An Extended Kalman Filter for NOx Sensor Ammonia Cross-Sensitivity Elimination in Selective Catalytic Reduction Applications

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