Experimental and Theoretical Analysis of Flame Development and Misfire Phenomena in a Spark-Ignition Engine

This paper describes theoretical analysis and experimental observations of very early stages of the flame development in a spark-ignition engine. The experimental work applies a high-speed imaging and image analysis techniques to the onset of spark and immediate post-spark stages of ignition, for steady state operation under a wide range of engine speeds, engine loads, equivalence ratios, spark advance and fuel injection timing. The results of the experimental studies are compared with a theoretical thermodynamic model of the flame kernel development. The theoretical analysis describes the situation from the onset of the spark discharge and includes input of electrical energy, combustion energy release and heat loss to the spark plug. In addition an approach is discussed which should prove of value in determining the combustion temperature during the very early stages after ignition. The method discussed determines the average expansion of the gas within the luminous part of the flame kernel and thus provides data on the mean temperature. In analysing the flame development it has been shown that if the flame is convected towards the electrodes, then the contact area of the flame with the electrodes is increased. This leads to unfavorable conditions for flame development due to increased heat transfer and recombination of active radicals. Where the flame is convected away from the electrodes, the contact area is small and a successful ignition is more likely to occur.