Emission characteristics and microstructural changes of particulate matter from diesel engine after catalyst preheating under cold start conditions

Under cold start conditions, there is still a large amount of particulate matter emissions at the outlet of the aftertreatment system. This study aims to investigate the effect of rapid preheating of diesel oxidation catalyst (DOC) and catalytic diesel particulate filter (CDPF) before engine start on the emission characteristics and microstructure of particulate matter (PM) during cold start of diesel engines. The results show that preheating the DOC or CDPF substrate significantly reduces the particle concentration at the CDPF outlet during cold start, and reduces the peak particle size at the CDPF outlet. At the same time, it also causes an increase in nucleation mode particles, which is mainly caused by the decomposition of aggregated soot particles into small particles and the condensation of volatile substances. After being filtered by CDPF, the shape of soot aggregates tends to a chain-like structure, and the catalyst preheating inhibits the surface growth of primary particles and reduces the degree of graphitization of primary particles at the outlet of the substrate.