LES investigations on effects of the residual bubble on the single hole diesel injector jet

Bubbles surviving from the last injection process play an important role in the early stage of the next injection process, and ultimately affect the quality of diesel spray characteristics. In this paper, a combination of the LES (Large Eddy Simulation) method and VOF (Volume of Fluid) model was applied to study the unsteady liquid jet flow at the early stage of injection coupling the cavitating flow inside orifices, especially to analyze the effects of the residual bubble on the diesel jet. It was found that the instability of the jet surface was intensified by the cavitating flow inside the nozzle. The development of jet instability waves and the cavitation collapse inside the jet aggravated the interactions between air and diesel jet, which caused the liquid core to separate into some large liquid bulks a bit earlier. Then, the ligaments formed from the bulks broke up into droplets. Furthermore, the double mushroom-like shape occurred with the residual bubble, while just a single mushroom head occurred without the residual bubble. The length of liquid core decreased with the increasing of injection pressure, and the phenomenon that the air inside the spray chamber was partly sucked into orifice was observed.