Morphological and mechanistic study of a continuous flash boiling liquid ammonia spray

As a zero-carbon fuel with superior properties, ammonia has attracted much attention from the combustion industry in recent years. In ammonia combustion for gas turbines (GTs), direct combustion of liquid ammonia (LNH3) is considered a way to increase power, simplify the system, and reduce energy consumption. However, due to the low boiling point and high vaporization latent heat of ammonia, LNH3 is prone to flash boiling under GT conditions, leading to significant changes in its spray characteristics. The current understanding of such a special spray is still insufficient. In this paper, particle droplet image analysis, Mie scattering, and thermocouple temperature measurement were conducted for continuous flash LNH3 spray in normal pressure. Furthermore, large eddy simulation was carried out. The quantitative characterization and detailed study of its spray morphology, parameter distribution, mass transfer, and heat transfer process were investigated. Combining this with the evaporation process, the formation reason for its spray morphology was explained, and suggestions for optimizing the combustion organization of the flash boiling spray were given. The results show that the spray angle θ decreases rapidly from 86° to about 10°, the spray SMD is 16 μm and the diameter spatial distribution is uniform. The spray temperature is 238.1 K at the nozzle exit, which is lower than the boiling point (239.8 K), and subsequently drops to approximately 209 K downstream the spray. The bubble behavior inside the nozzle and the gas diffusion in the near field of spray led to the expansion of near-field spray, and further changed the nozzle characteristics. The spray can be divided into three regions: Spray-core-region, Spray-main-region, and Spray-edge. The extremely high concentration of gaseous ammonia in Spray-core-region significantly deteriorates evaporation. The difference of droplet velocity and evaporation ability between Spray-main-region and Spray-edge leads to the formation of “willow leaf” shaped spray.