Scanning Electron Microscopic Visualization of Transition from Surface Pore Filtration to Cake Filtration Inside Diesel Particulate Filter Walls 2015-01-1018

Surface pores that are open to the inlet channel below the surface play a particularly important role in the filtration of particulate matter (i.e., soot) inside the walls of a diesel particulate filter (DPF); they are closely related to the pressure drop and filtration efficiency through the DPF as well as the performance of the regeneration process.

In this study, a scanning electron microscope (SEM) was used to dynamically visualize the soot deposition process at the particle scale as “time-lapse” images corresponding to the different increases in the pressure drop at each time step. The soot was first trapped at the deepest areas of the surface pores because the porous channels in this area were constricted by silicon carbide grains; soot dendrite structures were observed to grow and finally cause obstructions here. Once the constricted areas were bridged by soot, which caused the pressure drop of the DPF to increase sharply, no more soot particles could enter the pores below this area, therefore the soot was accumulated in the surface pore. After the surface pores were filled, the soot trap transited to soot cake filtration, which showed a constant increase rate in the pressure drop.

This visualization and measured pressure drop led to the conclusion that the surface pore filtration was driven by soot stacking at the first constricted point at the beginning of filtration. This caused radical increases in the pressure drop and filtration efficiency of the DPF during surface pore filtration.