A molecular dynamics study on supercritical evaporation of ammonia droplets in multi-component environments

Abstract

The evaporation characteristics of ammonia fuel droplets in single and multi-component supercritical environments were studied using molecular dynamics simulations. A new approach for determining the supercritical transition of droplet evaporation modes was proposed from the perspective of atomic pair entropy fingerprints. Some improvements of the previous pair entropy fingerprint formulas were conducted to better analyze the variations in the disorder of fuel molecules during evaporation. The transition moment of droplet evaporation under supercritical conditions was based on the degree of fuel molecular disorder within the vapor–liquid mixing layer. Then, the effects of ambient conditions on the mode transition of droplet evaporation were studied. The findings indicated that the supercritical transition would not be obvious if ambient pressure was high enough. The existence of polar molecules in the environment can accelerate the mode transition. In addition, the diffusion tendency of the ambient gas components into the droplets was investigated. It was found that polar molecules diffused more strongly into the ammonia droplet than non-polar molecules.