Effects of fuels on flash boiling spray from a GDI hollow cone piezoelectric injector

•Hollow cone spray from four fuels was tested under flash boiling and non-flash boiling conditions.•Spray plumes are created along the axis of the spray under strong flash boiling conditions.•Flash boiling becomes stronger for lower ambient pressure and higher fuel temperature.•Results imply that mixing a low boiling point fuel component could facilitate flash boiling. Flash-boiling of fuel sprays can have a significant effect on spray formation and its characteristics due to bubble nucleation, growth, and phase change, producing explosive-like atomization and complex spray structures. In this work, experiments were conducted to study the spray of both pure substance fuels (pure isooctane, pure ethanol) and multicomponent fuels (50/50 mixture of isooctane and ethanol, commercial gasoline), under flash boiling conditions and non-flash boiling conditions. Under different temperature and ambient pressure, different superheated degrees can be achieved for the fuels. Pure substances have a single vapor pressure curve, while mixtures do not have a single boiling point at a given pressure, and a two-phase region exists for multicomponent fuel. Under the same conditions, ethanol has higher superheated degree compared to isooctane, but the heat of vaporization for ethanol is also much higher. This contributes to the fact that less boiling is observed in the ethanol spray with longer penetration in several cases. Mixture 50/50 shows a good average of isooctane and ethanol for spray penetration and spray front plume ratio analysis. Gasoline, due to its low initial boiling point and wide range of components, has the widest plume ratio distribution and smallest gradient, as well as complex peak penetration velocity distribution. The results also imply that adding low boiling point (preferably with low heat of vaporization as well) additive or component to high boiling point fuel can facilitate flash boiling, fuel vaporization and mixing.