In spark-ignition direct-injection(SIDI)engines,fuel spray plays an important role since it significantly influences the combustion stability,engine efficiency as well as emission formations.In order to design more efficient and cleaner engines,further research is needed to understand the fuel spray characteristics under various ambient conditions of the engine cylinder.Planar laser induced exciplex fluorescence technique has been applied to record the liquid spray images under a wide range of operating conditions in a constant volume chamber.The macroscopic characteristics of liquid spray are analyzed using dimensionless analysis to study the effects of the injection operating parameters.Specifically,the effect of ambient temperature on the spray characteristics is investigated.Dimensionless parameters such as Reynolds number(Re),Weber number(We),and gas-to-liquid density ratio are used to represent the influences of the primary forces,including the inertia,viscous,surface tension,and aerodynamic drag forces,on the spray atomization and evaporation processes.The results show that the ambient temperature has a strong effect on the spray characteristics.Increasing the ambient temperature enhances the evaporation of the liquid spray,and reduces the gas-to-liquid density ratio which leads to a decreased aerodynamic drag force.The liquid spray penetration is dependent on the combined effect of the reduction of gas-to-liquid density ratio and the in-crease of evaporation.Based on the above analysis,new dimensionless correlations are established to quantitatively characterize spray penetration to take into account of the ambient temperature effect,and these correlations provide important insight into the spray breakup and atomization processes.