Investigation of Multi-Pole Spark Ignition Under Lean Conditions and with EGR 2017-01-0679
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 discharges. The multi-pole spark strategy displayed more advanced combustion phasing and lower phasing variability compared to single spark discharges. Under conditions where ignition requirements are modest, both strategies could achieve comparable performance with the appropriate adjustment of spark timing. Under conditions where the ignition demands are high, such as at high EGR rates or very lean conditions, the dilution limits could be increased with the multi-pole strategy. At the low load condition tested, the lean limit could be extended from lambda 1.8 to 2. The EGR rate could similarly be extended from 26% to 32%.