Model-Based NH3 Slip Detection for SCR + ASC System Control and OBD

Abstract

Since accuracy and adaptation of the closed-loop control in selective catalytic reduction (SCR) and ammonia slip catalytic (ASC) systems quite depend on the detection of ammonia (NH₃), the identification of NH₃ slip is important in the above systems. A model-based NH₃ slip detection method by a brief dosing-off maneuver is proposed, which is utilizing NO_x sensors’ cross-sensitivity between NH₃ and NO_x. When the operating conditions are suitable, NH₃ slip detection function would trigger once the deviation of the DeNO_x efficiency calculated by model and by sensor is over a limit. The NH₃ slip could be detected when the consumption of NH₃ storage exceeded a limit earlier than DeNO_x efficiency below a limit. Validation test results showed this NH₃ slip detection function can effectively detect the NH₃ slip of SCR + ASC system, and immediately send out a NO_x slip result if the tailpipe NO_x emission exceeds the OBD limit.