Abstract
Diesel oxidation catalyst (DOC) stores unburned hydrocarbons at low temperatures, such as during long-term idle operation, and then releases them rapidly at high temperatures during acceleration. The high level of unburned hydrocarbons result in visible white smoke emission at tailpipe. The purpose of this work is to get a better understanding of the phenomenon of white smoke emission originated from HC accumulation on DOC. Firstly, the component and size distribution of the HC white smoke has been analyzed. It was clarified that semi-volatile organic compounds and water are condensed around SOF component (e.g. C17~C24 heavy hydrocarbons in fuel), leading to a submicron-sized particulate emission. Furthermore, the effect of distillation characteristic and molecular structure of the HC accumulated on DOC has been examined. The experimental results show that the amount of adsorbed HC is strongly influenced by the 50% distillation temperature and also that aromatic hydrocarbons tend to increase white smoke emission compared with paraffinic hydrocarbons.
