Investigation of Multi-Pole Spark Ignition on Flame Kernel Development and in Engine Operation

In order to meet the future carbon dioxide legislation, advanced clean combustion engines are tending to employ low temperature diluted combustion strategies along with intensified cylinder charge motion. The diluted mixtures are made by means of excess air admission or exhaust gas recirculation. A slower combustion speed during the early flame kernel development because of the suppressed mixture reactivity will reduce the reliability of the ignition process and the overall combustion stability. In an effort to address this issue, an ignition strategy using a multi-pole spark igniter is tested in this work. The igniter uses three electrically independent spark gaps to allow three spatially distributed spark discharge. The multi-pole spark strategy, when observed in an optical combustion vessel with lean methane-air mixtures, visually showed increased early flame kernel growth rate. The strategy was tested on an engine using gasoline fuel and low load, lean operation at 1.35 excess air ratio. The results indicated that the combustion phasing parameters were consistently advanced under the multi-pole spark strategy. In conditions where a conventional single spark exhibited stable operation, relatively little additional benefits were seen with the multi-pole strategy. At later spark timings when cycle-to-cycle variations had a greater impact on the engine stability, the multi-pole spark reduced the combustion variability.