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In a direct injection (D.I) diesel engine with high efficiency, the blue and white smoke (cold smoke) exhaust at cold starting and warming-up are unsolved problems in the development of small D.I diesel engines. In this experiment, the fuel adhering on the combustion chamber wall, and which influences the cold smoke, was measured on a special engine which can be stopped immediately after a single injection. It is found that 30-40% of the injected fuel remained on the combustion chamber wall after burning at low compression ratios and under low temperature conditions.

Reductions in fuel consumption and pollutant emissions from direct injection diesel engines are important issues in engine research. To achieve these reductions, rapid and better fuel air mixing is the most important requirement. The mixing quality of diesel spray with air is generally improved by selecting the best injection parameters and improving the characteristics of air movement in the combustion chamber. The shape of the combustion chamber can also help to form better mixtures. In this study, improvement in mixture formation was attempted by changing the combustion chamber geometry. The fuel spray development was visualized from two directions in an actual engine with a transparent cylinder and piston arrangement. The place where spray impinges, the distance from impinging wall to nozzle tip, and the shape of the chamber entrance and bottom were varied to determine their effects on the fuel spray development in the combustion chamber.