Effect of ambient temperature on flash-boiling spray characteristics for a multi-hole gasoline injector

Fuel spray atomization is a critical process that can be optimized to improve fuel efficiency and reduce exhaust emissions for internal combustion engines, especially for gasoline direct-injection engines. Understanding the governing parameters of fuel sprays is essential for the advancement of fuel direct-injection technologies and further improvement of engine performance. However, the effect of the ambient temperature on fuel sprays has not been fully understood yet, especially for flash-boiling spray which is common under some representative engine conditions. In this study, the effects of the ambient temperature on spray characteristics under both non-flash-boiling and flash-boiling conditions were investigated using Mie scattering techniques, and the correlations between spray characteristics and dimensionless numbers were established to study the effects of governing parameters on fuel sprays. The results show that the evaporation of fuel spray was enhanced as the ambient temperature was elevated. In addition, increasing the ambient temperature could enhance the collapse of multi-hole fuel spray under flash-boiling conditions. Such observations indicate that increasing the ambient temperature has a similar effect on the collapse of fuel sprays, compared with decreasing the superheat index (Pa/Ps) of the fuel injected. Therefore, in this study, the effect of ambient temperature on the local superheat degree of fuel spray was accounted for. A universal correlation between spray penetration and the equivalent original superheat index was then found, incorporating the effects from both ambient temperature and superheat index. The formulation introduced above was found to significantly extend the scope of the previous research and provides useful information for the design of fuel injection systems.