The Effect of Enhanced Ignition Systems on Early Flame Development in Quiescent and Turbulent Conditions

Previous research on the effects of enhanced ignition systems has produced some conflicting results, possibly related to the various diagnostic methods used. In this investigation, several methods were used to measure the effects on flame development for different spark ignition circuits in quiescent and turbulent premixed gaseous mixtures. Sparks from a standard ignition circuit, typical of automotive use, were compared with sparks from a breakdown ignition circuit and from a plasma jet ignition circuit. It is shown that burning velocity calculation methods based on pressure trace analysis tend to be biased by any effects which provide a more spherical flame growth; particularly by projecting the spark kernel into the mixture away from the spark plug. Thus, the pressure trace-based burning velocity measurements gave false indications when comparing flames growing from dissimilar ignition systems. Instead, direct photographic flame growth measurements and simple combustion duration measurements were used for a less biased comparison. These diagnostics show that the higher energy ignition circuits provide much faster initial flame development. The same conclusion is demonstrated in both quiescent and turbulent mixtures. The apparent slight increase in burning velocity of developed flames for the breakdown and plasma jet ignition systems is thought to be a result of electromagnetically induced motion of the spark which results in a more favourable flame geometry.