Visualization of Oxidation of Soot Nanoparticles Trapped on a Diesel Particulate Membrane Filter

摘要

Through microscopic visualization experiments, a process generally known as depth filtration was shown to be caused by surface pores. Moreover, the existence of a soot cake layer was an important advantage for filtration performance because it could trap most of the particulates. We proposed an ideal diesel particulate filter (DPF), in which a silicon carbide (SiC) nanoparticle membrane (made from a mixture of 80 nm and 500 nm powders) instead of a soot cake was sintered on the DPF wall surface; this improved the filtration performance at the beginning of the trapping process and reduced energy consumption during the regeneration process. The proposed filter was called a diesel particulate membrane filter (DPMF). A diesel fuel lamp was used in the trapping process to verify the trapping and oxidation mechanisms of ultrafine particulate matter. Thus, the filtration performance of the membrane filters was shown to be better than that of conventional DPFs. Furthermore, we found that surface pore filtration was initiated by Brownian motion in the pore and by electrostatic force between the particulates and the SiC-particles. In the regeneration process, the activation energy for soot oxidation on the DPMF was lower than that on the conventional non-catalyzed DPF because the soot might react effectively with oxygen adsorbed on the thin oxide layer that completely covered the SiC-nanoparticles and since the soot came into close contact with the oxide layer owing to the large specific surface area of the DPMF. This suggests that the SiC nanoparticle membrane filter had some catalytic activity similar to that of the conventional catalyzed DPF.