Microscopic characteristics study of liquid ammonia spray under different flash boiling conditions

Liquid ammonia, as a zero-carbon fuel, has received widespread attention in the field of internal combustion engines. The development of ammonia spray and evaporation models urgently requires accurate particle size distribution data. In this study, microscopic characteristics of liquid ammonia spray were firstly experimentally investigated under conditions of high injection pressure (up to 80 MPa) and ambient pressure (up to 4 MPa) with a single-hole injector (0.3 mm). Statistical results of microscopic parameters, including Sauter Mean Diameter (SMD), characteristic droplet diameter, and droplet number density were obtained over a wide range. The results indicate that ambient pressure or R_P significantly affects the microscopic characteristics of ammonia spray. In flare flash boiling region (pressure ratio R_P ≤ 0.3), ammonia spray produces more droplets with smaller diameter and the statistical SMD is around 15 μm. The droplet size increases and number density decreases with the increasement of ambient pressure or R_P. In the transition flash (0.3 < R_P ≤ 1) and non-flash boiling region (R_P > 1), the SMD statistical results are approximately 20 and 24 μm, respectively. Increasing the injection pressure can promote atomization and generate more smaller droplets, with a more uniform distribution. Ambient temperature slightly affects the microscopic characteristics of liquid ammonia spray within the temperature range selected for this study, but evaporation becomes more pronounced as the ambient temperature increases. The wide range droplet size distribution and SMD are believed to provide important data for ammonia spray modeling and simulation.