Influence of spark discharge characteristics on ignition and combustion process and the lean operation limit in a spark ignition engine

•Ignition and combustion process of a lean burn engine was investigated.•A customized ignition system with 20 ignition coils was applied.•Lean limit was extended to excess air ratio of 2.1 with a discharge interval.•The longer discharge interval promoted the spark-shortening phenomena.•Repetition of spark-shortening phenomena promoted the formation of flame kernel.