Improvement in Selective Catalytic Reduction Model Accuracy for Predicting NO_x Conversion at High Temperature

摘要

As a result of WNTE regulations and the introduction of close-coupled aftertreatment systems, exhaust purification at high temperatures in commercial vehicles has become increasingly important in recent years. In this report, we improve the prediction accuracy for NO_x conversion at high temperatures in the kinetic model of conventional Cu-selective catalytic reduction (Cu-SCR). Reaction rate analysis indicated that the rate of NH_3 oxidation was extremely low compared to the rate of standard SCR. We found that NO_x concentration-dependent NH_3 oxidations (termed NO_x-assisted NH_3 oxidations) were key to the rate of NH_3 oxidation. The output of the improved Cu-SCR kinetic model was in agreed with experimental results obtained from the synthetic gas bench and engine dynamometer bench. We analyzed the contribution of each reaction to NH_3 consumption during Cu-SCR. Under NH_3 + NO + O_2, standard SCR was dominant at low temperature. At high temperatures, the rate of NO-assisted NH_3 oxidation increased, and this reaction competed with standard SCR. Under NH_3 + NO + NO_2 + O_2, fast SCR, NH_4NO_3 formation, and standard SCR were the dominant reactions at low temperature. With increasing temperature, NO_2-assisted NH_3 oxidation competed with the other reactions, resulting in a decreased NO_x conversion.