An extended Kalman filter for ammonia coverage ratio and capacity estimations in the application of Diesel engine SCR control and onboard diagnosis

Ammonia, as the reductant to convert NO_x to nitrogen molecules in a selective catalytic reduction (SCR) catalyst, plays an important role in Diesel engine SCR control. To achieve a sophisticated SCR control, the presence of ammonia in the SCR should be precisely monitored. Ammonia sensor for gaseous concentration measurement has been available recently. However, ammonia can also be adsorbed on the SCR substrate which is unmeasurable but dominates the NO_x reduction dynamics. And also the catalyst ammonia storage capacity serves as an important factor for the judgment of SCR catalyst aging. In this paper, an observer for SCR catalyst ammonia coverage ratio and storage capacity estimations is designed based on an extended Kalman filter (EKF). Simulation results verify that the EKF-based observer can estimate both the states well.