DE102018205966A1 - Evaluation unit for oxidant mass flow through a fuel cell assembly - Google Patents

Abstract

Evaluation unit (1) for measuring the mass flow dm / dt of an oxidant (21) through a cathode compartment (22) of a fuel cell or a fuel cell stack (2), wherein the fuel cell, or the fuel cell stack (2), an anode compartment (24) for the supply of a fuel (23) and wherein in a discharge (25) for the oxidizing agent (21) from the cathode space (22) a sensor (26) is installed, which is adapted to the entry of at least one combustible component (23a) of the fuel (23) to be detected in the discharge (25), wherein the measured variable used by the sensor (26) can be influenced both by the concentration of the combustible component (23a) and by the mass flow dm / dt of the oxidizing agent (21) the evaluation unit (1) with both the sensor (26) and with an ammeter for the current through the fuel cell, or through the fuel cell stack (2), current I connected and excluded ebildet is, the mass flow dm / dt from the measured value of the sensor (26) in conjunction with the current I evaluate.System (100) for power generation with a fuel cell or fuel cell stack (2) and the evaluation unit (1) .An associated computer program.

Description

The present invention relates to an evaluation unit, which is able to determine the oxidant mass flow through a fuel cell or a fuel cell stack using existing sensors.

State of the art

The drive of vehicles by means of electric motors is compared to the drive means of internal combustion engines to the effect that electric motors work quietly and locally emission-free and that they are structurally much simpler than internal combustion engines. However, the energy density of batteries for the storage of electrical energy supply so far not approach the energy density of liquid fuel, so that typically less energy can be carried as in a same size and equally heavy fuel tank.

The combination of an electric drive with a fuel cell system for the power supply makes it possible to obtain the primary energy from storable with significantly higher energy density chemical fuel. If the fuel cell system is operated with hydrogen, for example, the operation continues to be locally emission-free, since only water is produced in conjunction with atmospheric oxygen. An example of such a system is from the WO 2017/148 798 A1 known.

In case of damage in the fuel cell system, for example due to a membrane crack in a fuel cell, gaseous hydrogen can escape from the system. In order to prevent this form in combination with ambient air ignitable mixtures is from the DE 10 2016 210 518 A1 known to monitor the concentration of hydrogen in the exhaust air from the system with a sensor and, if necessary, introduce security measures.

Disclosure of the invention

In the context of the invention, an evaluation unit for measuring the mass flow dm / dt of an oxidant through a cathode compartment of a fuel cell or of a fuel cell stack has been developed. The fuel cell, or the fuel cell stack, has an anode space for the supply of a fuel. In a discharge for the oxidant from the cathode compartment, for example in the direction of the free atmosphere, a sensor is installed, which is designed to detect the entry of at least one combustible component of the fuel into the discharge. In this case, the measured variable used by the sensor can be influenced both by the concentration of the combustible constituent and by the mass flow dm / dt of the oxidant.

The combustible constituent may in particular be hydrogen, which can be obtained directly from a tank or storage material or, for example, can also be obtained by reforming from a hydrocarbon entrained as fuel.

The measured variable used by the sensor can be, for example, a measure of the density of the gas mixture present in the discharge. This density changes depending on the mass flow as well as the gas type. Specifically, hydrogen as a combustible component is excellent in that it is the gas with the lowest density at all.

The evaluation unit is connected both to the sensor and to a current measuring device for the current flowing through the fuel cell or through the fuel cell stack I connectable. The evaluation unit is designed to measure the mass flow dm / dt from the measured value of the sensor in conjunction with the current I evaluate.

It has been found that in this way the functionality of the sensor can be extended from a pure safety sensor to a sensor for the mass flow dm / dt of the oxidant. This makes it possible to save one or more sensors for this mass flow dm / dt elsewhere. As a result, the additional costs resulting from the installation of the safety sensor can be at least partially compensated.

This functional extension is possible because the measured variable used by the sensor depends both on the mass flow of this gas mixture and on its composition. Now, if a certain mass flow of the oxidizing agent in the fuel cell, or in the fuel cell stack is performed, then in an intact system each formula unit of the oxidizing agent either pass through the cathode room unused or converted there into the reaction product of the fuel cell, or the fuel cell stack become. What proportion of the oxidant is converted is from the stream I removable. Thus, at least in the normal operation of an intact system in which no fuel passes into the discharge, the composition of the gas mixture in the discharge is known. In conjunction with the measured value of the sensor, the mass flow of the gas mixture, and thus ultimately the desired mass flow dm / dt of the oxidizing agent, can be determined hereby.

The term "connectable" is not limited to a direct connection between the evaluation unit and the corresponding data source, ie the sensor or the ammeter, by cable or radio. Rather, in the context of the invention, this term encompasses any possibility of the evaluation unit of gaining knowledge of the values supplied by the respective data source. For example, in a vehicle, most data sources are connected to a bus system, such as a CAN bus. The evaluation unit then only needs one connection to this bus system in order to be able to access all data sources. The evaluation unit does not have to obtain the data directly from the respective data source, but it can, for example, retrieve it from a control unit in which they were cached.

In a particularly advantageous embodiment, the evaluation unit is designed to be out of the stream I to determine the mass flow dmp / dt to be generated by the fuel cell, or the fuel cell stack, gaseous reaction product. According to the reaction equation for the fuel cell used, the reaction of a certain number of formula units of the oxidizing agent with a certain number of formula units of the fuel releases a fixed number of charge carriers which contribute to the current. In this way, it results from the current I, how much reaction product per unit time was produced and can contribute to the gas mixture in the discharge.

In a fuel cell powered by hydrogen fuel, or a stack of such fuel cells, the reaction product is water. The evaluation unit is then advantageously designed to be out of the stream I to determine the amount of vapor and liquid product water formed by the fuel cell or fuel cell stack. This is the electricity I even a measure of the total amount of product water. The distribution of the product water on the well-known as condensate liquid phase on the one hand and on the vapor phase on the other hand, is dependent on the operating conditions due to the phase diagram of the water. These dependencies can be stored in the evaluation unit, for example in the form of maps or models.

An important factor that determines the distribution of product water between the liquid and the vapor phase is the temperature. Therefore, the evaluation unit in a further particularly advantageous embodiment with a temperature sensor for the temperature T in the discharge, and / or in the vicinity of the discharge, connectable and adapted to determine the amount of liquid product water taking into account this temperature T.

In fuel cell systems that pressurize the oxidant (such as air) with a compressor, the load conditions of the fuel cell or fuel cell stack, on the one hand, and the compressor, on the other hand, are not instantaneously synchronizable. At the same time there are boundary conditions, such as a maximum pressure against which the compressor can work. Therefore, in systems with a compressor often a bypass valve is provided, with which the compressor, bypassing the fuel cell, or the fuel cell stack, can be depressurized. The compressor can thus be protected against damage at high pressures and low mass flow.

When the pressure is released into the exhaust monitored by the sensor, it is no longer reasonable to assume that the gas mixture in the exhaust has come into being solely due to the supply of oxidant to the fuel cell or fuel cell stack. In order to be able to deduce from the measured value of the sensor on the desired mass flow dm / dt of the guided into the cathode space oxidant, the evaluation is in a particularly advantageous embodiment in addition to a transmitter for the switching position of a bypass valve, which oxidizing agent to the Fuel cell, or around the fuel cell stack, passes directly into the discharge, connectable and adapted to determine the guided through the bypass valve mass flow dm _B / dt of the oxidizing agent.

For a given flow cross-section of the bypass valve, the discharged mass flow dm _B / dt of the oxidant is operating point-dependent. This dependency can, for example, be stored in the evaluation unit via a characteristic diagram or model. Therefore, the evaluation unit advantageously contains a model or characteristic map which contains at least the information necessary for determining a pressure loss Δp of the oxidizing agent when the bypass valve is actuated. The maps or models can be determined, for example, on the basis of the software application of the vehicle.

The term "encoder" is not limited to a passive measuring instrument for the switching position on the valve itself, but also includes, for example, a memory in a control unit in which the switching position is stored.

In a further particularly advantageous embodiment of the invention, the evaluation unit is additionally connectable to an encoder for the speed of a compressor, the oxidant in the fuel cell, or in the fuel cell stack promotes. This speed is particularly useful for determining the mass flow dm _B / dt of the oxidant that passes through it in the open state of the bypass valve.

Regardless of whether the mass flow dm _B / dt of the oxidant derived by the bypass valve is determined in detail, the evaluation unit can determine from the measured value of the sensor and from the current I at least the sum of dm / dt and dm _B / dt. that is, the total mass flow of the oxidizing agent through the compressor.

Possible fault conditions, such as cell damage, through which fuel could get into the discharge, are the reason for the installation of the sensor sensitive to at least one combustible component of the fuel in this discharge. However, these fault conditions are not the only reasons that this combustible component may be in the exhaust. For example, it may be necessary to purge the anode compartment (purgen), i. Relieve pressure in the direction of the exhaust. While the combustible component of the fuel should therefore normally not be present in the discharge, this can very well be the case during rinsing. This changes the measured value registered by the sensor since the detection of the combustible component is the primary purpose of this sensor. In order to prevent the evaluation unit from drawing false conclusions with regard to the desired mass flow dm / dt of the oxidizing agent, in a further particularly advantageous embodiment the evaluation unit additionally comprises a sensor for the switching position of a flushing valve, the fuel from the anode chamber of the fuel cell, or the fuel cell stack, leads into the exhaust, connectable.

For example, the determination of the mass flow dm / dt of the oxidizing agent can be suspended as long as a purging process is active.

In a further particularly advantageous embodiment, the evaluation unit contains a model or characteristic diagram which describes the influence of the concentration of the combustible constituent of the fuel on the sensor on the measurement signal of the sensor. Then, a change in the measured value of the sensor due to a change in the mass flow dm / dt of the oxidizing agent may be discriminated from a change caused by, for example, a purging operation.

The evaluation unit is an independent unit that can be sold, for example, as a retrofit product for existing fuel cell systems or vehicles. However, their existence allows for hardware savings elsewhere in the fuel cell system.

Therefore, the invention also relates to a system for power generation. This system may be designed for stationary and / or mobile use and comprises at least one fuel cell or a fuel cell stack with an anode space for the supply of a fuel and a cathode space for the supply of an oxidizing agent. In a discharge for the oxidant from the cathode compartment, a sensor is installed which is adapted to detect the entry of at least one combustible component of the fuel into the discharge. In this case, the measured variable used by the sensor can be influenced both by the concentration of the combustible constituent and by the mass flow dm / dt of the oxidant. The system additionally has the previously explained evaluation unit according to the invention.

As explained above, this makes it possible, for example, to save a further sensor for the mass flow dm / dt of the oxidizing agent in the feed line to the fuel cell or to the fuel cell stack. The supply line can thus be free of sensors for the mass flow dm / dt of the oxidant. This relativises on the one hand the additional price, which results from the installation of the safety sensor for the combustible component of the fuel. On the other hand, the availability of the entire system is increased because a sensor that has been saved can not fail.

The sensor may be, for example, an ultrasonic sensor. Such a sensor makes use of the fact that the speed of sound in the gas mixture in the discharge changes both as a function of the density and as a function of the flow velocity of this gas mixture.

However, the sensor may also include, for example, a heated filament and means for measuring the temperature of that filament. The measurable via the temperature heat removal from the filament is influenced by both the mass flow and by the density of the gas mixture.

In a further particularly advantageous embodiment, a compressor for the oxidant and a bypass valve for the diversion of compressed oxidant in the discharge are additionally provided. The compressor causes a significant increase in the power density of the fuel cell, or the fuel cell stack, per unit volume. The bypass valve serves to protect the compressor when its load state does not match that of the fuel cell or the fuel cell stack. In certain operating conditions, a mass flow dm _B / dt, bypassing the Fuel cell, or the fuel cell stack, passed directly into the discharge. Nevertheless, the evaluation unit is still able to determine the desired mass flow dm / dt of the oxidant.

In a further particularly advantageous embodiment, the supply of the oxidizing agent in the compressor, and / or the connection between the compressor and the cathode space, free of sensors for the mass flow dm / dt of the oxidizing agent. By taking over the function of these additional sensors, the safety sensor for the combustible component of the fuel can be saved. This saves hardware and cabling, and sensors that are not available can not fail.

As mentioned above, in particular in a vehicle in which the sensors are connected to a bus system, for example to a CAN bus, each control unit can access the data of all the sensors without the need for further wiring. This means at the same time that even an existing control unit can be made by an extension in the form of software in the position to perform the function of the evaluation unit described above. This software can be sold, for example, as an update or upgrade for an existing control unit, for example, for a control unit of a fuel cell system, and is thus an independent product.

Therefore, the invention also relates to a computer program with machine-readable instructions which, when executed on a computer and / or on a control unit, upgrade the computer and / or the control unit to an evaluation unit according to the invention.

Likewise, the invention also relates to a machine-readable data carrier or a download product with the computer program.

Further, measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to a figure.

list of figures

• 1 Ausführungsbeispiel des Systems 100 mit der Auswerteeinheit 1.

It shows:

• 1 Embodiment of the system 100 with the evaluation unit 1 ,

To 1 includes the system 100 a fuel cell stack 2 with an anode compartment 24 for the supply of a fuel 23 and a cathode compartment 22 for the supply of an oxidizing agent 21 ,

The oxidizing agent 21 In this example, air is that of a compressor 33 via a supply line 38 with an air filter 31 is sucked. The oxidizing agent 21 will be in the connection 37 between the compressor 33 and the fuel cell stack 2 via a heat exchanger 34 cooled and enters the cathode compartment 22 of the fuel cell stack 2 , Not fuel 23 converted oxidizing agents 21 will be about the exhaustion 25 equipped with a shut-off valve 25a is provided, from the cathode compartment 22 deducted. Unless the bypass valve 35 is switched permeable, additionally passes a mass flow dm _B / dt of the oxidizing agent 21 bypassing the fuel cell stack 2 directly into the exhaustion 25 ,

The fuel 23 contains at least one combustible component 23a , In this example, the fuel is 23 Hydrogen. The share of fuel 23 in the anode room 24 not oxidized, can be via a purge valve 27 directly into the exhaustion 25 be directed.

By the oxidizing agent 21 reduced and at the same time the fuel 23 is oxidized, free carriers form, which is a current I can drive through an external electrical circuit.

In the exhaustion 25 there is a sensor 26 for a combustible ingredient 23a of fuel 23 , The reading of this sensor 26 and the current driven by the fuel cell stack I are the essential variables that the evaluation unit 1 to determine the mass flow dm / dt of the oxidant through the cathode compartment 22 be supplied. Especially from the stream I can the evaluation unit 11 directly the mass flow dmp / dt of the fuel cell stack 2 determine the product water formed. How this product water spreads to the liquid and the vapor phase, among other things by the temperature T in the vicinity of the exhaustion 25 certainly. This temperature T becomes the evaluation unit 11 also supplied.

In this example, the evaluation unit receives 1 In addition, the speed of the compressor 33 and the switching position of the bypass valve 35 , With a model or map 11 determines the evaluation unit 1 from this the pressure loss Δp and the derived mass flow dm _B / dt with activated bypass valve 35 ,

Furthermore, the evaluation unit receives 11 also the switching position of the purge valve 27 , Based on another model or map 12 from this, the influence of the presence of the combustible component can 23a in the exhaustion 25 on the sensor 26 measured signal is detected and from the be separated by the mere mass flow dm / dt caused signal.

As a result, both the supply line 38 to the compressor 33 as well as the connection 37 from the compressor 33 to the fuel cell stack 2 free of sensors 32 . 36 for the mass flow dm / dt of the oxidizing agent 21 However, there is still a sufficiently accurate knowledge of this mass flow dm / dt. Therefore, these sensors are in 1 dashed lines.

The evaluation unit 1 However, it also brings benefits when one of the two existing in the prior art sensors 32 . 36 is maintained. If these sensors 32 . 36 can not be saved, so their measured values can at least with the by the evaluation 1 plausibility of measured values. Also, the determination of the mass flow dm / dt with the sensor 26 and the evaluation unit 1 be used as an additional redundancy level in the event that one or both sensors 32 . 36 fail. In this case, there is still a continued operation of the system 100 possible. If the sensor 26 fails, however, its effect can not by one of the sensors 32 . 36 be replaced.

Between the cathode compartment 22 and the anode compartment 24 of the fuel cell stack 2 is the stack cooling 20 , The stack cooling 20 is from a cooling coil 42 criss-crossed by those with a pump 41 a flow of a coolant is driven. Via a directional valve 43 can be between circulation operation and delivery of heat to the cooling system 44 of the vehicle are switched.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• WO 2017/148798 A1 [0003]
• DE 102016210518 A1 [0004]

Claims (14)

Evaluation unit (1) for measuring the mass flow dm / dt of an oxidant (21) through a cathode compartment (22) of a fuel cell or a fuel cell stack (2), wherein the fuel cell, or the fuel cell stack (2), an anode compartment (24) for the supply of a fuel (23) and wherein in a discharge (25) for the oxidizing agent (21) from the cathode space (22) a sensor (26) is installed, which is adapted to the entry of at least one combustible component (23a) of the fuel (23) to be detected in the discharge (25), wherein the measured variable used by the sensor (26) can be influenced both by the concentration of the combustible component (23a) and by the mass flow dm / dt of the oxidizing agent (21) the evaluation unit (1) with both the sensor (26) and with an ammeter for the current through the fuel cell, or through the fuel cell stack (2), current I connected and excluded ebildet is to evaluate the mass flow dm / dt from the measured value of the sensor (26) in conjunction with the current I. Evaluation unit (1) to Claim 1 , wherein the evaluation unit (1) is adapted to determine from the current I, the mass flow dmp / dt to from the fuel cell, or the fuel cell stack (2), generated gaseous reaction product. Evaluation unit (1) to Claim 2 , wherein the evaluation unit (1) is adapted to determine from the current I, the amount of vapor and liquid product water formed by the fuel cell, or the fuel cell stack (2). Evaluation unit (1) to Claim 3 , wherein the evaluation unit (1) with a temperature sensor for the temperature T in the discharge (25), and / or in the vicinity of the discharge (25), connectable and adapted to the amount of liquid product water in consideration of this temperature T to determine. Evaluation unit (1) according to one of Claims 1 to 4 , wherein the evaluation unit in addition with a switch for the switching position of a bypass valve (35), the oxidizing agent (21) around the fuel cell, or around the fuel cell stack (2), directly into the discharge (25) passes, connectable and thereto is designed to determine the mass flow dm _B / dt of the oxidizing agent (21) conducted through the bypass valve (35). Evaluation unit (1) to Claim 5 containing a model or map (11) containing at least the information necessary for determining a pressure drop Δp of the oxidant (21) upon actuation of the bypass valve. Evaluation unit (1) according to one of Claims 1 to 6 , wherein the evaluation unit (1) in addition to a speed sensor for a compressor (33) is connectable, which promotes the oxidizing agent (21) in the fuel cell, or in the fuel cell stack (2). Evaluation unit (1) according to one of Claims 1 to 7 , wherein the evaluation unit (1) in addition to a switch for the switching position of a purge valve (27), the fuel (23) from the anode chamber (24) of the fuel cell, or the fuel cell stack (2), leads into the discharge is connectable. Evaluation unit (1) to Claim 8 , wherein the evaluation unit (1) contains a model or map (12) which describes the influence of the concentration of the combustible component (23a) of the fuel (23) on the sensor (26) on the measurement signal of the sensor (26). A power generation system (100) comprising at least one fuel cell or a fuel cell stack (2) with an anode space (24) for supplying a fuel (23) and a cathode space (22) for supplying an oxidant (21), wherein in a discharge (25) for the oxidizing agent (21) from the cathode chamber (22) a sensor (26) is installed, which is adapted to detect an entry of at least one combustible component (23a) of the fuel (23) in the discharge (25) , wherein the measured variable used by the sensor (26) can be influenced both by the concentration of the combustible constituent (23a) and by the mass flow dm / dt of the oxidizing agent (21), the system (100) additionally having an evaluation unit (1) according to a of the Claims 1 to 9 includes. System (100) after Claim 10 wherein the sensor (26) is an ultrasonic sensor or comprises a heated filament and means for measuring the temperature of that filament. System (100) according to one of Claims 10 to 11 , wherein in addition a compressor (33) for the oxidizing agent (21) and a bypass valve (35) for the diversion of compressed oxidizing agent (21) in the discharge (25) are provided. System (100) after Claim 12 in that the supply (38) for the oxidizing agent (21) into the compressor (33), and / or the connection (37) between the compressor (33) and the cathode chamber (22) are free of sensors (32, 36) for are the mass flow dm / dt of the oxidizing agent (21). Computer program, comprising machine-readable instructions, which, when executed on a computer, and / or on a control unit, the computer, and / or the control unit, to an evaluation unit (1) according to one of Claims 1 to 9 upgrade.

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