Adequacy of Reduced Order Models for Model-Based Control in a Urea-SCR Aftertreatment System 2008-01-0617

Model-based control strategies are important for meeting the dual objective of maximizing NO_x reduction and minimizing NH₃ slip in urea-SCR catalysts. To be implementable on the vehicle, the models should capture the essential behavior of the system, while not being computationally intensive. This paper discusses the adequacy of two different reduced order SCR catalyst models and compares their performance with a higher order model. The higher order model assumes that the catalyst has both diffusion and reaction kinetics, whereas the reduced order models contain only reaction kinetics. After describing each model, its parameter identification and model validation based on experiments on a Navistar I6 7.6L engine are presented. The adequacy of reduced order models is demonstrated by comparing the NO, NO₂ and NH₃ concentrations predicted by the models to their concentrations from the test data. It is observed that the 4 state model is a good representative of the physical system and is sufficient for model based control in urea-SCR aftertreatment systems.