Flash boiling in a multihole G-DI injector - Effects of the fuel distillation curve

The effects of fuel temperature and chamber pressure on the spray of a multi-hole G-DI injector were analyzed in a quiescent test chamber. The analysis was focused on the behavior of the global spray angles both close and far from the injector. Three pure hydrocarbons (n-hexane, n-heptane, and isooctane), three gasolines of known distillation curve and a commercial 95 RON gasoline from a gas station were utilized. The tests were performed at four chamber pressures (atmospheric, 80 kPa, 60 kPa and 40 kPa) and the fuel temperature was varied from 30 C to 110 C. The results for n-hexane and gasolines were very similar, while n-heptane and isooctane showed a different behavior. The ratio between the fuel saturation pressure at the operating temperature and the air pressure (ps/pa) is confirmed as a fundamental parameter for spray angle data reduction. The near field spray angle data for pure hydrocarbon fuels merge to a unique curve when plotted in function of ps/pa. An approximated method to deduce the gasoline saturation pressure curves starting from the distillation curve is presented. Using the calculated saturation pressures for the reduction of near field spray angle data for the gasolines, a unique curve is obtained, coincident with that of the tested pure hydrocarbons. In alternative, from the results obtained for a fuel of known saturation pressure curve, it is possible to obtain a direct correlation between near field spray angle and saturation pressure. From this relationship, an approximated saturation pressure curve from the experimental angle measurements obtained on the same injector for an unknown fuel can be derived.