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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 in-cylinder flow during induction and compression in the pentroof chamber of a four-valve, single-cylinder, spark-ignition optical engine was quantified by LDV and correlated with combustion development especially under lean mixture conditions. The tumble-generating capacity of the cylinder head was first characterised by a tumble adaptor under steady flow conditions and, subsequently, enhanced by two sleeves introduced into the intake ports which generated a stronger tumbling motion.