Micro-Simulation of NO-NO2 Transport and Reaction in the Wall of a Catalyzed Diesel Particulate Filter

Catalyzed Diesel Particulate Filters (CDPFs) continue to be an important emission control solution and are now also expanding to include additional functionalities such as gas species oxidation (such as CO, hydrocarbons and NO) and even storage phenomena (such as NOx and NH₃ storage). Therefore an in depth understanding of the coupled transport - reaction phenomena occurring inside a CDPF wall can provide useful guidance for catalyst placement and improved accuracy over idealized effective medium 1-D and 0-D models for CDPF operation. In the present work a previously developed 3-D simulation framework for porous materials is applied to the case of NO-NO₂ turnover in a granular silicon carbide CDPF. The detailed geometry of the CDPF wall is digitally reconstructed and micro-simulation methods are used to obtain detailed descriptions of the concentration and transport of the NO and NO₂ species in the reacting environment of the soot cake and the catalyst coated pores of the CDPF wall. From these results NO-NO₂ turnover is quantified and a comparison is made with the turnover predicted by an approximate 0-D analytical model. Good agreement is found between the two models, justifying the use of the approximate but fast analytical model in large scale simulations of CDPFs.