An Experimental and Modeling Study of Reaction Kinetics for a Cu-Zeolite SCR Catalyst Based on Engine Experiments

A high-fidelity multi-step global kinetic Selective Catalytic Reduction (SCR) model which can predict SCR performance in engine exhaust systems is desirable for optimizing the SCR system, designing on-vehicle control systems and on-board diagnostic (OBD) functions. In this study, a Cu-zeolite SCR catalyst in the exhaust of a 2010 Cummins 6.7L ISB diesel engine was experimentally studied under both steady-state and transient conditions. Steady-state engine tests spanned SCR inlet temperatures from 250 to 400°C with a constant space velocity of 60 khr^-1. A 1-D Cu-zeolite model originally developed from reactor data was improved and calibrated to the steady-state engine experimental data. The calibrated model is capable of predicting NO/NO₂ reduction, NH₃ slip, and NH₃ storage associated phenomena. A surrogate HD-FTP cycle was developed and transient engine tests with different urea injection levels were performed to test the SCR under specific transient conditions in order to validate the SCR model performance. In order to eliminate the effect of NH₃ measurement error caused by NH₃ adsorbing on the sample line wall, a sample line model was developed to simulate this NH₃ adsorption and desorption phenomena for post-processing the NH₃ measurements. Results show that the prediction of the NO, NO₂, and NH₃ from the calibrated SCR model is in good agreement with the experimental measurements. Significant differences in the kinetic parameters were observed between the calibrated SCR model based on the engine data and the SCR model calibrated to the reactor data, indicating that the system performed differently in the engine and the reactor.