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Experiments were conducted with 4-cylinder and single-cylinder direct injection diesel engines to examine the effects of combustion chamber insulation on heat rejection and thermal efficiency. The combustion chamber was insulated by using a silicon nitride piston cavity that was shrink-fitted into a titanium alloy crown. The effect of insulation on heat rejection was examined on the basis of heat release calculations made from cylinder pressure time histories. High-speed photography was used to investigate combustion phenomena. The results showed that heat rejection was influenced by the combustion chamber geometry and swirl ratio and that it was reduced by insulating the combustion chamber. However, because combustion deteriorated, it was not possible to obtain an improvement in thermal efficiency equivalent to the reduction in heat rejection.

The purpose of this paper is to clarify the mechanisms of unburnt hydrocarbon (HC) emissions from a small direct - injection (DI) diesel engine. HC emission levels of small DI diesel engines are considerably higher than those of corresponding indirect - injection (IDI) diesel engines, even when sacless injection nozzles that are effective in reducing HC emissions are installed on them. In this study, analytical engine tests were performed to evaluate the relative significance of various potential sources of HC emissions from a small DI diesel engine equipped with sacless type injectors.