Jesse Nachlas

Mixed-potential type ceramic sensor for NOx monitoring

Ceramatec, Inc. is developing a NO x sensor through a program funded by the Environmental Protection Agency (EPA) to support the implementation of new emission control systems proposed for future diesel engine applications. In order to effectively implement these new emission control systems, a NO x sensor, capable of making real time measurements with fast enough response times, needs to be incorporated into the control system in order to provide the necessary feedback to the control system. Mixed potential type sensors offer the advantages of high-temperature operation and very good sensitivity to low NO x concentrations due to the logarithmic response to NO x concentration. Previously, mixed-potential type NO x sensor technologies have been limited by problems of cross sensitivity with other gas constituents commonly found in diesel exhaust, as well as an inability to provide a meaningful signal in varying NO/NO 2 mixtures. A novel sensor system design developed at Ceramatec has overcome many of the problems previously associated with such NO x sensors. Sensors have been fabricated and tested that have the following characteristics: (1) Operation temperature of 500-600°C; (2) excellent sensitivity in NO x levels of 1-1200 ppm; (3) response times as fast as 1-3 seconds; (4) insensitivity to various NO/NO 2 ratios in the exhaust stream; (5) very low cross-sensitivity to CO, CO 2 , H 2 O and low levels of SO 2 ; (6) ability to operate in oxygen-containing environments with no requirement for a pumping cell. The primary application targeted for the new sensor technology is heavy-duty diesel trucks. Other potential applications include advanced turbines, light-duty trucks, automobiles, heavy farm and construction machinery, off-road vehicles, and power generation as well as applications that utilize natural gas as the combustion fuel.