Nonlinear observer designs for diesel engine selective catalytic reduction (SCR) ammonia coverage ratio estimation

This paper presents several nonlinear observer designs to estimate diesel engine selective catalytic reduction (SCR) ammonia coverage ratio, which significantly affects the SCR NO_x conversion and NH₃ slip, but is not directly measurable by onboard sensors. Sliding mode observer (SMO) technique was employed for the designs of different ammonia coverage ratio observers based on different selections of sensor measurements. The robustness of the observers with respect to sensor measurement uncertainties were theoretical analyzed. A full-vehicle model FTP75 test cycle simulation results show the robustness and estimation accuracies of the different observers in the presence of sensor measurement errors/uncertainties.