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In order to investigate the effects of a DC electric field and its polarity on the knock intensity in a spark-ignition engine, an experimental study was carried out with a rapid compression machine. To get a good understanding of the effect of an electric field on knocking combustion, the high-speed direct photographs were taken. The ionization current measurements were also carried out using the electrode as an ionization probe The major findings of present investigation of the effects of DC electric fields on the knocking combustion process in a spark-ignition engine could be summarized as follows: It was clearly indicated that the knock intensity decreases with the increase of the electric field regardless its polarity. The knock intensity was strongly dependent upon the burned mass fraction at the onset of the end-gas autoignition, and decreased as the burned mass fraction increased.

The initial breakup process from liquid fuel to spray droplets in the vicinity of the nozzle tip under high-pressure ambience is analyzed for the isothermal diesel spray injected into the optically accessible high-pressure vessel. The spray was observed both by the use of planar laser light and also by using diffused shadow light. The results obtained in the present study are summarized as follows. The initial breakup of the developing diesel spray could be photographed more clearly in the vicinity of the nozzle tip. The initial liquid jet from nozzle hole is divided into two zones; the intact liquid pillar zone and the umbrella-like thin liquid protrusion zone. The breakup happens mainly in the periphery of the thin liquid umbrella protruding from the tip of the intact liquid pillar. The high pressure ambience break-up mechanism can be analyzed from observation of the internal flow of the liquid pillar and it's protrusive umbrella.