Determination of the fuel cell inlet humidity via pressure sensors and mass flow-dependent control of the humidifier bypass

Abstract

Fuel cell arrangement (1) comprising at least one fuel cell (2) with a cathode (3) and an anode, wherein both the cathode (3) and the anode each have a reactant supply (4) and a reactant discharge (5), wherein at least one of the reactant supplies (4) is provided with a humidification device (10) and sensors (12, 13, 14), wherein the sensors (12, 13, 14) are at least one fluid mass sensor (12) and two pressure sensors (13, 14), wherein the fluid mass sensor (12) and one of the pressure sensors (13) are arranged upstream of the humidification device (10) and one of the pressure sensors (14) is arranged downstream of the humidification device (10), and that the humidification device (10) is operable in a controlled manner based on the measurements of the sensors (12, 13, 14), characterized in that the humidity of the reactant in the at least one Reactant supply (4) based on the sensor readings (12, 13,14) is calculated linearly dependent on a measured fluid mass flow rate and linearly dependent on a difference in the measured pressures.

Description

[0001] The present invention relates to a fuel cell arrangement according to the preamble of claim 1 and to a method for controlling the moisture of a reactant for a fuel cell arrangement according to the preamble of claim 6. STATE OF THE ART

[0002] Fuel cells, especially those powered by pure hydrogen, are considered the future of propulsion due to the fact that they emit only pure water. These fuel cells feature a fuel cell membrane that requires water in the form of steam for optimal operation. The water vapor is used to ensure sufficiently high ion conductivity across the membrane within the fuel cell.

[0003] In known fuel cell configurations, this water vapor can be supplied to the fuel cells containing at least one of the two reactants that react with each other. To enable optimal operation of the fuel cell configuration, it is necessary to monitor and, in particular, regulate or adjust this humidity. For example, DE 10 2008 020 102 A1 discloses a control arrangement for controlling or regulating the amount of water supplied to at least one of the reactants in the fuel cells. This arrangement includes a dew point sensor and a temperature sensor, which are used to determine the humidity of the at least one reactant. As is known, a dew point sensor can be implemented as a semiconductor sensor and, like other humidity sensors, is susceptible to interference from droplet formation in the reactant.In particular, the accumulation of liquid water can lead to measurement errors.

[0004] WO 2008 / 034253 A1 also discloses a control system for the humidity of a reactant in a fuel cell assembly. This system uses a pressure sensor and a temperature sensor to determine the reactant's humidity through a complex calculation. Furthermore, this calculation requires incorporating the reactant's mass flow rate and the mass flow rate of water supplied by a humidification device. This large number of input parameters makes the calculation susceptible to errors, particularly if just one sensor fails or malfunctions.

[0005] Document KR 10 0 957 364 B1 discloses a method for diagnosing an abnormal condition for a cathode air supply system, which can diagnose an abnormal phenomenon of a cathode air supply condition in its early stage by correlating the flow rate and the rotational speed of the air blower.

[0006] Document DE 102 22 422 A1 discloses a fuel cell system which is capable of controlling a fuel cell installed in a vehicle in an optimized state.

[0007] Further fuel cell systems and methods for controlling or operating them at low temperatures are shown in documents US 2002 / 0009623A1 and JP 2011-216416A. REVELATION OF THE INVENTION

[0008] It is therefore an object of the present invention to at least partially overcome the disadvantages of known fuel cell arrangements described above. In particular, it is an object of the present invention to provide a fuel cell arrangement and a method for controlling the moisture content of a reactant for a fuel cell arrangement, in which as few physical quantities as possible are used to determine the moisture content of the reactant, and which can also be measured simply and cost-effectively.

[0009] The foregoing problem is solved by a fuel cell arrangement having the features of independent claim 1 and by a method having the features of claim 6. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawing. The features and details described in connection with the fuel cell arrangement according to the invention naturally also apply in connection with the method according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always refers, or can refer, to each other.

[0010] In a first aspect of the invention, a fuel cell arrangement comprises at least one fuel cell with a cathode and an anode, wherein both the cathode and the anode each have a reactant supply and a reactant discharge, and wherein at least one of the reactant supplies is provided with a humidification device and sensors. In particular, a fuel cell arrangement according to the invention is characterized in that the sensors are at least one fluid mass sensor and two pressure sensors, wherein the fluid mass sensor and one of the pressure sensors are arranged upstream of the humidification device and one of the pressure sensors is arranged downstream of the humidification device, and the humidification device can be operated in a controlled manner based on the measurements of the sensors.

[0011] A fuel cell used in a fuel cell arrangement according to the invention can, in particular, be a fuel cell operated with pure hydrogen. The fluids used as reactants in this case are preferably pure hydrogen and air. The sensors provided in a fuel cell arrangement according to the invention are simple and already known sensors for the physical quantities mass flow and pressure. Therefore, especially for automotive applications of a fuel cell arrangement according to the invention, no additional new sensors need to be developed, thus saving development costs.

[0012] The fluid mass sensor determines the quantity of reactant supplied per unit of time. This reactant, which can be a fluid, particularly a gas, is humidified by the humidification device after passing through the fluid mass sensor. Pressure sensors positioned before and after the humidification device measure the pressure of the reactant both upstream and downstream of the device. The resulting pressure difference, calculated from these two pressure measurements, along with the measured mass flow rate, allows for the determination of the moisture content added to the reactant in the humidification device. Therefore, based on these measurements, the moisture content of the reactant can be reliably inferred.The use of only one fluid mass sensor and two pressure sensors represents a particularly simple, robust and also cost-effective way to determine the moisture content of a reactant.

[0013] Based on this humidity measurement, the invention provides that the humidification device can be operated in a controlled manner. This makes it possible to directly adjust or regulate the humidity by controlling the humidification device. Operation of the fuel cell assembly at optimal humidity can thus be ensured.

[0014] In the fuel cell arrangement according to the invention, the sensors and the humidification device are arranged in the reactant supply of the cathode. The cathode of a fuel cell arrangement according to the invention can, in particular, be operated with air as the reactant. In this way, it is possible to humidify, especially only, the air reactant. This is sufficient for the operation of a fuel cell arrangement according to the invention, since the moisture can also diffuse to the anode side through the membrane present in the fuel cell. Humidification on only one side, especially on the cathode side, is therefore advantageous, since only one reactant is humidified or needs to be humidified. This thus represents a particularly simple embodiment of a fuel cell arrangement according to the invention, which can also be more robust and therefore less susceptible to malfunctions.

[0015] Furthermore, in a fuel cell arrangement according to the invention, a bypass line, controllable by a valve, can be provided in at least one reactant supply line, by which the humidification device can be bypassed completely and / or partially. Dry reactant, in particular dry air, is routed past the humidification device via the bypass line. After the humidification device, this dry reactant portion is recombined with the reactant portion that was humidified in the humidification device. The mixture of the two reactant portions is then supplied to the fuel cell arrangement. The ratio of dry to humidified reactant portions determines the total moisture content of the reactant. Therefore, to change or control the total moisture content, only the valve that controls the flow of the reactant portion through the bypass line needs to be actuated.This allows for particularly simple control and adjustment of the total moisture content of the reactants supplied to the fuel cell.

[0016] Furthermore, in a fuel cell arrangement according to the invention, the humidification device can be a gas-gas humidifier. Such a gas-gas humidifier has an airtight but water-permeable membrane. The driving force for humidification in a gas-gas humidifier is the partial pressure difference of water vapor between the two sides of the membrane. If a dry reactant is passed through one side of the gas-gas humidifier, water diffuses through the membrane and humidifies this reactant. Since a gas-gas humidifier is thus constructed without pumps or other mechanical parts, it represents a particularly simple and robust humidification device.

[0017] According to a particularly preferred embodiment of a fuel cell arrangement according to the invention, the gas-gas humidifier can also be connected to the corresponding reactant discharge of the fuel cell. In the fuel cell, especially in a fuel cell operated with pure hydrogen, water is produced as a reaction product. This water is discharged from the fuel cell via the reactant discharge. By connecting the gas-gas humidifier to the reactant discharge, it is thus possible to reuse this water generated in the fuel cell to humidify the reactant in the reactant feed. The need for an external water supply for such a gas-gas humidifier can therefore be prevented or at least reduced. This also makes autonomous operation of a fuel cell arrangement according to the invention conceivable.

[0018] According to a second aspect of the invention, the problem is solved by a method for controlling the humidity of a reactant for a fuel cell arrangement, wherein the fuel cell arrangement is configured according to the first aspect of the invention. In particular, a method according to the invention is characterized in that the humidity of the reactant in the at least one reactant feed is calculated, especially approximately, based on the measured values ​​of the sensors. All the advantages described for a fuel cell arrangement according to the first aspect of the invention naturally also apply to a method according to the invention by which such a fuel cell arrangement is operated.

[0019] The mass flow and pressure sensors used in the process are simple sensors that are already available, particularly for automotive applications. This eliminates the need for costly new developments. In particular, the use of humidity sensors, which are highly susceptible to interference, especially in the presence of liquid water, can also be avoided by the inventive method. Thus, an inventive method for controlling the humidity of the reactant in a fuel cell assembly represents a particularly simple, robust, and cost-effective method for controlling the humidity of the reactant in a fuel cell assembly.

[0020] The inventive method for controlling the humidity of a reactant in a fuel cell arrangement is designed such that the calculated humidity is linearly dependent on a measured fluid mass flow rate and linearly dependent on a difference in the measured pressures. A linear dependence of humidity on measured quantities represents a particularly simple relationship and is therefore easy to calculate. This has a particularly positive effect on the speed with which such a calculation can be performed. The calculated humidity can, for example, be determined with an accuracy of ±20%. This accuracy is sufficient for optimal operation of the fuel cell arrangement. A further advantage of a linear dependence of the calculated humidity is that the calculation can also be performed in an analog circuit.This eliminates the need for complicated, expensive, and therefore costly digital electronics to calculate the moisture in the reactant.

[0021] Furthermore, in a method according to the invention for controlling the humidity of a reactant for a fuel cell arrangement, a bypass line can be provided in the at least one reactant feed, by which the humidification device is completely and / or partially bypassed and which is controlled by a valve, wherein the valve is regulated based on the measured fluid mass flow rate and the measured pressures. The valve regulates the flow through the bypass line. The portion of the reactant flowing through the bypass line is thus not humidified in the humidification device, unlike the portion of the reactant flowing through the humidification device. After the humidification device, both portions of the reactant are recombined, resulting in a uniform overall humidity level in the reactant.This total moisture content in the reactant can be calculated, particularly approximately, from the measured fluid mass flow rate and the measured pressures using the method according to the invention. Based on this calculation, the valve can also be controlled in such a way that an ideal moisture content in the reactant for optimal operation of the fuel cell assembly can be achieved. The control, like the calculation of the moisture content in the reactant, is therefore particularly simple and robust.

[0022] Furthermore, a method according to the invention for controlling the humidity of a reactant for a fuel cell arrangement can be designed such that the valve is controlled by a control voltage, and that the control voltage is calculated solely from the measured fluid mass flow rate. The relative degree of humidification of a quantity of reactant flowing through the humidification device is independent of this quantity. For this reason, with a higher mass flow rate of the reactant in the reactant feed, while maintaining a constant total humidity of the reactant at the fuel cell inlet, a higher flow rate through the bypass line is also required. Controlling the valve solely based on the fluid mass flow rate can therefore be sufficient to ensure consistent humidification of the reactant flowing into the fuel cell.Due to its dependence on only one input variable, such a control system is particularly simple and robust against the effects of other state variables of the fuel cell arrangement.

[0023] Particularly preferred in a further development of a method according to the invention for controlling the humidity of a reactant for a fuel cell arrangement is the calculation of the control voltage as a linear function of the measured fluid mass flow rate. A linear relationship is particularly simple and can be calculated very quickly. Here, too, implementation in purely analog electronics is conceivable, thus avoiding the need for complex digital electronics. The achievable accuracy of the set humidity in the reactant can advantageously be ±10%. This accuracy is sufficient for optimal operation of a fuel cell arrangement according to the invention. In this way, a particularly simple, robust, and cost-effective method for controlling the humidity of a reactant in a fuel cell arrangement is created. PREFERRED EXAMPLE OF EXECUTION

[0024] The fuel cell arrangement according to the invention and its further developments as well as its advantages, and the method according to the invention and its further developments as well as its advantages, are explained in more detail below with reference to a drawing. It schematically shows: Fig. 1 a fuel cell arrangement according to the invention.

[0025] In Fig.Figure 1 schematically depicts a part of a fuel cell arrangement 1 according to the invention. The fuel cell arrangement 1 comprises a fuel cell 2, of which only the cathode 3 is shown. The cathode 3 is connected to a reactant supply 4 and a reactant discharge 5. In the illustrated embodiment, air is used as the reactant for the cathode 3. Of course, other fluids, such as pure oxygen, are also conceivable as reactants. A fluid mass sensor 12 is located in the reactant supply 4. This fluid mass sensor 12 measures the mass per unit time of the air supplied to the fuel cell 2 in the reactant supply 4. A humidification device 10 is also arranged in the reactant supply 4.This device serves to humidify the reactant, in particular the air, since for optimal operation of the fuel cell 2, at least one of the two reactants, in this case the air supplied to the cathode 3 of the fuel cell 2, must have a certain level of humidity. The humidification device 10 shown is specifically designed as a gas-to-gas humidifier. The humidification device 10 has a membrane 11 that divides the device, shown schematically, into two sides. In the illustrated embodiment of the fuel cell 2, air on the cathode side 3 reacts with pure hydrogen on the anode side. The reaction product is water, which is removed from the fuel cell 2 through the reactant outlet 5. This water is supplied to one of the two sides of the humidification device 10.

[0026] The air flowing in the reactant feed 4 has no or only a low humidity. This air is supplied to the second side of the humidification device 10. The membrane 11, which is designed as an airtight but water-permeable membrane 11, thus allows, driven by the partial pressure difference of the water on the two sides of the membrane 11, the water to diffuse from the side of the humidification device 10 facing the reactant discharge 5 to the side of the humidification device 10 facing the reactant feed 4. Thus, humidification of the reactant in the reactant feed 4 is possible in the humidification device 10. An external water supply to the humidification device 10 is not necessary. A pressure sensor 13, 14 is arranged on the reactant feed 4 upstream and downstream of the humidification device 10, respectively.The pressure difference, which can be calculated from the measurements of the first pressure sensor 13 and the second pressure sensor 14, together with the measurement of the fluid mass sensor 12, enables a calculation, particularly an approximation, of the moisture supplied to the reactant in the humidification device 10. The magnitude of this moisture can be determined particularly easily via a bilinear relationship between the measurements of all three sensors 12, 13, 14, specifically each linearly dependent on the mass flow rate and the pressure difference.

[0027] To enable control of the reactant humidity, the fuel cell arrangement 1 according to the invention, in the embodiment shown, is equipped with a bypass line 16 that bypasses the humidification device 10 and can be controlled by a valve 15. Dry reactant, in particular dry air, can be routed past the humidification device 10 via the bypass line 16. The ratio of dry air in the bypass line 16 to humidified air that has flowed through the humidification device 10 yields the total reactant humidity at the inlet to the fuel cell 2. The valve 15 can preferably be operated, in particular linearly, depending on the measurement of the fluid mass sensor 12. This allows for particularly simple control of the reactant inlet humidity to the fuel cell 2.Since all components, in particular the fluid mass sensor 12 and the pressure sensors 13, 14, are already available for use in the automotive sector, such a fuel cell arrangement 1 according to the invention represents a particularly simple, robust and cost-effective way to ensure optimal operation of a fuel cell arrangement 1 according to the invention with optimal reactant humidity.

Claims

[1] Fuel cell arrangement (1) comprising at least one fuel cell (2) with a cathode (3) and an anode, wherein both the cathode (3) and the anode each have a reactant inlet (4) and a reactant outlet (5), wherein at least one of the reactant inlets (4) is provided with a humidification device (10) and sensors (12, 13, 14), wherein the sensors (12, 13, 14) are at least one fluid mass sensor (12) and two pressure sensors (13, 14), wherein the fluid mass sensor (12) and one of the pressure sensors (13) are arranged upstream of the humidification device (10) and one of the pressure sensors (14) is arranged downstream of the humidification device (10), and wherein the humidification device (10) can be operated in a controlled manner based on the measurements of the sensors (12, 13, 14). characterized by, that the moisture content of the reactant in the at least one reactant feed (4) is calculated based on the measured values ​​of the sensors (12, 13, 14) as being linearly dependent on a measured fluid mass flow rate and linearly dependent on a difference in the measured pressures. [2] Fuel cell arrangement (1) according to claim 1, characterized by , that the sensors (12, 13, 14) and the humidification device (10) are arranged in the reactant supply (4) of the cathode (3). [3] Fuel cell arrangement (1) according to any one of the preceding claims, characterized by , that in at least one reactant supply (4) a bypass line (16) controllable by a valve (15) is provided, by which the humidification device (10) can be bypassed completely and / or partially. [4] Fuel cell arrangement (1) according to any one of the preceding claims, characterized by , that the humidification device (10) is a gas-gas humidifier. [5] Fuel cell arrangement (1) according to claim 4, characterized by , that the gas-gas humidifier is also connected to the corresponding reactant discharge (5) of the fuel cell (2). [6] Method for controlling the moisture content of a reactant for a fuel cell arrangement (1), wherein the fuel cell arrangement (1) is configured according to one of the preceding claims, wherein the moisture content of the reactant in the at least one reactant feed (4) is calculated based on the measured values ​​of the sensors (12, 13, 14), characterized by , that the calculated humidity is calculated linearly dependent on a measured fluid mass flow rate and linearly dependent on a difference in the measured pressures. [7] Method for controlling the moisture of a reactant for a fuel cell arrangement (1) according to claim 6 , characterized by, that in the at least one reactant supply (4) a bypass line (16) is provided, by which the humidification device (10) is completely and / or partially bypassed and which is controlled by a valve (15), wherein the valve (15) is controlled based on the measured fluid mass flow rate and the measured pressures. [8] Method for controlling the moisture of a reactant for a fuel cell arrangement (1) according to claim 7, characterized by , that the valve (15) is controlled via a control voltage and that the control voltage is calculated only from the measured fluid mass flow rate. [9] Method for controlling the moisture of a reactant for a fuel cell arrangement (1) according to claim 8, characterized by , that the control voltage is calculated as a linear function of the measured fluid mass flow rate.

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