Development and Validation of a Cu-Zeolite SCR Catalyst Model

<div class="section abstract"><div class="htmlview paragraph">A one-dimensional numerical model for a Cu-zeolite SCR catalyst has been developed. The model is based on kinetics developed from laboratory microreactor data for the various NH₃-NO_X reactions, as well as for NH₃ oxidation. The kinetic scheme used is discussed and evidence for it presented. The model is capable of predicting the conversion of NO and NO₂, NH₃ slip and the formation of N₂O, as well as effects associated with NH₃ storage and desorption. To obtain a good prediction of catalyst temperature during cold start tests, it was found necessary to include storage and desorption of H₂O in the model; storage of H₂O is associated with a sizable exotherm and the subsequent desorption of this water produces a correspondingly large endotherm. Extensive validation of the model has been carried out against engine/vehicle data for both HDD (light-off, heavy-duty FTP transient cycle, NRTC) and LDD (NEDC) test cycles for a range of catalyst volumes, urea injection levels and upstream DOC volume and loading. In particular, data measured with an oversized DOC was used to test the models ability to predict N₂O formation. In general, good agreement between model prediction and the experimental data was achieved.</div><div class="htmlview paragraph">Examples of application of the model to aftertreatment design are given. The model can be used to predict the effect of changing system parameters (such as catalyst size, NH₃:NO_X ratio (or urea injection strategy) and NO₂/NO_X ratio) and the effect of modifying engine calibration (catalyst inlet temperature, etc.).</div></div>