A Comparative Study on the Ignition Mechanism of Multi-site Ignition and Continuous Discharge Strategy

Advanced combustion engines dominate all automotive applications. Future high efficiency clean combustion engines can contribute significantly to sustainable transportation. Effective ignition strategies are studied to enable lean and diluted combustion under considerably high-density mixture and strong turbulences, for improving the efficiency and emissions of future combustion engines. Continuous discharge and multi-site ignition strategies have been proved to be effective to stabilize the combustion process under lean and EGR diluted conditions. Continuous discharge strategy uses a traditional sparkplug with a single spark gap and multiple ignition coil packs. The ignition coil packs operate under a specific time offset to realize a continuous discharge process with a prolonged discharge duration. Multi-site ignition strategy also uses multiple ignition coil packs. The ignition coil packs are connected with a specially designed multi-core sparkplug, which has multiple high voltage electrodes to generate multiple flame kernels. The ignition performances of these two ignition strategies differ from each other because of the distinguished ignition mechanisms. In this paper, the ignition mechanisms of both ignition strategies are investigated empirically via constant volume combustion vessel and a single-cylinder research engine. Test results indicate that the multi-site ignition strategy outperforms the continuous discharge strategy under quiescent and less intensified flow conditions, because of the larger initial flame kernel size. The efficacy of the multi-site ignition strategy relies highly on the survivability of the multiple initial flame kernels. Under extreme lean conditions with intensified flow field, a continuous discharge with long discharge duration can secure the flame kernel initiation process more effectively.