Back-diffusion Modeling of NO2 in catalyzed diesel particulate filters

The present study emphasizes the coupling between reaction and diffusion phenomena in catalyst-coated diesel particulate filters. The main emphasis is placed on the effect of NO2 back-diffusion, which is responsible for higher-than-expected reaction rates at low temperatures. Unlike traditional modeling approaches that neglect diffusion effects, the model presented in this study considers the coupled diffusion-reaction phenomena by proper discretization in the porous layer and wall. With the aid of the model, a theoretical analysis is performed on the importance of individual operating parameters on the regeneration performance of a catalyst-coated filter. It is shown that the contribution of diffusion is responsible for about one-third of the total regeneration rate for the range of conditions typically found in medium-sized diesel engines. The results are sensitive to the values of the effective diffusivities of the species (in particular NO2) in the porous catalytic wall and the soot layer. For a deeper understanding of the involved processes, further work is needed to determine the effective diffusivities experimentally.