Characteristics of trans-critical propane spray discharged from multi-hole GDI injector

This paper is to investigate the characteristics of trans-critical propane spray compared with the flash boiling spray ejected from a multi-hole injector in a constant volume chamber by using the Schlieren and backlit imaging methods. The fuel temperature (T-f ) is set from 30 degrees C to 120 degrees C, injection pressure (p(f)) from 60 bar to 120 bar and ambient pressure (p(a)) from 0.2 bar to 10 bar. The results show that the trans-critical spray has longer vapor penetration and shorter liquid penetration than the flash boiling spray, but those two sprays have similar curve liquid boundaries near the nozzle. Several discernable collapsed shock structures near the nozzle are observed at T-f = 120 degrees C, p(f) = 120 bar, p(a) = 1 bar, but they disappear when p(f) drops to 60 bar for the transition path may not enter the two-phase region, and the liquid phase hardly occurs. The Mach disk distance of trans-critical spray in this study is larger than that of the underexpanded ideal gas jet because of the collapse phenomenon. At T-f = 120 degrees C, p(f) = 120 bar, the liquid length decreases when p(a) increases from 0.2 bar to 2.5 bar and increases when p(a) continues to rise.