Review on zirconia air-fuel ratio sensors for automotive applications

During the operation of a gasoline engine, the air-fuel ratio (A/F) is a key parameter in controlling fuel consumption and pollutant emissions. In this article, the various zirconia A/F sensors for automotive applications such as the stoichiometric λ sensor, the limiting current-type sensor, and the wide range A/F sensor were reviewed in the viewpoint of the necessity, structure, operation principle, long-term stability, and the algorithm for catalyst monitoring. The miniaturization and simplification of a sensor design using co-firing and planar processing technology will be an effective approach to improve the performance and cost-effectiveness of the sensor.