Flow Field Characterization of Superheated Sprays from a Multi-Hole Injector by Using High-Speed PIV

Superheated spray is expected to improve the fuel atomization and evaporation processes by introducing fuel temperature as a new control parameter in spark-ignited direct-injection (SIDI) engines. In this study, flow fields of n-hexane spray from a multi-hole injector in both vertical and cross-sectional directions were investigated by using high-speed particle image velocimetry (HS-PIV) within the lower density regions. The results provide insight to the spray-collapsing processes under various superheated conditions. It was found that in axial direction, the vertical velocity increases while the radial velocity decreases with increasing superheat degree, which determines the convergent spray structure. In cross-sectional direction, the dynamic variation of the spray structure and interaction among spray plumes were investigated. The relationship between the spray structure and flow field was found. The flow patterns during and after the injection are significantly different. Streamlines of fuel spray at various superheated degrees were analyzed and compared which provide an intuitive understanding of the flow patterns. This study reveals that the superheat degree is the predominant factor influencing the flow field, thus the structure of the superheated spray.