Electron microscopic time‐lapse visualization of surface pore filtration on particulate matter trapping process

Summary A scanning electron microscope (SEM) was used to dynamically visualize the particulate matter (PM) trapping process on diesel particulate filter (DPF) walls at a micro scale as ‘time‐lapse’ images corresponding to the increase in pressure drop simultaneously measured through the DPF. This visualization and pressure drop measurement led to the conclusion that the PM trapping in surface pores was driven by PM bridging and stacking at constricted areas in porous channels. This caused a drastic increase in the pressure drop during PM accumulation at the beginning of the PM trapping process. The relationship between the porous structure of the DPF and the depth of the surface pore was investigated in terms of the porosity distribution and PM penetration depth near the wall surface with respect to depth. The pressure drop calculated with an assumed surface pore depth showed a good correspondence to the measured pressure drop. Lay description A Diesel Particulate Filter (DPF) is one of the essential technologies to remove Particulate Matter (PM) from diesel exhaust. Because of its complex pore structure and the PM property of having small size less than 1 μm, not much visual data is available about the microscopic PM filtration process especially inside the porous wall of the DPF. The purpose of this work is to have a deep understanding of the detailed PM trapping process by grains composing the DPF through the visualization in particle scale. Therefore, a scanning electron microscope (SEM) was used to dynamically visualize the PM trapping process on the DPF walls at a micro scale as ‘time‐lapse’ images corresponding to the increase in DPF pressure drop simultaneously measured. Through this visualization it was observed that the PM build a bridge structure at the constricted area in a porous channel near the wall surface and PM was accumulated in the upstream pores of the bridge. Furthermore, the comparison to the measured pressure drop indicated that the PM filling in the wall after the bridge formation caused a large increase in the pressure drop at the beginning of the PM filtering process.