Importance of nitrates in Cu-SCR modelling: A validation study using different driving cycles

Both a mechanistic model, which accounts for ammonia, nitrate, and ammonium nitrate storage, and a global model, which only accounts for ammonia storage and no nitrates, were calibrated to the same data collected across a Cu-CHA catalyst. Once calibrated, the models were directly applied to simulate various driving cycles (cold WHTC, hot WHTC, FTP, NRTC, ETC, and WNTE), with different catalyst layouts (i.e., washcoat loading and cpsi) as part of the model validation process. It was demonstrated that the mechanistic model provides a notable improvement in the prediction of the NOx conversions for colder cycles (i.e., cold WHTC, hot WHTC, and FTP) due to its inclusion of nitrates and ammonium nitrate. The quality of prediction of the hotter cycles (i.e., NRTC, ETC, and WNTE) was close to the same for both models, since no ammonium nitrate accumulates at these higher temperatures. Despite the additional reactions and surface species included in the mechanistic model, no significant increase in simulation time is observed compared to the global model. Finally, the mechanistic model is applied to calibrate a simple NH3 dosing strategy. The dosing strategy is compared to a constant NH3/NOx approach, where it was shown through simulations, and confirmed experimentally, that the dosing approach allows for an increase in NOx conversion. Overall, this demonstrated that the model accurately predicts the increase in NOx conversion and that the model is a valuable tool to establish the catalyst's true potential during driving cycles.

Automated summary

The study compared a mechanistic model and a global model in predicting NOx conversion rates, with the mechanistic model showing better performance in colder cycles due to its consideration of nitrates. Both models performed similarly in hotter cycles as no ammonium nitrate accumulates at high temperatures. Despite the additional complexity in the mechanistic model, simulation times remained comparable. Additionally, a simple NH3 dosing strategy was found to increase NOx conversion rates, demonstrating the model's utility in optimizing catalyst potential during driving cycles.