High-Frequency Ignition Characteristics in a 4-Valve SI Engine with Tumble-Swirl Flows

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. Ignition energy and its distribution were measured through voltage and current measurements, and controlled in a high-frequency ignition system by changing spark duration and sparking frequency. Combustion performances were evaluated by pressure analyses and imaging of initial flame propagation with an ICCD camera in a single-cylinder optical engine. The improvement of lean burn performance by the optimum flow and ignition characteristics was found. High-frequency ignition enables successful ignition followed by stable flame development in highly turbulent strong flow field such as inclined tumble/swirl due to the supply of successive ignition energies resulting in the increased kernel volume. Longer spark duration, higher primary voltage and optimal discharge frequency(20KHz) provided better lean burn performances.