Liquid fuel atomization phenomena in a diesel engine have been investigated to improve its thermal efficiency and to decrease exhaust gas emissions.Since cavitation occurring in a nozzle of a fuel injector plays an important role in fuel atomization,a large effort has been paid to visualize cavitation in injector nozzles.A mini-sac nozzle injector has a sac with a complicated geometry,which is known to affect the characteristic of cavitating flow and injected fuel spray.However,the effects of the nozzle geometry on cavitation and the injected liquid jets remain unknown.In this study,experiment was carried out to visualize cavitation and to measure flow distribution in two-dimensional scale-up mini-sac injectors with various needle angles and nozzle angles.Particle Image Velocimetry(PIV)analysis was carried out to measure the flows in the sac and the nozzle.The results show that large needle angle increases the sac volume upstream of the nozzle and,therefore,decreases the thickness of the separated boundary layer and cavitation in the nozzle,which results in a short cavitation length and small deformation of the liquid jet interface.It also increases the turbulence of the inflow into the nozzle,which increases the fluctuations of cavitation thickness and length as well as liquid jet angle even at hydraulic flip.In inclined nozzles,cavitation film is thin due to the acute inlet edge,and the cavitation clouds shed from the tail of the thin cavitation are small,which results in a small jet angle.These results conclude that the lateral inflow velocity component,which is strongly affected by the flow in the sac,determines the cavitation thickness,and therefore cavitation length,cavitation cloud,and the resulting liquid jet atomization.