Fuel cell system control method and fuel cell system

Abstract

A control method for controlling a fuel cell system equipped with: a fuel cell that uses, as a fuel, a mixed gas comprising a plurality of types of components; a fuel supply mechanism that is equipped with a fuel tank and supplies the mixed gas to the fuel cell; and a combustor that generates combustion gas for heating air supplied to the fuel cell during startup, wherein the fuel composition and the fuel flow rate to the combustor are set as unknowns, a plurality of conditions for the air flow rate to the combustor are set, the composition ratios of the plurality of types of components constituting the mixed gas are estimated on the basis of simultaneous equations constituted from a first characteristic equation based on a relationship between the amount of air supplied to the combustor and the oxygen concentration in exhaust gas discharged from the combustor and / or a second characteristic equation based on a relationship between the amount of air supplied to the combustor and the temperature of the exhaust gas discharged from the combustor, and a composition equation representing the total composition ratio of the components of the mixed gas, and the flow rate of fuel supplied to the fuel cell is adjusted on the basis of the estimation results.

Description

[Technical Field]

[0001] The present invention relates to a control method for a fuel cell system and a fuel cell system. [Background technology]

[0002] The use of city gas as fuel for fuel cells has been proposed for some time. City gas (mixed gas) can be reformed in a reformer or in a fuel cell with a reforming function and used as fuel. However, city gas is specified by the calorific value per unit volume, and its composition can vary. Therefore, if the composition of city gas changes, the amount of hydrogen produced by reforming also changes, making it difficult to supply the amount of hydrogen required for the fuel cell's required output.

[0003] To solve this problem, JP2005-200260A burns fuel in the combustion section at startup, calculates the heat value per unit amount of fuel supplied at that time, and estimates the number of carbon atoms contained in the fuel based on a diagram prepared in advance. Summary of the Invention

[0004] However, it is difficult to accurately estimate the amount of hydrogen produced by reforming by simply estimating the carbon number as in the above document.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fuel cell system control method and a fuel cell system control device that are capable of accurately estimating the composition of a mixed gas.

[0006] According to one aspect of the present invention, there is provided a control method for controlling a fuel cell system including a fuel cell that uses a mixed gas composed of multiple types of components (saturated hydrocarbons or hydrogen) as fuel, a fuel supply mechanism that includes a fuel tank for storing the mixed gas and supplies the mixed gas to the fuel cell, and a combustor that generates combustion gas to heat air supplied to the fuel cell when the fuel cell is started. The control method uses the fuel composition and the fuel flow rate to the combustor as unknowns, sets multiple conditions for the air flow rate to the combustor, and estimates the composition ratio of the multiple types of components in the mixed gas based on simultaneous equations including at least one of a first characteristic equation based on the relationship between the amount of air supplied to the combustor and the oxygen concentration in the exhaust gas discharged from the combustor, a second characteristic equation based on the relationship between the amount of air supplied to the combustor and the temperature of the exhaust gas discharged from the combustor, and a composition equation that represents the sum of the composition ratios of the multiple types of components in the mixed gas. The flow rate of fuel supplied to the fuel cell is then adjusted based on the estimated composition ratio.

[0007] According to another aspect of the present invention, there is provided a fuel cell system including a fuel cell that uses a mixed gas composed of multiple components (saturated hydrocarbons or hydrogen) as fuel, a fuel supply mechanism that has a fuel tank for storing the mixed gas and supplies the mixed gas to the fuel cell, a combustor that generates combustion gas to heat air supplied to the fuel cell when the fuel cell is started, and a control unit that controls the flow rate of air supplied to the combustor and the flow rate of the mixed gas supplied to the combustor and the fuel cell. The control unit sets multiple conditions for the air flow rate to the combustor, with the fuel composition and the fuel flow rate to the combustor as unknowns, and estimates the composition ratio of the multiple components of the mixed gas based on simultaneous equations including at least one of a first characteristic equation based on the relationship between the amount of air supplied to the combustor and the oxygen concentration in the exhaust gas discharged from the combustor detected by an oxygen concentration sensor, and a second characteristic equation based on the relationship between the amount of air supplied to the combustor and the temperature of the exhaust gas discharged from the combustor detected by a temperature sensor, and a composition equation that represents the sum of the composition ratios of the multiple components of the mixed gas. The control unit then adjusts the flow rate of fuel supplied to the fuel cell based on the estimated composition ratio. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system to which a control method according to a first embodiment is applied. [Figure 2] FIG. 2 is a flowchart showing a control routine for the warm-up control. [Figure 3] FIG. 3 is a diagram showing the relationship between the gas flowing into the combustor 7 and the gas discharged therefrom. [Figure 4] FIG. 4 is a flowchart showing a control routine for composition estimation according to the first embodiment. [Figure 5] FIG. 5 is a table summarizing the heat of combustion, specific heat ratio, and molecular weight of each of the simple chain saturated hydrocarbons that can be contained in the mixed gas. [Figure 6] FIG. 6 is a table summarizing the composition ratio, specific heat ratio term, molecular weight term, and product of the specific heat ratio term and molecular weight term of first to third mixed gases each composed of two types of saturated hydrocarbons. [Figure 7] FIG. 7 is a flowchart showing a control routine for composition estimation according to the second embodiment. [Figure 8] FIG. 8 is a flowchart showing a control routine for composition estimation according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [First embodiment] 1 is a schematic diagram of a fuel cell system 100 to which the control according to this embodiment is applied. The fuel cell system 100 includes a fuel cell (also referred to as a fuel cell stack) 1, a fuel supply mechanism 2 that supplies a mixed gas serving as fuel to the anode of the fuel cell stack 1, a blower 5 that supplies air to the cathode of the fuel cell stack 1, and a controller 11 that controls the entire system. The fuel cell system 100 also includes a combustor 7 that generates combustion gas that heats the air supplied to the fuel cell stack 1 at startup, and a heat exchanger 8 that exchanges heat between the combustion gas generated in the combustor 7 and the air supplied from the blower 5. A gas flow path that discharges exhaust gas from the heat exchanger 8 is provided with a temperature sensor 9 that detects the temperature of the exhaust gas, a pressure sensor 10 that detects the pressure of the exhaust gas, and an oxygen concentration sensor (also referred to as an O2 sensor) 14 that detects the oxygen concentration in the exhaust gas.

[0011] The fuel cell stack 1 is a solid oxide fuel cell (SOFC) equipped with a catalyst on the anode side for reforming the mixed gas, but the reformer may be separate from the SOFC. The fuel cell stack 1 can reform the mixed gas to generate a reformed gas (anode gas) containing hydrogen. The fuel cell stack 1 generates electricity through an electrochemical reaction between the anode gas (hydrogen) and the cathode gas (oxygen) via an electrolyte.

[0012] The fuel supply mechanism 2 includes a fuel tank 3, a main injector 4 that supplies fuel to the fuel cell stack 1, and a startup injector 6 that supplies fuel to the combustor 7. Note that a pressure reducing valve and a pressure sensor (not shown) are installed in the gas flow paths between the fuel tank 3 and the main injector 4 and startup injector 6.

[0013] The fuel tank 3 stores a mixed gas at a predetermined pressure. City gas is used as the mixed gas. City gas may contain multiple types of saturated linear hydrocarbons, but its composition is not specified; instead, it is specified by the calorific value per unit volume. Therefore, when the fuel cell system 100 is installed in a vehicle, filling the vehicle with mixed gas in a different region may result in a change in the composition of the mixed gas in the fuel tank 3 before and after filling. Furthermore, the amount of hydrogen generated by the reforming reaction varies depending on the fuel composition. In other words, even if the fuel flow rate is constant, if the fuel composition changes, the amount of hydrogen supplied to the fuel cell stack 1 also changes, resulting in fluctuations in the output of the fuel cell stack 1. Furthermore, if the amount of hydrogen changes in the direction of a shortage, this may lead to deterioration of the fuel cell stack 1.

[0014] Therefore, in order to supply an amount of hydrogen according to the required output to the fuel cell stack 1, it is necessary to estimate the composition of the mixed gas in the fuel tank 3 with high accuracy.

[0015] The main injector 4 receives a signal from the control unit 11 and adjusts the amount of mixed gas supplied.

[0016] The flow path of the air supplied from the blower 5 includes a flow path that passes through the heat exchanger 8 and flows into the fuel cell stack 1, as well as a bypass flow path 13 that bypasses the heat exchanger 8 and flows into the fuel cell stack 1. A bypass valve 12 is installed in the bypass flow path 13 to adjust the flow rate of air flowing through that flow path.

[0017] The control unit 11 executes warm-up control, normal power generation control, stop control, etc. of the fuel cell stack 1. The normal control and stop control are conventional technologies, so a description thereof will be omitted. The control unit 11 also controls the fuel supply mechanism 2 to control the flow rate of the mixed gas.

[0018] Warm-up control is a control for warming up the fuel cell stack 1 when starting up the fuel cell system 100. Specifically, mixed gas and air are supplied to the combustor 7 and combusted to generate combustion gas, and air supplied from the blower 5 is heated by the combustion gas in the heat exchanger 8, and the heated air is supplied to the fuel cell stack 1. When this warm-up control is performed, the composition of the mixed gas is estimated using a method described below.

[0019] [Warm-up control] 2 is a flowchart showing a control routine for warm-up control executed by the control unit 11. The warm-up control is executed in response to a start request made by the driver or the like.

[0020] In step S100, a heater (not shown) is activated to start heating the combustor 7.

[0021] In step S101, it is determined whether the temperature of the combustor 7 has reached a first temperature. If it has reached a first temperature, the process of step S102 is executed. If it has not reached a first temperature, this determination is repeated. The first temperature here is the temperature at which combustion in the combustor 7 becomes possible.

[0022] In step S102, the mixed gas and air are supplied to the combustor 7 to start combustion. The mixed gas is supplied via the startup injector 6. Air is supplied from the blower 5 via the bypass flow path 13 to the fuel cell stack 1, and the air that has passed through the fuel cell stack 1 is supplied.

[0023] The upper limit of the flow rate (fuel flow rate) of the mixed gas to be supplied at this time is the fuel flow rate assuming that the saturated linear hydrocarbons that make up the mixed gas are methane and ethane, and that the calorific value per unit volume of the mixed gas is the upper limit of the calorific value of the mixed gas used in the region. As mentioned above, city gas is regulated by the calorific value per unit flow rate, so the upper limit of the calorific value can be obtained by storing the calorific value data for each region in the memory of the control unit 11 and comparing it with the location information obtained by a navigation system or the like. The reason for setting such an upper limit is to prevent the combustor 7 from overheating.

[0024] Here, the reason for setting the upper limit of the fuel flow rate as described above will be explained.

[0025] The temperature reached by the combustor 7 is determined by the amount of heat supplied, which is expressed as the product of the amount of heat per unit volume, the fuel flow rate, and time.

[0026] The fuel flow rate passing through the startup injector 6 can be regarded as the flow rate W of the fluid passing through the orifice, and can be expressed by equation (1).

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[0027] In equation (1), γ is a physical property of the fluid (mixed gas). Therefore, if the composition of the mixed gas is unknown, 2γ / (γ-1) on the right-hand side becomes unknown, and the flow rate W cannot be calculated.

[0028] In other words, if the composition of the mixed gas is unknown, the amount of heat per unit volume and the fuel flow rate are unknown, and the amount of heat supplied to the combustor 7 cannot be calculated.

[0029] Therefore, the calorific value per unit volume is assumed to be the upper limit calorific value of the mixed gas used in the area. The flow rate is calculated assuming that the components that make up the mixed gas are methane and ethane. If we make this assumption, since there are two components, the composition ratio can also be determined based on the calorific value per unit volume. Once the composition ratio is determined, the physical property value γ is also determined, and the flow rate can be calculated.

[0030] Here, the reason why the components constituting the mixed gas are assumed to be two components, methane and ethane, will be explained.

[0031] The right-hand side of equation (1) can be expanded as equation (2).

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[0032] In equation (2), the physical properties of the mixed gas are related to the 2 / (1-(1 / γ)) term (hereinafter also referred to as the specific heat ratio term), which is related to the specific heat ratio, and the R / M term (hereinafter also referred to as the molecular weight term), which is related to the molecular weight. The larger the specific heat ratio γ of the mixed gas, the larger the specific heat ratio term. The specific heat ratio γ of the mixed gas is determined according to the composition ratio of the components contained. The smaller the molecular weight M of the mixed gas, the larger the molecular weight term. The molecular weight M is also determined according to the composition ratio of the components contained.

[0033] Figure 5 is a table summarizing the heat of combustion, specific heat ratio, and molecular weight of each of the chain saturated hydrocarbons (methane, ethane, propane, and butane) that can be contained in the mixed gas. As shown in the figure, the lower the carbon number, the higher the specific heat ratio and the lower the heat of combustion and molecular weight. In other words, the more low-carbon components there are, the larger the specific heat ratio and molecular weight terms of the mixed gas.

[0034] Figure 6 is a table summarizing the composition ratio, specific heat ratio term, molecular weight term, and product of the specific heat ratio term and molecular weight term of the first to third mixed gases, which are composed of two types of saturated hydrocarbons. All of the first to third mixed gases have a calorific value per unit volume of 46 MJ / m 3 The first mixed gas is composed of two components, methane and butane, the second mixed gas is composed of two components, methane and propane, and the third mixed gas is composed of two components, methane and ethane. As shown in the figure, the third mixed gas, which has the highest amount of low-carbon components, that is, the mixed gas composed of two components, methane and ethane, has the largest specific heat ratio term and molecular weight term.

[0035] The upper limit of the fuel flow rate is set to prevent excessive temperature rise in the combustor 7, so the upper limit of the fuel flow rate is preferably set to the maximum flow rate among all possible combinations of constituent components. Therefore, the combination that maximizes the product of the specific heat ratio term and the molecular weight term, i.e., the combination of methane and ethane, is selected.

[0036] Returning to the explanation of the flowchart, in step S103, the composition of the mixed gas is estimated by a method to be described later.

[0037] In step S104, the supply of heated air to the fuel cell stack 1 is started. Specifically, by controlling the bypass valve 12 of the bypass flow path 13, air from the blower 5 is supplied to the heat exchanger 8, where heat exchange occurs between the air and the combustion gas generated in the combustor 7. The air heated in the heat exchanger 8 is then supplied to the fuel cell stack 1.

[0038] In step S105, it is determined whether the temperature of the fuel cell stack 1 has reached a second temperature. If it has, this routine ends, i.e., the warm-up control ends. If it has not reached the second temperature, this determination is repeated. The second temperature here is the warm-up completion temperature, i.e., the temperature at which the above-mentioned electrochemical reaction becomes possible.

[0039] [Estimation of mixed gas composition] Here, the composition estimation of the mixed gas executed in step S103 will be described.

[0040] In this embodiment, first, the fuel composition and the fuel flow rate to the combustor 7 are set as unknown quantities. Then, multiple conditions for the air flow rate to the combustor 7 are set, and a simultaneous equation is formulated, which is made up of a first characteristic equation based on the relationship between the amount of air supplied to the combustor 7 and the oxygen concentration in the exhaust gas discharged from the combustor, and a composition equation that represents the sum of the composition ratios of multiple types of components in the mixed gas. The composition ratio of each component is calculated by solving this simultaneous equation.

[0041] The first characteristic equation indicates the relationship (i.e., the law of conservation of mass) that the amount of oxygen in the air supplied to the combustor 7 at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the combustor 7.

[0042] Here, the composition equation and the first characteristic equation will be described with reference to FIG.

[0043] FIG. 3 is a diagram showing the relationship between gas flowing into the combustor 7 and gas discharged from the combustor 7. As shown in the figure, a mixture of air and fuel gas flows into the combustor 7. The air flow rate is Q an and the fuel flow rate is Q f The components of air can be considered to be 79% nitrogen (N2) and 21% oxygen (O2). The mixed gas contains several types of saturated carbon chains, specifically methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H 10 ) etc., with the respective composition ratios being x%, y%, z% etc.

[0044] The composition ratio satisfies the relationship of formula (3).

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[0045] When the components contained in the mixed gas are methane, ethane, and propane, if the combustion in the combustor 7 is complete, the components react as follows. CH4+2O2→CO2+2H2O C2H6+3.5O2→2CO2+3H2O C3H8+5O2→3CO2+4H2O The flow rate Q of the exhaust gas discharged from the combustor 7 out is expressed by equation (4).

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[0046] Furthermore, according to the law of conservation of mass for oxygen described above, the relationship of equation (5) holds. This equation (5) is defined as the first characteristic equation.

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[0047] The unknown fuel flow rate Q f is a fixed value, and the air flow rate Q a is changed to Qa1, Qa2, etc., and the oxygen concentration in the exhaust gas is detected to derive multiple equations (5). Then, the composition ratios x%, y%, and z% are calculated by solving simultaneous equations consisting of the composition equation and multiple equations (5). A specific estimation method will be explained below with reference to FIG. 4.

[0048] FIG. 4 is a flowchart showing the control routine for the composition estimation described above, that is, the control routine executed by the control unit 11 in step S103 of FIG.

[0049] In step S200, the oxygen concentration in the exhaust gas is detected.

[0050] In step S201, the first characteristic equation is derived as Equation (5). In the first calculation, Equation (5) is derived assuming that the only saturated hydrocarbon in the mixed gas is methane. The initial value of the air flow rate Qan in Equation (5) (Q a1 ) is the flow rate at which complete combustion occurs when the fuel flow rate is at the upper limit mentioned above.

[0051] In step S202, the simultaneous equations consisting of the composition equation and equation (5) are solved.

[0052] In step S203, it is determined whether any of the composition ratios of the components is 0%. If there is a component that is 0%, this routine ends and the processing of step S104 in FIG. 1 is executed; if not, the processing returns to step S200.

[0053] In the second and subsequent calculations, the air flow condition, i.e., the air flow rate Q an A, Q a2 , Q a3... and also add the types of components. In other words, by increasing the air flow rate condition, the number of equations (5) required to obtain a solution for the unknowns can be derived without increasing the number of unknowns. At this time, components are added in order of the number of carbon atoms. Also, the air flow rate Q an is the initial value Q a1 When increasing the air flow rate condition, that is, when changing the air flow rate, the change is made by an amount equal to or greater than the lower limit of the resolution of the O2 sensor 14.

[0054] This routine ends when any of the components reaches 0%, because 0% of any of the components means that there are no other components left.

[0055] The estimation of the composition ratio of the mixed gas described above may be performed when the fuel tank 3 is newly filled with the mixed gas. When the fuel cell system 100 is mounted on a vehicle, in order to fill the mixed gas, the vehicle travels to a station that supplies the mixed gas, turns the key off, opens the lid of the fuel tank 3 to fill the mixed gas, closes the lid after filling, turns the key on (i.e., starts the fuel cell system 100), and then travels from the station. The pressure (temperature) of the mixed gas in the fuel tank 3 changes not only due to a decrease in the temperature of the mixed gas after the fuel cell system 100 is shut down, but also due to changes in the outside air temperature. Therefore, the control unit 11 may determine that the mixed gas has been filled when the ratio of the pressure of the fuel tank 3 during the on-state to the pressure of the fuel tank 3 during the off-state exceeds a predetermined value that is equal to or exceeds the ratio caused by changes in the outside air temperature.

[0056] Considering the predetermined value for the ratio, the mixed gas is not released from the fuel tank 3 during the transition from the OFF state to the ON state, and the volume of the fuel tank 3 does not change. Therefore, the pressure p of the mixed gas in the fuel tank 3 during the OFF state off and the pressure p of the mixed gas in the fuel tank 3 during ON operation on is the temperature T of the mixed gas in the fuel tank 3 during off operation. offand the temperature T of the mixed gas in the fuel tank 3 when the ON operation on By P on / P off =T on / T off =(T off + daily range) / T off =1+daily range / T off If we consider the case of Japan, the maximum daily temperature difference (the difference between the highest and lowest temperatures) is 31.5°C (Nagano), and the minimum temperature is -41°C (Asahikawa). Therefore, 1 + daily temperature difference / T off Calculating the ratio of pressures P on / P off If the ratio exceeds 1.14, it can be determined that the fuel tank 3 has just been filled with mixed gas.

[0057] Furthermore, since the lid is opened and closed as described above when filling the fuel tank 3 with mixed gas, the control unit 11 may determine whether the ratio of the pressure in the fuel tank 3 during the ON operation to the pressure in the fuel tank 3 during the OFF operation described above exceeds a predetermined value when the control unit 11 determines, based on navigation information or the like, that the gas supplier is different from the station where the fuel tank 3 was previously filled.

[0058] Once the composition of the mixed gas is estimated as described above and the warm-up of the fuel cell stack 1 is complete (i.e., once the control routine in FIG. 2 is complete), the control unit 11 adjusts the flow rate of fuel supplied to the fuel cell stack 1. Specifically, the fuel flow rate is calculated using equation (1) based on the physical property value of the mixed gas (e.g., specific heat ratio γ) based on the estimated composition, the flow path index of the flow rate adjustment unit of the fuel supply mechanism 2 (e.g., orifice diameter A in equation (1)), and the index representing the state of the mixed gas (e.g., pressure and temperature), and a pressure reducing valve (not shown) is adjusted based on this.

[0059] As described above, this embodiment provides a control method for controlling a fuel cell system 100 including a fuel cell stack (fuel cell) 1 that uses a mixed gas composed of multiple types of components as fuel, a fuel supply mechanism 2 that includes a fuel tank 3 that stores the mixed gas and supplies the mixed gas to the fuel cell stack 1, and a combustor 7 that, when the fuel cell stack 1 is started, generates combustion gas that heats air that is supplied to the fuel cell stack 1. In this control method, the fuel composition and the fuel flow rate to the combustor 7 are set as unknowns, multiple conditions for the air flow rate to the combustor 7 are set, and the composition ratio of the multiple types of components in the mixed gas is estimated based on simultaneous equations consisting of a first characteristic equation based on the relationship between the amount of air supplied to the combustor 7 and the oxygen concentration in the exhaust gas discharged from the combustor 7 and a composition equation that represents the sum of the composition ratios of the multiple types of components in the mixed gas, and the flow rate of fuel supplied to the fuel cell stack 1 is adjusted based on the estimated composition ratio. The first characteristic equation indicates the relationship that the amount of oxygen in the air supplied to the combustor 7 at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the combustor 7. When estimating the composition ratio of multiple types of components in the mixed gas based on the simultaneous equations consisting of the first characteristic equation and the composition equation, the condition of the air flow rate to the combustor 7 is changed to derive as many first characteristic equations as necessary to obtain solutions for the unknowns.

[0060] According to this embodiment, the composition ratio can be estimated simply by increasing the air flow rate condition while leaving the fuel flow rate as an unknown. Since it is possible to estimate not only the carbon number but also the specific composition ratio, the accuracy of estimating the amount of hydrogen after reforming is improved. Furthermore, since the fuel flow rate can remain an unknown, a device for detecting the fuel flow rate is not required.

[0061] In this embodiment, the initial setting is a case where the only component contained in the mixed gas is methane, and then air flow rate conditions and component types are added, and the composition ratios of the multiple components are estimated based on simultaneous equations, and this estimation is repeated by changing the air flow rate conditions until one of the multiple components reaches 0%. This makes it possible to accurately estimate the composition and composition ratios of the components contained in the mixed gas without performing unnecessary calculations.

[0062] In this embodiment, the upper limit of the fuel flow rate is set to the fuel flow rate when the components are methane and ethane and the calorific value of the mixed gas is the upper limit of the calorific value of the mixed gas used in the region, thereby preventing the combustor 7 from overheating.

[0063] In this embodiment, the initial air flow rate is set to a flow rate that allows complete combustion at the upper limit of the fuel flow rate. When changing the air flow rate conditions, the initial air flow rate is set to the lower limit and is increased from there. This makes it possible to suppress the generation of carbon monoxide in the reaction in the combustor 7.

[0064] In this embodiment, when the fuel cell system 100 is mounted on a vehicle and the vehicle key is turned off and then turned on, if the ratio of the fuel tank pressure at the time of the on operation to the fuel tank pressure at the time of the off operation is equal to or greater than a predetermined value, it is determined that the mixed gas has just been filled. Also, if the lid of the vehicle's fuel tank 3 is opened between the on and off operations, it is determined whether the pressure in the fuel tank 3 has increased by a predetermined value. This makes it possible to determine whether the mixed gas has just been charged without adding any special configuration.

[0065] In this embodiment, the flow rate of the fuel supplied to the fuel cell stack 1 is adjusted based on the physical property values ​​of the fuel based on the estimated fuel composition, the flow path index of the flow rate adjuster of the fuel supply mechanism, and the temperature and pressure of the fuel. This improves the control accuracy of the flow rate of the fuel supplied to the fuel cell stack 1.

[0066] [Second embodiment] This embodiment differs from the first embodiment in the content of the mixed gas composition estimation executed in step S103 of the warm-up control routine shown in Fig. 2. Other control is the same as in the first embodiment. The following description will focus on the mixed gas composition estimation method of this embodiment.

[0067] In this embodiment, first, the fuel composition and the fuel flow rate to the combustor 7 are set as unknown quantities. Then, multiple conditions for the air flow rate to the combustor 7 are set, and a simultaneous equation is formulated, which is made up of a second characteristic equation based on the relationship between the amount of air supplied to the combustor 7 and the temperature of the exhaust gas discharged from the combustor 7, and a composition equation that represents the sum of the composition ratios of multiple types of components in the mixed gas. The composition ratio of each component is calculated by solving this simultaneous equation.

[0068] The second characteristic equation indicates the relationship (i.e., the law of conservation of energy) that the thermal energy of the gas (air and mixed gas) flowing into the combustor 7 at startup is equal to the sum of the thermal energy of the exhaust gas and the thermal energy consumed by combustion in the combustor 7.

[0069] That is, in the first embodiment, the composition of the mixed gas was estimated by solving a simultaneous equation consisting of a composition equation (equation (3)) and a plurality of first characteristic equations (equation (5)), whereas in this embodiment, the composition of the mixed gas is estimated by solving a simultaneous equation consisting of a composition equation and a plurality of second characteristic equations.

[0070] When the components contained in the mixed gas are methane, ethane, and propane, the composition equation is as explained in the first embodiment. In a steady state, all of the combustion heat appears as a temperature change in the mixed gas, so the relationship shown in equation (6) holds. This equation (6) is defined as the second characteristic equation.

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[0071] FIG. 7 is a flowchart showing a control routine for composition estimation according to this embodiment, that is, a control routine executed by the control unit 11 in step S103 of FIG.

[0072] In step S300, the temperature of the exhaust gas discharged from the combustor 7 is detected.

[0073] In step S301, the second characteristic equation, that is, equation (6), is derived. In the first calculation, equation (6) is derived assuming that the component contained in the mixed gas is only methane.

[0074] In step S302, the simultaneous equations consisting of the composition equation (equation (3)) and equation (6) are solved.

[0075] In step S303, it is determined whether any of the composition ratios of the components is 0%. If there is a component that is 0%, this routine ends and the processing of step S104 in FIG. 1 is executed; if not, the processing returns to step S300.

[0076] In the second and subsequent calculations, the air flow condition, i.e., the air flow rate Q an A, Q a2 , Q a3 ... and also add the types of components. In other words, by increasing the air flow rate condition, the number of equations (6) required to obtain a solution for the unknowns can be derived without increasing the number of unknowns. At this time, components are added in order of the number of carbon atoms. Also, the air flow rate Q an is the initial value Q a1 is set as the lower limit, and the value is changed in an increasing direction from there.

[0077] This routine ends when any of the components reaches 0%, because 0% of any of the components means that there are no other components left.

[0078] As described above, this embodiment provides a control method for controlling a fuel cell system 100 including a fuel cell stack 1 that uses a mixed gas composed of multiple types of components as fuel, a fuel supply mechanism 2 that includes a fuel tank 3 that stores the mixed gas and supplies the mixed gas to the fuel cell stack 1, and a combustor 7 that, when the fuel cell stack 1 is started, generates combustion gas that heats the air supplied to the fuel cell stack 1. In this control method, the fuel composition and the fuel flow rate to the combustor 7 are set as unknowns, multiple conditions for the air flow rate to the combustor 7 are set, and the composition ratio of the multiple types of components in the mixed gas is estimated based on simultaneous equations consisting of a second characteristic equation based on the relationship between the amount of air supplied to the combustor 7 and the temperature of the exhaust gas discharged from the combustor 7 and a composition equation that represents the sum of the composition ratios of the multiple types of components in the mixed gas, and the flow rate of fuel supplied to the fuel cell stack 1 is adjusted based on the estimated composition ratio. The second characteristic equation indicates the relationship that the thermal energy of the gas flowing into the combustor 7 at startup is equal to the sum of the thermal energy of the exhaust gas and the thermal energy consumed by combustion in the combustor 7. When estimating the composition ratio of multiple components of the mixed gas based on the simultaneous equations consisting of the second characteristic equation and the composition equation, the required number of second characteristic equations are derived to obtain solutions for the unknowns by changing the condition of the air flow rate to the combustor 7. This provides the same effects as the first embodiment.

[0079] [Third embodiment] This embodiment differs from the first and second embodiments in the content of the mixed gas composition estimation executed in step S103 of the warm-up control routine shown in Fig. 2. Other control is the same as in the first and second embodiments. The following description will focus on the mixed gas composition estimation method of this embodiment.

[0080] In this embodiment, the composition of the mixed gas is estimated by solving a simultaneous equation consisting of a composition equation, a first characteristic equation, and a second characteristic equation.

[0081] FIG. 8 is a flowchart showing a control routine for composition estimation according to this embodiment, that is, a control routine executed by the control unit 11 in step S103 of FIG.

[0082] Steps S400 to S401 are the same as steps S200 to S201 in FIG. 4 described in the first embodiment, and steps S402 to S403 are the same as steps S300 to S301 in FIG. 7 described in the second embodiment.

[0083] Steps S403 and S404 are the same processes as steps S202 and S203 in FIG. 4 and steps S302 and S303 in FIG.

[0084] As described above, this embodiment provides a control method for controlling a fuel cell system 100 including a fuel cell stack 1 that uses a mixed gas composed of multiple components as fuel, a fuel supply mechanism 2 that includes a fuel tank 3 for storing the mixed gas and supplies the mixed gas to the fuel cell stack 1, and a combustor 7 that generates combustion gas to heat air supplied to the fuel cell stack 1 when the fuel cell stack 1 is started. This control method uses the fuel composition and the fuel flow rate to the combustor 7 as unknowns, sets multiple conditions for the air flow rate to the combustor 7, and estimates the composition ratio of the multiple components of the mixed gas based on simultaneous equations including: a first characteristic equation based on the relationship between the amount of air supplied to the combustor 7 and the oxygen concentration in the exhaust gas discharged from the combustor 7; a second characteristic equation based on the relationship between the amount of air supplied to the combustor 7 and the temperature of the exhaust gas discharged from the combustor 7; and a composition equation that represents the sum of the composition ratios of the multiple components of the mixed gas. The flow rate of fuel supplied to the fuel cell stack 1 is then adjusted based on the estimated composition ratio. The first characteristic equation indicates the relationship that the amount of oxygen in the air supplied to the combustor 7 at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the combustor 7. The second characteristic equation indicates the relationship that the thermal energy of the gas flowing into the combustor 7 at startup is equal to the sum of the thermal energy of the exhaust gas and the thermal energy consumed by combustion in the combustor 7. When estimating the composition ratio of multiple components of a mixed gas based on the simultaneous equations consisting of the first characteristic equation, the second characteristic equation, and the composition equation, the condition of the air flow rate to the combustor 7 is changed to derive the number of first characteristic equations and second characteristic equations required to obtain solutions for the unknowns. This provides the same effects as the first and second embodiments.

[0085] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. a fuel cell that uses a mixed gas composed of multiple types of components as fuel; a fuel supply mechanism including a fuel tank for storing the mixed gas and for supplying the mixed gas to the fuel cell; a combustor that generates combustion gas for heating air supplied to the fuel cell when the fuel cell is started up; A control method for controlling a fuel cell system comprising: A fuel composition and a fuel flow rate to the combustor are unknowns, and a plurality of air flow rate conditions to the combustor are set; a first characteristic equation based on a relationship between an amount of air supplied to the combustor and an oxygen concentration in exhaust gas discharged from the combustor; at least one second characteristic equation based on a relationship between an amount of air supplied to the combustor and a temperature of the exhaust gas discharged from the combustor; a composition equation that represents the sum of the composition ratios of the plurality of components of the mixed gas; Estimating the composition ratio of the components constituting the mixed gas based on a simultaneous equation consisting of: A fuel cell system control method, comprising: adjusting the flow rate of the fuel supplied to the fuel cell based on the estimated composition ratio.

2. 2. The fuel cell system control method according to claim 1, the first characteristic equation expresses a relationship in which an amount of oxygen in air supplied to the combustor at startup is equal to a sum of an amount of oxygen in the exhaust gas and an amount of oxygen consumed by combustion in the combustor, a fuel cell system control method, wherein, when estimating a composition ratio of the plurality of components of the mixed gas based on a simultaneous equation consisting of the first characteristic equation and the composition equation, a required number of the first characteristic equations are derived to obtain solutions for unknown quantities by changing the condition of the air flow rate to the combustor.

3. 2. The fuel cell system control method according to claim 1, the second characteristic equation expresses a relationship in which thermal energy of gas flowing into the combustor at startup is equal to the sum of thermal energy of the exhaust gas and thermal energy consumed by combustion in the combustor, a fuel cell system control method, wherein, when estimating a composition ratio of the plurality of components of the mixed gas based on a simultaneous equation consisting of the second characteristic equation and the composition equation, a required number of the second characteristic equations are derived to obtain solutions for unknown quantities by changing the condition of the air flow rate to the combustor.

4. 2. The fuel cell system control method according to claim 1, the first characteristic equation expresses a relationship in which an amount of oxygen in air supplied to the combustor at startup is equal to a sum of an amount of oxygen in the exhaust gas and an amount of oxygen consumed by combustion in the combustor, the second characteristic equation expresses a relationship in which thermal energy of gas flowing into the combustor at startup is equal to the sum of thermal energy of the exhaust gas and thermal energy consumed by combustion in the combustor, a fuel cell system control method, wherein, when estimating a composition ratio of the plurality of types of components of the mixed gas based on a simultaneous equation consisting of the first characteristic equation, the second characteristic equation, and the composition equation, a required number of the first characteristic equation and the second characteristic equation are derived to obtain a solution for unknown quantities by changing a condition of an air flow rate to the combustor.

5. 5. The fuel cell system control method according to claim 1, a fuel cell system control method, which sets an initial setting as a case where the component contained in the mixed gas is only methane, then adds the air flow rate condition and the type of the component, estimates the composition ratio of the multiple types of components based on the simultaneous equations, and repeats the estimation by changing the air flow rate condition until any of the multiple types of components reaches 0%.

6. 6. The fuel cell system control method according to claim 1, A fuel cell system control method, wherein the fuel flow rate when the components are methane and ethane and the calorific value of the mixed gas is the upper limit calorific value of the mixed gas in the area where the mixed gas is filled is set as the upper limit of the fuel flow rate.

7. A fuel cell system control method according to claim 6, which is dependent on claim 5, 7. A method for controlling a fuel cell system, wherein the initial air flow rate is set to a flow rate that allows complete combustion at the upper limit fuel flow rate set in claim 6.

8. 8. The fuel cell system control method according to claim 7, A fuel cell system control method, wherein when changing the condition of the air flow rate, the air flow rate set in claim 7 is set as a lower limit and is increased from there.

9. 9. The fuel cell system control method according to claim 1, When the fuel cell system is mounted on a vehicle, when a key for the vehicle is turned off and then turned on, A fuel cell system control method that determines that the mixed gas has just been filled if the ratio of the pressure of the fuel tank when the on operation is performed to the pressure of the fuel tank when the off operation is performed is equal to or greater than a predetermined value.

10. 10. The fuel cell system control method according to claim 9, a fuel cell system control method for determining whether the pressure in the fuel tank has increased by the predetermined value when a lid opening operation of the fuel tank of the vehicle is performed between the on-operation and the off-operation;

11. 11. The fuel cell system control method according to claim 1, A fuel cell system control method that adjusts the flow rate of fuel supplied to the fuel cell based on the physical property values ​​of the fuel based on the estimated fuel composition, the flow path index of the flow rate adjustment unit of the fuel supply mechanism, and the temperature and pressure of the fuel.

12. a fuel cell that uses a mixed gas composed of multiple types of components as fuel; a fuel supply mechanism including a fuel tank for storing the mixed gas and for supplying the mixed gas to the fuel cell; a combustor that generates combustion gas for heating air supplied to the fuel cell when the fuel cell is started up; a control unit that controls the flow rate of air supplied to the combustor and the flow rate of the mixed gas supplied to the combustor and the fuel cell; A fuel cell system comprising: The control unit A fuel composition and a fuel flow rate to the combustor are unknowns, and a plurality of conditions for an air flow rate to the combustor are set; a first characteristic equation based on a relationship between an amount of air supplied to the combustor and an oxygen concentration in exhaust gas discharged from the combustor, the oxygen concentration being detected by an oxygen concentration sensor; at least one second characteristic equation based on a relationship between an amount of air supplied to the combustor and a temperature of exhaust gas discharged from the combustor detected by a temperature sensor; a composition equation that represents the sum of the composition ratios of the plurality of components of the mixed gas; Estimating the composition ratio of the components constituting the mixed gas based on a simultaneous equation consisting of: The fuel cell system adjusts the flow rate of the fuel supplied to the fuel cell based on the estimated composition ratio.

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