JPS6175250A - Method and apparatus for detecting fuel density liquid fuel battery - Google Patents

Abstract

PURPOSE:To achieve a stable and highly accurate measurement without electric contact with an electrolytic liquid from outside, by detecting a partial vapor pressure of a liquid fuel in the gaseous phase of the electrolytic liquid mixed with the liquid fuel with a semiconductor gas sensor. CONSTITUTION:A fuel pole chamber 11 and an air pole chamber 12 are arranged on both sides of a laminated fuel battery 10 and an electrolytic liquid 18 in an electrolytic liquid reservoir 17 is mixed with a liquid fuel 16 from a tank 15 to be supplied and circulated with a pump 14 to the fuel pole chamber 11 through an electrolytic liquid reservoir 17 and supply paths 11A and 11B. Air for an oxidizing agent is supplied to the air pole chamber 12 with a fan 13 through supply paths 12A and 12B. Moreover, a semiconductor gas sensor 26 is arranged in the gaseous phase of the liquid reservoir 17 and the partial vapor pressure of fuel in the gaseous phase, hence changes in the resistance of the gas sensor 26 due to the gas density thereof, is detected with an ammeter 21 to measure the density of the liquid fuel in the electrolytic liquid 18. Then, a temperature correction of a sensor 20 at a correcting section 20 is done with a temperature detection thermistor 25 while the supply of the liquid fuel 16 from the fuel tank 15 is controlled by adjusting the opening/closing frequency of a solenoid valve 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for measuring fuel concentration in an electrolyte of a fuel cell that generates electrical energy by directly electrochemically reacting liquid fuel.

[Background of the invention]

Normally, fuel cell performance (output voltage) strongly depends on the fuel concentration in the electrolyte, so it is necessary to detect the fuel concentration in the electrolyte and control it within a certain range. By the way, in acidic electrolyte fuel cells using methanol as fuel, if the fuel concentration in the electrolyte is too low, there will be insufficient reaction fuel, resulting in a decrease in cell performance, and if it is too high, the direct combustion of fuel will increase, leading to a decrease in cell performance. Therefore, it is necessary to control the methanol fuel concentration to the electrolytic solution 11 within a range of 0.5 to 1.5 mob/l.

A conventional example of a method for detecting the concentration of liquid fuel in an electrolyte in a fuel cell is a method for detecting methanol concentration in a methanol fuel cell, as disclosed in Japanese Patent Laid-Open No. 118273/1983. This method takes advantage of the fact that the methanol concentration in the electrolyte depends on the electric current under a constant potential.Both the positive and negative measuring electrodes are immersed in the electrolyte, and the stain layer is applied to the outside at a constant level. This is a method of applying an electrolytic voltage and quantitatively evaluating the electrolytic current flowing between the two electrodes. The electrolytic solution normally has a potential of about 70 to 80% of the fuel cell output voltage, and in the above method, the concentration measuring electrode, supply current source, and detection circuit are all externally isolated from the fuel cell system. It had to be a power supply system.

FIG. 2 shows a fuel supply system for a fuel cell using the above method. Liquid fuel 16 (methanol in this case) is mixed from the fuel tank 15 into the electrolytic solution 18 in the electrolytic solution reservoir 17, and the fuel supply bond 14 feeds the supply passages 11A, 11.
The mixed liquid is circulated and supplied to the fuel electrode chamber 11 of the stacked fuel cell main body 10 via B. The oxidizer air is supplied to the supply passage 12A by the fan 13.

It is supplied to the air cathode chamber 12 via 12B. Battery body 1
Within 0, fuel in the electrolyte is consumed depending on the external load. In order to detect the methanol fuel concentration in the electrolyte in such a fuel cell, according to the method described in JP-A-56-118273, the measuring electrodes 22 and 23 are immersed in the electrolyte 18 in the electrolyte reservoir 17. , which is connected to a power supply and correction section, and an electrolytic current depending on the concentration of liquid fuel in the electrolytic solution flowing to the electrode is detected by an ammeter 21, and this is corrected by a correction section 20 using the temperature detected by a thermocouple 24. evaluate. Based on this evaluation result, the valve 19 is adjusted to control the fuel concentration in the electrolytic solution 18 to be constant.

The biggest problem with the above fuel concentration detection method is that the measurement electrode 2
2.23 and the measurement system connected thereto, such as an electric circuit, must be completely electrically insulated from the fuel cell main body.

To explain this problem using the equivalent electric circuit diagram shown in FIG. 3, the fuel cell main body 30 supplies power to the electric load 31 via the switch 32. At the same time, the positive and negative electrodes of the battery body 30 are bridged by the equivalent resistance 34 of the circulating electrolyte 18.

Positive and negative measurement electrodes 22 and 2 immersed in electrolyte
3 attempts to obtain a potential divided by the layer liquid resistance 34 by the voltage of the fuel cell on the one hand, and on the other hand is affected by the voltage of the external power supply 35 for measurement electrolysis, and is a composite of these two power supply systems. When the ammeter 21 detects the electrolytic current as a potential, it becomes K.

Normally, the voltage of a fuel cell varies greatly depending on the load current, resulting in a large variation in the detected current.

Further, when the fuel cell is used as an independent power source in a place where no other power source exists, it is necessary to connect the measuring electrolysis power source 35 to the power source from the fuel cell.

For these reasons, it is necessary to completely electrically isolate the fuel cell system and the measurement electrolyte system, that is, to prevent electrical conduction between the two systems via the electrolyte. The problem was that it was extremely complicated.

Furthermore, platinum or a platinum catalyst coated on the surface of the platinum electrode is usually used as the measurement electrode, which has problems such as the electrode part being expensive and having a short lifespan and lacking in stability.

[Purpose of the invention]

In view of the above-mentioned conventional problems, an object of the present invention is to provide a method and apparatus that can stably and accurately detect the fuel concentration in an electrolyte of a fuel cell without applying electrical contact to the electrolyte from the outside. be.

[Summary of the invention]

The present invention utilizes the fact that, in a fuel cell using a liquid fuel, the vapor partial pressure of the liquid fuel in the gas phase of an electrolyte mixed with the liquid fuel is a function of the concentration of the liquid fuel in the electrolyte. By detecting the vapor partial pressure with a semiconductor gas sensor, the concentration of liquid fuel in the electrolyte is detected. Complex configurations are avoided.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. A fuel electrode chamber 11 and an air electrode chamber 12 are arranged on both sides of the stacked fuel cell body 10, and the liquid fuel 16 is mixed into the electrolyte 18 in the electrolyte reservoir 17 from the tank 15. The fuel electrode chamber 11 is supplied to the fuel electrode chamber 11 via the micro-layer liquid reservoir 17, the supply passages 11A and IIB by the input f14.
The supply can be circulated. On the other hand, the oxidizer air is supplied by the fan 13.
air cathode chamber 12 through supply passages 12A and 12B.
supply to. A semiconductor gas sensor 26 is disposed in the gas phase of the electrolyte reservoir 17, and the ammeter 21 detects changes in the resistance of the gas sensor 2σ due to the partial pressure of fuel vapor in the gas phase, and therefore the gas concentration, and detects the liquid in the electrolyte 18. Fuel concentration, electrolyte 18
Measurements are made in an electrically insulated state. Further, a thermistor 25 is disposed in the gas phase for temperature detection, and a correction section 20 performs temperature correction on the output of the gas sensor 26. Correction section 20
also includes a power source for the semiconductor gas sensor 26. Based on the detected sensor output, the supply of liquid fuel 16 from the fuel tank 15 is controlled by adjusting the opening/closing frequency (or time interval) of the electromagnetic pulp 19 so as to maintain the liquid fuel concentration in the electrolyte within a specified range. Control.

A semiconductor gas sensor detects gas concentration from a change in resistance between electrodes when a semiconductor interposed between electrodes to which a voltage is applied is exposed to gas (for example, see Document 1 below).
．． 2.3), in the present invention, suitable semiconductor gas sensors can be used from among known semiconductor gas sensors depending on the characteristics.

Literature l..."Electronics" June 1980 issue,
Reference 2, pp. 107-109...Ibid., January 1983 issue, pp. 47-55 Document 3...``Instrument J April 1983 issue, pp. 27-30 Figure 4 shows methanol as a liquid fuel. This figure shows an actual measurement example of fuel concentration detection using the methanol fuel cell used as an example.As a semiconductor gas sensor, a commercially available gas sensor (TGS+8 manufactured by Figaro) whose main component is 5n02 was used.
13) was used. The horizontal axis represents the methanol concentration (mob/l) in the electrolyte solution, and the vertical axis represents the semiconductor sensor resistance, and the relationship between the two is shown.

In methanol fuel cells, the concentration of liquid fuel methanol in the electrolyte solution is between 0.5 and 1.5 (mot/l).
It is known that the battery performance is the best and stable operation is possible within this concentration range.According to Figure 4, the change in sensor resistance within this concentration range is sufficiently large, making it a highly sensitive concentration sensor. I understand that.

Since the vapor pressure of liquid fuel depends on temperature (see FIG. 5), FIG. 4 also shows the temperature dependence of the semiconductor gas resistance. It can be seen that the sensor resistance change has sufficient sensitivity in the practical temperature range of 20° C. to 60° C.

FIG. 6 shows a temperature correction circuit system and a drive circuit for the fuel pulp 19. Fuel cell output voltage 100
is made into a constant voltage by a three-terminal regulator 101 and used as a heater power source for the semiconductor gas sensor 26. A temperature correction thermistor 25 is arranged in parallel with the semiconductor sensor output resistor, and the differential output between the output voltages of both is used as an opening/closing signal for the fuel supply pulp 19 via the connograph 104.

FIG. 7 shows the detected gas concentration characteristics (Figaro Catalog value TGS 813) of an element mainly composed of S no 2 as a semiconductor. It can be seen that the sensitivity to alcohol (vapor), which is most expected as a liquid fuel, is extremely high. This also means that it will be affected by other gases. In addition, S no 2 is H2SO4, KOI (.

It is also a preferred material for the semiconductor gas sensor for fuel cell concentration detection used in the present invention in that it has high resistance to acids such as H3PO4 and trace amounts of corrosive vapor in the gas phase derived from alkali IJK.

〔Effect of the invention〕

According to the present invention, in a liquid fuel cell, the concentration of liquid fuel in the electrolyte can be detected without the sensor coming into contact with the electrolyte. Since there is no problem of influence via the electrolyte between the system and the measurement system, the sensor is simple, reliable, and has a long service life.Also, since a commercially available semiconductor gas sensor can be used, it is inexpensive and easy to maintain. This can be done extremely easily by replacing the elements.

Of course, it goes without saying that the detected value of fuel concentration obtained by the present invention can be used to control the fuel concentration in the electrolyte of a fuel cell.

[Brief explanation of drawings]

FIG. 1 is a flow diagram of a fuel supply system of a fuel cell using the fuel concentration detection device of the present invention, FIG. 2 is a flow diagram of a fuel supply system of a fuel cell using a conventional fuel concentration detection device, and FIG. The figure is an electrical equivalent circuit diagram of Figure 2, Figure 4 is a correlation diagram between methanol fuel concentration in the electrolyte and semiconductor gas sensor resistance, Figure 5 is a correlation diagram between methanol concentration and temperature, and Figure 6 is a diagram of the main FIG. 7 is a temperature correction and fuel pulp drive circuit diagram of the concentration sensor in the embodiment of the invention, and a characteristic diagram of the SnO□ semiconductor gas chamber. Explanation of symbols 10...Stacked fuel cell main body 11...Fuel electrode chamber 12
... Air electrode chamber 13 ... Fan 14 ... Pump 15 ... Fuel storage tank 16 ... Liquid fuel 17 ... Electrolyte reservoir 18 ... Electrolyte
19... Fuel supply pulp 20... Correction electric circuit/power supply 21... Ammeter 22... Electrode for measuring electrolysis (positive) 23... Electrode for measuring electrolysis (negative) 24... Thermistor or Thermocouple 25...Thermistor 26...Semiconductor gas sensor 30...Fuel cell main body 3
1... Electric load 34... Electrolyte resistance 35.
...External power supply 36...Ammeter 100...Fuel cell main body 101...Constant voltage three-terminal regulator 104...
Comparator Fig. 1 Tile Fig. 2 Fig. 4 Fig. 4 Sufnor 3 breaths in electric cod J (-”//) Fig. 5 Slow j (t) &(%)

Claims (1)

[Claims] 1. In a fuel cell using liquid fuel, the vapor partial pressure of the liquid fuel in the gas phase of the electrolyte mixed with the liquid fuel is detected by a semiconductor gas sensor, so that the amount of liquid fuel in the electrolyte is detected. A method for detecting fuel concentration in a liquid fuel cell, characterized by detecting concentration. 2. The method for detecting fuel concentration in a liquid fuel cell according to claim 1, wherein the output of the semiconductor gas sensor is temperature-corrected based on the output of a temperature sensor that detects the temperature of the gas phase. 3. The method for detecting fuel concentration in a liquid fuel cell according to claim 1 or 2, wherein the liquid fuel is methanol and the semiconductor gas sensor is a semiconductor gas sensor containing SnO_2 as a main component. 4. A semiconductor gas sensor installed in the gas phase of a liquid reservoir provided in the supply system of an electrolyte mixed with liquid fuel in a fuel cell using liquid fuel, and depending on the vapor partial pressure of the liquid fuel in the gas phase. 1. A fuel concentration detection device for a liquid fuel cell, comprising: a detection circuit that responds to the output of the semiconductor sensor. 5. A temperature sensor is further installed in the gas phase of the liquid reservoir, and the detection circuit responds to the output of the semiconductor gas sensor whose temperature is corrected by the output of the temperature sensor. The fuel concentration detection device for the liquid fuel cell described above. 6. The fuel concentration detection device for a liquid fuel cell according to claim 4 or 5, wherein the liquid fuel is methanol and the semiconductor gas sensor is a semiconductor gas sensor containing SnO_2 as a main component.