Method for determining humidity of gas flow at measuring point of fuel cell system, fuel cell system, vehicle, computer program and computer readable medium

Abstract

The invention relates to a method for determining the humidity of a gas flow at a measuring point of a fuel cell system, a fuel cell system, a vehicle, a computer program and a computer readable medium. The invention relates to a method for determining (3) the humidity of a gas flow at a measurement point of a fuel cell system (7), the humidity of the gas flow at the measurement point being determined (3) on the basis of the difference between the hydrogen-nitrogen ratios of the gas flow measured by means of two sensors (9, 10). The invention also relates to a vehicle (6) and a fuel cell system (7). The invention also relates to a computer program (12) and a computer readable medium (13).

Description

Technical Field

[0001] The present invention relates to a method for determining the humidity of a gas flow at a measurement site of a fuel cell system, a fuel cell system, a vehicle, a computer program, and a computer-readable medium. Background Art

[0002] In a fuel cell system, nitrogen can accumulate at the anode of the fuel cell stack. This accumulation causes interference in the reaction between hydrogen and oxygen, which results in a loss of efficiency of the fuel cell.

[0003] Another aspect affecting the fuel cell efficiency is the water content / humidity of the proton exchange membrane of the fuel cell system. The relative air humidity where the proton exchange membrane is located is in the range of 70% to 80%. To achieve these operating conditions, the air on the cathode side is humidified so that the fuel cell operates at optimal efficiency. However, excessive humidity of the gas flow can hinder gas diffusion. The moisture generated when hydrogen and oxygen react can be an additional interfering factor, which further increases the humidity of the gas flow. The resulting effects are difficult to predict.

[0004] To achieve defined conditions at the fuel cell or counteract the effects of performance degradation, nitrogen and excess water are removed from the fuel cell by suddenly opening a valve in a so-called purge line. This process is called a purge process. Since the fuel cell lacks a necessary monitoring sensor system, the purge process is carried out at regular time intervals regardless of whether such a purge process is required. Therefore, hydrogen is wasted, and in the case of frequent but unnecessary purge processes, this means a reduction in the driving range of a vehicle powered by such a fuel cell.

[0005] Document CN 112490473 A discloses a humidity management system.

[0006] Document CN 113346110 A discloses a measuring device.

[0007] Document US 7858258 B2 discloses a fuel cell process.

[0008] Document US 10090544 B2 discloses a fuel cell system.

[0009] Document US 20060134480 A1 discloses a humidity sensor.

[0010] Document CN 113540529 A discloses a measuring system. Summary of the Invention

[0011] The object of the present invention is to propose an alternative method which, in particular, does not require the use of a humidity sensor to determine the humidity of the gas flow in a fuel cell system. Furthermore, the object is to provide a fuel cell system or a vehicle in which such a method can be implemented. Furthermore, another object is to provide a computer program which, in particular, facilitates the implementation of the method. Furthermore, another object is to provide a computer-readable medium having the computer program.

[0012] The object related to the method is achieved by a method having the features of claim 1.

[0013] An embodiment of the present invention relates to a method for determining the humidity of a gas flow at a measurement site in a fuel cell system, wherein the fuel cell system comprises a measurement site and a reference site, wherein the measurement site and the reference site are selected such that the gas flow has substantially the same hydrogen-nitrogen ratio on the reference site and at the measurement site, wherein the reference site is selected such that the gas flow has a known humidity at the reference site, and wherein the method comprises the following steps: measuring the hydrogen-nitrogen ratio of the gas flow at the measurement site by means of a first sensor; measuring the hydrogen-nitrogen ratio of the gas flow at the reference site by means of a second sensor; and determining the humidity of the gas flow at the measurement site based on the difference between the hydrogen-nitrogen ratios measured by means of the two sensors.

[0014] By means of the method according to the present invention, a humidity sensor for measuring the humidity of the gas flow can be dispensed with, which results in a cost advantage.

[0015] Preferably, the humidity of the gas flow means the fraction of liquid vapor or water vapor in the gas flow.

[0016] The term "approximately equal", i.e. "the hydrogen-nitrogen ratio is approximately equal", can preferably be understood as a maximum difference of 8%, 5%, 3% or 1% between the hydrogen-nitrogen ratios at the two sites. Alternatively, it is also conceivable that the hydrogen-nitrogen ratios at the two sites are equal rather than approximately equal.

[0017] Preferably, the gas flow is a gas flow mixture which particularly preferably comprises hydrogen and / or nitrogen.

[0018] Furthermore, preferably, the gas flow can be understood as a gas volume flow or a gas volume flow rate.

[0019] Preferably, determining the humidity of the gas flow at the measurement site based on the difference between the hydrogen-nitrogen ratios measured by means of the two sensors comprises: calculating, in particular, based on the hydrogen-nitrogen ratios measured at the two locations. Alternatively, for the determination, a preferably pre-determined table, characteristic curve family or transfer function is used. The table, characteristic curve family or transfer function can be determined mathematically or experimentally.

[0020] Particularly advantageously, the first sensor is arranged at the measurement site and / or the second sensor is arranged at the reference site. In this way, direct measurement can be achieved by means of one or more sensors at the respective sites.

[0021] Furthermore, it is advantageous that the measurement site is located at the anode of the fuel cell stack of the fuel cell system.

[0022] The known humidity can preferably be understood as a constant value, for example 95%, or as a value range, for example 90% to 98%. Preferably, this is understood as a value with 100% or approximately 100% humidity.

[0023] Also advantageously, the reference site is a site or position within the region of the water separator or on the water separator. Such a water separator is preferably part of the fuel cell system and is used to dehumidify the gas flow. The water separator is preferably arranged such that moisture can be removed from the gas flow by means of the water separator. Particularly preferably, the second sensor is arranged upstream of the water separator, especially directly upstream of the water separator not far away, or downstream of the water separator, especially directly downstream of the water separator not far away, when observing in the flow direction of the gas flow.

[0024] The preferred embodiment is characterized in that one or more hydrogen-nitrogen ratios are one or more hydrogen-nitrogen ratios of the gas flow.

[0025] Preferably, the difference between the hydrogen-nitrogen ratios measured by means of two sensors is formed by the difference between the measurement signals of the two sensors. Each of the sensors generates a measurement signal that represents the hydrogen-nitrogen ratio and / or is proportional to the hydrogen-nitrogen ratio.

[0026] Another preferred embodiment is characterized in that the two sensors measure or determine the hydrogen-nitrogen ratio based on the thermal properties / thermodynamic properties of the gas flow. Preferably, the thermal property is the heat capacity or thermal conductivity of the gas flow. For this purpose, it is preferred that the sensors are identical sensors. In any case, it is advantageous that each of the sensors includes a heater and a temperature sensor spaced apart from the heater. The gas in the gas flow is heated by means of the heater, and based on the temperature rise, temperature rise curve or the time elapsed until a determined temperature is reached measured by the temperature sensor, conclusions can be drawn about the gas composition or gas ratio, especially the hydrogen-nitrogen ratio. The difference in the temperature rise, temperature rise curve or the time elapsed until a determined temperature is reached is based on the heat capacity and / or thermal conductivity of the gas in the gas flow because this depends on the gas composition or gas ratio.

[0027] Furthermore, advantageously, the first sensor and the second sensor each have a measurement chamber which is designed such that the gas of the gas flow can penetrate into the measurement chamber, yet the gas has no flow rate or the flow rate of the gas is negligible. A negligible flow rate is a flow rate that does not affect or hardly affects the measurement of the respective sensor. Alternatively, the sensor is constructed and / or designed such that the gas flow to be measured generates the same or equal flow rate on the heater and the temperature sensor of the sensor. Thus, the influence of the flow rate of the gas flow can be eliminated.

[0028] Another preferred embodiment is characterized in that the two sensors are calibrated in the same way. Preferably, the sensors are calibrated in the same way and / or by means of the same gas, the same gas composition or the same hydrogen-nitrogen ratio. By the same calibration, it is ensured that the sensors provide the same measurement signal in the case of the same gas concentration. Thus, the humidity of the gas flow at the measurement site can be obtained from the difference between the two measurement signals of the sensors, because the hydrogen-nitrogen ratio is the same at the measurement site and the reference site, and the difference between the measurement signal at the measurement site and the measurement signal at the reference site is only based on the difference in the humidity of the gas flow at this site and the humidity at the other site.

[0029] Furthermore, preferably, the two sensors each provide a measurement signal and are calibrated in the same way, and wherein the difference between the sensor measurement signal at the measurement site and the sensor measurement signal at the reference site is caused only by the difference in the humidity of the gas flow at the reference site and the humidity of the gas flow at the measurement site. Preferably, both sensors are calibrated for the reference site and, in so doing, provide in particular the same measurement signal. Thus, the difference in the measurement signals is preferably only based on the difference in the humidity of the gas flow at the reference site and the humidity at the measurement site, whereby the humidity of the gas flow at the measurement site can be determined or can be determined from the difference in the measurement signals of the two measurement signals. This is also feasible even if the sensor is a gas concentration sensor rather than a humidity sensor.

[0030] Furthermore, preferably, the gas flow has the same gas proportion at the measurement site and the reference site, yet the humidity of the gas flow at the two sites is different from each other.

[0031] Another preferred embodiment is characterized in that the method further comprises the following steps: when the humidity of the gas flow at the measurement site exceeds a threshold value of the gas flow humidity, a purging process is initiated. This step is preferably part of an evaluation, in particular part of the evaluation of the measured values of two sensors. For this purpose, it is conceivable to provide an evaluation unit, which is preferably implemented in a controller. Preferably, a predetermined threshold value is involved, wherein the threshold value is preferably a limit value. In this way, the humidity of the gas flow is reduced because ambient air is supplied to the gas flow. The ambient air can preferably be pre-treated ambient air. The treatment is preferably a temperature control measure, filtration or water separation. When this step is executed, the method is preferably a method for initiating a purging process for a fuel cell system. The humidity of the gas flow is reduced by this method. In addition, the purging process is only initiated when it is really needed, i.e., when the humidity of the gas flow at the measurement site exceeds a predetermined threshold value.

[0032] Another preferred embodiment is characterized in that the method further comprises the following steps: if it is determined that at least one of the sensors has a functional failure, a load point-controlled or time-related purging process is initiated. In this way, it is prevented that the initiation of the purging process fails when one of the two sensors fails. The time correlation of the purging process particularly means that the purging process is initiated at the latest after a certain predetermined time, wherein this time period is selected to ensure that the humidity of the gas flow at the measurement site remains below the threshold value or another threshold value.

[0033] Another preferred embodiment is characterized in that the method further comprises the following steps: the two sensors are diagnosed by temporarily forming a gas flow with a water-free reference gas and, during this period, determining a functional failure of at least one of the two sensors based on the difference between the measurement signals of the two sensors. Here, the gas flow is preferably completely formed by the reference gas. Preferably, the two steps are executed simultaneously. The reference gas is preferably hydrogen, in particular pure hydrogen. Preferably, this step is executed before starting the fuel cell system. Preferably, before determining a functional failure of at least one of the sensors, the maximum allowable difference between the measurement signals is 1.5%, 5.5%, 8.5% or 10%. That is, when the maximum value of the difference between the measurement signals is exceeded, a functional failure is determined. The difference between the measurement signals is in particular the difference between the two measurement signals generated by the two sensors. The maximum value of the difference between the measurement signals (from which a functional failure can be determined) is in particular specified in such a way that it is higher than the difference in the hydrogen-nitrogen ratio of the gas flow expected at the measurement site and the reference site.

[0034] The object related to the fuel cell system is thus achieved: to provide a fuel cell system having a controller, a first sensor and a second sensor, as well as a measurement site and a reference site, wherein the first sensor is arranged at the measurement site, and the second sensor is arranged at the reference site, wherein the measurement site and the reference site are selected such that the gas flows through the measurement site and the reference site have the same hydrogen-nitrogen ratio at the reference site and the measurement site, wherein the reference site is selected such that the gas flow has a known humidity at the reference site, and wherein the controller is designed to implement the method according to the present invention.

[0035] The above-mentioned method according to the present invention and all its embodiments are applicable to the fuel cell system according to the present invention and / or can be implemented by the fuel cell system according to the present invention.

[0036] Equally preferably, all the above-mentioned design embodiments can be applied to the fuel cell system alone or together in any combination.

[0037] The object related to the vehicle is thus achieved, namely, to provide a vehicle having such a fuel cell system. The vehicle is preferably a motor vehicle, which is especially designed as a passenger car or a truck. In addition, it preferably relates to a vehicle having an electric drive, wherein the electric drive can especially be supplied with electrical energy by the fuel cell system. In this way, a particularly efficient vehicle is provided.

[0038] The object related to the computer program is thus achieved, namely, to provide a computer program which contains instructions that cause the fuel cell system, the vehicle or the controller to perform the steps according to the present invention.

[0039] The object related to the computer-readable medium is achieved by a computer-readable medium storing a computer program. The computer-readable medium is preferably a volatile or permanent memory. Preferably, the computer-readable medium or such a memory is part of the controller.

[0040] Advantageous improvements of the present invention are described in the dependent claims and the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be described in detail below with reference to the accompanying drawings by means of embodiments. Among them:

[0042] Figure 1 A vehicle is shown, and

[0043] Figure 2 A method for starting a purging process for a fuel cell system is shown. DETAILED DESCRIPTION OF THE INVENTION

[0044] Figure 1Vehicle 6 according to the invention is shown. The vehicle is a motor vehicle and has an electric drive device and a fuel cell system 7. The fuel cell system 7 supplies electrical energy to the electric drive device. The fuel cell system 7 includes a channel 8 through which a gas flow passes. Two sensors 9, 10 are arranged spaced apart from each other, and these sensors measure the hydrogen-nitrogen ratio of the gas flow at the respective locations of the sensors 9, 10. The first sensor 9 is arranged at a measurement location of the channel 8, and the second sensor 10 is arranged at a reference location of the channel 8. The reference location is arranged adjacent to the water separator, thereby ensuring that a known humidity of the gas flow is established at this location. The hydrogen-nitrogen ratio is the same at the measurement location and the reference location. Thus, the humidity of the gas flow at the measurement location can be determined based on the different measurement results of the two sensors 9, 10. For this purpose, the vehicle 6 includes a controller 11, and the controller includes a computer-readable medium 12 on which a computer program 13 is stored. The computer program 13 includes commands that cause Figure 1 the device shown in Figure 2 to implement the method according to the invention and / or the method as

[0045] Figure 2 A method according to the invention is shown, which can be implemented by means of Figure 1 the device. The description of the method according to the invention refers to Figure 1 the device. First, a measurement 1 is performed by means of the first sensor at the measurement location. Measurement 1 measures the hydrogen-nitrogen ratio of the gas of the gas flow based on the thermal conductivity of the gas of the gas flow. Simultaneously or immediately afterwards, another measurement 2 is performed by means of the second sensor at the reference location. Measurement 2 also measures the hydrogen-nitrogen ratio of the gas of the gas flow based on the thermal conductivity of the gas of the gas flow. Now, based on the hydrogen-nitrogen ratios measured twice at two different locations, the gas humidity of the gas flow is determined 3. Then an evaluation 4 is performed: whether the gas humidity of the gas flow at the measurement location exceeds a threshold value. If the threshold value is not exceeded, the method is restarted. However, if the gas humidity of the gas flow at the measurement location exceeds the threshold value, a purge process 5 is started, and the purge process purges the gas flow with ambient air, thereby greatly reducing the gas humidity of the gas flow. After starting the purge process 5, the method is restarted.

[0046] The embodiments of the drawings are not restrictive features in particular, but are only used to illustrate the concept of the invention.

[0047] List of reference numerals:

[0048] 1 Measurement

[0049] 2 Measurement

[0050] 3 Determination

[0051] 4 Evaluation

[0052] 5 Start

[0053] 6 Vehicle

[0054] 7 Fuel cell system

[0055] 8 Channel

[0056] 9 First sensor

[0057] 10 Second sensor

[0058] 11 Controller

[0059] 12 Computer program

[0060] 13 Computer-readable medium

Claims

1. A method for determining the humidity of a gas stream (3) at a measurement site of a fuel cell system (7), wherein, the fuel cell system (7) includes a measurement site and a reference site, wherein the measurement site and the reference site are selected such that the gas stream has an approximately equal hydrogen-nitrogen ratio at the reference site and the measurement site, and wherein the reference site is selected such that the gas stream has a known humidity at the reference site, the method comprising the steps of: - measuring (1) the hydrogen-nitrogen ratio of the gas stream at the measurement site by means of a first sensor (9), - measuring (2) the hydrogen-nitrogen ratio of the gas stream at the reference site by means of a second sensor (10), - determining (3) the humidity of the gas stream at the measurement site based on the difference between the hydrogen-nitrogen ratios measured by the two sensors (9, 10).

2. The method according to claim 1, characterized in that, the two sensors (9, 10) measure the hydrogen-nitrogen ratio respectively based on the thermal characteristics of the gas stream.

3. The method according to any one of the above claims, characterized in that, the two sensors are calibrated in the same way.

4. The method according to any one of the above claims, the method further comprises the following steps: - if the humidity of the gas stream at the measurement site exceeds the threshold value of the humidity of the gas stream, initiate (5) a purge process.

5. The method according to any one of the above claims, the method further comprises the following steps: - if it is determined that at least one of the sensors has a functional failure, initiate a load point controlled or time-related purge process.

6. The method according to any one of the above claims, the method further comprises the following steps: - performing a diagnosis of the two sensors by temporarily forming the gas stream with a reference gas free of water, and - determining a functional failure of at least one of the two sensors based on the difference in measurement signals between the two sensors.

7. A fuel cell system (7) having a controller (11), a first sensor (9) and a second sensor (10) as well as a measurement site and a reference site, wherein, the first sensor (9) is arranged at the measurement site, the second sensor (10) is arranged at the reference site, wherein the measurement site and the reference site are selected such that the gas stream flowing through the measurement site and the reference site has an approximately equal hydrogen-nitrogen ratio at the reference site and the measurement site, and wherein the reference site is selected such that the gas stream has a known humidity at the reference site, according to any one of the above claims, characterized in that the controller (11) is designed to implement the method according to any one of the above claims.

8. A vehicle (6) having the fuel cell system (7) according to claim 7.

9. A computer program (12) comprising instructions that cause the device (6, 7) according to claim 7 or 8 to perform the steps according to any one of claims 1 to 6.

10. A computer-readable medium (13) on which the computer program (12) according to claim 9 is stored.

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