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A high-frequency ignition system was developed to improve the stability of initial flame development under the lean burn condition. The electrical principle of the high-frequency ignition system is based on successive spark discharges in a spark plug. The ignition system provides electronically controlled charges in spark duration (1∼2msec) and restriking rates (10∼30kHz). Flow characteristics of tumble-swirl were varied with swirl control valve attached at the inlet ports. Four different flow patterns were tested by the combination of tumble and swirl strengths achieved by various shapes of swirl control valve. The effects of flow and ignition characteristics on the combustion performances and their interaction were investigated in a 4-valve SI engine. Flow characteristics were quantified by steady flow tests and in-cylinder flow measurements.

The surroundings around the diesel spray are entrained during the growth of the spray. The mixing process between the evaporated fuel oil and the entrained surroundings, that is, the entrainment, has a significant meaning for the combustion diesel engine. It is difficult to detect the movement of the entrainment because the diesel spray is the gas-liquid two-phase flow and the unsteady phenomenon within a few milliseconds. Then, in order to clarify and to generalize the movement of entrainment, following three experiments were done. 1)Two-dimensional steady water spray -flat spray- injected into the ambient atmosphere, using tuft and hot wire method. 2) Unsteady water jet injected into water, using tracer. 3)single diesel spray injected into the atmosphere with high pressure at room temperature, using smoke wire.