Investigations on near-field atomization of flash boiling sprays for gasoline direct injection related applications

Flash boiling sprays have been widely studied recently because of its potential in generating fuel sprays with improved atomization efficiencies. Due to the strong multiphase influence, the exact spray atomization mechanisms of flash boiling sprays are not well understood yet, especially in the near-field where the optical depth is usually high for optical measurements. This investigation utilized a two-hole gasoline direction injection fuel injector to analyze the near-field atomization performance of a single spray plume under flash boiling conditions with a lower injection pressure to avoid the interference from dense sprays under higher injection pressures. High-speed backlit and Schlieren techniques were used to capture the liquid phase and gas phase distributions in the near-field and a microscope was incorporated to obtain detailed structure information of the fuel spray near the nozzle exit. Boundary conditions including fuel temperatures and ambient pressures were varied to study fuel atomization under different superheat indices and Cavitation numbers. Plume characteristics at different stages of the injection were investigated and significant multiphase influence can be found within the transitional flash boiling regime, including a two-zone atomization behavior at the beginning of the injection, a liquid skirt structure during the fuel injection, and a fishnet ligament pattern at the end of injection, respectively. This work also examined the impact of Cavitation number, superheat index, and ambient pressure on the properties of the external spray and such influence was represented by the near-field cone angle defined from near-field measurements.