A NOx Sensor for Feedback Control and Emissions Reduction 2002-01-0479
Current emission control systems utilize a catalytic converter employing a three-way catalyst (TWC), composed of a mixture of noble metals to minimize the three main pollutant classes of NOx, CO, and HC. The TWC is most efficient when the air-to-fuel ratio (A/F) is at stoichiometry (i.e. A/F ≈ 14.7). The stoichiometric set-point region is maintained by the use of oxygen sensors composed of the solid-electrolyte yttria stabilized zirconia (YSZ) in an electronic feedback loop. As combustion gets leaner a different exhaust sensor can be utilized to give a measure of the level of pollutants. A NOx sensor is an alternative for an oxygen sensor that can be used for feedback control of engine combustion or exhaust NOx traps. A solid electrolyte disk composed of YSZ having two Pt electrodes with one being covered by a microporous zeolite material was tested as a sensor for combustion produced gases such as NO and NO2 in the presence of O2. At 500°C it was found that the sensor responded to the NOx gases and was hardly affected by changing O2 levels in the range of 1-10%. A modified sensor design was used in a prototype assembly constructed to allow in-situ testing in an I-4 automobile engine when the engine cycle was perturbed. The sensor showed a response with changing gas concentrations and was correlated with an on-line FTIR gas analyzer. The sensor assembly design may show promise for catalytic converter monitoring or engine control diagnostics.
Nicholas F. Szabo, Prabir K. Dutta, A. Soliman
The Ohio State Univ.
SAE 2002 World Congress & Exhibition
Electronic Engine Control Technologies-PT-73, Electronic Engine Controls 2002: Electronics and Information Gathering-SP-1690, Sensors and Transducers, Second Edition-PT-105, SAE 2002 Transactions Journal of Fuels and Lubricants-V111-4