Modeling the Interactions Of Soot and SCR Reactions in Advanced DPF Technologies with Non-homogeneous Wall Structure 2012-01-1298

The pressure for compact and efficient deNO

systems has led to increased interest of incorporating SCR coatings in the DPF walls. This technology could be very attractive especially if high amounts of washcoat loadings could be impregnated in the DPF porous walls, which is only possible with high porosity filters. To counterbalance the filtration and backpressure drawbacks from such high porosity applications, the layered wall technology has already been proposed towards minimizing soot penetration in the wall and maximizing filtration efficiency. In order to deal with the understanding of the complex interactions in such advanced systems and assist their design optimization, this paper presents an advanced modeling framework and selected results from simulation studies trying to illustrate the governing phenomena affecting deNO

performance and passive DPF regeneration in the above combined systems. More specifically, we compare a combined DPF+SCR (SDPF) device to a respective one which is equipped with an additional membrane layer on the inlet channel walls. The impact of the layer on soot oxidation, NO

conversion, filtration and N₂O formation is investigated during steady state operations with different temperature, NO₂/NO

ratio, initial soot load and inlet soot concentration. The benefit of the layer to the filtration performance is obvious; interestingly the passive regeneration is also significantly promoted in presence of NO₂. This results from a higher NO₂ concentration in the inlet channels as shown by the calculated axial and intra-wall NO₂ concentration profiles. On the other hand, the NO

conversion efficiency is negatively affected by the layer under most conditions in the range of practical interest. This is explained by the diffusion limitations imposed by the layer as well as to the NO₂ competition effects with the soot reactions which results in shifting of the NO₂/NO

ratio away from the optimal values for the specific Fe-zeolite catalyst formulation.