Automotive Exhaust Sensors Using Titania Ceramic

The resistivity of titania (TiO₂) ceramic depends upon the partial pressure of oxygen (P_O2) in the atmosphere surrounding the ceramic. Because there is a functional relationship between the P_O2 of the equilibrated exhaust gas and the air to fuel ratio (A/F) operating point of the internal combustion engine, the resistance of a TiO₂ ceramic sensor, when temperature controlled, can be used to determine quantitatively the A/F. TiO₂ sensors utilizing these principles have been built and found to work particularly well in the region rich of stoichiometry. Control of the A/F in the region rich of stoichiometry is desirable for engine/catalyst systems designed to meet low NO_x emission levels.

This paper reports on the design details and operating features of an experimental TiO₂ sensor and its associated electronic controller. In addition, experimental results are reported for the sensor/controller combination operating in engine dynamometer tests and on vehicles with feedback-controlled, electronic fuel injected engines. These results indicate that feedback control using the TiO₂ sensor represents a possible means of achieving the precision A/F control required to obtain efficient performance of vehicles using NO_x catalysts.