Performance of Spark Current Boost System on a Production Engine under Lean-Burn Conditions

In order to improve the fuel economy for future high-efficiency spark ignition engines, the applications of advanced combustion strategies are considered to be beneficial with an overall lean and/or exhaust gas recirculation diluted cylinder charge. Stronger and more reliable ignition sources become more favorable under extreme lean/EGR conditions. Existing research indicates that the frequency of plasma restrikes increases with increased flow velocity and decreased discharge current level, and a higher discharge current can reduce the gap resistance and maintain the stretched plasma for a longer duration under flow conditions. An in-house developed current boost control system provides flexible control of the discharge current level and discharge duration. The current boost ignition system is based on a multi-coil system with a discharge current level of 180mA. In this study, a comparative study has been conducted to investigate the efficacy of multi-coil and multi-core ignition systems on a spark-ignited inline-four cylinder production engine under lean-burn conditions. Both total ignition energy and discharge duration are kept the same. The ignition performance of both strategies has been investigated under various levels of engine loads, including idling (1.1 bar BMEP at 900rpm) and partial engine load (2.6 bar BMEP at 1500rpm) conditions. Using the multi-coil system, the spark advance window could be extended beyond that of the traditional transistor coil ignition. Furthermore, the application of the multi-core ignition system consistently realized a shorter ignition delay period by 2~4°CA regardless of boundary conditions.