Temperature Sensitivity Mapping of the Zirconia Oxygen Sensor: Engine Test Results

A closed loop control system for regulation of engine air-fuel ratio at the stoichiometric value is required for effective operation of a three-way catalytic converter. System performance depends directly on accuracy of the zirconia oxygen sensor which generates a feedback signal for the system. The sensor voltage signal is known to be sensitive to exhaust temperature. In the present investigation, temperature sensitivity of the oxygen sensor was measured over a wide range of engine operating conditions.

Sensor data were plotted in the form of contour lines of constant sensor voltage as a function of engine air-fuel ratio and exhaust temperature, thereby mapping sensor performance. It was found that, depending on the sensor, a fixed level of sensor voltage shifted from 0.1 to 0.7 ratios towards air-fuel ratios slightly rich of the stoichiometric ratio as exhaust temperature increased from 500°C to 700°C.