Spray dynamics and atomization characteristics of multi-hole GDI injectors under flash boiling conditions

Abstract

In the gasoline direct injection (GDI) engine, spray atomization contributes significantly to the formation of a uniform mixture and the effective combustion of the spray. In this study, a phase Doppler particle analyzer (PDPA) was used to measure the spray atomization characteristics of two five-hole GDI injectors with different hole arrangements under subcooled and mild flash-boiling conditions (superheated degree = 20 °C). Based on the spray patterns of the two injectors on a plane 30 mm below the injector tip, the two injectors were called triangle-patterned and pentagon-patterned injectors. A total of 100 measuring points were selected on a plane 30 mm below the injector tip, and the spray droplet diameter and velocity at these points were measured to understand the overall atomization characteristics of the spray in space. The experimental results indicated that as the spray transitioned from subcooled to flash boiling conditions, a polarization phenomenon occurred in which the velocity in the center of the plume increased and the velocity in the peripheral region of the plume decreased. However, the spray droplet diameter significantly decreased under flash-boiling conditions. The average Sauter mean diameter (SMD) of the two injectors on a plane 30 mm below the injector tip decreased by approximately 4 μm, and the uniformity of the spatial distribution of the SMD also increased. Compared with the triangle-patterned injector (injector A), the average SMD of the pentagon-patterned injector (injector B) was slightly smaller; this was attributed to the stronger air entrainment inside the spray and the enhanced air flow caused by the larger plume spacing of the pentagon-patterned injector.