An extended Kalman filter for NOx sensor ammonia cross-sensitivity elimination in selective catalytic reduction applications

Vehicle NO_x emission regulations are becoming more and more stringent worldwide. A selective catalytic reduction (SCR) system which uses ammonia as the reductant to reduce tailpipe NO_x emissions is widely adopted by Diesel engine applications. For SCR control, a NO_x sensor is commonly used to monitor the emissions, however it has been discovered that NO_x sensors typically are cross-sensitive to the presence of ammonia. Such a feature becomes a critical problem as ammonia slip can be present downstream of a SCR catalyst where the NO_x sensor is located. To address this issue, an extended Kalman filter (EKF) is designed in this paper to estimate the actual exhaust gas NO_x concentration and the cross-sensitive factor such that the cross-sensitivity error can be eliminated.