Spark Ignition, Early Flame Development and Cyclic Variation in I.C. Engines

Combustion and pressure development in spark ignition engines are marked by cycle to cycle variations which are especially severe if the mixture is lean. The variations in indicated mean effective pressure (IMEP) that arise from this could be sufficiently severe to cause problems in certain engine operating regimes even in engines which run smoothly at steady operating conditions. Cyclic variations in IMEP could be effectively reduced at source by reducing cyclic variations in combustion. These are known to originate during the initial stage of combustion which can be influenced by the ignition process. Of the various enhanced ignition devices, variants of the spark ignition system seem to be of most practical interest for automobile applications in the immediate future. In the paper, we review the literature on spark ignition, the nature of the spark discharge process and the attempts to improve stability of engine operation through changes in spark ignition.