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.

A new diesel particulate filter (DPF) with a highly porous membrane made of alumina submicron particles, which are aggregates of alumina nanoparticles, was proposed to eliminate the radical increase in pressure drop caused by the soot accumulation in surface pores at the beginning of soot trapping and to improve the initial filtration efficiency of the DPF. The alumina membrane was manufactured by introducing particles-suspended nitrogen gas into the conventional DPF. The particle size of alumina and the particle-carrying gas velocity, which are significant parameters to determine the permeability of the layer, were optimized to make a low pressure drop membrane.

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