ジルコニア酸素センサ出力に対する被測定ガス圧力脈動の影響

抄録

Zirconia oxygen sensors are widely used for automobiles and industrial furnaces. The sensor has an inner volume and two solid electrolyte cells, a pumping cell and a sensing cell. Output current of the sensor is proportional to the diffusing gas speed running through the pin hole which connects the inner volume and gas to be measured. The sensor is suitable to an extended range air-to-fuel ratio sensor which measures air-to-fuel ratio from rich to lean.
Output current of the sensor pulsates with the pressure pulsation of exhaust gas, and the average current shifts with the amplitude of the pressure pulsation, when the sensor is used to measure the air-to-fuel ratio of exhaust gas from an automobile. Dynamic characteristics of the sensor are simulated numerically to clarify the cause of the current pulsation and the shift. A physical model for gas diffusion and gas flow in the pin hole and the inner volume is made, and chemical reaction at electrodes are considered for the calculation. Gas flow and concentration distribution of gasses, and the output current of the sensor are calculated and compared with measured values.
Calculated maximum gas flow rate is 1.0m/sec. in the pin hole and corresponding current shift is 22% which agrees with the measured value. The calculation suggests that the shift of output current decreases as the volume of the inner volume is smaller, and that the shift is negligibly small if the volume is 0.5mm³ or less. A sensor which has the inner volume of 0.15mm³ is made and the effect of pressure pulsation on the output current is measured. The current shift is 1/5 of the shift of conventional oxygen sensors.