Effects of Washcoat on Initial PM Filtration Efficiency and Pressure Drop in SiC DPF 2011-01-0817
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. However, for PM over 30 nm, as amounts of W/C are increased, particle number concentration decreases rapidly and less PM leakage is observed for the initial filtration process. On the other hand, the initial backpressure and the backpressure during soot loading increased in accordance with W/C amount. Since the relationship between the filtration efficiency and the pressure loss has a trade-off, it is important to design DPF by considering W/C effects.