Characteristics of Spray Near the Nozzle and Tip Wetting in an Enlarged GDI Injector Step-Hole Nozzle

This study is to analyze the spray characteristics near the nozzle according to the cavitating flow and step-hole structure using a quartz nozzle simulating a gasoline direct injection (GDI) injector. Referring to the dimensions of the injector used in mass-produced vehicles, various step-hole and injection pressure conditions were used in this experiment. Based on the injector dimensions, the step-hole conditions were designed in the direction of decreasing the depth and diameter. The internal flow in nozzle and spray near the nozzle were visualized by the shadow graphic and Mie-scattering visualization technique. A solenoid valve was used to simulate fuel injection like injector. Basically, the tendency of cavitating flow and spray characteristics were analyzed under various step-hole conditions. In addition, the tip wetting of nozzle with different step-hole conditions was analyzed, and the nozzle tip wettings at initial injection and end of the injection were separated and compared in detail. It was found that the wetting intensity decreased reduced 44.9 % when reduce step-hole depth from 2.5 to 1.5 mm. Tip wetting mainly occurred at initial injection for most step-hole conditions, but the tip wetting at end of injection was dominant when both decreasing the step-hole depth and step-hole diameter.