Experimental study on spray break-up and atomization processes from GDI injector using high injection pressure up to 30Â MPa

Our experimental results show the existence of a leading edge of the jet observed at the initial stage of injection. This phenomenon revealed relatively large droplets ahead of the main jet then disappeared quickly as lose the droplets momentum. Furthermore, for all injection pressures, unique 'branch-like structure' was observed when the jet was fully developed. This structure had many counter rotating branches related to the effect of air-entrainment and rapidly broken down into droplet clusters and droplets. Especially, as increased injection pressure, the time to exhibit the structure and distance between two branches were decreased. In addition, based on the results of droplet diameter and velocity distribution at various injection pressures, we confirmed that the injection pressure plays a key role in droplet break-up, but a limit in injection pressure to enhance droplet break-up also occurred. That is, increasing injection pressure from 5 to 10 to 20 MPa led to a decrease in SMD (Sauter mean diameter) linearly by approximately 10 μm. However, an injection pressure above 20 MPa, did not result in any significant reduction in SMD.