TITANIA NOX SENSORS FOR EXHAUST MONITORING

Oxide semiconductors have been examined to develop NOx sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al3+, Sc3+, Ga3+ or In3+, has a good sensitivity and selectivity to NO between 450 and 550 degrees C, and shows rapid response. A sensor probe for monitoring exhaust NOx has been fabricated. Many kinds of interference gases, such as C3H6, CO and SO2, have been found to have only a slight influence on the sensor response to NO. The influence of O-2 and H2O is also negligible, except for the cases of 0% H2O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactorily in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases.