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Wall quenching plays a vital role on particulate formation. A single cylinder engine test has been carried out to clarify the effects of wall quenching on particulate emission. A completely warmed up engine is fired in variety of operating period under various engine load, and then stopped immediately. Deposits are collected from 25 positions on the combustion chamber wall. Area basis concentration of deposit is obtained at each position. Soluble organic fractions (SOF) extracted from deposit are analyzed with gel permeation chromatograph (GPC). Results show the correlation between SOF in exhaust particulate and in deposit. Deposit concentration is highest on the spray axis impinging region of piston cavity wall. GPC pattern of the SOF in deposit indicates that higher molecular weight composition generates as a result of polymerization of fuel where the main jet region of the spray impinges.

In the small high speed DI diesel engines, wall quenching plays an important role on the particulate formation process. In order to clarify the particulate formation process, authors have analyzed the deposit on the combustion chamber wall, which are the results of the wall quenching. Deposit is sampled at 22 locations on the combustion chamber wall. On the wall of the piston cavity, dry and SOF deposits generate. The deposit quantity is the highest on the side surface of the cavity, but SOF ratio is the smallest in the cavity.