The enhancement of the ignition discharge parameters has been proved as an efficient means to control homogeneous lean combustion, but its effects on the burning stages is still controversial. This work presents the results of a study about the effect of a moderate enhancement of the ignition systems on lean homogeneous mixtures combustion in a conventional engine. Three ignition systems were compared: a standard inductive system, (M1) a long duration glow discharge ignition system (M2) and a capacitor discharge system (M3). Effects on combustion, over a wide range of operating conditions were examined, based on the engine outputs and heat release analysis. Durations of the flame development stage and rapid burning stage were correlated to give a measure of the strength of the relationship between them. It was found that a positive influence on combustion efficiency and stability is exercised only at engine idle and light loads, M3 being the most efficient. At high load of the engine, the difference between M3 and M2 almost disappeared and in general, the influence of an increased energy and/or power of the electrical discharge on the engine outputs became insignificant. It was confirmed that the main effect of an increased power or energy of the spark appears on the flame development stage; the influence on the rapid burning stage is generally weak, and is associated with lean mixtures and delayed phasing of combustion process within the engine cycle.
