Experimental Investigation of Internal Flow and Jet Breakup for Gasoline Direct Injection Systems

The experimental investigation of the internal nozzle flow and near-nozzle liquid jet breakup in regard to gasoline direct injection (GDI) is performed. Various experimental approaches are combined based on real scale and large scale flow conditions. The large scale measurements are performed maintaining the representative enlarged nozzle design. The real scale measurements are performed on real-size acrylic glass nozzles by means of high-speed and ultra high-speed shadowgraph imaging techniques. Moreover, an additional approach is used, which involves the advanced high-speed X-ray phase-contrast imaging technique. The internal flow phenomena in GDI nozzles are particularly characterized by the cavitation. It is found that the vortex cavitation formation is governed by a strong large scale vortex inside the hole. In turn, the vortical flow in a nozzle hole is shown to significantly influence the associated discharging liquid jet behavior. It is shown that extreme needle overshooting can lead to the formation of hydraulic flip in the holes under low inclination, which significantly affects the characteristics of the near-nozzle liquid jet.
Apart from that, the profound internal flow investigation is performed by the micro particle image velocimetry (PIV) approach. The flow structure is reconstructed by manual particle tracking for a short time of the injection period. Furthermore, the velocity data in combination with Reynolds-averaged Navier-Stokes (RANS) equations are used to evaluate the pressure field inside the nozzle. It is shown that a particular estimation of a specific term of these equations facilitates the evaluation of vortex structures in nozzle holes, which provides additional information about internal nozzle flow.