Fe-Zeolite SCR Model Development, Validation and Application

Selective Catalytic Reduction (SCR) technology has been widely studied for removal of NO_X from the exhaust of diesel engines. To design and optimize diesel engine aftertreatment systems including an SCR catalyst component, a reliable SCR model is a very useful tool, to aid in system integration and control algorithm testing. In this paper, the development of a one-dimensional numerical model for a Fe-Zeolite-based SCR catalyst (hydrothermally aged for 100 hours at 650°C in 10% H₂O in air) is presented, followed by its validation and application. The resulting model is capable of predicting NO_X reduction efficiency under various operating conditions as a function of gas hourly space velocity (SV), temperature, NO₂/NO_X ratio and NH₃ to NO_X (ANR) ratios; NH₃ slip and N₂O formation are also correctly predicted by the model. Extensive validation of the model has been carried out against engine test data for both steady state light-off and the heavy-duty FTP transient cycle (HD-FTP). Good agreement between model prediction and the engine test results was achieved. Finally, the model is used to optimize the instantaneous ANR ratio before the SCR catalyst over the HD-FTP, by minimizing SCR outlet NO_X and NH₃ emissions. Results show very good potential for improving the urea/NH₃ dosing strategy for Fe-based SCR catalyst applications.