Cavitation in a fuel injector for Diesel engines plays an important role in the characteristics of a discharged liquid jet and spray.Hence,large efforts have been made to visualize cavitation in large-scale nozzles as well as real-scaled tiny nozzles.However,the effects of nozzle size on cavitation and the jets have not been clearly clarified yet in terms of cavitation length,cavitation thickness,bubble size,bubble shape and their impacts on the liquid jets.In this study we manufacture several two-dimensional nozzles in similarity with 4,2,1,0.5 and 0.25 mm in widths for visualization of cavitation and injected liquid jets.High-resolution still images of cavitation and the discharged jets using visible light source are obtained.Phase-contrast X-ray imaging of the cavitation in the small nozzles and the jets using the synchrotron radiation facility SPring-8 are also carried.As a result,we find that(1)the normalized cavitation width and length do not so much depend on nozzle size,(2)in the smaller nozzles,cavitation tends to be slightly thinner and,therefore,shorter due to the relatively larger radii R of curvatures for the nozzle inlet edges normalized by the nozzle width W,(3)the liquid jet angle θ increases at super cavitation.However,the effect of super cavitation is smaller in the smaller nozzles due to the relatively larger surface tension force acting on the liquid jet interface,(4)phase contrast X-ray imaging confirms that the shapes of cavitation bubbles in the nozzle are not always spherical,they are determined by the separation flow structure,and the diameters of the cavitation bubbles depend on nozzle size,and(5)the jet angle increases and the wavy jet structure becomes fine at super cavitation.However,the effect of super cavitation to enhance the jet deformation is smaller for the smaller nozzle due to the relatively larger surface tension force.