Model-based control system design in a urea-SCR aftertreatment system based on NH3 sensor feedback

This paper presents preliminary control system simulation results in a urea-selective catalytic reduction (SCR) aftertreatment system based on NH₃ sensor feedback. A four-state control-oriented lumped parameter model is used to analyze the controllability and observability properties of the urea-SCR plant. A model-based estimator is designed via simulation and a control system is developed with design based on a sliding mode control framework. The control system based on NH₃ sensor feedback is analyzed via simulation by comparing it to a control system developed based on NO_x sensor feedback. Simulation results show that the NH₃ sensor-based strategy performs very similarly in comparison to a NO_x sensor-based strategy. The control system performance metrics for NO_x index, urea index, urea usage, and NH₃ slip suggest that the NO_x sensor can be a potential alternative to a NO_x sensor for urea-SCR control applications.