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The washcoat (W/C) on a catalytic diesel particulate filter (DPF) greatly alters the pore structure and wall surface condition of the original substrate of DPF, which then affects the filtration efficiency and pressure drop behavior. In the present study, we examined this W/C effect on the initial PM filtration efficiency and pressure loss by changing amounts of washcoat on a SiC-DPF. We measured particle number concentration and particle size distribution in the diesel exhaust gas downstream of the DPF by EEPS. High filtration efficiency was achieved quickly when the W/C amount was increased. We introduced new parameters, T90 and T99, which were the filtration efficiencies that reach more than 90% and 99%, respectively, of the initial DPF usage. The PM trapping mechanisms could be classified according to the PM size. Trapping of PM whose diameter is smaller than 30 nm is little affected by the W/C.

In the exhaust gas after-treatment, it is difficult to evaluate the oxidation process of diesel soot, because we cannot observe the variation of particle size and the number concentration directly. Moreover, characteristics of soot depend on fuel properties, gas component, and engine conditions. Then, we used carbon particles as model soot, and particle size and its number concentration were experimentally measured in the presence of NO2. The particle size was measured by SMPS, together with the measurement of CO and CO2. Results show that, in the presence of NO2, the oxidation rate is close to the value of diesel soot with catalyzed DPF.

Particulate matter (PM) including soot in diesel exhaust gas is a serious atmospheric pollutant, and stricter exhaust emission standards are being set in many countries. As one of the key technologies, a diesel particulate filter (DPF) for PM trap in the after-treatment of the exhaust gas has been developed. Typically, the inlet size of filter monolith is about 2 mm, and the thickness of the filter wall is only 0.2 mm, where soot particles are removed. It is impossible to observe the small-scale phenomena inside the filter, experimentally. Then, in the present study, we conducted microfluidic simulation with soot oxidation. Here, a real cordierite filter was used in the simulation. The inner structure of the filter was scanned by a 3D X-ray CT Computed Tomography) technique. The advantage is that it is non-intrusive system, and it has a high spatial resolution in the micrometer.