DE102020117820A1 - Method for determining the fuel concentration in an anode circuit, fuel cell device and motor vehicle - Google Patents

Abstract

The invention relates to a method and a device for determining the fuel concentration in an anode circuit (7) of a fuel cell stack (4) of a fuel cell device (1) comprising an anode inlet (6) and an anode outlet (3), wherein the anode outlet (3) has a sensor measuring point (12) introduced in the anode exhaust gas flow, with a pressure sensor (p2p4) and a temperature sensor (T2T2), comprising the steps: - determining a water vapor content (yH2Ovapsat) of the gas mixture present at the anode outlet (3) with the assumption that at the sensor measuring point (12 ) fully saturated water vapor is present, by forming the quotient of the water vapor partial pressure (ppartH2ovapsat) using the known saturation vapor pressure curve for water vapor and a pressure value measured by the pressure sensor (p2p4), - determining a nitrogen content (yN2) of the gas mixture present at the anode outlet (3) through formation the quotient of the nitrogen pa tial pressure (ppartN2) and the pressure value measured by the pressure sensor (p2p4), whereby the nitrogen partial pressure (ppartN2) is determined from the thermal equation of state of ideal gases using a temperature value measured by the temperature sensor (T2T2), a known or estimated gas volume (VAnode) in the anode circuit (7 ) and a known or determined mass of nitrogen (mN2) present in the anode circuit (7), and - determination of the proportion of fuel (yH2) based on the determined proportion of water vapor (yH2ovapsat) and the determined proportion of nitrogen (yN2). The invention also relates to a motor vehicle.

Description

The invention relates to a method for determining the fuel concentration in an anode circuit of a fuel cell device. The invention also relates to a fuel cell device for carrying out the method and a motor vehicle.

Fuel cells are used to provide electrical energy in a chemical reaction between a fuel, usually hydrogen, and an oxygen-containing oxidizing agent, usually air. If the power requirement exceeds the power provided by the fuel cell, it is possible to combine several fuel cells in series to form a fuel cell stack, although the need for the reactants involved in the chemical reaction increases and there is a need on the cathode side to store the air in a compressor to compress. On the anode side, the fuel is usually provided from a fuel reservoir. The fuel and also the oxidizing agent are supplied to the fuel cells in a hyper-stoichiometric manner in order to maximize their efficiency. Fuel that has not reacted in the fuel cells is recirculated to conserve resources, i.e. fed back to the fuel cells. A recirculation fan or an ejector pump is used to convey the fuel that has not been converted, which also ensures that the recirculated fuel and the freshly supplied fuel are evenly mixed.

The fuel concentration in the anode gas of a PEM fuel cell device in vehicles must be able to be set depending on the operating point in order to achieve the extraction capacity and for safe operation, so that on the one hand, for reasons of efficiency, no more fuel than necessary, and on the other hand, to ensure a minimum supply of fuel as much fuel as possible in the Anode gas should be included. The latter case in particular can lead to fuel shortages (so-called "fuel starvation"), which must be avoided.

In order to be able to measure the fuel concentration in the anode circuit, it is known, for example, to use H ₂ concentration sensors, which, however, are expensive to purchase and sometimes supply unreliable measured values for the fuel concentration.

Methods for calculating the fuel concentration in the anode loop are in the references U.S. 2019/0 288 310 A1 , DE 10 2011 054 459 A1 and JP 2006 351 318 A specified.

It is the object of the present invention to specify a simplified and more robust method for determining the fuel concentration in the anode circuit. Furthermore, it is the object of the invention to specify a fuel cell device for carrying out the method and a motor vehicle with such a fuel cell device.

This object is achieved by a method having the features of claim 1, by a fuel cell device having the features of claim 7 and by a motor vehicle having the features of claim 8. Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

• - Ermitteln eines Wasserdampfanteils (y_H2Ovapsat) des am Anodenauslass vorhandenen Gasgemisches mit der Annahme, dass an der Sensormessstelle vollständig gesättigter Wasserdampf vorliegt, durch Bildung des Quotienten aus dem Wasserdampfpartialdruck (ppart_H2Ovapsat) anhand der bekannten Sättigungsdampfdruckkurve für Wasserdampf und aus einem vom Drucksensor (p_2p4) gemessenen Druckwert,
• - Ermitteln eines Stickstoffanteils (y_N2) des am Anodenauslass vorhandenen Gasgemisches durch Bildung des Quotienten aus dem Stickstoffpartialdruck (ppart_N2) und dem vom Drucksensor (p_2p4) gemessenen Druckwert, wobei der Stickstoffpartialdruck (ppart_N2) aus der thermischen Zustandsgleichung idealer Gase ermittelt wird anhand eines vom Temperatursensor (T_2T2) gemessenen Temperaturwerts, einem bekannten oder geschätzten Gasvolumen (V_Anode) im Anodenkreislauf und einer im Anodenkreislauf vorhandenen bekannten oder ermittelten Stickstoffmasse (m_N2), und
• - Ermitteln des Brennstoffanteils (y_H2) anhand des ermittelten Wasserdampfanteils (y_H2ovapsat) und des ermittelten Stickstoffanteils (y_N2).

The method according to the invention for determining the fuel concentration in an anode circuit of a fuel cell stack comprising an anode inlet and an anode outlet of a fuel cell device, wherein the anode outlet is assigned a sensor measuring point introduced into the anode exhaust gas flow with a pressure sensor (p _2p4 ) and a temperature sensor (T _2T2 ), includes in particular the following steps:

• - Determination of a water vapor _fraction (y H2Ovapsat ) of the gas mixture present at the anode outlet, assuming that fully saturated water vapor is present at the sensor measuring point, by forming the quotient of the water vapor partial pressure (ppart _H2Ovapsat ) based on the known saturation vapor pressure curve for water vapor and from a pressure sensor (p _2p4 ) measured pressure value,
• - Determination of a nitrogen _{fraction (y N2} ) of the gas mixture present at the anode outlet by forming the quotient of the nitrogen partial _{pressure (ppart N2 ) and the pressure value} measured by the pressure sensor (p 2p4 ), the nitrogen partial pressure (ppart _N2 ) being determined from the thermal equation of state for ideal gases based on a temperature value measured by the temperature sensor (T 2T2 ), a known or estimated volume of gas (V _anode ) in the anode circuit and _{a known or estimated mass of nitrogen (m N2} ) present in the anode circuit, and
• - Determining the proportion of fuel (y _{H2 ) based on the proportion of} water vapor determined (y H2ovapsat ) and the proportion of nitrogen determined (y _N2 ).

By using the temperature sensor and the pressure sensor at the anode outlet, a robust measuring system for determining or calculating the fuel concentration is created. A Flows on the determination of the fuel concentration from the individual components of the fuel cell device can be reliably determined and calculated out. In addition, variable influencing factors can be measured, which also improves the reliability of the determination of the fuel concentration.

It makes sense to use an initially known water vapor _fraction (y H2ovapsat ), an initially known nitrogen _{fraction (y N2} ) and an initially known fuel _{fraction (y H2} ) as a reference. A known initial situation for the anode gas composition can thus be used in order to calculate the detailed gas composition for a later point in time (measurement point) using the temperature sensor and pressure sensor at the sensor measuring point.

In this context, it is advantageous if an initially known nitrogen content (y _N2 ) is specified or measured at an initial point in time (Init), and if when determining the nitrogen content (y _N2 ) at a point in time when determining the fuel _{content (y H2} ) on the one hand each caused since the initial instant (Init) by diffusion, the anode circuit influent nitrogen mass flow (m _N2in) and on the other hand, each caused by purging, from the anode circuit flowing nitrogen mass flow (m _N2Aus) is considered.

When using a recirculation fan in the anode circuit, i.e. with an "active" recirculation of the anode gas, a gas volume flow can be calculated from the power consumption of the fan. It is important for a more precise determination of the fuel cell concentration, therefore, advantageous if the gas volume flow (V _ges) is taken into account in the anode circuit when determining the portion of fuel (y _H2), and if the gas volume flow (V _ges) based on the power consumption of an integrated in the anode circuit of the recirculation blower is determined.

In this context, it is possible for the gas volume flow (V̇ _gesPos3 ) present at the anode outlet to be determined from a difference between the gas volume flow (V̇ _{ges ) present at the recirculation fan and the gas volume flow (V̇ purge} ) exiting the anode circuit via a purge valve.

There is also the possibility that the gas volume flow (V _ges) is determined based on a model and takes into account when determining the portion of fuel (y _H2); for example, when a suction jet pump is used in the anode circuit instead of a recirculation fan.

The fuel cell device according to the invention comprises a fuel cell stack having an anode inlet and an anode outlet, the cathode side connected to a cathode gas supply and an anode circuit connected to the anode inlet and the anode outlet, which circuit is fluidically connected to a fuel reservoir for the supply of fresh fuel, and in which a purge valve for rinsing the anode circuit. Furthermore, the fuel cell device includes a control unit that is set up to carry out the above-mentioned method.

The advantages and advantageous effects mentioned in connection with the method according to the invention apply equally to the fuel cell device according to the invention and to the motor vehicle according to the invention that is equipped with such a fuel cell device.

The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the leave invention. Embodiments are therefore also to be regarded as included and disclosed by the invention which are not explicitly shown or explained in the figures, but which result from the explained embodiments and can be generated by means of separate combinations of features.

• 1 schematisch ein Brennstoffzellensystem mit einem in einen Anodenkreislauf eingebundenen Rezirkulationsgebläse, und
• 2 eine schematische Darstellung der Stoffströme auf der Anodenseite.

Further advantages, features and details of the invention result from the claims, the following description of preferred embodiments and with reference to the drawings. show:

• 1 schematically a fuel cell system with a recirculation fan integrated into an anode circuit, and
• 2 a schematic representation of the material flows on the anode side.

From the 1 It can be seen that in the part of a fuel cell device 1 shown to explain the invention, there is an anode circuit 7 with a fuel recirculation line 2 on the anode side, which leads from an anode outlet 3 of a fuel cell stack 4 to the fuel line 5 upstream of the anode inlet 6. The fuel recirculation line 2 can be associated with an anode separator, not shown in detail, in order to remove excess liquid from the anode to remove circuit 7. Since the reactants are provided over-stoichiometrically in a fuel cell, a recirculation fan 8 is integrated into the recirculation line in order to supply the fuel that has not been converted in the fuel cell or in a fuel cell stack 4 with a plurality of fuel cells again, i.e. to “recirculate” it. The fuel recirculation line 2 preferably opens into an in particular controllable ejector pump 9 of the fuel line 5 so that different proportions of the fresh fuel taken from a fuel reservoir 10 and the recirculated fuel can be fed back to the anode inlet 6 of the fuel cell stack 4 . Alternatively, the ejector pump 9 can also be dispensed with and the fuel recirculation line 2 can open directly into the fuel line 5 . A purge valve 11 is optionally arranged in the fuel recirculation line 2 downstream or alternatively upstream of the recirculation fan 8 in order to purge the anode circuit if the fuel concentration in the anode circuit 7 falls below a critical value or if the proportion of inert gases therein becomes too large.

Based on 2 the method according to the invention is explained together with its advantageous configurations. At the anode outlet there is a sensor measuring point 12 ( 1 ), which includes a temperature sensor (2T2) and a pressure sensor (2p4). An approximately known initial situation for the gas distribution is used as a reference, which is specified, for example, when the system (re)starts.

mit $y_{H2Ovapsat}=\frac{ppar{t}_{H2Ovapsat}}{p_{2P4}}$

wobei ppart_H2Ovapsat aus der Sättigungsdampfdruckkurve für Wasserdampf entnommen wird, da anzunehmen ist, dass der Wasserdampf zu 100% gesättigt am Anodenauslass 3 vorliegt. p_2P4 entspricht dem vom Drucksensor gemessenen Druck am Anodenauslass 3. Es ist anzunehmen, dass das Anteil an anderen Inertgases (zum Beispiel Argon) verschwindend gering ist und deshalb bei der Berechnung nicht zu berücksichtigen ist.Expressed in equations, in particular the following assumptions, transformations and calculations are carried out in the processing unit of the control device in order to determine the fuel concentration in the anode circuit 7 . The starting point is a general distribution of the proportions of water vapor (y _H2Ovapsat ), nitrogen (y _N2 ) and fuel (y _H2 ) in the anode gas, for which the following applies: $$\begin{array}{l}{y}_{H2Ovapsat}+{\mathrm{<figure-callout\; id="2"\; label="y\; N"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">y</figure-callout>}}_N+{\mathrm{<figure-callout\; id="2"\; label="y\; H"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">y</figure-callout>}}_H=1\\ y_{H2}=1-\left(y_{H2Ovapsat}+y_{N2}\right)\\ =>H2vOl.\%=100\ast y_{H2}\end{array}$$

With $y_{H2Ovapsat}=\frac{ppa\mathrm{right}{t}_{H2Ovapsat}}{p_{2\mathrm{<figure-callout\; id="4"\; label="P"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">P</figure-callout>}4}}$

where ppart _{H2Ovapsat is taken} from the saturation vapor pressure curve for water vapor, since it can be assumed that the water vapor is 100% saturated at the anode outlet 3. p _2P4 corresponds to the pressure measured by the pressure sensor at anode outlet 3. It can be assumed that the proportion of other inert gases (e.g. argon) is negligible and therefore not to be taken into account in the calculation.

wobei p_2P4 wiederum dem Druckwert des Drucksensors am Stapelausgang 3 entspricht.The proportion of nitrogen (y _N2 ) can be expressed by the partial pressure with ${\mathrm{<figure-callout\; id="2"\; label="y\; N"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">y</figure-callout>}}_N=\frac{ppa\mathrm{right}{t}_{N2}}{p_{2\mathrm{<figure-callout\; id="4"\; label="P"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">P</figure-callout>}4}},$

where p _2P4 in turn corresponds to the pressure value of the pressure sensor at stack outlet 3.

wobei R_N2 die spez. Gaskonstante von Stickstoff, T_2T2 die vom Temperatursensor gemessene Temperatur am Anodenauslass 3 und V_Anode das Gasvolumen im Anodenkreislauf 7 ist. R_N2 ist die ideale spezifische Gaskonstante von Stickstoff.Using the thermal equation of state for ideal gases, the nitrogen partial pressure can be determined as follows: p * V = m * R * T => $ppa\mathrm{right}{t}_{N2}=\frac{m_{N2}\ast R_{N2}\ast T_{2T2}}{V_{AnO\mathrm{i.e}e}},$

where R _N2 the spec. is the gas constant of nitrogen, T _{2T2 is} the temperature at the anode outlet 3 measured by the temperature sensor, and V _{anode is} the gas volume in the anode circuit 7. R _N2 is the ideal specific gas constant of nitrogen.

Damit ergibt sich eine Stickstoffmassenstrombilanz an den in den Figuren dargestellten Positionen Pos.1 bis Pos.5: $${\dot{m}}_{N2Pos4}={\dot{m}}_{N2Pos5}={\dot{m}}_{N2Pos1}={\dot{m}}_{N2Pos2}$$

$${\dot{m}}_{N2Pos4}={\dot{m}}_{N2Diff}+{\dot{m}}_{N2Pos2}$$

$${\dot{m}}_{N2Pos4}={\dot{m}}_{N2Pos3}-{\dot{m}}_{N2Purge}$$

The proportion of nitrogen in the anode circuit 7 changes as a result of diffusion of the nitrogen from the cathode side to the anode side and as a result of flushing processes. The following applies to the amount of nitrogen present in the anode circuit 7 - based on the initial reference time: $$m_{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">N</figure-callout>}2}={\displaystyle {\int }_{Init}^{Mess\mathrm{e.g}eitp\mathrm{and}nk}{\dot{m}}_{N2In}-{\dot{m}}_{N2A\mathrm{and}s}}$$

This results in a nitrogen mass flow balance at the positions shown in the figures Pos.1 to Pos.5: $${\dot{m}}_{N2POs4}={\dot{m}}_{N2POs5}={\dot{m}}_{N2POs1}={\dot{m}}_{N2POs2}$$

$${\dot{m}}_{N2POs4}={\dot{m}}_{N2Diff}+{\dot{m}}_{N2POs2}$$

$${\dot{m}}_{N2POs4}={\dot{m}}_{N2POs3}-{\dot{m}}_{N2P\mathrm{and}\mathrm{right}Ge}$$

mit $${\dot{m}}_{N2Diff}=\left(pPar{t}_{N2Diff}\ast A\ast \frac{k}{L}\right)\ast M_{N2},$$

wobei M_N2 die molare Masse von Stickstoff, L die Dicke der Membran der Brennstoffzelle, K die Permeabilität und A die Fläche der vom Stickstoff zu „durchlaufenden“ Membran ist.It is considered in particular at Pos. 4, since the proportion of water vapor (Y _H2Ovapsat ) in the anode gas is known here: $${\dot{m}}_{N2POsNEu}={\dot{m}}_{N2Diff}+{\dot{m}}_{N2POs2Diff}-{\dot{m}}_{N2P\mathrm{and}\mathrm{right}Ge}$$

With $${\dot{m}}_{N2Diff}=\left(pPa\mathrm{right}{t}_{N2Diff}\ast A\ast \frac{k}{L}\right)\ast M_{N2},$$

where M _{N2 is} the molar mass of nitrogen, L is the thickness of the fuel cell membrane, K is the permeability and A is the area of the membrane to be “traversed” by the nitrogen.

The law of conservation of mass applies to the diffusion partial pressure of nitrogen from the cathode side to the anode side, with the following relationship being obtained: $$pPa\mathrm{right}{t}_{N2Dif{f}_{N2Diff}}=pPa\mathrm{right}{t}_{N2KatHO\mathrm{i.e}e}-pPa\mathrm{right}{t}_{N2AnO\mathrm{i.e}e}$$

ṁ_Purge ergibt sich dabei aus einer Durchflussmengenvermessung des Purgeventils 11. Der aus dem Spülventil austretende Massenanteil (x_N2) an Stickstoff lässt sich auch ausdrücken durch $$x_{N2}=\frac{m_{N2Pos3}}{m_{ges}}=\frac{{\dot{m}}_{N2Pos3}}{{\dot{m}}_{ges}}$$

In addition, the rinsing processes of the anode circuit 7 are taken into account, where $${\dot{m}}_{N2P\mathrm{and}\mathrm{right}Ge}={\mathrm{<figure-callout\; id="2"\; label="x\; N"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">x</figure-callout>}}_N\ast {\dot{m}}_{P\mathrm{and}\mathrm{right}Ge}$$

ṁ _purge results from a flow rate measurement of the purge valve 11. The mass fraction (x _N2 ) of nitrogen exiting the purge valve can also be expressed as $${\mathrm{<figure-callout\; id="2"\; label="x\; N"\; filenames="DE102020117820A1\_0016.png"\; state="\{\{state\}\}">x</figure-callout>}}_N=\frac{m_{N2POs3}}{m_{Ges}}=\frac{{\dot{m}}_{N2POs3}}{{\dot{m}}_{Ges}}$$

In this case, m _{N2Pos3 is used} from the initial anode gas composition when the system is started or when the fuel cell device 1 is (re)started, for example after a specified shutdown time.

Für den Gasvolumenstrom (V̇_ges) lässt sich folgende Gleichung aufstellen: $$p\ast V=m\ast R\ast T=>{\dot{m}}_{gesPos3}=\frac{p\ast {\dot{V}}_{gesPos3}}{R\ast T}$$

Hierbei gilt es wiederum die Purgevorgänge zu berücksichtigen, so dass sich am Stapelausgang folgende Situation findet: V̇_gesPos3 = V̇_ges - V̇_Purge.Furthermore, the following applies - again based on the ideal gas equation - for the total mass (mges) of the anode gas: $$p\ast V=m\ast R\ast T=>m_{Ges}=\frac{p\ast V_{Ges}}{R\ast T}$$

_(Ges V) for the gas volume flow can be set up the following equation: $$p\ast V=m\ast R\ast T=>{\dot{m}}_{GesPOs3}=\frac{p\ast {\dot{V}}_{GesPOs3}}{R\ast T}$$

This applies in turn to consider the Purgevorgänge so that the stack output following situation is: V = V _{Total gesPos3} - V _Purge.

The total volume flow (V _ges) can either be determined based on a model or measured by a power consumption of the recirculation blower 8 / calculate, whereby thus, for example, V _ges results from the number of revolutions. The pressure value of the pressure sensor is used for p and the temperature value of the temperature sensor for T.

As a result, the fuel concentration in the anode circuit 7 can be determined at any point in time based solely on the measured values of the robust pressure sensor and the robust temperature sensor, without a concentration sensor.

Reference List

1

fuel cell device

2

fuel recirculation line

3

anode outlet

4

fuel cell stack

5

fuel line

6

anode inlet

7

anode circuit

8th

recirculation fan

9

ejector pump

10

fuel reservoir

11

purge valve

12

sensor measuring point

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 2019/0288310 A1 [0005]
• DE 102011054459 A1 [0005]
• JP2006351318A [0005]

Claims (8)

Method for determining the fuel concentration in an anode circuit (7) of a fuel cell stack (4) of a fuel cell device (1) comprising an anode inlet (6) and an anode outlet (3), the anode outlet (3) having a sensor measuring point (12) introduced into the anode exhaust gas flow is assigned to a pressure sensor (p _2p4 ) and a temperature sensor (T _2T2 ), comprising the steps of: - determining a water vapor content (y _H2Ovapsat ) of the gas mixture present at the anode outlet (3) with the assumption that water vapor is completely saturated at the sensor measuring point (12). is present, by forming the quotient from the water vapor partial pressure (ppart _H2ovapsat ) using the known saturation vapor pressure curve for water vapor and from a pressure _value measured by the pressure sensor (p 2p4 ), - determining a nitrogen content (y _N2 ) of the gas mixture present at the anode outlet (3) by forming the Quotient of the nitrogen partial pressure (ppart _N2 ) and that of the D pressure sensor (p _2p4 ), the nitrogen partial pressure (ppart _N2 ) being determined from the thermal equation of state for ideal gases using a temperature _value measured by the temperature sensor (T 2T2 ), a known or estimated gas volume (V _anode ) in the anode circuit (7) and a _{known or determined mass of nitrogen (m N2} ) present in the anode circuit (7), and - determining the _{proportion of fuel (y H2} ) based on the determined _{proportion of} water vapor (y H2ovapsat ) and the determined _{proportion of nitrogen (y N2} ). procedure after claim 1 , characterized in that an initially known water vapor _fraction (y H2Ovapsat ), an initially known nitrogen _{fraction (y N2} ) and an initially known fuel _{fraction (y H2} ) are used as a reference. procedure after claim 1 or 2 , characterized in that an initially known nitrogen content (y _N2 ) is specified or measured at an initial point in time (Init), and that when the nitrogen content (y _N2 ) is determined at a point in time, the fuel _{content (y H2} ) is determined since the initial point in time (Init) on the one hand each nitrogen _{mass flow (ṁ N2in ) caused by diffusion and flowing into the anode circuit (7) and on the other hand each nitrogen mass} flow (ṁ N2Aus ) flowing out of the anode circuit (7) caused by purge is taken into account. Procedure according to one of Claims 1 until 3 , Characterized in that the gas volume flow (V _ges) in the anode circuit (7) is taken into account when determining the portion of fuel (y _H2), and that the gas volume flow (V _ges) of the power consumption based on a integrated in the anode circuit (7), the recirculation blower (8 ) is determined. procedure after claim 4 , characterized _{in that the gas volume flow (V̇ gesPos3} ) present at the anode outlet (3) consists of a difference between the gas volume flow (V̇ _ges ) present in the recirculation fan (8) and the gas volume flow (V̇ _Purge ) is determined. Procedure according to one of Claims 1 until 3 Is characterized in that the gas volume flow is determined (V _ges) based on a model and taken into account when determining the portion of fuel (y _H2). Fuel cell device (1) with a fuel cell stack (4) having an anode inlet (6) and an anode outlet (3), which on the cathode side is connected to a cathode gas supply and which comprises an anode circuit (7) connected to the anode inlet (6) and the anode outlet (3), which is flow-mechanically connected to a fuel reservoir (10) for the supply of fresh fuel, and in which a purge valve (11) for flushing the anode circuit (7) is integrated, and to a control unit which is used to carry out the method according to one of Claims 1 until 6 to perform. Motor vehicle with a fuel cell device (1). claim 7 .

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