The effects of DOC and DPF on the particulate properties of diesel engine

In order to investigate the evolution law of structure and chemical composition of diesel engine particulates during passing through Diesel oxidation catalyst (DOC) and Diesel particulate filter (DPF), particulates samples emitted from a diesel engine with exhaust after-treatment devices were investigated using high resolution transmission microscopy (HRTEM) and Raman spectroscopy. Nanostructure and composition of the particulates were compared before and after the DOC and DPF at two operating conditions. The results of HRTEM reveal that the post-DOC primary particles possess more curved segments while the pre-DOC and post-DPF ones possess relatively extended and flat lamellae. At low speed and low load, there are more amorphous structures, while, at high speed and high load, laminated structure is more obvious and the lamellas are almost straight line segments. The results of Raman spectra show that Raman spectra of engine particulates are all composed of five peaks and the Raman shift of the peaks changes in a very narrow range. However, it can be seen that not only the degree of graphitization of the particulates but also the amount of organic fractions increased with the backward shift of the measuring point.