Effects of a split injection on spray characteristics for a common-rail type diesel injection system

This work was performed to investigate the effect of a split injection on spray characteristics of fuel sprays injected from a common rail system. In order to analyze the spray behavior and atomization characteristics at various rates of split injections, the injection durations of pilot and main injections were varied in experiments. The injection rate of split injection was measured to study the effect of the pilot injection on the main injection. By using a Nd:YAG laser and an ICCD camera, the development of the injected spray was visualized at various elapsed time from the start of injection. The microscopic characteristics such as SMD and axial velocity were analyzed by using a phase Doppler particle analyzer system. The results indicate that the ambient gas flow generated by the pilot injection affects the behavior of main spray, whereas the effect of pressure variation on the main spray is little. The spray tip penetration of a main spray with pilot injection is longer than that of the single injection by the effect of ambient gas flow. Also the main spray produces larger droplets than the pilot spray due to a small relative velocity between the droplets and ambient gas.