On the impact of DPF downsizing and cellular geometry on filtration efficiency in pre- and post-turbine placement

In the current work a computational study to evaluate the effect of the DPF downsizing on filtration efficiency is performed. The DPF is conventionally placed downstream of the turbine. However, its placement upstream of the turbine is growing in interest because of the benefits in specific fuel consumption, passive regeneration and aptitude to downsizing. Hence both pre- and post-turbine placement are considered in presence of clean and soot loaded substrates. An in-house 1D wall-flow DPF model for unsteady compressible flow is used. Volume reduction is approached considering diameter and length variation. In parallel, the cell density is also varied modifying the meso-geometry, i.e. cell size and porous wall thickness, imposing constant thermal integrity factor. The sensitivity to this last parameter is also analysed resulting its influence of second order in comparison to volume and cellular geometry effects. The lower Peclet number in the pre-turbine placement leads to higher filtration efficiency than post-turbine location comparing at the same DPF volume. Diameter based volume reduction provides slightly better results in filtration efficiency than length based reduction because of the way the filtration velocity field is varied. This general behaviour involves additional advantages to the potential for volume reduction of pre-turbine DPFs. Thus, different strategies with boundaries defined by volume reduction at constant filtration area or at constant specific filtration area can be approached looking for the best balance between fuel economy reduction and filtration efficiency increase provided by pre-turbine DPF placement.