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

Abstract

This paper focuses on the influence of injection pressures up to 30MPa on single liquid jet break-up and atomization processes. For this purpose, a single jet from a multi-hole GDI injector has been characterized performing visualization and PDPA (phase Doppler particle analyzer) experiments. Using a thin sheet of light generated by a Nd:Yag laser and capturing a sequence of jet development images with a CCD camera, the internal structure was visualized. In order to quantify the droplet diameter and velocity, a 2-D PDPA system were carried out in addition to the spray visualization. Analyzing the images of the internal structure of jet and the result of PDPA, including droplet diameter and velocity distribution with increasing injection pressure up to 30MPa, the elevated injection pressure on a jet break-up and atomization was characterized.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 20MPa led to a decrease in SMD (Sauter mean diameter) linearly by approximately 10μm. However, an injection pressure above 20MPa, did not result in any significant reduction in SMD.