Analysis of Droplets Evaporation Process of Diesel Spray at Ignition Delay Period using Dual Nano-spark Shadowgraph Photography Method

Evolution of evaporating diesel spray is complex phenomena; however, it is important process for ignition, combustion and emission formation in diesel combustion. In this research, droplets evaporation process at spray boundary was experimentally investigated focusing on the behavior of evaporating droplets during ignition delay period. In the experiment, nano-spark shadowgraph photography technique was applied to a rapid compression machine. This study developed a new optical system to observe spray evaporation process. The existing systems can hardly analyze transitional behavior of vapor phase of spray and droplets behavior in high number-density region. The new technology that is named dual nano-spark shadowgraph photography method can record both macro-scale and micro-scale continuous spray images clearly at very short time interval of 15µsec on normal photographic black and white film. This paper explains the characteristics and advantages of the new dual nano-spark shadowgraph photography method comparing with previously developed shadowgraph photography methods such as single-spark and double spark methods. It is suggested that fairly clear images of spray taken by dual nano-spark shadowgraph photography method offer good information for explanation of the behavior of evaporating spray boundary at early injection period.