Time- and space-resolved droplet sizing of intermittent diesel sprays

Time-resolved line-of-path integrated drop size measurements have been made at two-dimensional locations in a plane passing through the spray centerline of a single hole (pintle type) automotive diesel engine injector using a Malvern pulsed spray sizer. For internal sprays, measurements near the injector show that the mean droplet size decreases with time. This decrease is most likely due to the higher axial momentum of the larger drops as compared to that of smaller ones. The drop size is also found to be larger at the periphery of the spray relative to those near the centerline of the spray. This can be attributed to the higher tangential momentum of the larger droplets which carries them radially outwards. Further downstream from the injector, it is observed that the initial decrease of the mean drop size with time is delayed by the time-of-flight of the incipient spray cloud for internal sprays. While this temporal behavior of the mean drop size for external sprays is obscured by the existence of the lateral motion of the initial fuel cloud and by the lower drop velocity in the radial direction, the measured larger size drops almost always exist at the spray periphery.