Macro- and Micro-scale Observation on Dynamic Behavior of Diesel Spray Affected by Ambient Density and Temperature

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. Detailed observation and analysis of the images show that high ambient density affects the spray atomization at the upper stream of diesel spray at the early stage of injection. High temperature and high density air entrainment into spray promotes droplets evaporation, in particular, at the upper stream of spray. At high density ambience, spray evaporation and mixture formation are first promoted at the middle stream of spray region that is about 20mm from the injector outlet.