Fuel composition estimation method and fuel cell system

Abstract

To provide a fuel composition estimation method and a fuel cell system capable of estimating a composition of a mixed gas without interfering with control over a fuel cell, and reducing deterioration in accuracy of estimation.SOLUTION: In a method for estimating the composition of a gas mixture in a fuel cell system including a fuel cell using a mixed gas composed of a plurality of types of components as a fuel, and a fuel supply mechanism having a fuel tank for storing the mixed gas and supplying the mixed gas to the fuel cell, a characteristic equation representing the Joule-Thomson coefficient of the mixed gas and / or a characteristic equation representing the pressure coefficient of the mixed gas are calculated on the basis of pressure changes and temperature changes occurring in the fuel supply mechanism, and the composition ratios of the multiple types of components of the mixed gas are estimated on the basis of simultaneous equations consisting of the characteristic equation and a composition equation representing the total composition ratio of the components of the mixed gas.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fuel composition estimation method and a fuel cell system.

Background Art

[0002] Conventionally, it has been proposed to use city gas as fuel for a fuel cell. City gas (mixed gas) can be reformed in a reformer or a fuel cell having a reforming function and used as fuel. However, city gas is defined by the calorific value per unit volume, and its composition can vary. Therefore, when the composition of city gas changes, the amount of hydrogen generated by reforming changes, making it difficult to supply the amount of hydrogen corresponding to the required output of the fuel cell.

[0003] To solve this problem, Patent Document 1 discloses a system including a reformer that mixes a raw fuel and steam to generate a reformed gas and a fuel cell stack that generates electricity using the reformed gas as fuel. An oxygen sensor that measures the oxygen concentration is disposed at the anode inlet of the fuel cell stack, and the oxygen concentration when the amount of steam supplied to the reformer is small and the oxygen concentration when the amount of steam is large are measured respectively, and a technique for estimating the amount of hydrogen etc. from the information of the two oxygen concentrations is disclosed. By estimating the fuel composition in this way, it becomes possible to adjust the fuel flow rate according to the fuel composition and the required output.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 1, the anode inlet of the fuel cell stack has a high water vapor concentration and a high temperature, so the oxygen sensor placed at the anode inlet is prone to deterioration, which reduces the measurement accuracy and makes it difficult to estimate the fuel composition.In addition, it is necessary to obtain information on two oxygen concentrations by changing the amount of water vapor, but this interferes with the control of the fuel cell, making it difficult to implement in a vehicle.

[0006] An object of the present invention is to provide a fuel composition estimation method and a fuel cell system that are capable of estimating the composition of a mixed gas without interfering with the control of the fuel cell and that can reduce any decrease in estimation accuracy. [Means for solving the problem]

[0007] The fuel estimation method according to the present invention is a method for estimating the composition of a mixed gas in a fuel cell system that includes a fuel cell that uses a mixed gas composed of a plurality of components as fuel, and a fuel supply mechanism that includes a fuel tank for storing the mixed gas and supplies the mixed gas to the fuel cell. In the fuel estimation method, a characteristic equation that represents the Joule-Thomson coefficient of the mixed gas and / or a characteristic equation that represents the composition of the mixed gas based on pressure changes and temperature changes that occur in the fuel supply mechanism are calculated. Compression A characteristic equation expressing coefficients is calculated, and the composition ratios of a plurality of types of components in the mixed gas are estimated based on a simultaneous equation consisting of the characteristic equation and a composition equation expressing the sum of the composition ratios of the components in the mixed gas. Effect of the Invention

[0008] According to the present invention, a method for estimating fuel composition is provided that makes it possible to estimate the composition of a mixed gas without interfering with the control of a fuel cell, and also makes it possible to reduce deterioration in the accuracy of the estimation. [Brief description of the drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

MODE FOR CARRYING OUT THE INVENTION

[0010] [First Embodiment] FIG. 1 is a schematic diagram of a fuel cell system 100 to which the fuel composition estimation method of the first embodiment is applied. As shown in FIG. 1, in the first embodiment, the fuel cell system 100 includes a fuel cell stack 1, a fuel supply mechanism 2 that supplies a mixed gas serving as fuel to the fuel cell stack 1 (anode), pressure sensors 31, 32, 33 that detect the pressure of the mixed gas in the fuel supply mechanism 2, temperature sensors 41, 42, 43 that detect the temperature of the mixed gas in the fuel supply mechanism 2, and a control unit 5 that controls the entire system.

[0011] Also, although not shown, the fuel cell system 100 includes a compressor that supplies air (cathode gas) to the fuel cell stack 1 (cathode), a combustor that burns the mixed gas (anode off-gas) and air (cathode off-gas) exhausted from the fuel cell stack 1 to generate combustion gas, and a DC / DC converter that extracts power from the fuel cell stack 1. Note that the combustor heats the fuel cell stack 1 and the air supplied to the fuel cell gas with the combustion gas.

[0012] The fuel cell stack 1 is a solid oxide fuel cell (SOFC), and one equipped with a catalyst for reforming the mixed gas on the anode side is applied. The fuel cell stack 1 can reform the mixed gas to generate a reformed gas (anode gas) containing hydrogen. Then, the fuel cell stack 1 generates electricity by an electrochemical reaction between the anode gas (hydrogen) and the cathode gas (oxygen) through an electrolyte.

[0013] The fuel supply mechanism 2 includes a fuel tank 21, a pressure reducing valve 22 (pressure reducing means), and an injector 23 (pressure reducing means).

[0014] The fuel tank 21 stores the mixed gas at a predetermined pressure. Here, city gas is applied as the mixed gas. As described above, the composition of city gas is defined based on the calorific value and the composition is not defined. Therefore, the composition of the mixed gas may vary each time the fuel tank 21 is filled. For this reason, the amount of hydrogen generated by reforming in the fuel cell stack 1 also changes. Therefore, it becomes difficult to supply the amount of hydrogen corresponding to the required output for the fuel cell stack 1, that is, to supply the mixed gas.

[0015] However, in this embodiment, as will be described later, the composition of the mixed gas filled in the fuel tank 21 can be estimated. Then, by separately preparing a map showing the relationship between the composition of the mixed gas, the required output, and the supply amount of the mixed gas, the supply amount of the mixed gas can be calculated based on the input composition information and the required output information, and the mixed gas can be supplied to the fuel cell stack 1 without excess or deficiency.

[0016] The pressure reducing valve 22 is disposed between the fuel tank 21 and the injector 23 in the fuel supply mechanism 2, and reduces the pressure of the mixed gas stored in the fuel tank 21 and supplies it to the injector 23.

[0017] The injector 23 adjusts the supply amount of the mixed gas (the duty ratio of the on / off of the plunger rod) in response to a signal from the control unit 5.

[0018] The pressure sensor 31 detects the pressure of the mixed gas inside the fuel tank 21 (the high pressure side of the pressure reducing valve 22).

[0019] The pressure sensor 32 detects the pressure of the mixed gas on the low pressure side of the pressure reducing valve 22 (the high pressure side of the injector 23).

[0020] The pressure sensor 33 detects the pressure of the mixed gas on the low-pressure side of the injector 23, that is, between the injector 23 and the fuel cell stack 1.

[0021] The temperature sensor 41 detects the temperature of the mixed gas inside the fuel tank 21 (on the high-pressure side of the pressure reducing valve 22).

[0022] The temperature sensor 42 detects the pressure of the mixed gas on the low-pressure side of the pressure reducing valve 22 (on the high-pressure side of the injector 23).

[0023] The temperature sensor 43 detects the temperature of the mixed gas on the low-pressure side of the injector 23, that is, between the injector 23 and the fuel cell stack 1.

[0024] The control unit 5 executes warm-up control, normal power generation control, and stop control for the fuel cell stack 1. Since the warm-up control and stop control are prior arts, the description is omitted. Also, the control unit 5 controls the fuel supply mechanism 2 (the pressure reducing valve 22, the injector 23) to control the flow rate of the mixed gas.

[0025] The normal power generation control adjusts the supply amount of the mixed gas (the duty ratio of the injector 23) according to the required output for the fuel cell stack 1. At that time, the composition ratio of the mixed gas and the supply amount of the mixed gas corresponding to the required output are set.

[0026] [Joule-Thomson coefficient] Generally, the Joule-Thomson coefficient μ for a gas is expressed as follows by the temperature T and pressure p of the gas.

[0027]

Equation

[0028] Here, assuming that the pressure detected by the pressure sensor 31 is p1, the pressure detected by the pressure sensor 32 is p2, the temperature detected by the temperature sensor 41 is T1, and the temperature detected by the temperature sensor 42 is T2, the Joule-Thomson coefficient μ is based on the ratio of the pressure difference and the temperature difference between the high-pressure side and the low-pressure side of the pressure reducing valve 22. reg can be calculated as follows.

[0029]

Equation

[0030] When the mixed gas is composed of, for example, two components of methane (CH4) and ethane (C2H6), the Joule-Thomson coefficient μ reg can be expressed as the following characteristic equation representing the relationship with each component in the mixed gas.

[0031]

Equation

[0032] Here, X CH4 is the molar ratio of methane, X C2H6 is the molar ratio of ethane, a reg and b reg are coefficients respectively. Also, the molar ratio of methane and the molar ratio of ethane have the following relationship (composition equation).

[0033]

Equation

[0034] Therefore, Equation 3 can be transformed into a linear function of the molar ratio X CH4 of methane as follows using Equation 4.

[0035]

Equation

[0036] When the mixed gas is composed of, for example, two components of methane (CH4) and propane (C3H8), the Joule-Thomson coefficient μ reg can be expressed as follows.

[0037]

Equation

[0038] Here, X C3H8 is the molar ratio of propane, and c reg is a coefficient. Also, the molar ratio of methane and the molar ratio of propane have the following relationship.

[0039]

Equation

[0040] Therefore, Equation 6 can be transformed into a linear function of the molar ratio X CH4 of methane using Equation 7 as follows.

[0041]

Equation

[0042] Note that if the pressure detected by the pressure sensor 32 is p2, the pressure detected by the pressure sensor 33 is p3, the temperature detected by the temperature sensor 42 is T2, and the temperature detected by the temperature sensor 43 is T3, the Joule-Thomson coefficient μ inj can be calculated as follows using the pressure difference and temperature difference between the high-pressure side and the low-pressure side of the injector 23.

[0043]

Equation

[0044] And the above Equations 3 to 8 can also be applied to the Joule-Thomson coefficient μ inj .

[0045] [Relationship between the molar ratio of methane in the mixed gas and the Joule-Thomson coefficient] Figure 2 is a diagram showing the relationship between the molar ratio of methane in the mixed gas and the Joule-Thomson coefficient. Here, the source of the data shown in Figure 2 is from "THE JOULE-THOMSON EXPANSION FOR MIXTURES" A Thesis submitted for the Degree of Philosophy in the Faculty of Engineering of the University of London, by JOHN FRANCIS HEAD(1622614765951_0.pdf).

[0046] In Figure 2, when the mixed gas is composed of two components, methane (CH4) and ethane (C2H6), and the temperature of the mixed gas is 290K, when the molar ratio of methane changes from 75% to 100%, that is, when the molar ratio of ethane changes from 25% to 0%, the Joule-Thomson coefficient μ reg (μ inj is also acceptable) change is shown. As shown in Figure 2, the Joule-Thomson coefficient μ reg decreases linearly with the increase in the molar ratio of methane according to the above formula 5.

[0047] Also, in Figure 2, when the mixed gas is composed of two components, methane (CH4) and propane (C3H8), and the temperature of the mixed gas is 290K, when the molar ratio of methane changes from 75% to 100%, that is, when the molar ratio of propane changes from 25% to 0%, the Joule-Thomson coefficient μ reg (μ inj is also acceptable) change is shown. As shown in Figure 2, the Joule-Thomson coefficient μ reg decreases linearly with the increase in the molar ratio of methane according to the above formula 8.

[0048] Here, considering the case where the mixed gas contains three components of methane, ethane, and propane, the Joule-Thomson coefficients of the two-component systems of methane-ethane and methane-propane are linear with respect to the composition, and since they are stable substances with respect to each other, it is considered that they will be linear with respect to the composition even when present in three components. Therefore, the Joule-Thomson coefficient μ reg (μ inj ) can be set as follows.

[0049]

Number

[0050] By the way, in FIG. 2, when the mixed gas is composed of two components of methane (CH4) and ethane (C2H6), when the temperature of the mixed gas is 310 K and the molar ratio of methane is changed from 75% to 100%, that is, when the molar ratio of ethane is changed from 25% to 0%, the change in the Joule-Thomson coefficient μ reg (μ inj may also be) is shown. This Joule-Thomson coefficient μ reg (310 K) is a different value from the Joule-Thomson coefficient μ reg (290 K).

[0051] In the fuel supply mechanism 2 of the present embodiment, since the pressure is p1 > p2 > p3, the temperature is also t1 > t2 > t3. Therefore, the Joule-Thomson coefficient μ ing is established as a different formula from the Joule-Thomson coefficient μ reg as follows.

[0052]

Number

[0053] Furthermore, the following relationship holds for the mixed gas composed of methane, ethane, and propane.

[0054]

Number

[0055] Therefore, by solving the three - variable simultaneous equations consisting of Equation 10, Equation 11, and Equation 12, the molar ratio (composition ratio) of methane, the molar ratio (composition ratio) of ethane, and the molar ratio (composition ratio) of propane can be estimated respectively.

[0056] Here, a reg , b reg , c reg , a inj , b ing , c inj are obtained by changing the composition in a mixed gas with a known composition, calculating a large number of Joule - Thomson coefficient data each time, and setting a straight line connecting multiple data.

[0057] Note that the above Equation 10, Equation 11, and Equation 12 can be simply applied even when the mixed gas is composed of four components and the molar ratio (composition ratio) of any one of them is small and known compared to other components.

[0058] For example, when the molar ratio M 10 of butane (C4H C4H10 ) is known (for example, 2%), the following equation holds.

[0059]

Number

[0060]

Number

[0061]

Number

[0062] Therefore, by solving the three - variable simultaneous equations of Equation 13, Equation 14, and Equation 15, the molar ratios (composition ratios) of methane, ethane, and propane can be simply estimated respectively.

[0063] [Compression Factor of Mixed Gas] The ideal gas law is expressed as pV = nRT, where p is the pressure, V is the volume, T is the temperature, n is the number of moles, and R is the gas constant. On the other hand, the equation of state for a real gas is expressed as pV = znRT, which is obtained by multiplying the ideal gas law by the compression factor z. The compression factor z of a real gas is expressed as a polynomial that depends on, for example, the composition, pressure, and temperature as defined in ISO 12213-2.

[0064] Therefore, for example, when the mixed gas is composed of two components, methane and ethane, by changing these compositions and changing the pressure and temperature each time, a map (function) of the compression factor z can be created as follows.

[0065] [Number]

[0066] The fuel cell system 100 of this embodiment is mounted on a vehicle (electric vehicle). When the fuel cell system 100 is driven in the vehicle, the heat generated during driving propagates to the fuel tank 21, and the temperature of the mixed gas in the fuel tank 21 rises. However, for example, when the fuel cell system 100 is stopped by turning off the vehicle key (ignition key), the temperature of the fuel tank 21 drops, and when the key is turned on again, the temperature may drop by a predetermined amount from when the off operation was performed. At this time, as shown in FIG. 3, the pressure in the fuel tank 21 drops by a predetermined pressure (ΔP) from the off operation to the on operation.

[0067] The equation of state for the mixed gas in the fuel tank 21 during the off operation is as follows.

[0068] [Number]

[0069] On the other hand, the equation of state for the mixed gas in the fuel tank 21 during the on operation is as follows.

[0070]

Number

[0071] During the above-mentioned OFF operation to ON operation, since no mixed gas is released from the fuel tank 21, the number of moles n is the same in Formulas 17 and 18. Similarly, since there is no change in the volume of the fuel tank 21, the volume V is the same in Formulas 17 and 18. Therefore, the following relationship is derived from Formulas 17 and 18.

[0072]

Number

[0073] Therefore, from Formulas 16 and 19, the composition ratios (X CH4 , X C2H6 ) of the respective components of the mixed gas in a closed space such as the fuel tank 21, two different pressure and temperature states (p off , T off ), (p on , T on ) of the mixed gas, and Compression the characteristic equation representing the relationship with the coefficient (z) is obtained as follows.

[0074]

Number

[0075] Therefore, based on Formulas 4 and 20, the molar ratio (composition ratio) of each of the mixed gases composed of two components such as methane and ethane can be estimated. Here, Formula 20 can be calculated based on the difference between two pressures detected at different times by the pressure sensor 31 and the difference between two temperatures detected at different times by the temperature sensor 41 when the pressure reducing valve 22 (or the opening of the fuel tank 21) is closed.

[0076] In this embodiment, Equations 10, 11, 12, and 20 are extended, and for example, it is possible to estimate the molar ratio of each component in a mixed gas of four components: methane, ethane, propane, and butane. That is, as shown in the following Equations 21 to 24, the molar ratio of each component can be estimated by solving a system of four linear equations.

[0077]

Number

[0078]

Number

[0079]

Number

[0080]

Number

[0081] Here, Equation 21 and Equation 22 are characteristic equations showing the relationship between the Joule-Thomson coefficient and the composition ratio of each component, Equation 23 is a characteristic equation showing the relationship between the compression coefficient and the composition ratio of each component, etc., and Equation 24 is a composition equation showing the sum of the composition ratios of each component added together.

[0082] As described above, the fuel cell system 100 of this embodiment is mounted on a vehicle. When filling with the mixed gas, move to the station that supplies the mixed gas, turn off the key, open the lid of the vehicle's fuel tank 21 (the lever for opening the lid located in the driver's seat), fill the fuel tank 21 with the mixed gas, close the lid after filling, turn on the key (start the fuel cell system 100), and move away from the station.

[0083] In this embodiment, the molar ratio (composition ratio) of the mixed gas is estimated as described above, but it is only necessary to estimate it once for the mixed gas newly filled in the fuel tank 21. By the way, the pressure (temperature) of the mixed gas in the fuel tank 21 changes not only due to the temperature drop of the mixed gas after the fuel cell system 100 stops, but also due to the change in the outside air temperature. Therefore, when the ratio of the pressure of the fuel tank 21 during the on-operation to the pressure of the fuel tank 21 during the off-operation based on the pressure of the fuel tank 21 during the off-operation exceeds a predetermined value that is equal to or greater than the ratio caused by the change in the outside air temperature, if it is assumed that the mixed gas has been filled, Equation 5 or Equation 8 may be executed. Similarly, the simultaneous equations of Equation 10, Equation 11, and Equation 12, and the simultaneous equations of Equation 13, Equation 14, and Equation 15 may be solved.

[0084] Here, considering the predetermined value regarding the above ratio, no mixed gas is released from the fuel tank 21 from the off-operation to the on-operation, and there is no change in the volume of the fuel tank 21. Therefore, the pressure p of the mixed gas in the fuel tank 21 during the off-operation off and the pressure p of the mixed gas in the fuel tank 21 during the on-operation on are related to the temperature T of the mixed gas in the fuel tank 21 during the off-operation off and the temperature T of the mixed gas in the fuel tank 21 during the on-operation on such that P on / P off =T on / T off =(T off + daily difference) / T off =1 + daily difference / T off can be converted. Considering the case in Japan, the maximum value of the daily difference (the difference between the maximum temperature and the minimum temperature) is 31.5 °C (Nagano), and the minimum temperature is -41 °C (Asahikawa). Therefore, when calculating 1 + daily difference / T off it becomes = 1 + 31.5 / (273 - 41) = 1.14. Therefore, when the pressure ratio P on / P off exceeds 1.14, the control unit 5 can determine that the fuel tank 21 is immediately after the mixed gas has been filled.

[0085] Also, when filling the fuel tank 21 with the mixed gas, since the lever is operated as described above, the control unit 5 can determine that the fuel tank 21 is immediately after filling with the mixed gas when there is a lever operation.

[0086] When supplying the mixed gas to the fuel cell stack 1 immediately after filling the fuel tank 21 with the mixed gas in this way, the pressure difference and temperature difference between the upstream side and the downstream side of the pressure reducing valve 22, and the pressure difference and temperature difference between the upstream side and the downstream side of the injector 23 become the largest. Therefore, the estimation accuracy when estimating the composition ratio of each component by the above formulas 21 to 24 can be improved.

[0087] Also, when the key is turned on after being turned off and the fuel tank 21 is not filled with the mixed gas, the difference between the pressure of the mixed gas in the fuel tank 21 immediately after the off operation and the pressure of the mixed gas in the fuel tank 21 immediately after the on operation, and the difference between the temperature of the mixed gas in the fuel tank 21 immediately after the off operation and the temperature of the mixed gas in the fuel tank 21 immediately after the on operation are both likely to be the largest.

[0088] Therefore, in the above case, when the pressure difference (pressure ratio) exceeds a predetermined value (for example, P on / P off is 1.14), it is preferable to calculate the characteristic equation of formula 23 and solve the simultaneous equations of formulas 21 to 24 to estimate the molar ratio (composition ratio) of the four components of the mixed gas. As a result, the accuracy of the characteristic equation of formula 22 is improved, so that the accuracy of the solution of the simultaneous equations of formulas 20 to 23, that is, the estimation accuracy of the molar ratio (composition ratio) of the four components of the mixed gas can be improved.

[0089] [Effects of the First Embodiment] According to the fuel estimation method of the first embodiment, in a fuel cell system 100 including a fuel cell (fuel cell stack 1) that uses a mixed gas composed of a plurality of types of components as fuel, a fuel tank 21 that stores the mixed gas, and a fuel supply mechanism 2 that supplies the mixed gas to the fuel cell (fuel cell stack 1), a method for estimating the composition of the mixed gas, based on the pressure change and temperature change generated in the fuel supply mechanism 2, a characteristic equation representing the Joule-Thomson coefficient of the mixed gas (for example, Equation 3, Equation 10, Equation 21, Equation 22), and / or a characteristic equation representing the coefficient of the mixed gas (for example, Equation 20, Equation 23) is calculated, and based on a system of simultaneous equations consisting of the characteristic equation and a composition equation (for example, Equation 4, Equation 12, Equation 24) representing the sum of the composition ratios of the components of the mixed gas, the composition ratios of the plurality of types of components of the mixed gas are estimated. Compression Based on the system of simultaneous equations consisting of the characteristic equation and the composition equation, the composition ratios of the plurality of types of components of the mixed gas are estimated.

[0090] With the above configuration, it is possible to estimate the composition of the mixed gas without interfering with the control of the fuel cell stack 1, and since no oxygen sensor is used, it is a fuel composition estimation method that can reduce the decrease in estimation accuracy.

[0091] In the first embodiment, when the mixed gas contains two types of components, the fuel supply mechanism 2 includes a pressure reducing valve 22 that reduces the pressure of the mixed gas supplied from the fuel tank 21. Based on the difference between the pressure on the high-pressure side of the pressure reducing valve 22 (the pressure detected by the pressure sensor 31) and the pressure on the low-pressure side of the pressure reducing valve 22 (the pressure detected by the pressure sensor 32), and the difference between the temperature on the high-pressure side of the pressure reducing valve 22 (the temperature detected by the temperature sensor 41) and the temperature on the low-pressure side of the pressure reducing valve 22 (the temperature detected by the temperature sensor 42), a characteristic equation representing the Joule-Thomson coefficient of the mixed gas (for example, Equation 3, Equation 6) is calculated, and based on a system of simultaneous equations consisting of the characteristic equation and the composition equation, the composition ratios of the two types of components of the mixed gas are estimated.

[0092] With the above configuration, for a mixed gas containing two types of components, the composition ratio of the components can be easily estimated.

[0093] In the first embodiment, when the mixed gas contains three types of components, the fuel supply mechanism 2 includes a pressure reducing valve 22 that reduces the pressure of the mixed gas supplied from the fuel tank 21, and a flow rate adjustment unit (injector 23) that adjusts the flow rate of the mixed gas decompressed by the pressure reducing valve 22 and supplies it to the fuel cell (fuel cell stack 1). As a characteristic equation representing the Joule-Thomson coefficient of the mixed gas, the difference between the pressure on the high-pressure side of the pressure reducing valve 22 (the pressure detected by the pressure sensor 31) and the pressure on the low-pressure side of the pressure reducing valve 22 (the pressure detected by the pressure sensor 32), and the difference between the temperature on the high-pressure side of the pressure reducing valve 22 (the temperature detected by the temperature sensor 41) and the temperature on the low-pressure side of the pressure reducing valve 22 (the temperature detected by the temperature sensor 42), a first characteristic equation (for example, Equation 10), and the difference between the pressure on the high-pressure side of the flow rate adjustment unit (injector 23) (the pressure detected by the pressure sensor 32) and the pressure on the low-pressure side of the flow rate adjustment unit (injector 23) (the pressure detected by the pressure sensor 33), and the difference between the temperature on the high-pressure side of the flow rate adjustment unit (injector 23) (the temperature detected by the temperature sensor 42) and the temperature on the low-pressure side of the flow rate adjustment unit (injector 23) (the temperature detected by the temperature sensor 43), a second characteristic equation (for example, Equation 11), are respectively calculated. Based on a system of simultaneous equations consisting of the first characteristic equation, the second characteristic equation, and a composition equation (for example, Equation 12), the composition ratios of the three types of components of the mixed gas are estimated.

[0094] With the above configuration, for a mixed gas containing three types of components, the composition ratio of the components can be easily estimated.

[0095] In the first embodiment, when the mixed gas contains four types of components, the fuel supply mechanism 2 includes a pressure reducing valve 22 that reduces the pressure of the mixed gas supplied from the fuel tank 21, and a flow rate adjustment unit (injector 23) that adjusts the flow rate of the mixed gas reduced by the pressure reducing valve 22 and supplies it to the fuel cell (fuel cell stack 1). As a characteristic equation representing the Joule-Thomson coefficient of the mixed gas, the difference between the pressure on the high-pressure side of the pressure reducing valve 22 (the pressure detected by the pressure sensor 31) and the pressure on the low-pressure side of the pressure reducing valve 22 (the pressure detected by the pressure sensor 32), and the difference between the temperature on the high-pressure side of the pressure reducing valve 22 (the temperature detected by the temperature sensor 41) and the temperature on the low-pressure side of the pressure reducing valve 22 (the temperature detected by the temperature sensor 42), a first characteristic equation (for example, Equation 21) is calculated. Based on the difference between the pressure on the high-pressure side of the flow rate adjustment unit (injector 23) (the pressure detected by the pressure sensor 32) and the pressure on the low-pressure side of the flow rate adjustment unit (injector 23) (the pressure detected by the pressure sensor 33), and the difference between the temperature on the high-pressure side of the flow rate adjustment unit (injector 23) (the temperature detected by the temperature sensor 42) and the temperature on the low-pressure side of the flow rate adjustment unit (injector 23) (the temperature detected by the temperature sensor 43), a second characteristic equation (for example, Equation 22) is calculated. Compression As a characteristic equation representing the coefficient of the mixed gas, a third characteristic equation (for example, Equation 23) is calculated based on the difference between two pressures (the pressure detected by the pressure sensor 31) detected at different times (for example, the time when the vehicle key is turned off and the time when it is turned on) in the fuel tank 21 and the difference between two temperatures (the temperature detected by the temperature sensor 41) detected at the different times (for example, the time when the vehicle key is turned off and the time when it is turned on) in the fuel tank 21. Based on the first characteristic equation, the second characteristic equation, the third characteristic equation, and the composition equation (for example, Equation 24), the composition ratio of the four types of components of the mixed gas is estimated.

[0096] With the above configuration, for a mixed gas containing four types of components, the composition ratio of the components can be easily estimated.

[0097] In the first embodiment, the control unit 5 calculates the pressure difference and the temperature difference immediately after the mixed gas is filled into the fuel tank 21 and at the start of the supply of the mixed gas to the fuel cell (fuel cell stack 1).

[0098] With the above configuration, the estimation accuracy of the composition ratio of the components contained in the mixed gas can be improved.

[0099] In the first embodiment, when the fuel cell system 100 is mounted on a vehicle and the on operation is performed after the off operation is performed on the vehicle key, the control unit 5 determines that it is immediately after the mixed gas is filled when the ratio of the pressure of the fuel tank 21 at the time of the on operation to the pressure of the fuel tank 21 at the time of the off operation is equal to or greater than a predetermined value.

[0100] With the above configuration, it is possible to determine whether or not the mixed gas is immediately after being filled without adding a special configuration.

[0101] In the first embodiment, the control unit 5 determines whether or not the pressure of the fuel tank 21 has increased by a predetermined value when the lid of the fuel tank 21 of the vehicle is opened between the on operation and the off operation.

[0102] With the above configuration, it is possible to determine whether or not the mixed gas is immediately after being filled without adding a special configuration.

[0103] In the first embodiment, when the mixed gas contains two types of components, based on the difference between two pressures (pressures detected by the pressure sensor 31) detected at different times (for example, the time when the off operation is performed on the vehicle key and the time when the on operation is performed) in the fuel tank 21 and the difference between two temperatures (temperatures detected by the temperature sensor 41) detected at the different times (for example, the time when the off operation is performed on the vehicle key and the time when the on operation is performed) in the fuel tank 21, a characteristic equation (for example, Equation 20) representing the coefficient of the mixed gas is calculated, and based on the simultaneous equations composed of the characteristic equation and the composition equation (for example, Equation 4), the composition ratio of the two types of components of the mixed gas is estimated. Compression Based on the simultaneous equations consisting of the characteristic equation and the composition equation (for example, Equation 4), the composition ratio of the two types of components of the mixed gas is estimated.

[0104] With the above configuration, it is possible to estimate the composition ratio of the two components constituting the mixed gas without consuming the mixed gas.

[0105] In the first embodiment, when the fuel cell system 100 is mounted on a vehicle and the on operation is performed after the off operation is performed on the vehicle key, when the difference between the pressure of the fuel tank 21 at the time of the on operation and the pressure of the fuel tank 21 at the time of the off operation is greater than a predetermined value, the Compression Characteristic equation (for example, Equation 20) representing the coefficient of the mixed gas is calculated.

[0106] With the above configuration, the estimation accuracy of the composition ratio of the components contained in the mixed gas can be improved.

[0107] Further, the fuel cell system 100 according to the first embodiment includes a fuel cell (fuel cell stack 1) that uses a mixed gas composed of a plurality of types of components as fuel, a fuel tank 21 that stores the mixed gas, and a fuel supply mechanism 2 that supplies the mixed gas to the fuel cell (fuel cell stack 1). In the fuel cell system 100 including pressure sensors 31, 32, 33 that detect the pressure of the mixed gas in the fuel supply mechanism 2, temperature sensors 41, 42, 43 that detect the temperature of the mixed gas in the fuel supply mechanism 2, and a control unit 5 that controls the fuel supply mechanism 2, the control unit 5 is based on the pressure change detected via the pressure sensors 31, 32, 33 and the temperature change detected via the temperature sensors 41, 42, 43. A characteristic equation (for example, Equation 3, Equation 10, Equation 21, Equation 22) representing the Joule-Thomson coefficient of the mixed gas, and / or a characteristic equation (for example, Equation 20, Equation 23) representing the coefficient of the mixed gas is calculated, and based on a system of simultaneous equations consisting of the characteristic equation and a composition equation (for example, Equation 4, Equation 12, Equation 24) representing the sum of the composition ratios of the components of the mixed gas, the composition ratios of the plurality of types of components of the mixed gas are estimated. Compression Based on a system of simultaneous equations consisting of the characteristic equation and a composition equation (for example, Equation 4, Equation 12, Equation 24) representing the sum of the composition ratios of the components of the mixed gas, the composition ratios of the plurality of types of components of the mixed gas are estimated.

[0108] With the above configuration, it is possible to estimate the composition of the mixed gas without interfering with the control of the fuel cell stack 1, and since no oxygen sensor is used, the fuel cell system 100 can reduce the degradation of the estimation accuracy.

[0109] [Second Embodiment] FIG. 4 is a schematic diagram of a fuel cell system 100 to which the fuel composition estimation method of the second embodiment is applied. In the second embodiment, in the fuel cell system 100, a plurality of pressure reducing valves 22, pressure sensors 31, and temperature sensors 41 are alternately arranged along the flow path of the mixed gas, and the pressure sensors 31 and temperature sensors 41 are arranged so as to sandwich the pressure reducing valve 22 (and the injector 23) from the front and rear of the flow path.

[0110] More specifically, (N - 1) pressure reducing valves 22 (N: an integer of 2 or more) are connected in series, and an injector 23 (pressure reducing means) is arranged downstream of the last-stage pressure reducing valve 22(N - 1) (pressure reducing means), and the form is such that N pressure reducing means are arranged. Correspondingly, (N + 1) pressure sensors 31 and temperature sensors 41 are arranged.

[0111] Also, a pressure sensor 31(1) and a temperature sensor 41(1) are arranged in the fuel tank 21 (upstream side of the pressure reducing valve 22(1)). Also, a pressure sensor 31(k + 1) and a temperature sensor 41(k + 1) are arranged between the pressure reducing valve 22(k) (k = 2 to (N - 2)) and the pressure reducing valve 22(k + 1). Then, a pressure sensor 31(N) and a temperature sensor 41(N) are arranged between the pressure reducing valve 22(N - 1) and the injector 23, and a pressure sensor 31(N + 1) and a temperature sensor 41(N + 1) are arranged between the injector 23 and the fuel cell stack 1.

[0112] Here, the Joule-Thomson coefficient for the k-th (k = 1 to (N - 1)) pressure reducing valve 22(k) is as follows, where the pressure detected by the pressure sensor 31(k) is pk and the temperature detected by the temperature sensor 41(k) is Tk.

[0113]

Equation

[0114] Similarly, the Joule-Thomson coefficient for the injector 23 is as follows.

[0115] [Equation]

[0116] Therefore, by using N pressure reducing means, the following simultaneous equations can be obtained, and the composition ratios of (N + 1) types of components in the mixed gas can be estimated.

[0117] [Equation]

[0118] Here, X1, X2, ··· X N , X N+1 represent the molar ratios (composition ratios) of the respective components in the mixed gas containing (N + 1) types of components.

[0119] Furthermore, by following the above formula 21 and using the relationship of the compression coefficient with respect to the mixed gas in the fuel tank 21, the following simultaneous equations can be obtained, and the composition ratios of (N + 2) types of components in the mixed gas can be estimated.

[0120] [Equation]

[0121] Here, X1, X2, ··· X N+1 , X N+2 represent the molar ratios (composition ratios) of the respective components in the mixed gas containing (N + 2) types of components.

[0122] [Effects of the Second Embodiment] In the fuel composition estimation method of the second embodiment, the fuel cell system 100 includes a pressure sensor 31 that detects the pressure of the mixed gas in the fuel supply mechanism 2 and a temperature sensor 41 that detects the temperature of the mixed gas in the fuel supply mechanism 2. The fuel supply mechanism 2 includes a plurality of pressure reducing means (pressure reducing valves 22, injectors 23) arranged in series to reduce the pressure of the mixed gas and supply it to the fuel cell (fuel cell stack 1). The pressure sensor 31 and the temperature sensor 41 are alternately arranged with the pressure reducing means (pressure reducing valves 22, injectors 23) along the path for supplying the mixed gas of the fuel supply mechanism 2, and a plurality of each are arranged so as to sandwich the pressure reducing means (pressure reducing valves 22, injectors 23). When the number of the pressure reducing means (pressure reducing valves 22, injectors 23) is N and the number of the pressure sensor 31 and the temperature sensor 41 is each (N + 1), the difference between the pressure detected by one pressure sensor 31 sandwiching one pressure reducing means (pressure reducing valves 22, injectors 23) and the pressure detected by the other pressure sensor 31, and the difference between the temperature detected by one temperature sensor 41 sandwiching one pressure reducing means (pressure reducing valves 22, injectors 23) and the temperature detected by the other temperature sensor 41 are used to calculate a characteristic equation representing the N Joule-Thomson coefficients of the mixed gas. Based on the system of simultaneous equations (for example, Equation 27) consisting of the N characteristic equations and the composition equation, the composition ratios of the (N + 1) types of components of the mixed gas are estimated.

[0123] With the above configuration, for a mixed gas containing (N + 1) types of components, the composition ratio of the components can be easily estimated.

[0124] In the second embodiment, in the pressure sensor 31(1) that detects the pressure of the mixed gas in the fuel tank 21, by calculating one more characteristic equation representing the Joule-Thomson coefficient of the mixed gas based on the difference (pressure ratio) between two pressures detected at different times (for example, the time when the vehicle key is turned off and the time when it is turned on) and the difference between two temperatures detected at the same different times (for example, the time when the vehicle key is turned off and the time when it is turned on) by the temperature sensor 41(1) that detects the temperature of the mixed gas in the fuel tank 21, (N + 1) characteristic equations are calculated, and based on the simultaneous equations (for example, Equation 28) composed of the (N + 1) characteristic equations and the composition equation, the composition ratios of the (N + 2) components of the mixed gas are estimated.

[0125] With the above configuration, for a mixed gas containing (N + 2) components, the composition ratios of the components can be easily estimated.

Explanation of Reference Numerals

[0126] 100 Fuel cell system, 1 Fuel cell stack, 2 Fuel supply mechanism, 21 Fuel tank, 22 Pressure reducing valve, 23 Injector, 31 Pressure sensor, 32 Pressure sensor, 33 Pressure sensor, 41 Temperature sensor, 42 Temperature sensor, 43 Temperature sensor, 5 Control unit

Claims

1. A fuel cell using a mixed gas composed of a plurality of types of components as fuel, A fuel cell system including a fuel tank for storing the mixed gas and a fuel supply mechanism for supplying the mixed gas to the fuel cell, and a method for estimating the composition of the mixed gas, Calculating a characteristic equation representing the Joule-Thomson coefficient of the mixed gas and / or a characteristic equation representing the compression coefficient of the mixed gas based on the pressure change and temperature change occurring in the fuel supply mechanism, A fuel composition estimation method for estimating the composition ratios of the plurality of types of components of the mixed gas based on a system of simultaneous equations consisting of the characteristic equation and a composition equation representing the sum of the composition ratios of the components of the mixed gas.

2. The fuel cell system, A pressure sensor for detecting the pressure of the mixed gas in the fuel supply mechanism, A temperature sensor for detecting the temperature of the mixed gas in the fuel supply mechanism, and The fuel supply mechanism, Includes a plurality of pressure reducing means arranged in series to reduce the pressure of the mixed gas and supply it to the fuel cell, The pressure sensor and the temperature sensor, Are alternately arranged with the pressure reducing means along the path for supplying the mixed gas of the fuel supply mechanism and a plurality of each are arranged so as to sandwich the pressure reducing means, When the number of the pressure reducing means is N and the number of the pressure sensor and the temperature sensor is each (N + 1), The characteristic equation representing N Joule-Thomson coefficients of the mixed gas is calculated based on the difference between the pressure detected by one of the pressure sensors sandwiching one of the pressure reducing means and the pressure detected by the other pressure sensor and the difference between the temperature detected by one of the temperature sensors sandwiching one of the pressure reducing means and the temperature detected by the other temperature sensor, and based on the system of simultaneous equations consisting of the N characteristic equations and the composition equation, the composition ratios of (N + 1) types of components of the mixed gas are estimated. The fuel composition estimation method according to Claim 1.

3. When the mixed gas contains two components, the fuel supply mechanism includes a pressure reducing valve that reduces the pressure of the mixed gas supplied from the fuel tank, calculates the characteristic equation representing the Joule-Thomson coefficient of the mixed gas based on the difference between the pressure on the high-pressure side and the pressure on the low-pressure side of the pressure reducing valve and the difference between the temperature on the high-pressure side and the temperature on the low-pressure side of the pressure reducing valve, and estimates the composition ratio of the two components of the mixed gas based on the simultaneous equations composed of the characteristic equation and the composition equation, according to the fuel composition estimation method described in Claim 1.

4. When the mixed gas contains three components, the fuel supply mechanism includes a pressure reducing valve that reduces the pressure of the mixed gas supplied from the fuel tank, and a flow rate adjustment unit that adjusts the flow rate of the mixed gas decompressed by the pressure reducing valve and supplies it to the fuel cell, calculates, as the characteristic equation representing the Joule-Thomson coefficient of the mixed gas, a first characteristic equation based on the difference between the pressure on the high-pressure side and the pressure on the low-pressure side of the pressure reducing valve and the difference between the temperature on the high-pressure side and the temperature on the low-pressure side of the pressure reducing valve, and a second characteristic equation based on the difference between the pressure on the high-pressure side and the pressure on the low-pressure side of the flow rate adjustment unit and the difference between the temperature on the high-pressure side and the temperature on the low-pressure side of the flow rate adjustment unit, respectively, and estimates the composition ratio of the three components of the mixed gas based on the simultaneous equations composed of the first characteristic equation, the second characteristic equation, and the composition equation, according to the fuel composition estimation method described in Claim 1.

5. When the mixed gas contains four components, the fuel supply mechanism includes a pressure reducing valve that reduces the pressure of the mixed gas supplied from the fuel tank, and a flow rate adjusting unit that adjusts the flow rate of the mixed gas depressurized by the pressure reducing valve and supplies the mixed gas to the fuel cell, calculating, as the characteristic equation expressing a Joule-Thomson coefficient of the mixed gas, a first characteristic equation based on a pressure difference between a high-pressure side of the pressure reducing valve and a pressure difference between a high-pressure side of the pressure reducing valve and a temperature difference between a high-pressure side of the pressure reducing valve and a temperature difference between a low-pressure side of the pressure reducing valve, and a second characteristic equation based on a pressure difference between a high-pressure side of the flow rate adjustment unit and a pressure difference between a low-pressure side of the flow rate adjustment unit and a temperature difference between the high ..., a third characteristic equation based on a difference between two pressures detected in the fuel tank at different times and a difference between two temperatures detected in the fuel tank at different times, as the characteristic equation representing a compression coefficient of the mixed gas; 2. The method for estimating a fuel composition according to claim 1, further comprising estimating a composition ratio of the four types of components of the mixed gas based on the simultaneous equations consisting of the first characteristic equation, the second characteristic equation, the third characteristic equation, and the composition equation.

6. 6. The method for estimating fuel composition according to claim 3, wherein the pressure difference and the temperature difference are calculated immediately after the mixed gas is filled into the fuel tank and when the supply of the mixed gas to the fuel cell is started.

7. When the fuel cell system is mounted on a vehicle and the key for the vehicle is turned off and then turned on, 7. The fuel composition estimation method according to claim 6, further comprising the step of determining that the mixed gas has just been filled if a ratio of the pressure in the fuel tank when the on operation is performed to the pressure in the fuel tank when the off operation is performed is equal to or greater than a predetermined value.

8. 8. The method for estimating fuel composition according to claim 7, further comprising the step of determining whether or not the pressure in the fuel tank has increased by the predetermined value when a lid of the fuel tank of the vehicle is opened between the on-state operation and the off-state operation.

9. When the mixed gas contains two types of components, calculate the characteristic equation representing the compression coefficient of the mixed gas based on the difference between two pressures detected at different times in the fuel tank and the difference between two temperatures detected at the different times in the fuel tank; The fuel composition estimation method according to claim 1, wherein the composition ratio of the two types of components of the mixed gas is estimated based on the simultaneous equations composed of the characteristic equation and the composition equation.

10. calculate one more characteristic equation representing the Joule-Thomson coefficient of the mixed gas based on the difference between two pressures detected at different times in the pressure sensor for detecting the pressure of the mixed gas in the fuel tank and the difference between two temperatures detected at the different times in the temperature sensor for detecting the temperature of the mixed gas in the fuel tank, thereby calculating (N + 1) characteristic equations; The fuel composition estimation method according to claim 2, wherein the composition ratio of (N + 2) types of components of the mixed gas is estimated based on the simultaneous equations composed of the (N + 1) characteristic equations and the composition equation.

11. in the case where the fuel cell system is mounted on a vehicle and the key of the vehicle is turned off and then turned on, when the difference between the pressure of the fuel tank when the on operation is performed and the pressure of the fuel tank when the off operation is performed is greater than a predetermined value, calculate the characteristic equation representing the compression coefficient of the mixed gas. The fuel composition estimation method according to claim 9 or claim 10.

12. a fuel cell using a mixed gas composed of a plurality of types of components as fuel; a fuel tank for storing the mixed gas and a fuel supply mechanism for supplying the mixed gas to the fuel cell; a pressure sensor for detecting the pressure of the mixed gas in the fuel supply mechanism; a temperature sensor for detecting the temperature of the mixed gas in the fuel supply mechanism; A fuel cell system comprising: a control unit that controls the fuel supply mechanism. The control unit: Calculates a characteristic equation representing the Joule-Thomson coefficient of the mixed gas, and / or a characteristic equation representing the compression coefficient of the mixed gas, based on the pressure change detected via the pressure sensor and the temperature change detected via the temperature sensor. A fuel cell system that estimates the composition ratios of the plurality of types of components of the mixed gas based on a system of simultaneous equations comprising the characteristic equation and a composition equation representing the total of the composition ratios of the components of the mixed gas.

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