Cycle-Resolved PDA Measurement of Size-Classified Spray Structure of Air-Assist Injector 970631

Very high data rate Phase Doppler Measurements were carried out in order to demonstrate the spray characteristics at each cycle and how each injection differed from each other. Conventional time-averaged data analysis can hardly provide information to analysis cyclic variation of spray formation and droplet dynamics so that a cycle-resolved PDA system was developed in the study. A direct gasoline injector for two-stroke marine engine was used for the experiment. For data analysis, droplet dynamics and characteristics of different droplet diameter were examined. The results show mat cycle variation of injector was remarkable, the maximum spray tip velocity differed from 63 m/s to 93 m/s even for the consecutive injection. The data rate obtained was over 40 kHz (Max: 85 kHz) and bin width was carefully examined to show the spray collision to air and entrained air motion. The high speed cycle formed large velocity fluctuation and small vortex time scale, while the low speed cycle was not so clear for the vortex entrainment.