Visualization Study of PM Trapping and Reaction Phenomena in Micro-structural Pores through Cross Section of DPF Wall

Trapping of diesel particulates and phenomena of chemical reaction in regeneration were investigated by visualization through the cross-sectional area of a diesel-particulate-filter wall, using a digital-microscope with a high focusing depth. Herein, SiC-DPF walls were polished up to make a uniform height and to create a mirror-like surface on each SiC-particle-grain. At the beginning of the trapping process, it was observed that large particulates were trapped once in the small pores inside the wall, and then, since the flow-pattern was changed drastically, the trapped particulates were pushed out and blown off again, and finally, trapped in a region further downstream. As time passed, image analysis disclosed that since fine particulates were deposited around the SiC-particle-grain surface, the flow-channels became increasingly narrow. As a result, most of the particulates were trapped in the vicinity of the inlet of the wall, resulting in transition from depth-filtration to surface-filtration. In the regeneration process, on the other hand, the crevices made on the surface-filtrated particulate-cake were strongly dependent on the configuration of the DPF-wall inlet. In the inside of the wall, trapped particulates reacted with oxygen heterogeneously at each location.