JP2007128758A - Fuel cell system and gas constituent state detection method in fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of accurately knowing the quantity of water in the fuel cell stack, and thereby capable of obtaining high power generation efficiency. <P>SOLUTION: The fuel cell system is provided with a fuel cell which generates power by receiving supply of an oxidizer gas and a fuel gas. The system is provided with an ultrasonic transmitter 10, an ultrasonic receiver 11, and a detector 12 which detects gas component state in the fuel cell stack 20, based on the oscillation waveform transmitted from the ultrasonic transmitter 10 and the receiving waveform received by the ultrasonic receiver 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a gas component state detection method in a fuel cell, and more particularly to a technique that enables measurement of a gas component state in a fuel cell with a simple structure.

  For example, a solid polymer electrolyte fuel cell has a minimum power generation unit in which both sides of a membrane-electrode assembly (hereinafter referred to as MEA) are sandwiched by a separator having a fuel gas (hydrogen, etc.) channel and an oxidizing gas (oxygen, etc.) channel. Each of the single cells is stacked, and a large number of the single cells are stacked to form a fuel cell stack (hereinafter referred to as a stack).

If an excessive amount of water generated by power generation is present in the stack (so-called flooding), gas flow in the stack is hindered and power generation performance decreases. On the contrary, when the electrolyte membrane in the stack is dried from a predetermined wet state (so-called dry-up), proton conductivity is lowered and power generation performance is lowered, or durability of the electrolyte membrane is lowered. Therefore, in order to control the water balance in the stack, a technique has been developed in which an electrode is disposed inside the electrolyte membrane and the moisture content in the stack is measured by measuring impedance (for example, Patent Document 1).
JP 2004-146267 A

  However, when the electrodes are arranged inside the electrolyte membrane as in Patent Document 1, it is advantageous in that the gas component state in the stack can be directly measured, but the structure of the electrolyte membrane and thus the structure of the stack are complicated. Become.

  The present invention has been made in view of the above circumstances, and an object thereof is to enable detection of a gas component state in a fuel cell with a simple structure.

  The fuel cell system of the present invention is a fuel cell system including a fuel cell that generates power upon receiving gas supply, and a sound wave transmitting means that transmits a sound wave to the inside of the fuel cell on a gas flow path, and the sound wave transmission And a sound wave receiving means for receiving a sound wave transmitted from the means and propagated through at least a part of the fuel cell, and a transmission waveform transmitted by the sound wave transmitting means and received by the sound wave receiving means. And a detecting means for detecting a gas component state in the fuel cell based on the received waveform.

  According to this configuration, the gas component state in the fuel cell is measured by, for example, measuring a time difference from transmission to reception of sound waves with a simple structure of the sound wave transmission means and the sound wave reception means arranged on the gas flow path. For example, the amount of water vapor present in the fuel cell can be measured.

  However, since the propagation time of the sound wave changes depending on the temperature and the gas flow rate, preferably, the measurement is separately performed, and the detection result is calculated together with the result. In addition, the amount of water droplets can be measured by comparing the waveforms (amplitude, phase, etc.) at the time of transmission and reception of sound waves.

  The detection unit may detect a gas component state in the fuel cell based on a comparison result of at least one of an amplitude and a period of the transmission waveform and the reception waveform.

  When water droplets are present in the fuel cell, changes in amplitude and period due to reflection, interference, etc., waveform disturbance, etc. occur in the sound wave. Therefore, in the fuel cell system of the present invention, the amount of water droplets can be set as the gas component state based on the difference between the transmission waveform and the reception waveform. This measurement may be performed based on one comparison result of amplitude or period, or may be performed based on both comparison results.

  In the fuel cell system of the present invention, at least one of the sound wave transmitting means and the sound wave receiving means may be provided in a gas pipe connected to the fuel cell.

  According to this configuration, sound waves are transmitted and received from the outside of the fuel cell to the inside or from the inside to the outside through the gas pipe. For example, the sound wave transmitting means can be installed on the oxidizing gas inlet side or the fuel gas inlet side of the fuel cell, while the sound wave receiving means can be installed on the oxidizing gas outlet side or the fuel gas outlet side.

  In the fuel cell system of the present invention, the gas flow path in the fuel cell has a bent part and a straight part (for example, a serpentine flow path), and the sound wave transmitting means and the sound wave receiving means are the straight lines. The portions may be arranged to face each other at a predetermined interval.

  According to this configuration, there is no obstacle (a wall surface of the bent portion) in the propagation path of the sound wave as in the case where the sound wave transmitting unit or the sound wave transmitting unit is arranged in the bent portion of the gas flow path for measurement. Therefore, processing such as correction required when the obstacle is present is unnecessary, and higher-precision measurement is possible.

  A method for detecting a gas component state in a fuel cell according to the present invention is a detection method for detecting a gas component state in a fuel cell that generates power upon receiving a gas supply, and is provided inside the fuel cell via a gas flow path. A sound wave is transmitted, and the sound wave propagated through at least a part of the fuel cell is received, and a gas component state in the fuel cell is detected based on the transmission waveform and the received waveform.

  According to this configuration, a sound wave is transmitted into the fuel cell through the gas flow path, and a gas component state in the fuel cell, for example, in the fuel cell is measured, for example, by measuring a time difference from transmission to reception of the sound wave. The amount of water vapor present can be detected.

  However, since the propagation time of the sound wave changes depending on the temperature and the gas flow rate, preferably, the measurement is separately performed, and the detection result is calculated together with the result. In addition, the amount of water droplets can be detected by comparing waveforms (amplitude, phase, etc.) at the time of transmission and reception of sound waves.

  According to the present invention, it is possible to detect the gas component state in the fuel cell with a simple structure by the sound wave transmitting means and the sound wave receiving means arranged on the gas flow path.

<First Embodiment>
Next, an embodiment of a fuel cell system according to the present invention will be described.

  Hereinafter, the case where this fuel cell system is applied to an in-vehicle power generation system of a fuel cell vehicle will be described. However, the present invention is not limited to such an application example, and is applicable to all moving objects such as ships, airplanes, trains, and walking robots. For example, the present invention can be applied to a stationary power generation system in which a fuel cell is used as a power generation facility for a building (house, building, etc.).

  As shown in FIG. 1, air (outside air) as an oxidizing gas is supplied to the air supply port of the fuel cell stack 20 via an air supply path 71. The air supply path 71 is provided with an air filter A1 that removes particulates from the air, a compressor A3 that pressurizes the air, a pressure sensor P4 that detects the supply air pressure, and a humidifier A21 that adds required moisture to the air. The compressor A3 is driven by a motor (auxiliary machine). This motor is driven and controlled by a control unit 50 described later. The air filter A1 is provided with an air flow meter (flow meter) (not shown) that detects the air flow rate.

  The air off gas discharged from the fuel cell stack 20 is discharged to the outside through the exhaust path 72. The exhaust path 72 is provided with a pressure sensor P1 that detects the exhaust pressure, a pressure adjustment valve A4, and a heat exchanger for the humidifier A21. The pressure sensor P <b> 1 is provided in the vicinity of the air exhaust port of the fuel cell stack 20. The pressure adjustment valve A4 functions as a pressure regulator (pressure reduction) that sets the air pressure supplied to the fuel cell stack 20.

  Detection signals (not shown) of the pressure sensors P4 and P1 are sent to the control unit 50. The control unit 50 sets the supply air pressure and the supply air flow rate to the fuel cell stack 20 by adjusting the motor rotation speed of the compressor A3 and the opening area of the pressure adjustment valve A4.

  Hydrogen gas as fuel gas is supplied from the hydrogen supply source 30 to the hydrogen supply port of the fuel cell stack 20 via the fuel supply path 74. The hydrogen supply source 30 corresponds to, for example, a high-pressure hydrogen tank, but may be a so-called fuel reformer, a hydrogen storage alloy, or the like.

  The fuel supply path 74 includes a shutoff valve H100 that supplies or stops supplying hydrogen from the hydrogen supply source 30, a pressure sensor P6 that detects the supply pressure of hydrogen gas from the hydrogen supply source 30, and hydrogen to the fuel cell stack 20. A hydrogen pressure regulating valve H9 for reducing and adjusting the gas supply pressure, a pressure sensor P9 for detecting the hydrogen gas pressure downstream of the hydrogen pressure regulating valve H9, and a cutoff for opening and closing between the hydrogen supply port of the fuel cell stack 20 and the fuel supply path 74. A pressure sensor P5 for detecting the inlet pressure of the valve H21 and the fuel cell stack 20 of hydrogen gas is provided.

  As the hydrogen pressure regulating valve H9, for example, a pressure regulating valve that performs mechanical pressure reduction can be used. However, a valve whose opening degree is linearly or continuously adjusted by a pulse motor may be used. Detection signals (not shown) of the pressure sensors P5, P6, and P9 are supplied to the control unit 50.

  The hydrogen gas that has not been consumed in the fuel cell stack 20 is discharged to the hydrogen circulation path 75 as a hydrogen off-gas and returned to the downstream side of the hydrogen pressure regulating valve H9 in the fuel supply path 74. The hydrogen circulation path 75 includes a temperature sensor T31 that detects the temperature of the hydrogen off-gas, a shutoff valve H22 that communicates / blocks the fuel cell stack 20 and the hydrogen circulation path 75, a gas-liquid separator H42 that collects moisture from the hydrogen off-gas, and a recovery A drain valve H41 that collects the generated water in a tank (not shown) outside the hydrogen circulation path 75, a hydrogen pump H50 that pressurizes the hydrogen off gas, and a backflow prevention valve H52 are provided.

  The shutoff valves H21 and H22 close the anode side of the fuel cell stack 20. A detection signal (not shown) of the temperature sensor T31 is supplied to the control unit 50. The operation of the hydrogen pump H50 is controlled by the control unit 50.

  The hydrogen off gas merges with the hydrogen gas in the fuel supply path 74 and is supplied to the fuel cell stack 20 for reuse. The backflow prevention valve H52 prevents the hydrogen gas in the fuel supply path 74 from flowing back to the hydrogen circulation path 75 side. The shutoff valves H100, H21, and H22 are driven by a signal from the control unit 50.

  The hydrogen circulation path 75 is connected to the exhaust path 72 by the purge flow path 76 via the discharge control valve H51. The discharge control valve H51 is an electromagnetic shut-off valve, and discharges (purges) hydrogen off-gas to the outside by operating according to a command from the control unit 50. By performing this purge operation intermittently, it is possible to prevent a cell voltage from being lowered due to an increase in the impurity concentration in the hydrogen gas.

  A cooling path 73 for circulating the cooling water is provided at the cooling water inlet / outlet of the fuel cell stack 20. In the cooling path 73, a temperature sensor T1 that detects the temperature of the cooling water drained from the fuel cell stack 20, a radiator (heat exchanger) C2 that radiates the heat of the cooling water to the outside, and the cooling water is pressurized and circulated. A temperature sensor T2 that detects the temperature of the cooling water supplied to the pump C1 and the fuel cell stack 20 is provided. The radiator C2 is provided with a cooling fan C13 that is rotationally driven by a motor.

  The control unit 50 receives control information from a requested load such as an accelerator signal of a vehicle (not shown) and sensors (pressure sensor, temperature sensor, flow rate sensor, output ammeter, output voltmeter, etc.) of each part of the fuel cell system 100, and the system Control the operation of valves and motors in each part.

  The control unit 50 is configured by a control computer system (not shown). The control computer system has a known configuration such as a CPU, ROM, RAM, HDD, input / output interface, and display, and is configured by a commercially available control computer system.

  The fuel cell stack 20 is configured as a fuel cell stack in which a required number of unit cells 20a that generate power upon receipt of fuel gas and oxidant gas are stacked. The electric power generated by the fuel cell stack 20 is supplied to a power control unit (not shown). The power control unit consists of an inverter that supplies electric power to the drive motor of the vehicle, an inverter that supplies electric power to various auxiliary devices such as a compressor motor and a motor for a hydrogen pump, and charging of power storage means such as a secondary battery. A DC-DC converter or the like that supplies power to the motors from the power storage means is provided.

  In the present embodiment, the ultrasonic transmitter (sound wave transmission means) 10 is installed on the air inlet side (air supply path 71) or the hydrogen inlet side (fuel supply path 74) of the fuel cell stack 20. In addition, an ultrasonic receiver (sound wave receiving means) 11 is installed on the air outlet side (exhaust passage 72) or the hydrogen outlet side (hydrogen circulation passage 75).

  Furthermore, a detector (detection means) 12 that detects a gas component state in the fuel cell stack 20 based on the transmission waveform transmitted by the ultrasonic transmitter 10 and the reception waveform received by the ultrasonic receiver 11. Is provided. The detector 12 receives the transmission waveform transmitted from the ultrasonic transmitter 10 and the received waveform received by the ultrasonic receiver 11 from the ultrasonic transmitter 10 and the ultrasonic receiver 11, respectively. While detecting the state in the battery stack 20, the detection result is given to the control unit 50.

  In the fuel cell system 100 of the present embodiment configured as described above, when the detector 12 that has received the drive signal from the control unit 50 operates the ultrasonic transmitter 10 during operation of the fuel cell stack 20, The ultrasonic transmitter 10 transmits ultrasonic waves into the fuel cell stack 20. The ultrasonic wave transmitted by the ultrasonic transmitter 10 propagates through the fuel cell stack 20 and is received by the ultrasonic receiver 11.

  The detector 12 detects the amount of water vapor present in the fuel cell stack 20 by measuring the time difference from transmission to reception of ultrasonic waves. However, since the propagation time of the ultrasonic wave changes depending on the temperature and the gas flow rate, these measurements are separately performed, and the detection result is calculated together with the measurement result.

  For example, the velocity of sound waves in the air is 471.5 m / sec for water vapor at 100 ° C., 343.5 m / sec for dry air at 20 ° C., and 331.45 m / sec at 0 ° C. In addition, the higher the temperature, the faster the sound wave propagation speed, and the faster the sound wave propagation speed, the shorter the time from transmission to reception (sound wave arrival time). For this reason, the relationship between the sound wave arrival time, the water vapor amount, and the temperature has a tendency as shown in FIG. 3, for example.

  The detector 12 calculates the amount of water vapor based on the relationship between these three elements and the above measurement results. Specifically, the gas temperature is measured by a temperature sensor installed in the gas pipe or the fuel cell stack 20. The gas flow rate is calculated from the pressure value measured by the pressure sensor installed in the gas pipe or the fuel cell stack 20 and the gas flow path cross-sectional area, or a flow meter is installed in the gas pipe or the fuel cell stack 20. Install and measure.

  The gas flow path includes both a gas flow path in the gas pipe connected to the fuel cell stack 20 and a gas flow path in the fuel cell stack 20.

  In the present embodiment, it is possible to detect the amount of water droplets by comparing the waveforms (amplitude, phase, etc.) at the time of transmission and reception of ultrasonic waves. That is, for example, as shown in FIG. 4, since it is known that the received waveform includes a change in amplitude or period due to reflection or interference due to water droplets, a disturbance in the waveform, etc. By comparing the difference between the transmission waveform and the reception waveform, particularly the difference between one or both of the amplitude and the period, it is possible to detect the amount of water droplets.

  As described above, according to the fuel cell system 100 of the present embodiment, the state of the gas component such as the electrode inside the electrolyte membrane is detected by the ultrasonic transmitter 10 and the ultrasonic receiver 11 arranged on the gas flow path. The humidity (water vapor amount) and the amount of water droplets in the fuel cell stack 20 can be detected simultaneously with a simple structure as compared with the configuration in which the means is provided.

  Therefore, water balance control in the fuel cell stack 20 can be performed with high accuracy, generation of flooding and dry-up can be suppressed, high power generation efficiency can be maintained, and further, the inside of the single cell 20a can be maintained. The durability of the electrolyte membrane can be improved by appropriately controlling the amount of water.

  In this embodiment, an ultrasonic transmitter / receiver that generates ultrasonic waves is used. However, ultrasonic waves may not be used as long as they are sound waves. Further, the transmitter and the receiver may be provided on either the inlet side or the outlet side of the oxidizing gas or the fuel gas. Further, the ultrasonic transmitter 10 and the ultrasonic receiver 11 may be provided in both the oxidizing gas supply / discharge system and the fuel gas supply / discharge system, or may be provided only in one. Further, part or all of the functions of the detector 12 may be performed by the control unit 50.

Second Embodiment
The fuel cell system according to the present invention may be configured as shown in FIG.

  Each unit cell 20a, 20a,..., 20a constituting the fuel cell stack 20 has a configuration in which both surfaces of the electrolyte membrane-electrode assembly are sandwiched by a separator having a fuel gas channel and an oxidizing gas channel. A straight portion 21 is formed in the gas flow path. The ultrasonic transmitter 10 and the ultrasonic receiver 11 are attached to both ends of the straight portion 21 of the gas flow path so as to face each other. Thereby, it becomes possible to detect the amount of moisture and humidity inside each single cell 20a.

  In the present embodiment, first, the moisture content of the straight portion 21 of the gas flow path is measured in the same manner as in the above embodiment. Next, based on the measurement result, the detector 12 or the control unit 50 estimates the total moisture amount and humidity from the moisture amount per unit area of the measurement portion. However, since water droplets accumulate in the lower part, correction is performed in the vertical direction (the direction of gravity) in the on-vehicle state.

  As a result, water balance control in the fuel cell stack 20 can be performed with high accuracy, generation of flooding and dry-up can be suppressed, high power generation efficiency can be maintained, and further, the inside of the single cell 20a By appropriately controlling the amount of water, the durability of the electrolyte membrane can be improved.

  Further, in the present embodiment, since the ultrasonic transmitter 10 and the ultrasonic receiver 20 are arranged and measured in the straight portion 21 of the gas flow path in the single cell 20a, for example, it is super There is no obstacle (wall surface of the bent portion) in the sound wave propagation route indicated by the broken line in FIG. 2 as in the case where the sound wave transmitter 10 or the ultrasonic wave receiver 11 is arranged and measured. Processing such as correction required when the obstacle is present becomes unnecessary, and measurement with higher accuracy becomes possible.

  For this reason, when the gas flow path in the single cell 20a is a serpentine flow path in which a straight portion and a bent portion are continuous, the ultrasonic transmitter 10 and the ultrasonic receiver are connected to the straight portion of the serpentine flow path. It is preferable to arrange 20 to face each other at a predetermined interval.

<Third Embodiment>
As an application of the above-described embodiment, when it is detected that the inside of the fuel cell stack 20 has been dried to a predetermined wetness or less, the ultrasonic transmitter 10 is installed at a position where water droplets are likely to accumulate, and the predetermined frequency and amplitude are exceeded. It is possible to perform ultrasonic humidification by applying the ultrasonic wave to a water droplet.

  Also, in the drainage treatment (drying treatment) in the fuel cell stack 20 when the system is stopped, which is implemented as a low-temperature start-up measure, water droplets (moisture) are atomized by ultrasonic waves, and this is gas purged, whereby the fuel cell The moisture in the stack 20 can be effectively taken outside.

It is a schematic block diagram of the fuel cell system shown as one Embodiment of this invention. It is the schematic shown about the state which attached the ultrasonic transmitter and the ultrasonic receiver with respect to the fuel cell stack. It is the figure which showed the relationship between sonic wave arrival time, the amount of water vapor | steam, and temperature. It is the figure shown about the transmission waveform of the ultrasonic transmitter. It is the figure shown about the change of the received waveform by the presence or absence of the water droplet by an ultrasonic receiver, (a) has shown the case where there is no water droplet, (b) has shown the case where there is a water droplet.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Ultrasonic transmitter (sonic wave transmission means), 11 ... Ultrasonic receiver (sonic wave reception means), 12 ... Detector (detection means), 20 ... Fuel cell stack, 20a ... Single cell, 50 ... Control part, 71 ... Air supply path (gas flow path), 72 ... Exhaust path (gas flow path), 74 ... Fuel supply path (gas flow path), 75 ... Hydrogen circulation path (gas flow path), 100 ... Fuel cell system

Claims (5)

A fuel cell system including a fuel cell that generates electricity by receiving gas supply,
On the gas flow path, a sound wave transmitting means for transmitting a sound wave to the inside of the fuel cell, and a sound wave receiving means for receiving a sound wave transmitted from the sound wave transmitting means and propagated through at least a part of the fuel cell are disposed. And
A fuel cell system comprising detection means for detecting a gas component state in a fuel cell based on a transmission waveform transmitted by the sound wave transmission means and a reception waveform received by the sound wave reception means.   2. The fuel cell system according to claim 1, wherein the detection unit detects a gas component state in the fuel cell based on a comparison result of at least one of an amplitude and a period of the transmission waveform and the reception waveform.   3. The fuel cell system according to claim 1, wherein at least one of the sound wave transmitting unit and the sound wave receiving unit is provided in a gas pipe connected to the fuel cell. The gas flow path in the fuel cell has a bent portion and a straight portion,
3. The fuel cell system according to claim 1, wherein the sound wave transmitting unit and the sound wave receiving unit are disposed to face the linear portion at a predetermined interval. A detection method for detecting a gas component state in a fuel cell that generates electricity by receiving gas supply,
A sound wave is transmitted to the inside of the fuel cell via the gas flow path, and the sound wave propagated through at least a part of the fuel cell is received, and the sound wave in the fuel cell is received based on the transmission waveform and the received waveform. A gas component state detection method in a fuel cell for detecting a gas component state.

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