Direct injection is frequently employed in the combustion applications as internal combustion engine and gas turbine. Liquid injection aims to inject the fuel directly inside the combustion chamber and to vaporize it as fast as possible but also due to the heat of vaporization to cool down the ambient temperature to enhance the charge and the thermal NOx emissions. The fuel spray is first broken up into small droplets to increase the surface between liquid and air. Then, the vaporization of droplets is greatly significant for the spatial distribution of fuel vapor/air, the ignition, and the combustion itself. However, the use of new carbon-free fuels such as ammonia with completely different thermodynamics properties needs fundamental studies to improve the knowledge and its application itself. Pelé et al. [1] explored the sprays of liquid ammonia with a current Bosch GDI injector. The geometry of the ammonia sprays for different conditions of air densities and temperatures was compared to the sprays of classic fuels such as gasoline and ethanol. The impact of the flash boiling (Psaturation(Tfuel) > Pambient) was investigated on the spray morphology. Some numerical studies [2,3] have reproduced the ammonia sprays and found a good agreement on the spray morphologies between numerical and experimental results. However, local features and atomisation levels require further theoretical development for calibration-free models. Zhang et al. [4] have shown that no obvious differences in terms of spray macroscopic and microscopic properties between the results from the normal evaporation model and the flash boiling model used. The vaporization process is a complex phenomenon, especially in the case of flash boiling. Back to a simplified configuration as one unique droplet model allow us to better understand the physical basis of the vaporization process of ammonia with or without flash boiling. The model of droplet vaporization developed in this work is compared to experimental data obtained in a single-hole injector.