Effects of Spark Characteristics on Engine Combustion with Gasoline and Propane

This paper describes an experimental study of the effects of ignition spark characteristics on combustion behaviour in a light duty automotive engine. A prototype programmable energy ignition system was used to investigate the influence of both spark energy and the current/time profile used to deliver a given amount of energy. The engine was tested under part load conditions using a stoichiometric air/fuel ratio and relatively high levels of exhaust gas recirculation (EGR). In addition to tests with port-injected gasoline, tests were also carried out using propane (premixed upstream of the throttle) in order to investigate the possibility that improvements in the homogeneity of the mixture might influence the impact of varying the spark characteristics.

The results focus upon the Coefficient of Variation of Indicated Mean Effect Pressure (COV of IMEP) and the 10% Mass Fraction Burn (MFB) duration versus concurrent measurements of the electrical energy delivered into the spark plug gap. Different spark waveforms in which current was delivered continuously during the spark produced similar reductions in the 10% MFB duration as the delivered spark energy was increased, while sparks with intermittent current delivery (multi-spark approaches) were somewhat less effective in this regard. COV levels with port injected gasoline were substantially higher than those with premixed propane when the delivered spark energy was very low, but the two fuels produced similar COV levels when the spark energy was increased. Significant differences in spark plug erosion would be expected for the various types of spark current waveforms due to differences in the integrated current required to deliver a given amount of ignition energy and the proportioning of the current between arc and glow discharge.