Performance of Spark Energy Distribution Strategy on a Production Engine under Lean-Burn Conditions

Stronger ignition sources become more favorable under extreme lean/EGR conditions. Under those conditions, the reduced pumping loss and low combustion temperature can contribute to further engine efficiency improvement for spark ignited engines. Multicoil ignition system can enhance ignition energy as well as modulate discharge profile. The ignition energy can either be deployed through single spark gap to enhance the ignition capability of the plasma channel, or be distributed to multiple ignition sites to establish multiple flame kernels to secure flame kernel initiation. The multiple ignition coils used for energy distribution ignition strategy also consume more power, in order to maintain the stable operation of the engine under lean operation limit. In this paper, efficacy of concentrated and distributed multicoil ignition strategies were investigated on a spark ignited inline 4-cylinder production engine using a three-ignition-coil pack. Both total ignition energy and discharge duration were kept the same. Power consumption of the added ignition coils were compared with the power gain under lean burn conditions. Ignition performance of both strategies was investigated under various levels of engine loads, from idling condition (1.1 bar BMEP) to medium engine load (5.5 bar BMEP). The test results revealed that the multiple ignition sites technique can effectively decrease the ignition delay throughout the testing cases, but its contribution to lower engine cycle to cycle variation was more significant under low load, lean burn conditions, where the ignition process received more challenges.