Method for controlling a fuel concentration in the cathode off-gas, fuel cell system, vehicle, computer program product and storage medium

Abstract

According to the invention, the proposed technology relates to a method for controlling a fuel concentration in the cathode off-gas of a fuel cell system (10), comprising the steps of: determining a fuel mass flow through a purge path (18), determining a dilution gas mass flow through a dilution gas portion (26), and controlling the dilution gas mass flow on the basis of the determined fuel mass flow. The technology further relates to a fuel cell system (10), a vehicle (100) and a computer program product (70) for carrying out the method, as well as to a computer-readable storage medium (80) on which the computer program product (70) is stored.

Description

[0001] Description

[0002] Method for controlling fuel concentration in cathode exhaust, fuel cell system, vehicle, computer program product and storage medium

[0003] The technology disclosed herein relates to a method for controlling a fuel concentration in the cathode exhaust of a fuel cell system, a fuel cell system for carrying out the method, and a vehicle with the fuel cell system. The technology further relates to a computer program product for executing the method and a computer-readable storage medium on which such a computer program product is stored.

[0004] Fuel cell systems for mobile applications are known in the prior art. These systems are configured in a vehicle to provide electrical energy for the vehicle's drive motor. The fuel cell system comprises a fuel cell in which fuel reacts with oxygen via reverse electrolysis, generating electricity. The fuel can be supplied to the fuel cell stack from one or more pressure vessels within the vehicle. The oxygen is typically drawn from the ambient air.

[0005] During operation of the fuel cell system, fuel can be routed from an anode exhaust path to a cathode exhaust path via a purge path. Unburned fuel enters the cathode exhaust path through the anode exhaust. This fuel is typically diluted to prevent the formation of an ignitable gas mixture in the vicinity of the fuel cell system. The fuel can be diluted with cathode exhaust directly from a cathode outlet of the fuel cell and / or with cathode gas from a bypass path. The bypass path connects a cathode inlet path directly to the cathode exhaust path, thus bypassing the fuel cell. In various operating states of the fuel cell system, not only the cathode exhaust but also the cathode gas is used to dilute the fuel in the cathode exhaust path. Introducing cathode gas into the cathode exhaust path requires a compressor in the cathode inlet path to operate at a higher power output.Furthermore, conventional fuel cell systems do not directly measure how much fuel enters the cathode exhaust path during a purge. To ensure the necessary operational safety, therefore, an unnecessarily large amount of cathode gas is often introduced into the cathode exhaust path and / or a purge process is prevented, even though a purge process would be possible and advantageous.

[0006] The object of the present invention is to create improved methods and devices for controlling the fuel concentration in the cathode exhaust gas of a fuel cell system.

[0007] The aforementioned problem is solved by the patent claims. In particular, the aforementioned problem is solved by the method according to claim 1 and by the fuel cell system, the vehicle, the computer program product, and the computer-readable storage medium according to the dependent claims. Further advantages of the disclosed technology will become apparent from the subclaims, the description, and the figures. Features described in connection with the method also apply in connection with the fuel cell system, the vehicle, the computer program product, and the storage medium, and vice versa, so that the disclosure always makes and / or can make reciprocal references to the individual aspects.

[0008] According to a first aspect of the present technology, a method for controlling the fuel concentration in the cathode exhaust of a fuel cell system is proposed. The fuel cell system comprises:

[0009] - a fuel cell with an anode and a cathode,

[0010] - an anode inlet path for guiding an anode gas into an anode inlet of the anode,

[0011] - an anode exhaust path for directing anode exhaust from an anode outlet of the anode,

[0012] - a cathode inlet path for directing a cathode gas into a cathode inlet of the cathode,

[0013] - a cathode exhaust path for directing cathode exhaust from a cathode outlet of the cathode,

[0014] - a purge path to direct anode exhaust from the anode exhaust path into the cathode exhaust path,

[0015] - a bypass path for directing cathode gas from the cathode inlet path upstream of the cathode inlet into the cathode exhaust path downstream of the cathode outlet and - a dilution gas section for directing a dilution gas downstream of the cathode outlet through the cathode exhaust path, wherein the dilution gas comprises cathode gas from the bypass path and cathode exhaust from the cathode outlet.

[0016] The procedure consists of the following steps:

[0017] - Determining a fuel mass flow through the purge path,

[0018] - Determining a dilution gas mass flow rate through the dilution gas section and

[0019] - Controlling dilution gas mass flow rate based on the determined fuel mass flow rate.

[0020] By controlling the dilution gas mass flow rate, the amount of dilution air in the cathode exhaust path can be controlled. Appropriate control of the dilution air ensures that the cathode exhaust, which is released into the environment of the fuel cell system, is non-ignitable. Furthermore, it allows for purging of the anode exhaust gas to regulate the anode exhaust flow rate whenever necessary. Unlike conventional methods and systems, this approach controls the dilution gas mass flow rate, not the purging of the anode exhaust gas. The proposed method was previously unsuitable primarily because determining the fuel mass flow rate, which forms the basis for this control, was either impossible or at least not trivial with the sensors available in conventional fuel cell systems.Until now, it was only common practice to roughly estimate the available dilution air. By controlling not the anode exhaust gas, but rather the dilution air or the dilution gas mass flow, the operating conditions at the anode can be optimized particularly easily. This, in turn, results in a correspondingly optimized operation of the fuel cell system.

[0021] Determining the fuel mass flow rate can refer to determining the fuel and / or the amount of fuel in the anode exhaust, not the total amount of anode exhaust, within the purge path. Determination can involve measuring, calculating, and / or estimating. The fuel mass flow rate can be determined, for example, using suitable sensors within, on, and / or upstream of the purge path. These sensors can then be used to perform measurements that provide data upon which the fuel mass flow rate can be calculated. These calculations can be performed using mathematical formulas, algorithms, and / or virtual models.

[0022] Determining the dilution gas mass flow rate can be understood as determining the amount of cathode gas and / or cathode exhaust gas fed into the cathode exhaust path. The dilution gas mass flow rate can be determined using suitable sensors in the cathode inlet path, the bypass path, and / or the cathode exhaust path. For example, measurements can be taken using these sensors to obtain data from which the dilution gas mass flow rate can be calculated. These calculations can be performed using mathematical formulas, algorithms, and / or a virtual model. The dilution gas mass flow rate can, for example, be calculated based on a mass flow-dependent pressure drop across the exhaust system of the fuel cell system. This pressure drop can be measured using suitable pressure sensors or at least one pressure sensor.Alternatively or additionally, the dilution gas mass flow rate can be measured using at least one mass flow sensor. This sensor can be positioned in the cathode exhaust path upstream of a diluter in the fuel cell system. In simplified terms, the dilution gas mass flow rate can be understood as the dilution air used to dilute the fuel in the cathode exhaust path.

[0023] Control can be understood as adjusting, steering, and / or regulating. Furthermore, it can be understood as taking process engineering measures to change the fuel concentration in the cathode exhaust gas or to maintain it at a desired value. The fuel cell system can have a measurement unit to determine the fuel mass flow and the diluent mass flow. This measurement unit can include the sensors described above and / or at least one processing unit configured to determine the fuel mass flow and the diluent mass flow.

[0024] To perform the procedure, a purge process and / or a drain process can be determined. That is, it can be determined whether a purge process and / or a drain process is being carried out. Furthermore, it is possible to determine the fuel mass flow rate, the diluent gas mass flow rate, and the diluent gas mass flow rate based on the determined purge process and / or the determined drain process. For example, the procedure can be implemented such that determining the fuel mass flow rate, determining the diluent gas mass flow rate, and checking the diluent gas mass flow rate are only carried out if it has been determined that no drain process was carried out during a determined purge process.This prevents water, which is discharged from the anode exhaust path via a purge valve during the drain process, from interfering with the determination of the fuel mass flow rate and thus negatively impacting the control of the dilution gas mass flow rate. In other words, by considering the determined purge and drain processes, control inaccuracies can be prevented or at least reduced.

[0025] The purge process can be understood as the removal of a process gas, particularly anode exhaust gas, from the anode exhaust path. The drain process can be understood as the flushing of a process fluid, such as water and / or a water-containing fluid that may form, for example, in a water separator on the anode exhaust path, out of the water separator.

[0026] To carry out the procedure, a fuel concentration in the anode exhaust path can be determined, i.e., measured, estimated, and / or calculated. The dilution gas mass flow rate can then be monitored based on the determined fuel concentration. In other words, the fuel mass flow rate can be determined, among other things, based on the fuel concentration in the anode exhaust path. In this context, "fuel" can be understood to refer specifically to hydrogen.

[0027] According to one implementation variant of the procedure described here, the following steps can be carried out:

[0028] - Determining an anode exhaust pressure in the anode exhaust path and

[0029] - Determining the fuel mass flow rate based on the anode exhaust pressure determined in the anode exhaust path.

[0030] It has been shown that the fuel mass flow rate can be determined particularly easily, yet reliably and accurately, based on the anode exhaust pressure in the anode exhaust path. At least one pressure sensor can be used to determine the anode exhaust pressure. The pressure sensor can be configured to determine the anode exhaust pressure at the anode outlet and / or downstream of the anode outlet. Specifically, the pressure sensor can be configured to measure the anode exhaust pressure downstream of a water separator in the fuel cell system and upstream of a purge valve in the fuel cell system. Therefore, for the method proposed here, the anode exhaust pressure can be determined downstream of the anode outlet, downstream of the water separator, and / or upstream of the purge valve.Determining the anode exhaust pressure can be understood as calculating an anode exhaust pressure value based on a measured value obtained using at least one pressure sensor.

[0031] Furthermore, it is possible that a procedure as described above comprises the following steps:

[0032] - Determining anode exhaust pressure in the purge path and

[0033] - Determining the fuel mass flow rate based on the anode exhaust pressure determined in the purge path.

[0034] It has been shown that the fuel mass flow rate can be determined particularly easily, yet reliably and accurately, based on the anode exhaust pressure in the purge path. At least one pressure sensor can be used to determine the anode exhaust pressure in the purge path. The pressure sensor can be configured to determine the anode exhaust pressure downstream of a purge valve in the fuel cell system. Therefore, the anode exhaust pressure can be determined downstream of the purge valve for the method proposed here. For particularly accurate determination of the fuel mass flow rate, the anode exhaust pressure can be determined both upstream and downstream of the purge valve. Alternatively or additionally, it is possible to estimate and / or simulate the anode exhaust pressure in the purge path.

[0035] The procedure described here may further include the following steps:

[0036] - Determining an anode exhaust gas temperature and

[0037] - Determining the fuel mass flow rate based on the determined anode exhaust gas temperature.

[0038] Based on the anode exhaust temperature, the fuel mass flow rate can be determined particularly easily, yet reliably and accurately. The anode exhaust temperature can be determined in the anode exhaust path and / or the purge path. That is, the temperature of the anode exhaust flowing through the anode exhaust path and / or the purge path can be determined. At least one temperature sensor can be used to determine the anode exhaust temperature. Furthermore, the procedure described here can include the following steps:

[0039] - Providing a target fuel concentration,

[0040] - Providing a safety factor and

[0041] - Controlling the dilution gas mass flow rate based on the target fuel concentration and based on the safety factor.

[0042] The dilution gas mass flow rate should be set as low as possible to prevent any undesirable additional power consumption by a compressor in the cathode inlet path. Undesirable and / or excessive pressure losses in the cathode inlet path can be easily and reliably prevented using the safety factor. A value between 1 and 3 or between 1 and 2, for example, 1.5, can be selected for the safety factor. The target fuel concentration and the safety factor can be stored on a computer-readable, non-volatile memory within the fuel cell system and made available there for use. Alternatively, the target fuel concentration and / or the safety factor can be stored from a decentralized storage system and made available, for example, via the internet.

[0043] In the process described here, the dilution gas mass flow rate can be controlled by monitoring the cathode gas flow through the bypass path. This allows the dilution gas mass flow rate to be adjusted to the desired value particularly quickly, reliably, and easily. Monitoring the cathode gas flow through the bypass path means that the fluid flow through the bypass path can be controlled and / or regulated to adjust the dilution gas mass flow rate to the desired value. In other words, the dilution air of the cathode gas, which is introduced into the cathode exhaust path in addition to the dilution air of the cathode exhaust, can be adjusted.

[0044] Another aspect of the present technology concerns a fuel cell system for controlling the fuel concentration in the cathode exhaust. The fuel cell system features:

[0045] - a fuel cell with an anode and a cathode,

[0046] - an anode inlet path for guiding an anode gas into an anode inlet of the anode,

[0047] - an anode exhaust path for directing anode exhaust from an anode outlet of the anode, - a cathode inlet path for directing cathode gas into a cathode inlet of the cathode,

[0048] - a cathode exhaust path for directing cathode exhaust from a cathode outlet of the cathode,

[0049] - a purge path to direct anode exhaust from the anode exhaust path into the cathode exhaust path,

[0050] - a bypass path for directing cathode gas from the cathode inlet path upstream of the cathode inlet to the cathode exhaust path downstream of the cathode outlet,

[0051] - a dilution gas section for guiding a dilution gas downstream of the cathode outlet through the cathode exhaust path, wherein the dilution gas comprises cathode gas from the bypass path and cathode exhaust from the cathode outlet,

[0052] - a detection unit configured to determine a fuel mass flow through the purge path and a dilution gas mass flow through the dilution gas section and

[0053] - a control unit configured to control the dilution gas mass flow rate based on the determined fuel mass flow rate.

[0054] The fuel cell system thus offers the same advantages as described in detail with reference to the process. The fuel cell system is preferably configured for mobile applications such as vehicles. The fuel cell system can be configured to provide electrical energy for at least one of the vehicle's drive units. The drive unit can be a machine, for example, an electric motor, used to propel the vehicle. The term "fuel cell" can refer to a single fuel cell or a fuel cell stack with multiple fuel cells. In its simplest form, the fuel cell is an electrochemical energy converter that converts fuel and oxidant into reaction products, generating electricity and heat in the process. The anode and cathode of a single fuel cell can be connected by an ion-selective or...The anode and cathode sections of the fuel cell stack are separated by an ion-permeable separator. If the fuel cell is configured as a fuel cell stack, the anode can refer to the anode section of the fuel cell stack, and the cathode to the cathode section of the fuel cell stack. The fuel cell system can refer to a PEM fuel cell system. The fuel cell system can include a diluent in which the anode exhaust gas can be diluted with the diluent gas. That is, the diluent can have a mixing section for mixing the diluent gas with the anode exhaust gas. The diluent can have a diluent gas inlet, an anode exhaust gas inlet, and a gas mixture outlet. A gas mixture of the diluent gas and the anode exhaust gas can be discharged from the diluent through the gas mixture outlet. The gas mixture can be understood as a mixed cathode exhaust gas.The proposed method can therefore be understood as a method for controlling the fuel concentration in a mixed cathode exhaust gas of a fuel cell system. At least a portion of the diluent can be considered part of the cathode exhaust gas path. The mass flow sensor described above can be positioned upstream of the diluent or directly upstream of it in the cathode exhaust gas path. That is, the diluent gas mass flow can be measured upstream of or directly upstream of the diluent.

[0055] The fuel cell system may include a humidifier through which a portion of the cathode inlet path passes upstream of the cathode, and a portion of the cathode exhaust path passes downstream of the cathode. The bypass path may be configured to divert cathode gas from the cathode inlet path upstream of the humidifier to the cathode exhaust path downstream of the humidifier. The fuel cell system may include a bypass valve to control the flow of cathode gas through the bypass path.

[0056] According to one embodiment of the fuel cell system, the detection unit can be configured to determine the anode exhaust pressure in the anode exhaust path and to determine the fuel mass flow rate based on this pressure. The detection unit can also be configured to determine the anode exhaust pressure in the purge path and to determine the fuel mass flow rate based on this pressure. Furthermore, the detection unit can be configured to determine the anode exhaust temperature and to determine the fuel mass flow rate based on this temperature.Furthermore, the fuel cell system can include a delivery unit for providing a target fuel concentration and a safety factor, whereby the control unit can be configured to control the diluent gas mass flow based on the provided target fuel concentration and the provided safety factor. The control unit can also be configured to control the diluent gas mass flow by controlling a cathode gas flow through the bypass path.

[0057] Another aspect of the proposed technology concerns a vehicle with a fuel cell system as described above, wherein the fuel cell system is configured to generate electricity in the vehicle. The vehicle may have at least one electric motor for propelling the vehicle, and the fuel cell system may be configured to supply power to this at least one electric motor. Thus, the vehicle offers the same advantages as described in detail above. The term "vehicle" can refer to a motor vehicle such as a motorized two-wheeler, a passenger car, or a truck. It can also refer to a road vehicle, an aircraft, a watercraft, a rail vehicle, or a robot.The term "vehicle" can also refer to a purely electric vehicle and a hybrid electric vehicle, which, in addition to at least one electric motor, has an internal combustion engine for propulsion. The term "vehicle" can also refer to a so-called FCEV (Fuel Cell Electric Vehicle).

[0058] Furthermore, the technology disclosed herein comprises a computer program product and a computer-readable, in particular non-volatile, storage medium on which the computer program product is stored. Thus, the computer program product and the computer-readable storage medium also offer the advantages described above. The computer program product may include instructions which, when executed by a computer, cause the computer to execute the proposed method in a fuel cell system and / or vehicle as described above.

[0059] The computer program product can be implemented as machine-readable instruction code in any suitable programming language and / or machine language, such as Java, C++, C#, and / or Python. The computer program product can be stored on a machine-readable storage medium such as a data disk, removable drive, volatile or non-volatile memory, and / or onboard memory / processor. The instruction code can program a computer and other programmable devices, such as a control unit, to perform the desired functions. Furthermore, the computer program product can be made available on a network, such as the internet, from which it can be downloaded by a user as needed.The computer program product can be implemented using software, one or more special electronic circuits (i.e., in hardware), or in any hybrid form (i.e., using software components and hardware components).

[0060] Further features and combinations of features of the proposed technology will become apparent from the following description of various embodiments, which are schematically illustrated in the figures. All features and / or advantages arising from the claims, the description, and the figures, including design details and spatial arrangements, can be significant both individually and in combination with one another.

[0061] They each show schematically:

[0062] Fig. 1 shows a fuel cell system according to an embodiment of the present technology,

[0063] Fig. 2 shows a computer-readable storage medium with a computer program product stored thereon according to an embodiment of the present technology,

[0064] Fig. 3 shows a vehicle with a fuel cell system according to an embodiment of the present technology and

[0065] Fig. 4 is a flowchart to explain a process according to an embodiment of the present technology.

[0066] Elements with the same function and mode of operation are each provided with the same reference symbols in the figures.

[0067] Fig. 1 shows a fuel cell system 10 for controlling a fuel concentration in the cathode exhaust according to one possible embodiment. The fuel cell system 10 shown comprises a fuel cell 11 with an anode 12 and a cathode 13. The fuel cell system 10 further comprises an anode inlet path 14 for directing an anode gas into an anode inlet 41 of the anode 12, an anode exhaust path 15 for directing anode exhaust from an anode outlet 42 of the anode 12, a cathode inlet path 16 for directing cathode gas into a cathode inlet 43 of the cathode 13, and a cathode exhaust path 17 for directing cathode exhaust from a cathode outlet 44 of the cathode 13. The fuel cell system also includes a purge path 18 and a bypass path 19. Purge path 18 is configured to direct anode exhaust from anode exhaust path 15 into cathode exhaust path 17.The bypass path 19 is configured to direct cathode gas from the cathode inlet path 16 upstream of the cathode inlet 43 into the cathode exhaust path 17 downstream of the cathode outlet 44. A bypass valve 25 is positioned in the bypass path 19 to control the flow of cathode gas through the bypass path 19. The fuel cell system 10 shown has a dilution gas section 26 for directing a dilution gas downstream of the cathode outlet 44 through the cathode exhaust path 17. The dilution gas contains cathode gas from the bypass path 19 and cathode exhaust from the cathode outlet 44. The dilution gas section 26 can therefore be understood as a subsection of the cathode exhaust path 17.

[0068] The fuel cell system 10 shown comprises a diluent 20, a compressor 21, and a humidifier 22. The compressor 21 is located in the cathode inlet path 16. The diluent 20 is located in the cathode outlet path 17. The humidifier 22 is located in both the cathode inlet path 16 and the cathode outlet path 17. The fuel cell system 10 also includes an injector / ejector 23 in the anode inlet path. A water separator can be positioned in and / or on the anode exhaust path 15, through which anode exhaust gas can be recirculated to the injector / ejector 23 and from which anode exhaust gas can be directed into the purge path 18. A first pressure sensor 31 and a temperature sensor 34 are located in the anode exhaust path 15. A second pressure sensor 32 is positioned in purge path 18. A purge valve 30 is positioned between the anode exhaust path 15 and purge path 19.The anode exhaust can be routed from the anode exhaust path 15 via the purge valve 30 into the purge path 18. The first pressure sensor 31 and the second pressure sensor 32 are configured to measure the anode exhaust pressure upstream and downstream of the purge valve 30, respectively.

[0069] The fuel cell system shown in Fig. 1 comprises a control unit 50 with a detection unit 51, a control unit 52, and a supply unit 53. The supply unit 53 has non-volatile, computer-readable memory. The control unit 50 can be understood as part of a vehicle control unit. The detection unit 51 is configured to detect a fuel mass flow rate through the purge path 18 and a dilution gas mass flow rate through the dilution gas section 26. To detect the dilution gas mass flow rate, a mass flow sensor 35 is positioned on the cathode exhaust path 17 downstream of the bypass path 19, downstream of the humidifier 22, and upstream of the diluent 20. The control unit 50, the detection unit 51, the control unit 52, and the supply unit 53 may have further functional components, which are distinguished from those shown in Fig.The elements extend beyond the rectangles shown in point 1 and / or are positioned outside the rectangles shown. A control unit can be understood as a device for monitoring, adjusting, measuring, calculating, controlling, and / or regulating.

[0070] The detection unit 51 is configured to determine an anode exhaust pressure in anode exhaust path 15 using the first pressure sensor 31, an anode exhaust pressure in purge path 18 using the second pressure sensor 32, and an anode exhaust temperature in anode exhaust path 15 using the temperature sensor 34. Furthermore, the detection unit is configured to determine the fuel mass flow rate based on the anode exhaust pressure determined in anode exhaust path 15, the anode exhaust pressure determined in purge path 18, and the anode exhaust temperature determined in anode exhaust path 15. The provisioning unit 53 is configured to provide a target fuel concentration and a safety factor.The control unit 52 is configured to control the dilution gas mass flow rate based on the determined fuel mass flow rate, the provided target fuel concentration, and the provided safety factor. In the fuel cell system 10 shown in Fig. 1, the dilution gas mass flow rate can be controlled, in particular, by actuating the bypass valve 25.

[0071] Fig. 2 shows a computer-readable and non-volatile storage medium 80 on which a computer program product 70 is stored. The storage medium 80 is in the form of a flash drive. The computer program product 70 comprises instructions which, when executed by a computer, cause the computer to carry out a method for controlling a fuel concentration in the cathode exhaust gas in the fuel cell system 10 shown.

[0072] Figure 3 shows a vehicle 100 in the form of a passenger car. The vehicle 100 has a fuel cell system 10 as described above, comprising a fuel cell 11 and a pressure vessel 60 for fuel. The vehicle 100 also has two electric motors 90 for propelling the vehicle 100. The fuel cell system 10 is configured to generate electrical current in the vehicle 100, which can be used to power the electric motors 90. Furthermore, the vehicle 100 has a control unit 50, which is configured to perform a procedure in the vehicle 100 for controlling a fuel concentration in the cathode exhaust.

[0073] With reference to Fig. 4, a method for controlling the fuel concentration in the cathode exhaust of the fuel cell system 10 shown is described below. In a first step S1, a fuel mass flow rate through the purge path 18 is determined. In a second step S2, a dilution gas mass flow rate through the dilution gas section 26 is determined. In a third step S3, the dilution gas mass flow rate is controlled based on the determined fuel mass flow rate. Steps S1 to S3 do not have to be carried out in the sequence shown. Steps S1 to S3 can be carried out at least partially simultaneously.

[0074] The technology disclosed here allows for further design principles in addition to those illustrated. That is to say, the technology should not be considered limited to the embodiments explained with reference to the figures.

[0075] To carry out the procedure, a distinction can be made, for example, between supercritical and subcritical flow at purge valve 30. For supercritical flows through purge valve 30, the following can apply: where

[0076] A° = critical area (unknown constant) that is fitted,

[0077] R = for the Reynolds number,

[0078] M = Molar mass,

[0079] PAnodout = measured anode exhaust pressure,

[0080] TAnodout = measured, calculated and / or estimated anode exhaust temperature, y = isentropic coefficient, x = concentration.

[0081] For subcritical flows through purge valve 30, the following may apply: where

[0082] A° = critical area (unknown constant) that is fitted,

[0083] R = for the Reynolds number (gas constant),

[0084] M = Molar mass,

[0085] PAnodout = measured anode exhaust pressure upstream of the purge valve 30,

[0086] TAnodout = measured, calculated, or estimated anode exhaust temperature, ppurgeout = measured, calculated, or estimated anode exhaust pressure downstream of the

[0087] Purge valve 30, y = isentropic coefficient, x = concentration.

[0088] The fuel mass flow rate can then be determined as follows:

[0089] W( % H2) — X N2 * ^N2 + X H2 * ^H2 + X H2O * ^H2O and

[0090] ^H2Purge ^71 Purge ' -^H2

[0091] Controlling the dilution gas mass flow rate based on the determined

[0092] Fuel mass flow can be calculated using the following equation: where

[0093] S = Safety factor and

[0094] XH2Exhaust = Fuel concentration in the cathode exhaust (maximum 4 [Vol%]). Reference symbol list

[0095] Fuel cell anode

[0096] Cathode anode inlet path anode exhaust path cathode inlet path cathode exhaust path purge path

[0097] Bypass path diluter compressor humidifier injector / ejector bypass valve

[0098] Dilution gas section

[0099] Purge valve, first pressure sensor, second pressure sensor, temperature sensor, mass flow sensor

[0100] Anode inlet Anode outlet Cathode inlet Cathode outlet

[0101] Control unit, investigation unit, control unit, provisioning unit, pressure vessel

[0102] Computer program product

[0103] Storage medium

[0104] electric motor

[0105] vehicle

Claims

Patent claims 1. Method for controlling a fuel concentration in the cathode exhaust of a fuel cell system (10), wherein the fuel cell system (10) comprises: - a fuel cell (11) with an anode (12) and a cathode (13), - an anode inlet path (14) for guiding an anode gas into an anode inlet (41) of the anode (12), - an anode exhaust path (15) for directing an anode exhaust from an anode outlet (42) of the anode (12), - a cathode inlet path (16) for directing a cathode gas into a cathode inlet (43) of the cathode (13), - a cathode exhaust path (17) for directing a cathode exhaust from a cathode outlet (44) of the cathode (13), - a purge path (18) for directing anode exhaust gas from the anode exhaust path (15) into the cathode exhaust path (17), - a bypass path (19) for directing cathode gas from the cathode inlet path (16) upstream of the cathode inlet (43) into the cathode exhaust path (17) downstream of the cathode outlet (44) and - a dilution gas section (26) for guiding a dilution gas downstream of the cathode outlet (44) through the cathode exhaust path (17), wherein the dilution gas comprises cathode gas from the bypass path (19) and cathode exhaust from the cathode outlet (44), wherein the method comprises: - Determining a fuel mass flow through the purge path (18), - Determining a dilution gas mass flow rate through the dilution gas section (26) and - Controlling the dilution gas mass flow rate based on the determined fuel mass flow rate.

2. Method according to claim 1, comprising: - Determining an anode exhaust pressure in the anode exhaust path (15) and - Determining the fuel mass flow rate based on the anode exhaust pressure determined in the anode exhaust path (15).

3. A method according to any of the preceding claims, comprising: - Determining an anode exhaust pressure in the purge path (18) and - Determining the fuel mass flow rate based on the anode exhaust pressure determined in the purge path (18).

4. A method according to any of the preceding claims, comprising: - Determining an anode exhaust gas temperature and - Determining the fuel mass flow rate based on the determined anode exhaust gas temperature.

5. A method according to any of the preceding claims, comprising: - Providing a target fuel concentration, - Providing a safety factor and - Controlling the dilution gas mass flow rate based on the target fuel concentration and based on the safety factor.

6. Method according to one of the preceding claims, wherein the dilution gas mass flow is controlled by controlling a cathode gas flow through the bypass path (19).

7. Fuel cell system (10) for controlling a fuel concentration in the cathode exhaust, comprising: - a fuel cell (11) with an anode (12) and a cathode (13), - an anode inlet path (14) for guiding an anode gas into an anode inlet (41) of the anode (12), - an anode exhaust path (15) for directing an anode exhaust from an anode outlet (42) of the anode (12), - a cathode inlet path (16) for directing a cathode gas into a cathode inlet (43) of the cathode (13), - a cathode exhaust path (17) for directing a cathode exhaust from a cathode outlet (44) of the cathode (13), - a purge path (18) for directing anode exhaust gas from the anode exhaust path (15) into the cathode exhaust path (17), - a bypass path (19) for directing cathode gas from the cathode inlet path (16) upstream of the cathode inlet (43) into the cathode exhaust path (17) downstream of the cathode outlet (44), - a dilution gas section (26) for guiding a dilution gas downstream of the cathode outlet (44) through the cathode exhaust path (17), wherein the dilution gas comprises cathode gas from the bypass path (19) and cathode exhaust gas from the cathode outlet (44), - a detection unit (51) configured to detect a fuel mass flow through the purge path (18) and a dilution gas mass flow through the dilution gas section (26) and - a control unit (52) configured to control the dilution gas mass flow rate based on the determined fuel mass flow rate.

8. Fuel cell system (10) according to claim 7, wherein the detection unit (51) is configured to determine an anode exhaust pressure in the anode exhaust path (15) and to determine the fuel mass flow based on the anode exhaust pressure determined in the anode exhaust path (15).

9. Fuel cell system (10) according to one of claims 7 to 8, wherein the detection unit (51) is configured to determine an anode exhaust pressure in the purge path (18) and to determine the fuel mass flow based on the anode exhaust pressure determined in the purge path (18).

10. Fuel cell system (10) according to one of claims 7 to 9, wherein the detection unit (51) is configured to determine an anode exhaust temperature and to determine the fuel mass flow rate based on the determined anode exhaust temperature.

11. Fuel cell system (10) according to one of claims 7 to 10, comprising a provision unit (53) for providing a target fuel concentration and for providing a safety factor, wherein the control unit (52) is configured to control the dilution gas mass flow based on the provided target fuel concentration and based on the provided safety factor.

12. Fuel cell system (10) according to any one of claims 7 to 11, wherein the control unit (52) is configured to control the dilution gas mass flow by controlling a cathode gas flow through the bypass path (19).

13. Vehicle (100) with a fuel cell system (10) according to any one of claims 7 to 12, wherein the fuel cell system (10) is configured to generate electrical current in the vehicle (100).

14. Computer program product (70), comprising instructions which, when the computer program product (70) is executed by a computer, cause it to execute the method according to one of claims 1 to 6 in a fuel cell system (10) according to one of claims 7 to 12 and / or in a vehicle (100) according to claim 13.

15. Computer-readable storage medium (80) with a computer program product (70) stored thereon according to claim 14.

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