AN EXPERIMENT STUDY ON PHENOMENON AND MECHANISM OF FLASH BOILING SPRAY FROM A MULTI-HOLE GASOLINE DIRECT INJECTOR

Flash boiling spray could produce superior atomization and promote the formation of fuel/air mixture for a gasoline direct injection engine. However, the spray atomization deteriorates at a high degree of superheat of fuel, and the mechanism still remains unclear. In the present work, the macroscopic characteristics of flash boiling spray from a multi-hole gasoline direct injector were obtained by a Mie scattering technique to enhance understanding of the atomization process. The spray morphology and the macroscopic parameters with variations of fuel temperature and ambient pressure were analyzed. Two spray parameters were proposed to quantify the extent of spray collapse and micro-explosion, namely (1) the ratio of collapse (the ratio of penetration to width) and (2) the spray span of the near field. The correlation was identified between fuel temperature/ambient pressure and the spray characteristics (i.e., penetration, spray cone angle, spray span of near field, and ratio of collapse). By comparing the differences in spray characteristics among single-hole, two-hole, and six-hole injectors, the effects of the low-pressure core and the overlap region were decoupled. It was revealed that flash boiling spray collapse was caused by the combined effect of the low-pressure core and the overlap region. This combined effect resulted from micro-explosion and thus enhanced with increasing degree of superheat.