Abstract
White smoke emission is observed at tailpipe of diesel engine when unburned hydrocarbons (HCs) are stored on diesel oxidation catalyst (DOC) under low gas temperatures. In this research, relationships among behavior of white smoke emission and the amount or quality of HCs adsorbed on DOC were investigated by change of DOC specifications, such as zeolite content, platinum metal group (PGM) content and Pt / Pd ratio contained as PGM, under two HC adsorption temperature conditions, 120℃ and 180℃. It was clarified that the adsorbed ratio of heavy HCs which have higher boiling point than that of nC16 becomes larger with decrease in the zeolite content at 120℃, leading to a dense white smoke emission at the same amount of adsorbed HCs on DOC. On the other hand, comparing to zeolite content, the PGM content or Pt / Pd ratio has less impact on the adsorbed HC amount on DOC and white smoke emission for both HC adsorption temperatures. In addition, it was assumed that the zeoliteless DOC has a higher catalyst activity compared with zeolite-containing DOC under the gas temperature of 180℃, which results in the drastic reduction in white smoke emission.
