Experimental study on the efficiency of inductive ignition systems with different flow speed conditions and ignition strategies to boost the spark energy in lean-burn engines

Lean combustion in spark-ignition engines has been attracting attention as a technology for next-generation engines, owing to its advantages of engine efficiency due to the reduction of combustion temperature caused by supercharging. To overcome problems such as low reactivity and slow flame propagation results from the lean-mixture characteristics, sufficient ignition energy must be transferred to the mixture through the spark channel to stably form the initial flame kernel. To analyze the phenomenon of energy transfer through the spark channel, an experimental device was constructed to simulate the conditions similar to the inside of the engine cylinder, and the electrical and geometric characteristics of the spark channels were measured. In this study, different ignition strategies for enhancing spark energy were tested, and the effects of the flow speed on each strategy were analyzed. The first strategy was to increase the charging time, which had two simultaneous effects: a robust spark channel but an increased resistive loss fraction in the circuits. Thus, an optimal charge time exists in terms of spark energy transfer efficiency, with the former effect being more pronounced under high-speed conditions. In the second ignition strategy, a dual-coil ignition system was adopted. Under low-speed conditions, it showed lower spark energy and efficiency than the single-coil ignition system, owing to a larger fraction of resistive losses. However, under high-speed conditions, the spark power improved because the stretched spark channel was maintained with an intensified discharge current. The final ignition strategy was alternately charging and discharging the dual-coil ignition system, to maintain the spark channel for a longer duration. If the charging and discharging rates are balanced, a constant discharge power can be produced for a long duration. However, if the speed increases and the discharge rate exceeds the charge rate, the spark channel cannot be maintained with constant power.