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.