CoO Sensors for Measurement and Control of Exhaust from Lean-Burn Engines 760312
An experimental exhaust sensor using CoO ceramic is being developed for measuring and controlling air-to-fuel ratio (A/F) of internal combustion engines operating under lean-burn conditions. The operation of the sensor is based on the fact that at elevated temperatures the electrical resistance of CoO depends on the oxygen partial pressure (PO2). At controlled temperatures, the combination of good PO2 sensititivty, high reproducibility of the electrical properties and small temperature coefficient of resistance of CoO materials make this sensor suitable for the lean A/F range (15-20) where exhaust PO2 depends only weakly on A/F ratio. At low PO2 (A/F<13.5) and high temperatures, CoO reduces to Co; therefore, prolonged exposure of the sensor to these conditions must be avoided. The material properties and the sensor characteristics are discussed and results of tests on car-mountable CoO sensors are presented. Durability and large-scale manufacturability of these sensors have not yet been established.