Simulation of Ammonia SCR-Catalytic Converters: Model Development, Calibration and Application

An efficient aftertreatment technique is driven by the need to maintain strict emission norms for heavy-duty and medium-duty ground vehicles. The design of the SCR system involves catalyst selection, complex controller development like urea dosing strategy and the interaction between engine setup and aftertreatment system. It is quite difficult and costly in reality to test the performance of such a complex process. For this purpose, the SCR model must be computationally efficient to allow full drive cycle analysis and application to real-time simulation and testing. The present work is a simplified zero-dimensional physics-based dynamic SCR model developed for real-time applications. The holdup of reacting species on the catalytic surface is assumed to be negligible and hence termed as a pseudo 2-phase model. The chemical kinetics is coupled with the thermal behavior to form a complete SCR model. A reaction scheme is proposed based on the test data obtained. For determination of the intrinsic kinetics of various NH₃-NOx reactions, the laboratory catalyst rig test data is used. Steady engine test data is applied for validation purposes. The Japanese transient cycle confirms the use of this model for real-time simulation. This model with the proposed kinetics is able to simulate faster than real time with acceptable level of accuracy.