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This study has experimentally clarified the effects the pilot injection fuel quantity and pilot injection timing have on the mode of combustion of the pilot spray and exhaust emissions. The result shows that one of the points to effectively reduce exhaust emissions by pilot injection is to reduce the emissions produced by the pilot combustion itself. For that purpose it is effective to advance the pilot injection timing and to increase of pilot quantity. In this case, dividing the pilot injection into multiple small-quantity shots is a solution to avoid cylinder wall wetting.

Reduction of smoke emission from diesel engines is important in order to meet upcoming stringent exhaust gas regulations and also for improving fuel economy. In this paper, the reduction of smoke from DI diesel engines for heavy duty vehicles is discussed. A single cylinder engine test and three dimensional numerical analysis were carried out in order to obtain necessary and useful information for designing a combustion chamber and a fuel injection nozzle that could realize reduced smoke emission. This study is focused particularly on the behavior of the fuel spray which impinges on the piston cavity wall in the case of a reentrant type combustion bowl. As a result, it was found that the spray wall-impingement angle performs an important role in promoting fuel-air mixing. It is thus an important parameter which controls the main combustion region.