Investigation of spark discharge processes and ignition systems for spark-ignited internal combustion engines

Abstract

Spark ignition of the air-fuel mixture at the appropriate time is important for successful flame initiation and complete combustion thereafter without unnecessary emissions. The physical and chemical reactions taking place between the spark plug electrodes during spark delivery determine the intensity of the spark and subsequent flame initiation. The energy of spark and the duration of its delivery are dependent on the ignition system design. The characteristics of the spark plug determine the interaction of the spark with the air-fuel mixture. The compression pressure, combustion chamber temperature and mixture motion at the time of spark generation play a significant role in the flame initiation process. All of these parameters are responsible for the resulting spark discharge and flame initiation process. The objectives of this research include investigation of the different phases of spark discharge and development of a thermodynamic analysis to determine the rate of change of the spark kernel temperature with time during the initial phases of the spark discharge. The effect of spark energy delivery rate, heat transfer losses and mass entrainment on the spark kernel temperature was determined through the thermodynamic analysis. This research also includes an evaluation of the various types of conventional as well as high-energy ignition systems for lean burn engines. An experimental ignition system was constructed to determine the effect of ignition energy, spark plug electrode geometry and gas pressure on the characteristics of the spark discharge. Images of spark discharge were captured through photography using three different types of electrode geometries and also by varying the pressure and by changing the ignition energy using different condensers in the ignition system. Finally, the results of the thermodynamic analysis were compared with the results from the experiment.