Masamichi Tanaka

A Study of SIC-Nanoparticles Porous Layer Formed on SIC-DPF Wall for Soot Oxidation

The pore structure of DPF is known to have a significant effect on filtration efficiency, pressure drop, and soot oxidation. It is reported that the formation of a nanoparticle porous layer on the surface of the DPF inlet wall promotes soot oxidation [1, 2, 3]. However, the correlation between pore size in the nanoparticle layer and soot oxidation performance, the effect of the layer in actual use environments, and the oxidation mechanism involved have not yet been clarified. The research discussed in this paper therefore formed SiC nanoparticle porous layers of various pore sizes on the inlet wall surfaces of SiC-DPF (creating what will be termed “NPL-DPF” here) using the dip-coating method [4]. The NPL thickness was set at 20 μm to help enable uniform coating samples to be obtained. With regard to filter pressure drop without soot loading, results for a bare DPF and a Pt/γ-Al2O3-coated DPF (catalyzed DPF; Pt = 1 g/L) were virtually identical. For the NPL-DPF, pressure drop increased as pore size was reduced. By contrast, in the case of pressure drop following soot loading (3 g/L), despite the fact that results for pressure drop for the NPL-DPF were higher than those for the bare DPF, they were lower than those for the catalyzed DPF. It is possible to stop deep-bed filtration by forming a nanoparticle porous layer on the surface of the DPF inlet wall [1, 5]. With regard to soot oxidation performance, the T80 of an NPL-DPF (NPL pore size = 350 nm) was found to be 40 % lower than that of a bare DPF and identical to that of a catalyzed DPF. In addition, reducing the NPL pore size enhanced soot oxidation performance. X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), and hydrogen temperature-programmed desorption (H2-TPD) results indicated that the SiC nanoparticle surface was covered by a 5 nm SiO2 oxide film. It was found that these oxidized SiC nanoparticles desorbed oxygen at around 450 °C. This desorbed oxygen promoted the oxidation of diesel soot. In addition, the filtration efficiency of the NPL-DPF without soot loading was 92 % against 78 % for the bare DPF.