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An experimental study was carried out on visualization of liquid phase temperature distributions in high-pressure diesel sprays impinging on a heated wall. Naphthalene/TMPD-exciplex fluorescence method and pyrene-excimer fluorescence method were utilized for the thermometry. The sprays were injected into a high-pressure and high-temperature gaseous environment. The nozzle hole diameter was 0.100 mm or 0.139 mm. The results showed that cool pockets were formed at the tip and in the impinging part of the sprays. The spray for the nozzle with 0.100 mm hole was heated up faster near the nozzle than for the nozzle with 0.139 mm hole.

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.