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A fundamental study on spray behavior for small quantity injection under high boosting and high temperature conditions was carried out by applying dual nano-spark shadowgraph photography method to constant volume spray chamber filled with inert gas. The study showed macro-scale and micro-scale spray structures and dynamic changes of diesel spray affected by ambient density and temperature right after the pilot injection. Detailed observation and analysis of the images showed that high density surrounding gas decreases the mainstream velocity of the spray after injection, which restrains air entrainment into the spray. There is a change of flying direction of the droplets at spray boundary under high density condition. Many droplets move outward from the spray after the lapse of time. Spray evaporation is promoted by vaporization of droplets at spray boundary. High density condition greatly promotes droplets evaporation at spray boundary.

High boosting technology is commonly applied to diesel engines in recent years. Amid this trend, the study of spray behavior at ignition delay period still plays an important role in diesel combustion. This study focuses on the effect of ambient condition on diesel spray. The study investigates both macro-scale and micro-scale dynamic behaviors of diesel spray affected by ambient density and temperature at early stage of injection. A study via dual nano-spark shadowgraph method and rapid compression machine has been carried out to simulate real diesel engine combustion and to further understand the dynamics behavior of droplet evaporation and size distribution at early stage of mixture formation in the chamber. The micro-scale images captured reveal a shape variation of branch-like structures formed at the spray boundary. The evaporation of droplets is also captured clearly in macro- and micro scale photographs under the condition of high temperature ambient.