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This paper confirms a structure for the soot formation process inside a burning diesel jet plume of oxygenated fuels. An explanation of how the soot formation process changes by the use of oxygenated fuel in comparison with that for using a conventional diesel fuel, and why oxygenated fuel drastically suppresses the soot formation has been derived from the chemical kinetic analysis. A detailed chemical kinetic mechanism, which is combined with various proposed chemical kinetic models including normal paraffinic hydrocarbon oxidation, oxygenated hydrocarbon oxidation, and poly-aromatic hydrocarbon (PAH) formation, was developed in present study. The calculated results are presented to elucidate the influence of fuel mixture composition and fuel structure, especially relating to oxygenated fuels, on PAH formation. The analysis also provides a new insight into the initial soot formation process in terms of the temperature range of PAH formation.

OH radical generated in a DI diesel engine has a close relationship to soot oxidation. To clarify this fact, the distribution of the natural emission of OH radical was captured by means of an interference filter system and that of soot was detected by the simultaneous application of a laser induced incandescence (LB) and a laser induced scattering (LIS). The experiments were carried out in a small sized high-speed DI diesel engine installed with an optical access view. The generation of OH radical and the formation/oxidation of soot are discussed by using both images.

There is a concept that the increase in the temperature of charge in a combustion chamber and the shield of heat transferred through a chamber wall can facilitate the oxidation of soot and reduce the discharge of soot from the engine. In the experiments presented here in, an IDI diesel engine was used to inspect the concept. The engine was installed a bigger sized cylindrical swirl chamber which was equipped with two flat quarts windows, in order to observe the combustion phenomena and to apply the optical measurement. The experiments were carried out using two types of divided chambers, that is, the swirl chamber made of ceramics and that made of steel, to examine the the effects mentioned above.