calculating based on the power generation amount generated in
For each of the plurality of small areas, the amount of movement of each gas component from the small area to the small area located downstream of the flow of the reactive gas is calculated according to the movement characteristics of the gas component along the flow of the reactive gas. A gas transfer amount calculation step;
A liquid that calculates the amount of liquid water transferred from the small area to the small area located downstream of the reactive gas flow for each of the plurality of small areas in accordance with the liquid water movement characteristics along the flow of the reactive gas. A water transfer amount calculation step;
The power generation environment in which each of the plurality of small areas is placed is based on the movement amount of each gas component and the movement amount of liquid water between adjacent small areas, and the reaction gas consumption amount and the water generation amount in the small area. Power generation environment update step to be updated,
It is characterized by including.

The tenth invention is the ninth invention, wherein
The power generation environment update step includes:
The amount of liquid water present in each of the plurality of small regions is added to the amount of liquid water transferred from the small region located upstream of the flow of the reaction gas to the amount of liquid water present in the small region, and the flow of the reaction gas And a step of updating by subtracting the liquid water movement amount to the small area located downstream of the liquid area from the liquid water amount existing in the small area.

The eleventh aspect of the invention is the tenth aspect of the invention,
According to the generation evaporation characteristic that defines the relationship between the generation or evaporation amount of liquid water in the membrane electrode assembly and the power generation environment, the generation amount of liquid water or the evaporation amount of liquid water in each of the plurality of small regions Including a liquid water generation evaporation amount calculating step for calculating based on the power generation environment where
The power generation environment update step includes:
The amount of liquid water existing in each of the plurality of small regions is added to the amount of liquid water generated in the small region, or the amount of liquid water evaporated in the small region is present in the small region. And a step of updating by subtracting from the amount of liquid water to be performed.

  According to the first invention, the power generation amount in each of the virtually divided small areas can be obtained based on the power generation environment in which the small areas are placed. The power generation environment includes the amount of reaction gas and the amount of liquid water that inhibits the diffusion of reaction gas, but these amounts in each small area change due to power generation and also due to movement between adjacent small areas. Change. According to the first invention, when the amount of power generation is known, the reaction gas consumption amount and the water generation amount generated in the small region can be calculated based on the consumption generation characteristics. Further, the movement amount of the gas component between the small areas can be calculated based on the gas movement characteristic, and the movement amount of the liquid water between the small areas can be calculated based on the liquid water movement characteristic. For each small region, the amount of reaction gas consumption and water production generated in the small region, the amount of reaction gas and liquid water transferred from the previous stage to the small region, the reaction gas and liquid water transferred from the small region to the subsequent stage By knowing each quantity, it is possible to always accurately grasp the power generation environment in which each small area is placed. Therefore, according to the present invention, the in-plane power generation amount distribution in the membrane electrode assembly can be accurately estimated by accurately grasping the power generation environment in each of the plurality of small regions.

  According to the second invention, for each of the plurality of small areas, the balance between the liquid water movement amount from the small area located on the upstream side and the liquid water movement amount to the small area located on the downstream side is obtained. Can do. By knowing the balance of the liquid water movement amount, it becomes possible to accurately estimate the liquid water amount existing in each small area. In other words, according to the present invention, the in-plane liquid water amount distribution in the membrane electrode assembly can be accurately estimated.

  According to the third aspect of the invention, the generation amount of liquid water or the evaporation amount of liquid water in each small region is accurately predicted by using the generation evaporation characteristic that defines the relationship between the generation or evaporation amount of liquid water and the power generation environment. can do. If the amount of liquid water generated or the amount of liquid water evaporation can be predicted, the amount of liquid water existing in each small area can be estimated more accurately.

  According to the fourth invention, it is possible to accurately estimate the liquid water movement amount between the small regions by associating the liquid water movement amount from each small region with the flow velocity of the gas component in the small region.

  According to the fifth invention, it is possible to accurately estimate the liquid water movement amount between the small regions by associating the liquid water movement amount from each small region with the pressure difference between the small regions.

  According to the sixth aspect of the invention, by associating the liquid water movement amount from each small region with the liquid water amount existing in the small region, the liquid water movement between the small regions when the in-plane liquid water amount distribution is not uniform. The quantity can be estimated accurately.

  According to the seventh invention, the liquid water movement amount from each small region is associated with the channel shape of the small region, so that when the channel shape changes in the direction of the reaction gas flow, It is possible to accurately estimate the amount of liquid water movement.

  According to the eighth invention, by using the water crossing movement characteristic that defines the relationship between the water crossing movement amount from the cathode to the anode and the power generation environment, the water crossing movement amount in each small region can be accurately predicted. Can do. Since the power generation environment changes according to the amount of water moved across the membrane electrode assembly, according to the present invention, the power generation environment in which each small region is placed is predicted by predicting the amount of water crossing movement. Can be grasped more accurately.

  According to the ninth aspect of the present invention, the amount of reaction gas consumed and the amount of water produced in each region, the amount of reaction gas and liquid water transferred from the previous stage to the small region, the reaction gas from the small region to the subsequent stage, and Based on the movement amount of liquid water, it is possible to accurately grasp the power generation environment in which each small region is placed, thereby accurately estimating the in-plane power generation amount distribution in the membrane electrode assembly.

  According to the tenth invention, the in-plane liquid water amount distribution in the membrane electrode assembly can be accurately estimated.

  According to the eleventh aspect, the amount of liquid water existing in each small region can be estimated more accurately by predicting the amount of liquid water generated or the amount of liquid water evaporation in each small region.

Embodiment 1 FIG.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the spirit of the present invention.

[Configuration of FC system]
FIG. 1 is a diagram for explaining the configuration of the FC system according to the embodiment of this invention. The FC system shown in FIG. 1 includes a fuel cell 2. The fuel cell 2 includes a plurality of laminated membrane electrode assemblies. The membrane electrode assembly is a plate-like structure having a spread in the depth direction of the sheet of FIG. An anode and a cathode are formed inside the membrane electrode assembly with the electrolyte membrane interposed therebetween. On the anode side, there is formed a gas flow path for allowing a fuel gas containing hydrogen (in this embodiment, hydrogen gas) to flow in the plane. In addition, a gas flow path for allowing an oxidizing gas containing oxygen (in this embodiment, air) to flow in the plane is formed on the cathode side. Furthermore, each membrane electrode assembly is isolated from the adjacent membrane electrode assembly by a current collector plate having a cooling water passage formed therein. Since the configurations of the fuel cell 2 and the membrane electrode assembly are known, further description is omitted here.

  In the FC system, the fuel cell 2 is controlled by the ECU 6 via a plurality of FC system auxiliary devices 4. The FC system auxiliary device 4 includes a compressor that supplies air to the cathode of the fuel cell 2, a humidifier that humidifies the air, a back pressure adjusting valve disposed in an off-gas passage from the cathode, and supply of hydrogen gas to the anode Devices such as a supply pressure adjusting valve for adjusting the pressure and an exhaust valve arranged in an off gas passage from the anode are included. In the case of an FC system in which hydrogen gas is circulated, circulation equipment such as a circulation pump and an ejector is also included in the FC system auxiliary device 4.

  The FC system is provided with a plurality of sensors 8 for acquiring the operating state of the fuel cell 2. The sensor 8 includes a pressure gauge and a dew point meter provided in an air supply passage connected to the fuel cell 2, a pressure gauge provided in an air off-gas discharge passage, a pressure gauge and a dew point meter provided in a hydrogen supply passage, A pressure gauge provided in the hydrogen off-gas discharge passage and a thermometer arranged in the cooling water discharge passage are included.

[Estimation of in-plane state of membrane electrode assembly]
The ECU 6 acquires information on the pressure and temperature inside the fuel cell 2 from the outputs of the various sensors 8, and based on the information, the in-plane state of each membrane electrode assembly, specifically, the in-plane related to the power generation amount. The state is estimated. Hereinafter, a method for estimating the in-plane state of the membrane electrode assembly employed in the FC system of the present embodiment will be described.

  The ECU 6 estimates the in-plane state of the membrane electrode assembly by simulation (hereinafter referred to as state estimation simulation). A model of a membrane electrode assembly is used for the state estimation simulation. As shown in FIGS. 2 and 3, this model is obtained by virtually dividing a membrane electrode assembly (MEA) into a plurality of small regions along the flow path of the reaction gas. FIG. 2 is a two-dimensional model in which the surface of the membrane electrode assembly is divided along the flow path of the reaction gas, and FIG. 3 is a one-dimensional model in which the two-dimensional model is developed along the flow path. As shown in this one-dimensional model, the fuel cell 2 of the present embodiment has a counter flow channel in which the cathode side gas and the anode side gas flow opposite to each other with the membrane electrode assembly interposed therebetween.

  The membrane electrode assembly generates power at a current density corresponding to the power generation environment in the plane. “Power generation environment” is a general term for a plurality of parameters that determine the power generation state of the membrane electrode assembly among various parameters representing the in-plane state of the membrane electrode assembly. In the state estimation simulation by the ECU 6, it is assumed that the power generation environment in which each small area of the divided model shown in FIGS. 2 and 3 is placed is uniform in each small area, and the power generation environment estimation calculation is performed for each small area. Is done.

  The power generation environment includes the relative humidity of the anode side gas, the relative humidity of the cathode side gas, the anode pressure, the cathode pressure, the hydrogen concentration in the anode side gas, the oxygen concentration in the cathode side gas, the amount of liquid water in the anode, The amount of liquid water and the temperature of the membrane electrode assembly are included. Of these parameters, the anode pressure and the cathode pressure are approximately the same pressure. In addition, the influence of the former on the power generation state is sufficiently smaller than the influence of the latter. For this reason, in this embodiment, the influence of the anode pressure is ignored. Of the above parameters, the hydrogen concentration is almost 100% regardless of the position, and the temperature is almost the same as the cooling water temperature regardless of the position. For this reason, in this embodiment, the hydrogen concentration and temperature are also treated as constant values.

  Therefore, the parameters to be considered in the state estimation simulation are the relative humidity of the anode side gas, the relative humidity of the cathode side gas, the cathode pressure, the oxygen concentration in the cathode side gas, the amount of liquid water in the anode, and the amount of liquid water in the cathode. . The ECU 6 stores a map (power generation characteristic map) that defines the relationship between the power generation environment determined by these parameters and the current density. The ECU 6 also stores a map (water crossing movement characteristic map) that defines the relationship between the amount of water moving across the membrane electrode assembly from the cathode to the anode of the membrane electrode assembly and the power generation environment. Yes. Further, the ECU 6 also stores a map (consumption generation characteristic map) that defines the relationship between the current consumption and the oxygen consumption, hydrogen consumption, water generation amount and current density.

  If the power generation environment in which each small area is placed is specified, the current density generated in the power generation environment can be predicted by referring to the power generation characteristic map. Further, by referring to the water crossing movement characteristic map, it is possible to predict the amount of water crossing movement that occurs in the power generation environment. When the current density is specified by the power generation characteristic map, the oxygen consumption amount, the hydrogen consumption amount, and the water generation amount in the power generation environment can be predicted by referring to the consumption generation characteristic map.

  Oxygen consumption, hydrogen consumption, water production, and water crossing movement are all factors that affect the power generation environment. In addition to these, other factors that affect the power generation environment include each gas component and each amount of liquid water moved from a small region located upstream of the reaction gas flow, and downstream of the reaction gas flow. Each movement amount of each gas component and liquid water to a small area is included. In the state estimation simulation, the values of these factors are acquired for the individual small areas, and the power generation environment in which the individual small areas are placed is updated based on the values.

[Specific method for renewing power generation environment]
The content of the power generation environment update performed in the state estimation simulation will be specifically described with reference to FIG. FIG. 4 is a diagram for explaining a procedure for updating the power generation environment in which the n region is placed, taking an arbitrary small region (n region) of the division model as an example. In the state estimation simulation, each small region is divided into a cathode (Ca) side and an anode (An) side. Each small area has a state quantity (number of moles) of each component existing therein as an internal parameter. Specifically, as shown in FIG. 4, the n region has an oxygen amount n_O2_Ca, a nitrogen amount n_N2_Ca, a water vapor amount n_gasH2O_Ca, and a liquid water amount n_liqH2O_Ca as cathode state quantities, and a hydrogen amount n_H2_An as anode state quantities. , Nitrogen amount n_N2_An, water vapor amount n_gasH2O_An, and liquid water amount n_liqH2O_An.

  The n region also has the pressure P, volume V, and temperature T of the region as internal parameters. The volume V is a preset fixed value, and the temperature T is the same constant value as the cooling water temperature. The pressure P can be calculated by the equation of state (PV = nRT).

  In the state estimation simulation, the relative humidity of the anode side gas, the relative humidity of the cathode side gas, and the oxygen concentration in the cathode side gas in the n region are calculated using the plurality of state quantities. Each relative humidity can be calculated from the water vapor partial pressure P_H2O and the temperature T. The oxygen concentration can be calculated from the ratio of the oxygen amount n_O2_Ca to the amount (number of moles) of all gas components on the cathode side.

  Thus, by specifying the relative humidity of the anode side gas, the relative humidity of the cathode side gas, the cathode pressure, the oxygen concentration in the cathode side gas, the amount of anode liquid water, and the amount of cathode liquid water in the n region, The power generation environment in which the n region is placed is specified. In the state estimation simulation, the current density I in the n region is specified by comparing the specified power generation environment with the above-described power generation characteristic map. Then, by comparing the current density I with the above-described consumption generation characteristic map, the oxygen consumption amount and water generation amount on the cathode side in the n region and the hydrogen consumption amount on the anode side are specified. Further, the cross-H2O water crossing movement amount from the cathode side to the anode side in the n region is specified by collating the specified power generation environment with the water crossing movement characteristic map described above. Note that the oxygen consumption, hydrogen consumption, water generation amount, and water crossing movement amount are all amounts per predetermined calculation interval.

  In the state estimation simulation, in parallel with the above calculation of each consumption generation amount, or before and after the calculation, the movement amount (moles) of each component from the n region to the n + 1 region downstream thereof per calculation time. Number). Specifically, as shown in FIG. 4, the oxygen transfer amount dn_O2_Ca, the nitrogen transfer amount dn_N2_Ca, the water vapor transfer amount dn_gasH2O_Ca, and the transfer amount dn_liqH2O_Ca are calculated on the cathode side, and the hydrogen transfer amount dn_H2_An and nitrogen transfer are calculated on the anode side. The amount dn_N2_An, the water vapor transfer amount dn_gasH2O_An, and the liquid water transfer amount dn_liqH2O_An are calculated.

  It should be noted here that in the counterflow channel employed by the fuel cell 2 of the present embodiment, the n + 1 region on the cathode side and the n + 1 region on the anode side are not in a reverse relationship. The same applies to the n-1 region. It is only the n region that is the object of calculation that the anode side and the cathode side are in the relationship of front and back with the membrane electrode assembly interposed therebetween. In FIG. 4, since the gas flow on the cathode side and the gas flow on the anode side are drawn in the same direction, it seems that the cathode side and the anode side correspond to each other in the n + 1 region and the n−1 region. Actually, the n + 1 region on the anode side corresponds to the n + 1 region on the cathode side, and the n + 1 region on the anode side corresponds to the n-1 region on the cathode side. If the cathode side gas and the anode side gas flow in parallel, the n + 1 region on the cathode side and the n + 1 region on the anode side have a front / back relationship. The same applies to the n-1 region. The present invention can also be applied to a fuel cell having a coflow channel.

In calculating the movement amount of each component, different logic is used for the gas component and liquid water. Specifically, as schematically shown in FIG. 5, it is assumed that the liquid water moves at a speed of k times the gas component. k is a positive value smaller than 1, and for example, a value obtained in advance by experiment can be used. When the moving speed of liquid water is V_liq and the moving speed of gas components is V_gas, the relationship is expressed by the following equation (1). The ECU 6 stores the rule indicated by the expression (1) as the liquid water transfer characteristic.
V_liq = k × V_gas (1)

  The gas moving speed V_gas is calculated from the pressure difference between the n region and the n + 1 region. The ECU 6 stores a rule defining the relationship between the pressure difference and the gas moving speed V_gas as a gas moving characteristic. The gas moving speed V_gas is calculated separately on the anode side and the cathode side, and the liquid water moving speed V_liq is calculated separately on the anode side and the cathode side accordingly. That is, the amount of movement of each gas component on the cathode side is calculated from the gas movement speed V_gas_An on the cathode side and the amount of each gas component, and from the liquid water movement speed V_liq_Ca and the amount of liquid water n_liqH2O_Ca on the cathode side The liquid water transfer amount dn_liqH2O_Ca is calculated. Further, the movement amount of each gas component on the anode side is calculated from the gas movement speed V_gas_Ca on the anode side and the amount of each gas component. From the liquid water movement speed V_liq_An on the anode side and the liquid water amount n_liqH2O_An, the anode side The liquid water transfer amount dn_liqH2O_An is calculated.

  In addition, the liquid water movement logic (this is called the liquid water movement logic 1) used by said calculation is only an example of the logic which can be taken in implementation of this invention. In addition to this, for example, logic as schematically shown in FIGS. 6, 7, and 8 can be employed.

FIG. 6 is a diagram schematically showing the liquid water transfer logic 2. In the liquid water movement logic 2, the liquid water (droplet) is moved by a pressure difference before and after the position where the liquid water exists, that is, a pressure difference between the n region and the n + 1 region. In this case, when the moving speed of liquid water is V_liq and the pressure difference is ΔP, the relationship is expressed by the following equation (2). As the value of the coefficient k, for example, a value obtained in advance by experiments can be used. When the liquid water transfer logic 2 is employed, the ECU 6 stores the rule indicated by the expression (2) as the liquid water transfer characteristic.
V_liq = k × ΔP (2)

  FIG. 7 is a diagram schematically showing the liquid water transfer logic 3. In the liquid water transfer logic 3, it is assumed that the liquid water locally inhibits the diffusion of gas and thereby the pressure rises locally, thereby moving the liquid water. In other words, when the gas is difficult to flow, the pressure Pn in the n region increases, and as a result, the pressure difference ΔP before and after the liquid water increases and the liquid water transfer amount increases. This logic can be realized by taking into account gas diffusion inhibition by liquid water in the calculation of the gas flow amount required when calculating the pressure difference ΔP of the above equation (2).

FIG. 8 is a diagram schematically showing the liquid water transfer logic 4. In the liquid water movement logic 4, it is assumed that the movement amount of liquid water depends on the size of the liquid water and the shape of the flow path. The reason for considering the size of the liquid water is that the propulsive force received by the pressure difference between the front and rear becomes larger as it is larger. The reason for considering the shape of the flow path is that when the straight part and the turn part of the flow path are compared, liquid water is likely to accumulate in the turn part and the liquid water is less likely to move than the straight part. When this logic is adopted, the coefficient k in the above equation (1) or (2) may be set according to the following equation (3).
k = k ′ × S × N (3)

  K ′ in the above formula (3) is a basic value of the coefficient, and corresponds to the coefficient k described in the formula (1) or the formula (2). S is a parameter corresponding to the amount of liquid water or the cross-sectional area of the liquid water in the gas flow direction. The cross-sectional area of the liquid water can be calculated from the amount of liquid water and the water repellency parameter (a value corresponding to the contact angle of the droplet). The larger the amount of liquid water and the larger the water repellency parameter, the larger the liquid-water cross-sectional area. N is a parameter corresponding to the shape of the flow path. The value of N is set to 1 in the straight part and is smaller than 1 in the turn part. FIG. 8 shows the value of the coefficient k when the n-1 region is a turn portion and the n region and the n + 1 region are straight portions.

  The above is an explanation of the calculation of the amount of liquid water and gas component movement from the n region to the n-1 region. However, in the state estimation simulation, each small region has its components downstream from the small region. The amount of movement is calculated. Therefore, the movement amount (outflow amount) of each substance from the n region to the n-1 region is calculated, and the movement amount (inflow amount) of each substance from the upstream n-1 region to the n region is also calculated. Has been.

  In addition, in the state estimation simulation, the amount of nitrogen that moves across the membrane electrode assembly from the cathode to the anode of the membrane electrode assembly is calculated. This amount of crossing nitrogen is determined by the partial pressure difference between the nitrogen partial pressure on the cathode side and the nitrogen partial pressure on the anode side. The ECU 6 stores a map (nitrogen crossing movement characteristic map) that defines the relationship between the nitrogen crossing movement amount and the partial pressure difference of nitrogen.

  Through the above series of calculations, the amount of reaction gas consumed and the amount of water produced in the n region, the amount of movement of each component from the preceding n-1 region to the n region, and the movement of each component from the n region to the subsequent n + 1 region The amount of each component and the amount of movement of each component between the anode and the cathode in the n region are determined. By reflecting these consumption generation amount and movement amount on the state amount of each component in the n region, it is possible to grasp the latest state amount of each component.

  However, regarding water vapor and liquid water among the components, it is necessary to consider that condensation from water vapor to liquid water occurs due to the power generation environment in the n region, and conversely, evaporation from liquid water to water vapor occurs. is there. Assuming that all the water present in the cathode or anode in the n region is water vapor, if the relative humidity at that time exceeds 100%, condensation of water vapor occurs, and if the relative humidity is less than 100%, Water evaporation occurs. In the state estimation simulation, the liquid water generation amount or liquid water evaporation amount per calculation step time is calculated, and in addition to the above-mentioned various consumption generation amounts and movement amounts, the liquid water generation evaporation amount is reflected and n Update the state quantity of each component in the region.

The liquid water generation evaporation rate calculation logic described below is used for calculating the liquid water generation evaporation amount. In this logic, the liquid water generation rate Vc is defined by the following equation (4). In Equation (4), k is a coefficient, and σc is the degree of supersaturation.
Vc = k × σc (4)

The coefficient k in the above equation (4) is defined by the following equation (5). In Equation (5), α is a value corresponding to a change in enthalpy of water condensation, β is a value corresponding to a change in entropy of water condensation, T is a temperature, w is a liquid water amount, and θ is a water repellency parameter (contact of a droplet). Value corresponding to an angle).
kc = (α−T × β) × (w × θ) (5)

  As shown in the above equation (5), the coefficient kc depends on the temperature factor, the amount of liquid water, and the water repellency factor. The temperature factor α−T × β corresponds to the free energy change amount ΔG = ΔH−T × ΔS. Since the condensation of water is an exothermic reaction, ΔH is a negative value. Further, since the volume is reduced by condensation, ΔS becomes a negative value. Therefore, the smaller the temperature T is, the smaller the value of ΔG is, so that water is likely to condense. The amount of liquid water and the water repellency factor correspond to the surface area (liquid water generation area) of the liquid water. If the water repellency is good, the liquid water tends to be spherical and the surface area is small, so that the water is unlikely to condense. Conversely, if the water repellency is poor, the liquid water tends to be flat and the surface area becomes large, so water condensation tends to occur.

The degree of supersaturation σc in the above equation (5) is defined by the following equation (6). % RH is the relative humidity when all moisture is considered as water vapor.
σc =% RH−100 (6)

In this logic, the liquid water evaporation rate Ve is defined by the following equation (7). In Equation (7), k is a coefficient defined by Equation (3) described above, and σe is the degree of unsaturation.
Ve = k × σe (7)

  As described above, the temperature factor of the coefficient k corresponds to the free energy change amount ΔG = ΔH−T × ΔS. Since the evaporation of water is an exothermic reaction, ΔH has a positive value. Further, since the volume increases by evaporation, ΔS becomes a positive value. Therefore, the greater the temperature T, the smaller the value of ΔG, and water evaporation tends to occur.

The degree of unsaturation σe in the equation (7) is defined by the following equation (8). % RH is the relative humidity when all moisture is considered as water vapor.
σc = 100−% RH (8)

  In the state estimation simulation, for each of the cathode side and the anode side, it is determined whether or not the relative humidity when all the moisture is considered as water vapor exceeds 100%. For example, when the relative humidity on the cathode side exceeds 100%, the liquid water generation rate Vc is obtained according to the above equation (4), and the liquid water generation amount per calculation interval is calculated based on this. Then, the calculated liquid water generation amount is subtracted from the water vapor amount n_gasH2O_Ca and added to the liquid water amount n_liqH2O_Ca. On the other hand, for example, if the relative humidity on the cathode side is less than 100%, the liquid water evaporation rate Ve is obtained according to the above equation (7), and the liquid water evaporation amount per calculation time is calculated based on this. Then, the calculated liquid water evaporation amount is subtracted from the liquid water amount n_liqH2O_Ca and added to the water vapor amount n_gasH2O_Ca. ECU6 has memorize | stored each rule which said Formula (4) and Formula (7) shows as a production | generation evaporation characteristic.

In addition, the said Formula (4) and Formula (7) are the formula which deform | transformed the exact formula which shows the production | generation rate and evaporation rate of liquid water. The exact formula is, for example, a formula used for meteorology and numerical modeling of precipitation formation as shown in the following formula (9). In Equation (9), Xw is the mass of liquid water, rd is the radius of liquid water, Dv is the water vapor molecular diffusion coefficient, and dρv / dr is the water vapor density gradient on the surface of the liquid water. You may calculate liquid water production | generation amount and liquid water evaporation amount using such exact | strict expressions.
dXw / dt = 4 × π × rd ² × Dv × (dρv / dr) (9)

[Estimated results of in-plane state of membrane electrode assembly]
According to the state estimation simulation described above, it is possible to always accurately grasp the power generation environment in which each small area of the divided model is placed. Then, by accurately grasping the power generation environment in each small region, the power generation amount distribution in the surface of the membrane electrode assembly can be accurately estimated.

  Further, according to the above-described state estimation simulation, the in-plane distribution of various parameter values related to the power generation environment can be obtained. The amount of liquid water, which is one of such parameters, is a particularly important parameter that serves as an index value for flooding. FIG. 9 shows an in-plane distribution of the amount of liquid water obtained by the above-described state estimation simulation. By obtaining the amount of liquid water for each small region, it is possible to accurately grasp at which position in the surface the liquid water is accumulated and to what extent.

  The liquid water accumulated in the surface inhibits the diffusion of the reaction gas and generates an abnormal potential in the membrane electrode assembly. FIG. 10 is a diagram illustrating the relationship between the amount of liquid water in a small region and the amount of hydrogen supplied to the small region. When the amount of liquid water increases to a certain extent, the amount of hydrogen supplied to the catalyst layer of the membrane electrode assembly, that is, the amount of effective hydrogen supplied to the reaction, decreases rapidly as the amount of liquid water increases. The relationship between the liquid water amount and the effective hydrogen amount varies depending on the shape of the flow path. In FIG. 10, the solid line indicates the relationship at the straight line portion, and the broken line indicates the relationship at the turn portion. Since liquid water and gas are separated into an outer side and an inner side in the turn part, the decrease in the effective hydrogen amount with the same liquid water quantity is smaller than that in the straight part.

  FIG. 11 is a diagram illustrating the relationship between the amount of liquid water in a small region and the abnormal potential generated in the small region. As the amount of liquid water increases, the amount of effective hydrogen decreases. As a result, the abnormal potential increases as the amount of liquid water increases. When the amount of liquid water exceeds a certain threshold value (threshold value shown in FIG. 9), the abnormal potential exceeds a threshold value that is a measure of damage to the membrane electrode assembly (for example, deterioration of the catalyst). That is, flooding has occurred.

[Fuel cell control flow by ECU]
FIG. 12 is a flowchart of a routine executed by the ECU 6 in order to reflect the above estimation result in the control of the fuel cell 2. The routine shown in FIG. 12 is started when the fuel cell 2 is started, and is repeatedly executed with the above-described calculation step time as one cycle.

  In the routine shown in FIG. 12, first, a state estimation simulation is executed (step S101). And the estimation result of the liquid water amount state in the surface of a membrane electrode assembly is output (step 102). Next, it is determined whether or not a gas shortage avoidance operation is necessary based on the estimation result (step S103). The necessity of the gas shortage avoidance operation is determined by the presence or absence of a small region where the liquid water amount exceeds the threshold value. As shown by the solid line in FIG. 9, if there is even a small area where the amount of liquid water exceeds the threshold, it is determined that the gas shortage avoidance operation is necessary. The gas shortage avoidance operation is one of the operation modes of the fuel cell 2 and is an operation mode for avoiding a gas shortage caused by flooding, that is, a shortage of reaction gas necessary for the catalytic reaction.

  If the result of determination in step S103 is that no out-of-gassing avoidance operation is required, processing returns to step S101 and a state estimation simulation is executed. On the other hand, when it is determined that the gas shortage avoidance operation is necessary, the operation condition of the fuel cell 2 is changed to the condition for the gas shortage avoidance operation. Note that the content of the gas shortage avoidance operation differs depending on whether the gas shortage occurs on the cathode side or the anode side. In the case of cathode gas shortage, as a gas shortage avoidance operation, it is possible to increase the cathode stoichiometric ratio by increasing the rotational speed of the compressor, or increase the opening of the back pressure adjustment valve to decrease the cathode back pressure. Done. On the other hand, in the case of lack of anode gas, as a gas shortage avoidance operation, the anode stoichiometric ratio is increased by increasing the opening of the supply pressure adjusting valve, the anode back pressure is lowered by opening the exhaust valve, or For example, the humidification amount of air by the humidifier is reduced.

  By executing the above routine, it is possible to reduce the amount of liquid water to below the threshold value as shown by the broken line in FIG. 9 and to reliably avoid out of gas due to flooding. In addition, since the execution of the gas shortage avoidance operation, which is an operation under special operation conditions, can be minimized, the fuel consumption can be improved by the operation under the optimized operation conditions.

It is a figure for demonstrating the structure of the FC system of embodiment of this invention. It is a figure which shows the two-dimensional model which divided | segmented the surface of a membrane electrode assembly (MEA) used along the flow path of a reactive gas used in the state estimation simulation of embodiment of this invention. It is the one-dimensional model which developed the two-dimensional model shown in FIG. 2 along the flow path. It is a figure for demonstrating the procedure of the update of the electric power generation environment where the arbitrary small area | regions (n area | region) of the division | segmentation model shown in FIG.2 and FIG.3 are set | placed. It is a figure for demonstrating the liquid water movement logic 1 used in embodiment of this invention. It is a figure for demonstrating the liquid water movement logic 2 used in embodiment of this invention. It is a figure for demonstrating the liquid water movement logic 3 used in embodiment of this invention. It is a figure for demonstrating the liquid water movement logic 4 used in embodiment of this invention. It is a figure which shows in-plane distribution of the amount of liquid water obtained by the state estimation simulation of embodiment of this invention. It is a figure which shows the relationship between the amount of liquid water in the small area | region of the division | segmentation model shown in FIG.2 and FIG.3, and the hydrogen amount supplied to the small area | region. It is a figure which shows the relationship between the amount of liquid water in the small area | region of the division | segmentation model shown in FIG.2 and FIG.3, and the abnormal electric potential which generate | occur | produces in the small area | region. It is a flowchart of the routine which ECU performs in order to reflect the estimation result by the state estimation simulation of embodiment of this invention in control of a fuel cell.

Explanation of symbols

2 Fuel cell 4 FC system auxiliary 6 ECU
8 Sensor I Current density R Resistance
n_O2_Ca Oxygen content
n_H2_An Hydrogen amount
n_N2_Ca, n_N2_An Nitrogen content
n_liqH2O_Ca, n_liqH2O_An Liquid water volume
n_gasH2O_Ca, n_gasH2O_An amount of water vapor
dn_O2_Ca Oxygen transfer
dn_H2_An Hydrogen transfer amount
dn_N2_Ca, dn_N2_An Nitrogen transfer
dn_liqH2O_Ca, dn_liqH2O_An Liquid water transfer amount
dn_gasH2O_Ca, dn_gasH2O_An Water vapor transfer amount
cross_H2O Cross-water travel

Claims (11)

A membrane electrode assembly of a fuel cell that generates power by receiving supply of a reaction gas to each of an anode and a cathode;
A power generation characteristic storage means for storing a power generation characteristic defining a relationship between a power generation amount of the membrane electrode assembly and a power generation environment;
Consumption generation characteristic storage means for storing consumption generation characteristics defining the relationship between the amount of reaction gas consumption and water generation amount of the membrane electrode assembly and the amount of power generation;
Gas movement characteristic storage means for storing movement characteristics of gas components along the flow of the reaction gas;
Liquid water movement characteristic storage means for storing liquid water movement characteristics along the flow of the reaction gas;
A small region defining means for virtually dividing the membrane electrode assembly into a plurality of small regions arranged along the flow of the reaction gas;
A power generation amount calculating means for calculating a power generation amount in each of the plurality of small regions based on the power generation characteristics based on a power generation environment in which the small region is placed;
A consumption generation amount calculating means for calculating a reaction gas consumption amount and a water generation amount in each of the plurality of small regions according to the consumption generation characteristic based on the power generation amount generated in the small region;
For each of the plurality of small areas, a gas movement amount calculating means for calculating the movement amount of each gas component from the small area to the small area located downstream of the flow of the reaction gas according to the gas movement characteristics;
For each of the plurality of small areas, a liquid water movement amount calculating means for calculating the movement amount of liquid water from the small area to the small area located downstream of the flow of the reaction gas according to the liquid water movement characteristics;
The power generation environment in which each of the plurality of small areas is placed is based on the movement amount of each gas component and the movement amount of liquid water between adjacent small areas, and the reaction gas consumption amount and the water generation amount in the small area. Power generation environment updating means for updating
A fuel cell in-plane state estimation system comprising:   The power generation environment updating means adds the amount of liquid water existing in each of the plurality of small regions to the amount of liquid water transferred from the small region located upstream of the flow of the reaction gas to the amount of liquid water existing in the small region. 2. The fuel cell in-plane according to claim 1, wherein the amount of liquid water transferred to a small area located downstream of the flow of the reaction gas is updated by subtracting from the amount of liquid water existing in the small area. State estimation system. Generation evaporation characteristic storage means for storing generation evaporation characteristics defining the relationship between the generation or evaporation amount of liquid water in the membrane electrode assembly and the power generation environment;
Liquid water generation evaporation amount calculating means for calculating the liquid water generation amount or liquid water evaporation amount in each of the plurality of small regions according to the generation evaporation characteristics based on the power generation environment in which the small region is placed. ,
The power generation environment updating means adds the amount of liquid water existing in each of the plurality of small regions, adds the amount of liquid water generated in the small regions to the amount of liquid water present in the small regions, or evaporates liquid water in the small regions. The fuel cell in-plane state estimation system according to claim 2, wherein the amount is updated by subtracting the amount from the amount of liquid water existing in the small area.   The liquid water movement characteristic is characterized in that the amount of liquid water moved from each small region to a small region located downstream of the flow of the reaction gas is related to the flow rate of the gas component in the small region. Item 4. The fuel cell in-plane state estimation system according to Item 1 above.   2. The liquid water movement characteristic is characterized in that a movement amount of liquid water from each small region to a small region located downstream of the flow of the reaction gas is related to a pressure difference between the small regions. 5. The fuel cell in-plane state estimation system according to 1 to 4.   The liquid water movement characteristic is characterized in that the amount of liquid water transferred from each small region to a small region located downstream of the flow of the reaction gas is related to the amount of liquid water existing in the small region. Item 6. The fuel cell in-plane state estimation system according to Item 1 above.   The liquid water movement characteristic is characterized in that a movement amount of liquid water from each small region to a small region located on the downstream side of the flow of the reaction gas is associated with a flow path shape of the small region. 7. The fuel cell in-plane state estimation system according to 1 to 6. Water crossing movement characteristic storage means for storing water crossing movement characteristics that define the relationship between the amount of water that moves across the membrane electrode assembly from the cathode to the anode of the membrane electrode assembly and the power generation environment;
A water crossing movement amount calculating means for calculating a water crossing movement amount in each of the plurality of small areas based on the water crossing movement characteristic based on a power generation environment in which the small area is placed;
8. The fuel according to claim 1, wherein the power generation environment updating unit updates the power generation environment in which each of the plurality of small areas is placed, reflecting the amount of water crossing movement in the small area. Battery state estimation system. Supplying a reactive gas to the anode and cathode of the membrane electrode assembly of the fuel cell,
A small region defining step of virtually dividing the membrane electrode assembly into a plurality of small regions arranged along the flow of the reaction gas;
Power generation amount for calculating the power generation amount in each of the plurality of small regions based on the power generation environment in which the small region is placed according to the power generation characteristics that define the relationship between the power generation amount of the membrane electrode assembly and the power generation environment A calculation step;
In accordance with the consumption generation characteristics that define the relationship between the reaction gas consumption amount and the water generation amount of the membrane electrode assembly and the power generation amount, the reaction gas consumption amount and the water generation amount in each of the plurality of small regions A consumption generation amount calculating step for calculating based on the power generation amount generated in
For each of the plurality of small areas, the amount of movement of each gas component from the small area to the small area located downstream of the flow of the reactive gas is calculated according to the movement characteristics of the gas component along the flow of the reactive gas. A gas transfer amount calculation step;
A liquid that calculates the amount of liquid water transferred from the small area to the small area located downstream of the reactive gas flow for each of the plurality of small areas in accordance with the liquid water movement characteristics along the flow of the reactive gas. A water transfer amount calculation step;
The power generation environment in which each of the plurality of small areas is placed is based on the movement amount of each gas component and the movement amount of liquid water between adjacent small areas, and the reaction gas consumption amount and the water generation amount in the small area. Power generation environment update step to be updated,
A fuel cell in-plane state estimation method comprising: The power generation environment update step includes:
The amount of liquid water present in each of the plurality of small regions is added to the amount of liquid water transferred from the small region located upstream of the flow of the reaction gas to the amount of liquid water present in the small region, and the flow of the reaction gas The fuel cell in-plane state estimation method according to claim 9, further comprising a step of updating the amount of liquid water transferred to a small region located downstream of the subregion by subtracting from the amount of liquid water existing in the small region. According to the generation evaporation characteristic that defines the relationship between the generation or evaporation amount of liquid water in the membrane electrode assembly and the power generation environment, the generation amount of liquid water or the evaporation amount of liquid water in each of the plurality of small regions Including a liquid water generation evaporation amount calculating step for calculating based on the power generation environment where
The power generation environment update step includes:
The amount of liquid water existing in each of the plurality of small regions is added to the amount of liquid water generated in the small region, or the amount of liquid water evaporated in the small region is present in the small region. The fuel cell in-plane state estimation method according to claim 10, further comprising a step of updating by subtracting from the amount of liquid water to be performed.

Images