The electrical characteristics of transistorized coil ignition (TCI) and capacitor discharge ignition (CDI) systems were investigated in spark-ignited quiescent and flowing propane/air mixtures within an optically-accessible, cylindrical constant-volume combustion chamber. Under quiescent flow conditions, the initial pressure, temperature and equivalence ratio of the mixture as well as the spark gap width and geometry were varied systematically in order to examine the relationship between ignition characteristics and flame initiation and development. The effect of the flow in the spark gap on the electrical characteristics of the ignition system, mixture ignitability and flame development was also examined by varying the pre-ignition mean flow and turbulence as well as the spark plug orientation relative to the mean flow.
Under quiescent flow conditions and despite differences in the electrical characteristics of the two ignition systems examined, TCI and CDI gave rise to similar flame development which implies the absence of a correlation between breakdown/total energy and early flame development; the TCI system, however, with its longer spark duration and higher breakdown energy, allowed extension of the lean ignition limit especially at large spark gaps. For a given ignition system, lower initial mixture pressure, higher initial temperature and wider spark gaps resulted in faster flame propagation.
Under flowing mixture conditions, combustion duration was shortened and the lean limit was extended when the mean flow and turbulence in the spark gap were high provided the orientation of the ground electrode was not in the upwind side of the mean flow direction. As the flow velocities were reduced, the effect of spark plug orientation on ignitability became smaller.