Effect of intake boundary conditions on the performance for diesel particulate filter coated with selective catalytic oxidation-selective catalytic reduction catalyst

Abstract

The diesel particulate filter coated with selective catalytic oxidation and reduction (SCO/SCR) catalysts (SDPF) plays a crucial role in meeting increasingly escalating emission regulations. The SCO-SCR catalyst coated on SDPF (n-SDPF) exhibits improved performance in both soot oxidation and NOx reduction compared with SDPF coated with Cu-SSZ-13 catalyst. Intake boundary conditions are essential for n-SDPF performance. A multiphysics model was constructed to quantitatively evaluate the effect of various operating parameters on soot oxidation behavior and NOx conversion efficiency. Results indicate that higher gas hourly space velocity (GHSV) and ammonia-to-NOx ratio (ANR), combined with a lower NO₂/NOx ratio, lead to a rose pressure drop across the soot cake layer. Increasing GHSV or ANR can enhance NH₃ oxidation and inhibit NO oxidation. Reducing GHSV or increasing ANR can increase N₂O emissions; NO₂/NOx has little effect on NH₃ oxidation, increasing NO₂/NOx will significantly inhibit NO oxidation and promote N₂O generation. A reduction in GHSV or an increase in the ANR markedly enhances NOx reduction performance. However, a higher NO₂/NOx ratio slightly decreases the NOx conversion efficiency, likely owing to the suppression of NO oxidation and the predominance of the slow SCR reaction. Moreover, increasing GHSV shifts the temperature corresponding to the peak NOx conversion efficiency toward a higher range. Changing ANR and NO₂/NOx will not affect the temperature with the highest NOx conversion efficiency. Reducing GHSV and ANR, or increasing NO₂/NOx can improve soot oxidation efficiency. This study explored the coupling relationship between intake conditions and catalytic reactions, providing a theoretical basis for the application of novel catalysts and optimizing the working conditions of n-SDPF.