Method for determining volume percent content of hydrogen in fuel cell system and fuel cell system

Abstract

The invention relates to a method for determining the volume percent content of hydrogen in a fuel cell system (1) and to a fuel cell system (1). A hydrogen gas sensor is not mounted in the fuel cell system (1). The volume percent content of hydrogen in the anode gas is determined based on the pressure difference between the anode inlet and the anode outlet of the fuel cell taking into account the current drawn from the fuel cell system.

Description

Technical Field

[0001] The invention relates to a method for determining the volume percentage content of hydrogen in a fuel cell system and a fuel cell system. Background Art

[0002] Fuel cell systems are high energy carriers that generate energy by reacting hydrogen with oxygen. Here, the oxygen is provided in the form of air containing oxygen. In order to increase the efficiency of the fuel cell system, it is necessary to know the hydrogen content, especially the hydrogen concentration on the anode side of the fuel cell system. Today, the hydrogen concentration is determined in a complex and expensive manner using highly sensitive hydrogen sensors. Summary of the invention

[0003] Based on the prior art, the object of the present invention is to provide a simplified and cost-effective method for determining the volume percentage content of hydrogen on the anode side of a fuel cell system. In addition, the object of the present invention is to provide a fuel cell system, by means of which the volume percentage content of hydrogen on the anode side of the fuel cell system can be determined, so as to be able to improve the efficiency of the fuel cell system.

[0004] These objects are achieved by the independent claims. The dependent claims contain the content of advantageous developments and embodiments of the invention.

[0005] Accordingly, the object is achieved by a method for determining the volume percentage content of hydrogen which is present in a gas mixture on the anode side of a fuel cell system, the method comprising the following steps.

[0006] First, a fuel cell system is provided. The fuel cell system comprises at least one fuel cell, in particular a plurality of fuel cells connected in series in the form of a cell stack. Here, each fuel cell comprises an anode with an anode inlet and an anode outlet, a cathode and a membrane located between the anode and the cathode. If there is only one fuel cell in the fuel cell system, the anode side corresponds to one side of an anode present in the fuel cell. If there are two or more fuel cells, the anode side of the fuel cell system refers to the sum of the anodes of all fuel cells connected in series and therefore connected to each other in the gas cycle.

[0007] The fuel cell system is in operation, which means that the fuel cell system is not in the start-up process but is in continuous energy-generating operation.

[0008] During operation of the fuel cell system, at the anode inlet, in particular upstream of the anode inlet (in the case of a plurality of fuel cells connected in series, this corresponds to the region on the anode side located before the first fuel cell, in other words upstream of the first anode), a pressure sensor is used to measure the pressure. This pressure corresponds essentially to the pressure of the gas mixture at the anode inlet, in other words to the anode gas pressure. The gas mixture may contain very small amounts of water vapor, but this has no substantial effect on the measurement result, since this is the same extent for the fuel cell system and the reference system to be described, and this effect is therefore already included in the reference characteristic curve.

[0009] Also during operation of the fuel cell system, at the anode outlet, in particular downstream of the anode outlet (in the case of a plurality of fuel cells connected in series, this corresponds to the area on the anode side after the last fuel cell, in other words, downstream of the last anode), a pressure is measured using another pressure sensor. This pressure corresponds essentially to the pressure of the gas mixture on the anode side of the fuel cell system. In addition to hydrogen, the gas mixture may also contain nitrogen and water vapor, which are detected together in the measurement. Since the content of water vapor in the anode gas mixture is very small, it can also be ignored.

[0010] According to the pressure measured at the anode inlet (p Anodeneinlass ) and the pressure measured at the anode outlet (p Anodenauslass ), the pressure difference (Δp) can be determined. Here, the pressure difference (Δp) is composed as follows:

[0011] Δp=p Anodeneinlass -p Anodenauslass =p stromentnahme +p volumenstrom

[0012] Here, pressure is expressed in kilopascals (kPa).

[0013] Here, p stromentnahme corresponds to the hydrogen pressure used to draw current from the fuel cell system, and p volumenstrom It is the pressure generated due to friction losses on the anode side of the fuel cell stack as the gas mixture flows through the fuel cell stack.

[0014] In order to determine p stromentnahme In an additional method step, the current drawn from the fuel cell system is measured using a sensor. The current is measured in amperes (A) here. stromentnahme It can be determined according to the following formula 1 and formula 2:

[0015] P stromentnahme =n H2_Stromentnahme ×R×T / V Formula 1

[0016] In Formula 1:

[0017] -n H2_Stromentnahme = the amount of hydrogen used to generate the current [mole]

[0018] - R = Universal gas constant: 8.3145 [joule / (mole·Kelvin)]

[0019] - T = fuel cell temperature [Kelvin] (in the case of two or more fuel cells, T corresponds to the average temperature of the fuel cell stack; in any case, T represents the temperature of the anode gas mixture measured by the temperature sensor)

[0020] - V = volume of the anode in the direction of the volume flow between the two pressure measurement areas (usually between the two pressure sensors, i.e. between the pressure sensor at the anode inlet and the pressure sensor at the anode outlet) [cubic meters] (in the case of two or more fuel cells in a fuel cell system, V corresponds to the total volume of all anodes)

[0021] n H2_Stromentnahme =I×t×n Zellen / F / 2 Formula 2

[0022] In Formula 2:

[0023] I = Current drawn from the fuel cell system [amperes]

[0024] t = time [seconds] (acquisition current action time)

[0025] n Zellen = Number of cells connected in series in a fuel cell system

[0026] F = 96485.3 [Coulomb / mole] (Faraday constant)

[0027] The number 2 represents each hydrogen molecule H 2 The number of electrons.

[0028] In order to further determine the volume percentage content of hydrogen, a reference value needs to be provided. The reference value is obtained in substantially the same manner as the value of the above-mentioned fuel cell system. In order to determine the reference value, a reference fuel cell system is provided, which is advantageously of the same construction as the above-mentioned fuel cell system and includes at least one reference fuel cell with a reference anode (having a reference anode inlet and a reference anode outlet), a reference cathode, and a reference membrane located between the reference anode and the reference cathode. If the fuel cell system includes a plurality of fuel cells, the reference fuel cell system also advantageously includes a plurality of fuel cells.

[0029] The reference values ​​required for the method are obtained from the reference fuel cell system as follows. Here, the same principles and assumptions as for the fuel cell system can be used, and the same definitions disclosed above also apply in the corresponding sense:

[0030] First, a reference pressure is measured at the reference anode inlet using a pressure sensor. As indicated for the previously disclosed fuel cell system, the "reference electrode inlet" refers to upstream of the reference anode, and in the case of multiple reference fuel cells connected in series, upstream of the first reference anode of the reference fuel cell stack.

[0031] The reference pressure is then measured at the reference anode outlet. "Reference electrode outlet" here again means downstream of the reference anode and, in the case of a plurality of reference fuel cells connected in series, downstream of the last reference anode of the reference fuel cell stack.

[0032] During the measurement of the reference pressure, the gas flow in the reference fuel cell system is changed from 100 volume percent nitrogen to 100 volume percent hydrogen by adding hydrogen, and the volume percentage content of each hydrogen can be determined. This can be achieved, for example, by gas chromatography, that is, the partial volume flow to be measured is directed to a gas chromatograph. In order to reduce errors, the hydrogen concentration and the additional nitrogen concentration are preferably determined twice, respectively, at a position as close as possible to the measurement of the pressure at the anode inlet and the pressure at the anode outlet. All calculations are based on an average anode gas concentration, which is determined by the average of the two concentration sensor values ​​and represents the average hydrogen concentration in the fuel cell stack. In addition, the current obtained from the reference fuel cell system is measured in amperes using a current sensor. In addition, the water concentration in the gas mixture can also be determined to further reduce errors.

[0033] Based on the determined pressure, determine the reference pressure difference Δp ref , where the following formula applies:

[0034] Δp ref =p ref_Stromentnahme +p ref_Volumenstrom

[0035] Here, p ref_stromentnahme corresponds to the hydrogen pressure used to draw current from the reference fuel cell system, and p ref_volumenstrom is the pressure generated due to friction losses when the gas mixture flows through the reference fuel cell stack on the anode side of the reference fuel cell stack. Due to the large difference in density between nitrogen and hydrogen, the magnitude of the friction losses depends significantly on the amount of hydrogen gas present in the gas mixture on the anode side of the reference fuel cell system.

[0036] In order to determine p stromentnahme, the current that needs to be obtained and measured from the reference fuel cell system.

[0037] p ref_Stromentnahme It can be determined according to the following formula 3 and formula 4:

[0038] p ref_Stromentnahme =n ref_H2_Stromentnahme ×R×T ref / V ref Formula 3

[0039] In Formula 3:

[0040] -n ref_H2_Stromentnahme = the amount of hydrogen used to generate the current [mole]

[0041] - R = Universal gas constant: 8.3145 [joule / (mole·Kelvin)]

[0042] -T ref = reference fuel cell temperature [Kelvin] (in the case of two or more reference fuel cells, T ref corresponds to the average temperature of the reference fuel cell stack; in any case, T ref represents the temperature of the reference anode gas mixture measured by the temperature sensor)

[0043] -V ref = the volume of the reference anode in the direction of volume flow between two pressure measurement areas (usually between two pressure sensors, i.e. between the pressure sensor at the anode inlet and the pressure sensor at the anode outlet) [cubic meters] (in the case of two or more reference fuel cells in the reference fuel cell system, V corresponds to the total volume of all reference anodes).

[0044] n ref_H2_Stromentnahme =I ref ×t×n ref_Zellen / F / 2 Formula 4

[0045] In Formula 4:

[0046] -I ref = Current drawn from the reference fuel cell system [amperes]

[0047] -t = time [seconds] (to obtain the duration of the current)

[0048] -n ref_Zellen = Number of cells connected in series in a reference fuel cell system

[0049] -F = 96485.3 [Coulomb / mole] (Faraday constant)

[0050] The number 2 represents each hydrogen molecule H 2The number of electrons.

[0051] p ref_volumenstrom The reference pressure difference is known from the corresponding nitrogen / hydrogen gas mixture supplied to the anode side of the reference fuel cell system, since hydrogen and nitrogen are mixed in a predetermined ratio here, and is determined thereby.

[0052] In a further method step, the pressure difference (Δp) determined for the fuel cell system is compared to a reference pressure difference (Δp ref ) are compared to obtain the volume fractions of nitrogen and hydrogen (respectively in volume percentage) corresponding to the determined pressure difference (Δp).

[0053] Since for the corresponding reference pressure difference (Δp ref ), the volume percentage ratio of hydrogen to nitrogen is known, so the pressure difference (Δp) can be used to calculate the pressure difference for the same reference pressure difference (Δp ref )Determine the volume percentage content of hydrogen.

[0054] The reference data can be determined for the same fuel cell system as used in the method and used to determine the fuel cell system whose volume percentage content of hydrogen is to be determined on the anode side. The method is simple and inexpensive to implement, since it only requires the provision of a reference fuel cell system once to determine the reference data, and then only a pressure sensor is required in the fuel cell system. Temperature and current are standard outputs anyway. The method is therefore inexpensive, also because it can avoid the use of expensive and sensitive hydrogen sensors.

[0055] Advantageously, the fuel cell system can be operated in static operation or in dynamic operation. Dynamic operation is understood here to be an operation in which the current varies by more than 10% (minimum variation 2 amperes) (in the case of very small fuel cell stack currents <20 amperes) or by more than 15 amperes (in the case of higher fuel cell stack currents (>150 amperes), for example, this limit can be lower than 10%) relative to the current average value determined over the last 100 milliseconds of the measuring time. Dynamic operation provides less accurate values ​​for the volume percentage content of hydrogen than static operation.

[0056] It is therefore particularly preferred that the pressure measurement is not activated again until the above-mentioned condition of more than 10% of the dynamic operation (or <15 Amperes) is not met for 1 second. The system then reaches a stable state.

[0057] Static operation of the fuel cell system is preferred over dynamic operation since the respective pressure difference is easier to determine for a static system and thus the volume fraction of hydrogen in the gas mixture on the anode side of the fuel cell system can be determined more accurately.

[0058] Preferably, the anode exhaust gas flowing out of the anode outlet is recycled from the anode outlet to the anode inlet, and is therefore also referred to as recycled gas. This not only enables the recycling of the anode exhaust gas, but also contributes to the stable operation of the fuel cell system, thereby making it easier and more accurate to determine the volume percentage content of hydrogen on the anode side.

[0059] In order to further reduce errors that may occur when determining the volume percentage content of hydrogen on the anode side, it is advantageously provided that water is separated from the anode exhaust gas. It is particularly advantageous here to separate the water before measuring the pressure at the anode outlet. It is further advantageous if the anode exhaust gas is actively recirculated, in particular by means of an electric motor, or passively recirculated. Passive recirculation is achieved by supplying hydrogen to the fuel cell system from a storage container such as a tank. Active recirculation is preferred here because it produces a particularly constant volume flow on the anode side of the fuel cell system.

[0060] To further improve the method, in particular to increase the accuracy of the volume percentage values ​​of hydrogen, preferably only those reference pressures are taken into account for determining the reference data for which the reference pressure difference is substantially constant over a measuring duration of at least 100 milliseconds.

[0061] Furthermore, a fuel cell system is described according to the invention. The fuel cell system is particularly configured to carry out the method described above according to the invention. Therefore, all the above definitions and explanations about the method according to the invention also apply to the fuel cell system according to the invention. The corresponding advantageous improvements also apply to each other.

[0062] To this end, the fuel cell system comprises at least one fuel cell with an anode (with an anode inlet and an anode outlet), a cathode and a membrane between the anode and the cathode. There may also be two or more fuel cells connected in series in a fuel cell stack.

[0063] The fuel cell system includes a first pressure sensor at the anode inlet for measuring the pressure at the anode inlet (in the case of two or more fuel cells, measuring the pressure before flowing into the first series-connected anode), and includes a second pressure sensor at the anode outlet for measuring the pressure at the anode outlet (in the case of two or more fuel cells, measuring the pressure after flowing out from the last series-connected anode).

[0064] Furthermore, the fuel cell system comprises a temperature sensor for determining the temperature in Kelvin in the fuel cell or the fuel cell stack, which corresponds to the temperature of the gas mixture on the anode side of the fuel cell system.

[0065] In addition, the fuel cell system includes a sensor and a storage device for determining the current (measured in amperes) drawn from the fuel cell system. The storage device includes:

[0066] A reference value obtained for a reference fuel cell system comprising at least one reference fuel cell having a reference anode (having a reference anode inlet and a reference anode outlet), a reference cathode, and a reference membrane located between the reference anode and the reference cathode, wherein the reference value is obtained as follows:

[0067] - by measuring a reference pressure at a reference anode inlet, by measuring a reference pressure at a reference anode outlet, wherein during the measurement of the reference pressure, the gas flow in the reference fuel cell system is changed from 100 volume percent nitrogen to 100 volume percent hydrogen by adding hydrogen,

[0068] - reference values ​​representing the current respectively drawn from the reference fuel cell system, and

[0069] -Reference pressure difference Δp ref ,in

[0070] Δp ref =p ref_Stromentnahme +p ref_Volumenstrom

[0071] where p ref_stromentnahme The current drawn from the reference fuel cell system is determined from the measured value according to the following equations 3 and 4:

[0072] p ref_Stromentnahme =n ref_H2_Stromentnahme ×R×T ref / V ref Formula 3

[0073] in

[0074] -n ref_H2_Stromentnahme = the amount of hydrogen used to generate the current [mole]

[0075] - R = Universal gas constant: 8.3145 [joule / (mole·Kelvin)]

[0076] -T ref = reference fuel cell temperature [Kelvin] (in the case of two or more reference fuel cells, T ref corresponds to the average temperature of the reference fuel cell stack; in any case, T ref represents the temperature of the anode gas mixture measured by the temperature sensor)

[0077] -V ref= volume of the reference anode in the direction of volume flow between two pressure measurement areas (usually between two pressure sensors, i.e. between the pressure sensor at the anode inlet and the pressure sensor at the anode outlet) [m3] (in the case of two or more fuel cells in a fuel cell system, V corresponds to the total volume of all anodes)

[0078] n ref_H2_Stromentnahme =I ref ×t×n ref_Zellen / F / 2 Formula 4

[0079] -I ref = Current drawn from the reference fuel cell system [amperes]

[0080] -t = time [seconds] (to obtain the duration of the current)

[0081] -n ref_Zellen = Number of cells connected in series in a reference fuel cell system

[0082] -F = 96485.3 [Coulomb / mole] (Faraday constant)

[0083] The number 2 represents the number of electrons in each hydrogen molecule.

[0084] p ref_volumenstrom Determined by the corresponding nitrogen / hydrogen gas mixture.

[0085] The fuel cell system further comprises a control device configured to determine a pressure difference (Δp) between a pressure at an anode inlet and a pressure at an anode outlet (a pressure difference between a first pressure sensor and a second pressure sensor), wherein the pressure difference (Δp) is composed as follows:

[0086] Δp=p stromentnahme +p volumenstrom

[0087] The control device is further configured to compare the determined pressure difference (Δp) with a reference pressure difference (Δp ref ) to determine the volume fraction (in volume percent) of nitrogen and hydrogen corresponding to the determined pressure difference (Δp), and to obtain the reference fuel cell system at a specific reference pressure difference (Δp ref ) is determined from the volume fractions of nitrogen and hydrogen obtained under ), where the volume percentage content of hydrogen is measured for a reference fuel cell system and is therefore known.

[0088] Furthermore, the fuel cell system advantageously comprises an output device for outputting the determined hydrogen content, which output device can be designed, for example, in the form of a monitor or a display.

[0089] The fuel cell system according to the invention is constructed identically to a conventional fuel cell system and has two pressure sensors for determining the pressure difference between the anode inlet and the anode outlet. The fuel cell system is therefore very efficient and cost-effective and can reliably determine the volume percentage content of hydrogen on the anode side of the fuel cell system. This can also increase the efficiency of the fuel cell system.

[0090] It is further advantageous that the fuel cell system includes a recirculation loop for recirculating the anode exhaust gas flowing out of the anode outlet from the anode outlet to the anode inlet. This enables more efficient use of the fuel gas and helps to more evenly distribute the gas mixture in and out of the anode, which reduces errors in determining the volume percentage content of hydrogen on the anode side of the fuel cell system.

[0091] Furthermore, from the perspective of reducing measurement errors associated with determining the volume percentage content of hydrogen, it is advantageous if the fuel cell system comprises a water separator in the recirculation loop, wherein the water separator is particularly arranged upstream of the second pressure sensor.

[0092] In order to improve the stationary operation of the fuel cell system, it is further advantageously provided that the recirculation circuit comprises an electric machine for actively recirculating the anode exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Further details, features and advantages of the invention are apparent from the following description and the accompanying drawings, which show:

[0094] Figure 1 is a fuel cell system according to a first advantageous refinement; and

[0095] Figure 2 is an example diagram for determining the volume percentage content of hydrogen in a fuel cell system according to a second advantageous refinement. DETAILED DESCRIPTION

[0096] Only the essential aspects of the invention are shown in the drawings. All other aspects are omitted for the sake of clarity.

[0097] Figure 1 A fuel cell system 1 according to a first advantageous development is shown in a simplified and schematic manner. The fuel cell system 1 comprises a fuel cell stack. As an example of a fuel cell stack, individual fuel cells 2 are shown. In a fuel cell stack, a plurality of fuel cells 2 are connected in series. Each fuel cell 2 comprises an anode 3 with an anode inlet 3a and an anode outlet 3b, a cathode 4 and a membrane 5 located between the anode 3 and the cathode 4.

[0098] At the anode inlet 3a, i.e., slightly upstream of the anode inlet 3a, a first pressure sensor 6 is arranged, which is configured to measure the pressure at the anode inlet 3a. At the anode outlet 3b, i.e., slightly downstream of the anode outlet 3b, a second pressure sensor 7 is arranged to measure the pressure at the anode outlet 3b. Upstream of the second pressure sensor 7, a water separator 8 is integrated in the anode exhaust gas pipeline.

[0099] Anode exhaust gas discharged from anode outlet 3b is recycled to the anode inlet through recirculation loop 9. In addition, hydrogen can be fed into recirculation loop 9 through hydrogen supply pipe 10 (for example, from storage tank 11) and delivered to anode inlet 3a.

[0100] Furthermore, a temperature sensor 12 is installed upstream of the anode outlet 3a, ie directly at the anode outlet, for determining the temperature in the fuel cell 2 and thus in the anode exhaust gas on the anode side of the fuel cell. Alternatively, a temperature sensor can also be arranged in the cooling circuit of the fuel cell system 1.

[0101] The fuel cell system 1 further comprises a sensor (not shown) for determining the current drawn from the fuel cell system 1 and a storage device 20. The storage device 20 contains reference values ​​obtained for a reference fuel cell system having a reference fuel cell stack, the reference fuel cell stack comprising a number of reference fuel cells corresponding to the number of fuel cells in the fuel cell stack, each reference fuel cell having a reference anode (having a reference anode inlet and a reference anode outlet), a reference cathode and a reference membrane located between the reference anode and the reference cathode, wherein the reference values ​​are obtained as follows:

[0102] On the one hand, by measuring a reference pressure at a reference anode inlet, by measuring a reference pressure at a reference anode outlet, wherein during the measurement of the reference pressure, the gas flow in the reference fuel cell system is changed from 100 volume percent nitrogen to 100 volume percent hydrogen by adding hydrogen. On the other hand, reference values ​​representing the currents respectively drawn from the reference fuel cell system and the reference pressure difference Δp are stored. ref , where Δp ref =p ref_Stromentnahme +p ref_Volumenstrom , where p ref_stromentnahme The current drawn from the reference fuel cell system is determined from the measured value according to the following equations 3 and 4:

[0103] p ref_Stromentnahme =n ref_H2_Stromentnahme ×R×T ref / V ref Formula 3

[0104] in,

[0105] -n ref_H2_Stromentnahme = the amount of hydrogen used to generate the current [mole]

[0106] - R = Universal gas constant: 8.3145 [joule / (mole·Kelvin)]

[0107] -T ref = reference fuel cell temperature [Kelvin] and

[0108] -V ref = volume of the reference anode [m3]; and

[0109] n ref_H2_Stromentnahme =I ref ×t×n ref_Zellen / F / 2 Formula 4

[0110] in:

[0111] -I ref = Current drawn from the reference fuel cell system [amperes]

[0112] -t = time [seconds] (to obtain the duration of the current)

[0113] -n ref_Zellen = Number of cells connected in series in the reference fuel cell system

[0114] -F = 96485.3 [Coulomb / mol]

[0115] - Number 2 corresponds to each H 2 The number of electrons in a molecule,

[0116] And p ref_volumenstrom Determined by the corresponding nitrogen / hydrogen gas mixture.

[0117] For reference data, see Figure 2 . Figure 2 Four curves A, B, C and D are shown. The current drawn in a reference fuel cell system (in amperes) is plotted versus Δp ref relationship.

[0118] - Curve A is obtained for a reference gas mixture comprising 80% by volume of nitrogen and 20% by volume of hydrogen.

[0119] - Curve B is obtained for a reference gas mixture comprising 50% by volume of nitrogen and 50% by volume of hydrogen.

[0120] - Curve C is obtained for a reference gas mixture comprising 20% ​​by volume of nitrogen and 80% by volume of hydrogen.

[0121] - Curve D is obtained for a reference gas mixture comprising 100% by volume of hydrogen.

[0122] "X" indicates a measurement point. Circled measurement points are estimated values.

[0123] The fuel cell system 1 further comprises a control device 30, which is arranged to determine a pressure difference (Δp) between a pressure at an anode inlet 3a and a pressure at an anode outlet 3b of the fuel cell system 1, wherein the pressure difference (Δp) is composed as follows:

[0124] Δp=p stromentnahme +p volumenstrom

[0125] p stromentnahme It can be determined according to the following formula 1 and formula 2:

[0126] p stromentnahme =n H2_Stromentnahme ×R×T / V Formula 1

[0127] in,

[0128] -n H2_Stromentnahme = the amount of hydrogen used to generate the current [mole]

[0129] - R = Universal gas constant: 8.3145 [joule / (mole·Kelvin)]

[0130] - T = fuel cell temperature [Kelvin] and

[0131] - V = volume of the anode [m3]; and

[0132] n H2_Stromentnahme =I×t×n Zellen / F / 2 Formula 2

[0133] in:

[0134] - I = current drawn from the fuel cell system (1) [amperes]

[0135] -t = time [seconds] (to obtain the duration of the current)

[0136] -n Zellen = the number of cells (2) connected in series in the fuel cell system (1)

[0137] -F = 96485.3 [Coulomb / mol].

[0138] The number 2 corresponds to each H 2 The number of electrons in a molecule.

[0139] The control device 30 is further configured to compare the determined pressure difference (Δp) with a reference pressure difference (Δp ref ) to determine the volume fraction (in volume percent) of nitrogen and hydrogen corresponding to the determined pressure difference (Δp). Figure 2 The pressure difference Δp determined by the control device 30 for the fuel cell system 1 is compared with the reference pressure difference Δp ref Compare. Where these two values ​​intersect on the Y axis, Δp = Δp ref .

[0140] Since the current I obtained from the fuel cell system 1 is also measured and provided to the control device 30, the control device is also configured to determine the volume percentage content of hydrogen in the anode exhaust gas from the volume fractions of nitrogen and hydrogen in the reference system and output the value in the output device 40.

[0141] This step is also in Figure 2 , that is, on the X-axis, the X-axis represents the current obtained from the reference fuel cell system. Since the current obtained from the fuel cell system 1 is measured, Figure 2 In the case of the current of about 200 amperes, the nitrogen-hydrogen concentration ratio (in volume percent, respectively) can be read or determined at the intersection of the horizontal curve obtained by Δp and the vertical curve of the measured acquisition current. Since the exact gas mixture composition of nitrogen and hydrogen is known for the respective reference curves A to D based on gas chromatography measurements for determining the hydrogen content (in volume percent) in the reference gas mixture, the concentration of hydrogen in the anode 3 of the fuel cell system 1, i.e. the volume percent content of hydrogen, can also be derived from the intersection of the lines.

[0142] The fuel cell system 1 and the method for determining the volume percentage content of hydrogen on the anode side of the fuel cell system 1 are designed to be simple. The fuel cell system 1 corresponds to a conventional fuel cell system, expanded by a storage device, a control device and a first pressure sensor 6 and a second pressure sensor 7. The method is simple and cost-effective and can be applied without using a hydrogen sensor.

[0143] List of reference numerals:

[0144] 1 Fuel Cell System

[0145] 2 Fuel Cells

[0146] 3 Anode

[0147] 3a Anode inlet

[0148] 3b Anode outlet

[0149] 4 Cathode

[0150] 5. Membrane

[0151] 6. First pressure sensor

[0152] 7 Second pressure sensor

[0153] 8 Water separator

[0154] 9 Recirculation loop

[0155] 10 Hydrogen supply pipeline

[0156] 11 Hydrogen storage tank

[0157] 12 Temperature Sensor

[0158] 20 Storage Device

[0159] 30 Control device

[0160] 40 Output device.

Claims

1. A method for determining the volume percentage content of hydrogen on the anode side of a fuel cell system (1), the method comprising the following steps: operating a fuel cell system (1) comprising at least one fuel cell (2), the fuel cell (2) having an anode (3) with an anode inlet (3a) and an anode outlet (3b), a cathode (4) and a membrane (5) located between the anode (3) and the cathode (4); ·Measure the pressure at the anode inlet (3a); · measuring the pressure at the anode outlet (3b); Determining the pressure difference (Δp) between the pressure at the anode inlet (3a) and the pressure at the anode outlet (3b); determining the current (I) drawn from the fuel cell system (1), The pressure difference (Δp) is composed as follows: Δp=p stromentnahme +p volumenstrom Among them, p stromentnahme It can be determined according to the following formula 1 and formula 2: p stromentnahme =n H2_Stromentnahme ×R×T / V Formula 1 -n H2_stromentnahme = the amount of hydrogen used to obtain the current [moles], - R = Universal gas constant: 8.3145 [joules / (mole·Kelvin)], - T = fuel cell temperature [Kelvin], and - V = the volume of the anode in the direction of volume flow between the two pressure measurement areas [cubic meters]; and n H2_Stromentnahme =I×t×n Zellen / F / 2 Formula 2 - I = current [amperes] drawn from the fuel cell system (1), - t = time [seconds] (the duration of the current action), -n Zellen = the number of cells (2) connected in series in the fuel cell system (1), -F = 96485.3 [Coulomb / mol], -The number 2 corresponds to the number of electrons per H2 molecule; Providing reference values, which are obtained for a reference fuel cell system, the reference fuel cell system comprising at least one reference fuel cell, the reference fuel cell having a reference anode with a reference anode inlet and a reference anode outlet, a reference cathode, and a reference membrane between the reference anode and the reference cathode, wherein the reference values ​​are obtained as follows: - measuring the reference pressure at the inlet of the reference anode; - measurement of the reference pressure at the reference anode outlet, wherein, during the measurement of the reference pressure, the gas flow in the reference fuel cell system is changed from 100 volume percent nitrogen to 100 volume percent hydrogen by adding hydrogen, and the corresponding volume percent content of hydrogen is determined, and the current obtained from the reference fuel cell system is measured respectively; ●Determine the reference pressure difference Δp ref , in: Δp ref =P ref_Stromentnahme +P ref_Volumenstrom Among them, p ref_stromentnahme It can be determined according to the following formula 3 and formula 4: P ref_stromentnahme =n ref_H2_Stromentnahme ×R×T ref / V ref Formula 3 -n ref_H2_Stromentnahme = the amount of hydrogen used to obtain the current [moles], - R = Universal gas constant: 8.3145 [joules / (mole·Kelvin)], -T ref = reference fuel cell temperature [Kelvin], and -V ref = the volume of the reference anode between the two pressure measurement areas in the direction of volume flow [m3]; and n ref_H2_Stromentnahme =I ref ×t×n ref_Zellen / F / 2 Formula 4 -I ref = the current drawn from the reference fuel cell system [amperes], - t = time [seconds] (the duration of the current action), -n ref_Zellen = the number of cells connected in series in the reference fuel cell system, -F = 96485.3 [Coulomb / mol], -The number 2 corresponds to the number of electrons per H2 molecule, And where p ref_volumenstrom Determined by the corresponding nitrogen / hydrogen gas mixture; Compare the determined pressure difference (Δp) with the reference pressure difference (Δp ref ) to determine the volume fractions of nitrogen and hydrogen (in units of volume percentage, respectively) corresponding to the determined pressure difference (Δp); Determine the volume percentage of hydrogen from the volume fractions of nitrogen and hydrogen.

2. The method according to claim 1, wherein: The fuel cell system (1) is operated in static operation or dynamic operation.

3. A method according to any one of the preceding claims, wherein: The anode exhaust gas is recirculated from the anode outlet (3b) to the anode inlet (3a).

4. The method according to claim 3, wherein: Water is separated from the anode exhaust gas, in particular before the pressure at the anode outlet (3b) is measured.

5. The method according to claim 3 or 4, wherein: The anode exhaust gas is actively recirculated, in particular by means of an electric machine, or the anode exhaust gas is passively recirculated.

6. A method according to any one of the preceding claims, wherein: The first reference pressure difference Δp determined at intervals of 100 milliseconds is not taken into account. ref_1 The second reference pressure difference Δp 10% higher or lower ref_2 .

7. A method according to any one of the preceding claims, wherein: Only those reference pressures are considered for which the reference pressure difference is constant over a measurement duration of at least 100 milliseconds.

8. A fuel cell system (1), comprising: - at least one fuel cell (2) comprising an anode (3) with an anode inlet (3a) and an anode outlet (3b), a cathode (4) and a membrane (5) located between the anode (3) and the cathode (4); - a first pressure sensor (6) located at the anode inlet (3a) for measuring the pressure at the anode inlet (3a); - a second pressure sensor (7) located at the anode outlet (3b) for measuring the pressure at the anode outlet (3b); - a temperature sensor (12) for determining the temperature [Kelvin] in the fuel cell (2); - a sensor for determining the current [amperes] drawn from the fuel cell system (1); - a storage device (20), the storage device comprising: a reference value obtained for a reference fuel cell system, the reference fuel cell system comprising at least one reference fuel cell, the reference fuel cell having a reference anode with a reference anode inlet and a reference anode outlet, a reference cathode and a reference membrane between the reference anode and the reference cathode, wherein the reference value is obtained as follows: a) By measuring the reference pressure at the reference anode inlet, By measuring the reference pressure at the reference anode outlet, wherein, during the measurement of each reference pressure, the gas flow in the reference fuel cell system is changed from 100 volume percent nitrogen to 100 volume percent hydrogen by adding hydrogen; b) reference values ​​representing the current respectively drawn from a reference fuel cell system; and c) Reference pressure difference Δp ref ,in: Δp ref =P ref_Stromentnahme +P ref_Volumenstrom where p ref_stromentnahme Determined from the measured value of the current taken from the reference fuel cell system according to the following Equations 3 and 4: P ref_stromentnahme =n ref_H2_Stromentnahme ×R×T ref / V ref Formula 3 -n ref_H2_Stromentnahme = the amount of hydrogen used to obtain the current [moles], - R = Universal gas constant: 8.3145 [joules / (mole·Kelvin)], -T ref = reference fuel cell temperature [Kelvin], and -V ref = volume of the reference anode [m3]; and n ref_H2_Stromentnahme =I ref ×t×n ref_Zellen / F / 2 Formula 4 -I ref = the current drawn from the reference fuel cell system [amperes], - t = time [seconds] (the duration of the current action), -n ref_Zellen = the number of cells connected in series in the reference fuel cell system, -F = 96485.3 [Coulomb / mol], -The number 2 corresponds to the number of electrons per H2 molecule, And p ref_volumenstrom Determined by the corresponding nitrogen / hydrogen gas mixture; - a control device (30) configured to: - determining the pressure difference (Δp) between the pressure at the anode inlet (3a) and the pressure at the anode outlet (3b), wherein the pressure difference (Δp) is composed as follows: Δp=p stromentnahme +p volumenstrom - Compare the determined pressure difference (Δp) with the reference pressure difference (Δp ref ) to determine the volume fractions of nitrogen and hydrogen (in volume percentages) corresponding to the determined pressure difference (Δp), - determining the volume percentage content of hydrogen in the anode exhaust gas from the volume fractions of nitrogen and hydrogen; and - Optionally, output means (40) for outputting the determined hydrogen content.

9. The fuel cell system (1) according to claim 8, further comprising a recirculation loop (9) for recirculating the anode exhaust gas from the anode outlet (3b) to the anode inlet (3a).

10. The fuel cell system (1) according to claim 9, further comprising a water separator (8) located in the recirculation loop (9), wherein: The water separator (8) is in particular arranged upstream of the second pressure sensor (7); and / or the recirculation circuit (9) further comprises a motor for actively recirculating the anode exhaust gas.

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