Method for detecting liquid water in a fuel cell, fuel cell system, and fuel cell vehicle

Abstract

The invention relates to a method for detecting liquid water in a fuel cell (1) of a fuel cell system (2), wherein - at least one of the following parameters is measured, - a pressure difference between an inlet (4) and an outlet (5) of the fuel cell (1), - the power consumption of an electric turbocharger (9) which supplies compressed charge air to the fuel cell (1) and which is driven by exhaust gas of the fuel cell (1), - the differential temperature of a coolant flowing through the fuel cell (1) between a coolant inlet (14) and a coolant outlet (15) of the fuel cell (1), and - the valve position of a pressure control valve (18) in an exhaust gas channel (11) of the fuel cell (1); - the measured parameter is compared with a predefined parameter; and - a signal is generated and / or an action is initiated if the difference between the measured parameter and the predefined parameter reaches or exceeds a predefined threshold. In this manner, the output of the fuel cell (1) as well as the service life thereof can be increased.

Description

[0001] Method for detecting liquid water in a fuel cell, fuel cell system and fuel cell vehicle

[0002] The present invention relates to a method for detecting liquid water in a fuel cell of a fuel cell system. The invention also relates to a fuel cell system with a computer device for implementing this method, as well as to a fuel cell vehicle with such a fuel cell system.

[0003] Due to ecological aspects, electric vehicles are increasingly becoming the focus of consumers, as they have significantly lower emissions than vehicles powered by combustion engines. In addition to battery-electric vehicles, fuel cell vehicles are also being used more and more. These generate electrical energy using a fuel cell, which is then used via an electric drive system to power the fuel cell vehicle. In a fuel cell, the chemical reaction energy of a continuously supplied fuel, usually hydrogen, and an oxidizing agent, usually the oxygen present in air, is converted into electrical energy. The only exhaust gas from the fuel cell is water. In order to keep the performance of the fuel cell at a consistently high level, the supply air stream is usually humidified using a humidifier.

[0004] However, at very high fuel cell loads, the water in the fuel cell can precipitate into liquid form, posing the risk of mechanical damage to downstream components, such as an exhaust gas turbocharger. Furthermore, the enthalpy of condensation increases the waste heat in the coolant. Whether too much water precipitates into liquid form in the fuel cell is often only detected by the resulting damage or malfunction, both of which lead to significant disadvantages.

[0005] The present invention therefore addresses the problem of providing a method for detecting liquid water in a fuel cell by means of which the disadvantages known from the prior art can be overcome.

[0006] This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0007] The present invention is based on the general idea of ​​monitoring and detecting the occurrence of liquid water in the fuel cell during operation of a fuel cell of a fuel cell system, in particular in a fuel cell vehicle, and not using additional sensors to be installed for this purpose, but rather using sensors already present in the fuel cell system and indirectly inferring the presence of liquid water in the fuel cell via measured values ​​detected by these sensors.In the method according to the invention for detecting liquid water in the fuel cell of a fuel cell system, at least one of the following parameters is therefore measured: a pressure difference between an inlet and an outlet of the fuel cell, in particular of a fuel cell stack, a power consumption of an electric exhaust gas turbocharger which supplies compressed charge air to the fuel cell and is driven by an exhaust gas from the fuel cell, a temperature difference of a coolant flowing through the fuel cell between a coolant inlet and a coolant outlet, and / or a valve position of a pressure control valve in an exhaust gas duct of the fuel cell.

[0008] The first embodiment utilizes the knowledge that liquid water present in the fuel cell or in the fuel cell stack clogs or blocks fine gas channels of a bipolar plate, resulting in a higher pressure loss in the fuel cell stack, which can be detected via a pressure difference at the two pressure sensors.

[0009] The second embodiment, in which the power consumption of the electric exhaust gas turbocharger is measured, is based on the idea that the exhaust gas turbocharger or the compressor thereof requires more electrical energy to adjust to a desired load point if, due to pressure loss in the exhaust gas flow, less mechanical power is made available to drive the turbine of the exhaust gas turbocharger and thus to drive the compressor of the exhaust gas turbocharger.

[0010] The third embodiment utilizes the knowledge that the condensation of water in the fuel cell stack or in the fuel cell produces measurably more waste heat output, so that with an increasing outlet temperature and thus an increasing differential temperature of the coolant flowing through the fuel cell between the coolant inlet and the coolant outlet, more liquid water is present in the fuel cell or its fuel cell stack.

[0011] The fourth embodiment, in turn, is based on the fact that the pressure control valve on the exhaust side must be adjusted to compensate for a pressure loss. A correlation between the air mass flow and the valve position of the pressure control valve provides information about the internal condition of the air path, which in turn can be used to determine the presence of water droplets in the fuel cell stack.

[0012] The four embodiments mentioned above can be carried out alternatively or cumulatively or in any groups.

[0013] The measured parameter(s) are then compared with associated predefined parameters, whereupon a signal is generated and / or an action is initiated if a difference between the measured parameter(s) and the predefined parameter(s) reaches or exceeds a respective predefined limit. The method according to the invention thus makes it possible to use sensors already present in the fuel cell system to draw conclusions about the presence of liquid water in the fuel cell stack, thereby increasing the performance of the fuel cell and extending its service life.

[0014] In an advantageous embodiment of the method according to the invention, a bypass valve of a bypass channel bypassing a humidifier is opened, thereby supplying drier air to the fuel cell stack or fuel cell, provided the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit. In this context, "dry air" means that the air supplied to the fuel cell via the bypass channel is drier than the air flowing through the humidifier. Thus, in the fuel cell stack or fuel cell, drier air is supplied.If water is detected in the fuel cell by means of the method according to the invention, a computer device which is designed to carry out the method according to the invention together with the individual sensors can open the bypass valve and thus the bypass channel at least partially, as a result of which the air to be supplied to the fuel cell stack no longer flows through the humidifier, but is guided past it on the outside and thus reaches the fuel cell stack in a significantly drier state. This can reduce the moisture in the fuel cell stack and increase the performance of the fuel cell again. It is particularly important in this case that the reduced moisture content of the air in the fuel cell orThe air supplied to the fuel cell stack can also reduce the risk of the presence of liquid water droplets in the fuel cell stack, whereby in particular mechanical damage to downstream components, such as a turbine of the exhaust gas turbocharger, can at least be reduced.

[0015] In a further advantageous embodiment of the method according to the invention, the speed of the exhaust gas turbocharger is increased if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit. By increasing the speed of the exhaust gas turbocharger, more air is supplied to the fuel cell, which can achieve a certain drying effect and thus reduce the risk of water droplets in the fuel cell stack.

[0016] A fuel cell stack current is advantageously reduced, thus shifting a load point, if the difference between the measured parameter and the predefined parameter reaches or exceeds the previously defined limit. This makes it possible, for example, to reduce the current generated by the fuel cell and thus also reduce the humidity in the fuel cell. In this case, this might have to be compensated by a battery in order to continue to provide the same amount of electrical energy to an electric drive device.

[0017] In another particularly preferred embodiment of the method according to the invention, a coolant inlet temperature into the fuel cell or fuel cell stack is / is increased and / or a flow rate of a coolant pump is / is reduced if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit. By increasing the coolant inlet temperature and / or reducing the flow rate of the coolant pump, the temperature in the fuel cell or fuel cell stack can be increased, thereby reducing the risk of water failure in the fuel cell or fuel cell stack.

[0018] It is of course clear that the actions described above in individual paragraphs can be carried out both alternatively and in any combination with each other, provided that the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value and the presence of liquid water in the fuel cell stack can thus be concluded by means of the method according to the invention.

[0019] It is also conceivable that only a signal is displayed to a user, in particular acoustically and / or visually, if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value. The present invention is further based on the general idea of ​​specifying a fuel cell system having a fuel cell with a fuel cell stack, wherein an air supply duct is connected to the fuel cell on the inlet side and an exhaust duct is connected to the outlet side. Furthermore, a cooling system with a coolant pump for cooling the fuel cell is provided. The fuel cell system further has a first pressure sensor at the inlet of the fuel cell stack or at the inlet of the fuel cell in the region of the air supply duct and a second pressure sensor at the outlet of the fuel cell stack or at the outlet of the fuel cell in the region of the exhaust duct.An electric exhaust gas turbocharger is arranged in the supply air duct. This turbocharger supplies compressed charge air to the fuel cell stack or fuel cell via its compressor. It is connected to a turbine in the exhaust duct, where it is driven by the exhaust gas from the fuel cell or fuel cell stack. A first temperature sensor is provided at the coolant inlet of the fuel cell stack or fuel cell, and a second temperature sensor is provided at the coolant outlet of the fuel cell stack or fuel cell. A humidifier integrated into the supply air duct and the exhaust duct allows the supply air to be supplied to the fuel cell stack to be humidified using the exhaust gas flowing out of the fuel cell stack. Such humidifiers have a corresponding membrane and are well known.

[0020] In order to be able to adjust the humidity of the supply air to the fuel cell stack, a bypass channel with a bypass valve is provided that bypasses the humidifier.

[0021] In the exhaust duct, a pressure control valve is also located downstream of the humidifier and upstream of the exhaust turbocharger. This valve can be used, for example, to regulate the pressure in the fuel cell stack, which can be detected by the first and second pressure sensors. An increasing pressure in the fuel cell stack, i.e., an increasing pressure difference between the first pressure sensor and the second pressure sensor, can indicate the presence of liquid water in the fuel cell stack, which, for example, is clogging the fine gas channels of the bipolar plate. An increase in the pressure increase in the fuel cell stack caused by droplets can be compensated for by adjusting the position of the pressure control valve.

[0022] An evaluation of the air mass to valve position of the pressure control valve enables the evaluation of pressure increases in the air path, for example due to droplet formation in the fuel cell stack.

[0023] A computer device is also provided for carrying out the method described in the previous paragraphs. With the fuel cell system according to the invention, it is thus possible for the first time to detect liquid water, particularly in droplet form, in the fuel cell stack or in the fuel cell exclusively using the sensors already present, for example, the temperature sensors or pressure sensors, the valve position of the pressure control valve, or the power consumption of the electric exhaust gas turbocharger, and to initiate appropriate countermeasures or at least generate signals using the computer device.

[0024] Such a fuel cell system according to the invention has a significantly higher performance and a significantly longer service life, both of which represent a considerable advantage for a user.

[0025] In a further advantageous embodiment of the fuel cell system according to the invention, a charge air cooler is arranged in the intake air duct. This is located downstream of the exhaust gas turbocharger or its compressor and cools the already compressed charge air, helping to prevent the maximum permissible inlet temperature into the fuel cell stack from being exceeded. At excessively high temperatures, the membrane materials used lose their functionality (proton conduction) and can also be damaged. This can be avoided by using the charge air cooler.

[0026] In an advantageous development of the fuel cell system according to the invention, an air filter device is arranged in the intake air duct upstream of the exhaust turbocharger. Such air filter devices can filter out not only dirt particles but also substances such as salts, nitrogen oxides, or compounds containing sulfur or ammonia, in order to protect sensitive components of the fuel cell. Such an air filter device can thus increase both the service life and the performance of the fuel cell.

[0027] The present invention is further based on the general idea of ​​equipping a fuel cell vehicle with a fuel cell system described in the previous paragraphs, thereby transferring the advantages described with regard to the fuel cell system to the fuel cell vehicle. Specifically, these advantages lie in the fact that water precipitation in the fuel cell stack or in the fuel cell can be detected early, and a signal can be generated early on, or appropriate countermeasures can be initiated, thereby maintaining the performance of the fuel cell over the long term and extending its service life.

[0028] Further important features and advantages of the invention emerge from the subclaims, from the drawings and from the associated description of the figures based on the drawings.

[0029] It is understood that the features mentioned above and those to be explained below can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention defined by the claims. Components mentioned above and to be mentioned below of a higher-level unit, such as a device, apparatus, or arrangement, which are designated separately, may form separate parts or components of this unit or be integral areas or sections of this unit, even if this is shown differently in the drawings.

[0030] Preferred embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components.

[0031] They show, schematically,

[0032] Figure 1 shows individual method steps of a method according to the invention for detecting liquid water in a fuel cell of a fuel cell system,

[0033] Figure 2 shows a fuel cell system according to the invention.

[0034] According to Figure 1, a method according to the invention for detecting liquid water in a fuel cell 1 (see Figure 2) of a fuel cell system 2, in particular in a fuel cell vehicle 3, comprises a plurality of method steps A to F. The method according to the invention for detecting liquid water in the fuel cell 1 starts in method step A, with at least one of the following parameters being measured in method steps B to E: In method step B, for example, a pressure difference between an inlet 4 and an outlet 5 of the fuel cell 1 or a fuel cell stack 6 of the fuel cell 1 is measured. This is done via pressure sensors already present in the fuel cell system 2, namely a first pressure sensor 7 at the inlet 4 and a second pressure sensor 8 at the outlet 5 of the fuel cell 1.

[0035] Additionally or alternatively, in a method step C, the power consumption of an electric exhaust gas turbocharger 9 (see Figure 2) can be measured. This turbocharger supplies compressed charge air to the fuel cell 1 or the fuel cell stack 6 and is driven, at least in a supporting manner, by an exhaust gas from the fuel cell 1 or the fuel cell stack 6. The exhaust gas turbocharger 9 is integrated with a compressor 12 into an air supply duct 10 and with a turbine 13 into an exhaust duct 11 of the fuel cell 1.

[0036] Alternatively or additionally, in a method step D, a temperature difference of a coolant flowing through the fuel cell 1 between a coolant inlet 14 and a coolant outlet 15 of the fuel cell stack 6 or the fuel cell 1 can be detected. For this purpose, for example, a first temperature sensor 16 at the coolant inlet 14 and a second temperature sensor 17 at the coolant outlet 15 of the fuel cell 1 can be used. The first and second temperature sensors 16, 17 are also already present anyway.

[0037] As a fourth additional or alternative possibility, a valve position of a pressure control valve 18 in the exhaust duct 11 of the fuel cell 1 can be measured in a method step E. In the subsequent method step F, the measured parameter is compared with a predefined parameter, and a signal is generated or a corresponding action is initiated if the difference between the measured parameter and the predefined parameter reaches or exceeds a predefined limit. Reaching or exceeding the predefined limit indicates the presence of liquid water, for example, water droplets, in the fuel cell 1 or in the fuel cell stack 6.

[0038] In process step B, the pressure difference between the inlet

[0039] 4 and the outlet 5 of the fuel cell 1 or the fuel cell stack 6, whereby an increased pressure loss in the fuel cell stack 6, ie a comparatively high pressure difference between the inlet 4 and the outlet

[0040] 5 indicates a blockage of fine gas channels in a bipolar plate of the fuel cell stack 6 and may therefore indicate the presence of liquid water blocking the fine gas channels of the bipolar plate.

[0041] If the electrical power consumption of the electric exhaust gas turbocharger 9 increases, this indicates a lower mechanical power provided to the turbine 13, which can also indicate an increased proportion of liquid water in the fuel cell stack 6.

[0042] For example, if the temperature differential of the coolant flowing through the fuel cell 1 between the coolant inlet 14 and the coolant outlet 15 of the fuel cell stack 6 increases in process step D, this may indicate the presence of liquid water in the fuel cell stack 6, since significant waste heat is generated by the water condensation. The presence of liquid water in the fuel cell 21 or fuel cell stack 6 can also be determined by process step E, which measures or monitors the valve position of the pressure control valve 18, since the pressure control valve 18 must be adjusted on the exhaust side to compensate for the pressure loss.If, for example, a large pressure loss occurs between the inlet 4 and the outlet 5 due to liquid water in the fuel cell stack 6, which blocks the fine gas channels of the bipolar plate, the pressure control valve 18 must be closed in order to obtain sufficient energy in the turbine 13 to compress the supply air in the supply air channel 10.

[0043] If the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value, in process step F, for example, the bypass valve 19 of the bypass channel 21 is opened, where the humidifier 20 is bypassed and drier supply air is then supplied to the fuel cell 1 or the fuel cell stack 6.

[0044] If the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value, the speed of the exhaust gas turbocharger 9 can also be increased in method step F, thereby supplying more air to the fuel cell stack 6. This can also increase the proportion of dry supply air or the dry supply air mass flow, particularly if, for example, the bypass valve 19 is also opened. The increase in the speed of the exhaust gas turbocharger can be achieved by increasing the speed of an electric motor driving the compressor 12 of the exhaust gas turbocharger 9.

[0045] Additionally or alternatively, a fuel cell stack current can be reduced if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit, thereby achieving a load point shift. This shifts the load toward a battery, so that the fuel cell stack 6 has to generate less power, which also leads to a reduction in the humidity in the fuel cell 1.

[0046] Additionally or alternatively, the coolant inlet temperature into the fuel cell 1 or the fuel cell stack 6 is increased and / or the flow rate of a coolant pump 23 (see Figure 2) is reduced. This also allows the proportion of liquid water in the fuel cell 1 or the fuel cell stack 6 to be reduced, since the reduced cooling of the fuel cell 1 reduces the precipitation of liquid water.

[0047] The method according to the invention is carried out, for example, in a fuel cell system 2, as shown in Fig. 2, wherein the fuel cell system 2 has the fuel cell 1 with the fuel cell stack 6, to which the supply air duct 10 is connected on the inlet side and the exhaust gas duct 11 is connected on the outlet side.

[0048] The fuel cell system 2 furthermore has a cooling system 24 with the coolant pump 23 for cooling the fuel cell 1 as well as a first pressure sensor 7 at the inlet 4 of the fuel cell stack 6 or the fuel cell 1 and a second pressure sensor 8 at the outlet of the fuel cell stack 6 or the fuel cell 1. The fuel cell system 2 further comprises the electric exhaust gas turbocharger 9, which supplies compressed charge air to the fuel cell stack 6 or the fuel cell 1 and is driven cumulatively or alternatively by an exhaust gas from the fuel cell stack 6 or the fuel cell 1 and an electric motor. The fuel cell system 2 furthermore has the first temperature sensor 16 at the coolant inlet 14 of the fuel cell stack 6 or the fuel cell 1 and the second temperature sensor 17 at the coolant outlet 15 of the fuel cell stack 6 or the fuel cell 1, via which a temperature difference of the coolant flowing into the fuel cell 1 orin the fuel cell stack 6 and out of the fuel cell 1 or out of the fuel cell stack 6 can be determined.

[0049] Also provided is the humidifier 20, which is integrated into the supply air duct 10 and the exhaust duct 11 and serves to humidify the inherently dry circulating air. A bypass duct 21 with a bypass valve 19 arranged therein bypasses the humidifier 20. The pressure control valve 18 is arranged in the exhaust duct 11 downstream of the humidifier 20 and upstream of the exhaust turbocharger 9 or its turbine 13. Also provided is the computer device 22 for implementing the method according to the invention.

[0050] An air filter device 26 can be arranged in the supply air duct 10 upstream of the exhaust gas turbocharger 9 or its compressor 12, which filters out particles or other substances, in particular, such as salts, nitrogen oxides or compounds with sulfur or ammonia, in order to protect sensitive components of the fuel cell 1 and to maintain the performance of the fuel cell 1 in the long term.

[0051] Furthermore, a charge air cooler 25 can be arranged in the intake air duct 10. This cooler is located downstream of the exhaust gas turbocharger 9 or its compressor 12 and cools the already compressed charge air. This allows the maximum permissible inlet temperature into the fuel cell stack 6 to be limited to prevent the membrane used from losing its functionality (proton conduction) at excessively high temperatures.

[0052] The fuel cell system 2 according to the invention is used in the fuel cell vehicle 3 according to the invention.

[0053] With the fuel cell system 2 according to the invention, the fuel cell vehicle 3 according to the invention and the method according to the invention, water in the fuel cell 1 or its fuel cell stack 6 can be detected and calculated for the first time and a signal can thereby be generated or appropriate countermeasures can be initiated in order to reduce the moisture in the fuel cell 1 or the fuel cell stack 6, whereby the performance of the fuel cell 1 and its service life can be increased in the long term.

[0054] *****

Claims

Claims 1 . Method for detecting liquid water in a fuel cell (1) of a fuel cell system (2), in which - at least one of the following parameters is measured, - a pressure difference between an inlet (4) and an outlet (5) of the fuel cell (1), - a power consumption of an electric exhaust gas turbocharger (9) which supplies compressed charge air to the fuel cell (1) and is driven by an exhaust gas from the fuel cell (1), - a difference temperature of a coolant flowing through the fuel cell (1) between a coolant inlet (14) and a coolant outlet (15), - a valve position of a pressure control valve (18) in an exhaust gas duct (11) of the fuel cell (1), - the measured parameter is compared with a predefined parameter and a signal is generated and / or an action is initiated if a difference between the measured parameter and the predefined parameter reaches or exceeds a predefined limit.

2. Method according to claim 1, characterized in that if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value, a bypass valve (19) of a bypass channel (21) bypassing a humidifier (20) is opened and drier air is thereby supplied to the fuel cell (1).

3. Method according to claim 1 or 2, characterized in that if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value, a speed of the exhaust gas turbocharger (9) is increased.

4. Method according to one of the preceding claims, characterized in that if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value, a fuel cell stack current is reduced.

5. Method according to one of the preceding claims, characterized in that if the difference between the measured parameter and the predefined parameter reaches or exceeds the predefined limit value, a coolant inlet temperature into the fuel cell (1) is increased and / or a delivery rate of a coolant pump (23) is reduced.

6. Fuel cell system (2), - with a fuel cell (1) with a fuel cell stack (6), to which an air supply duct (10) is connected on the inlet side and an exhaust duct (11) is connected on the outlet side, - with a cooling system (24) with a coolant pump (23) for cooling the fuel cell (1), - with a first pressure sensor (7) at an inlet (4) of the fuel cell (1) and a second pressure sensor (9) at the outlet (5) of the fuel cell (1), - with an electric exhaust gas turbocharger (9) which supplies compressed charge air to the fuel cell (1) and is driven by an exhaust gas from the fuel cell (1), - with a first temperature sensor (16) at the coolant inlet (14) of the fuel cell (1) and a second temperature sensor (17) at the coolant outlet (15) of the fuel cell (1), - with a humidifier (20) integrated into the supply air duct (10) and the exhaust gas duct (11), - with a bypass channel (21) bypassing the humidifier (20) with a bypass valve (19), - with a pressure control valve (18) arranged in the exhaust duct (11) downstream of the humidifier (20) and upstream of the exhaust turbocharger (9), - with a computer device (22) for carrying out the method according to one of the preceding claims.

7. Fuel cell system according to claim 6, characterized in that an air filter device (26) is arranged in the supply air duct (10) upstream of the exhaust gas turbocharger (9).

8. Fuel cell system according to claim 6 or 7, characterized in that a charge air cooler (25) is arranged in the supply air duct (10).

9. Fuel cell vehicle (3) with a fuel cell system (2) according to one of claims 6 to 8. *****

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