Single hole ammonia spray macroscopic and microscopic characteristics at flare and transition flash boiling regions

As a potential zero-carbon fuel for internal combustion engine to mitigate the greenhouse gas emission, ammonia's unique flash boiling spray behaviors have not been well understood. In this study, the macroscopic and the microscopic characteristics of the liquid ammonia spray at the flare and transition flash boiling regions were experimentally investigated under different pressure ratios (RP, the ambient over the saturated pressure) and ambient temperatures. The spray macroscopic morphologies captured from the high-speed camera in the flare flash boiling region (RP = 0.47) show that the spray expands significantly in radial direction while that in the transition flash boiling region (0.47 < RP = 1.06) is more contracted in the penetration direction. Additionally, in flare flash boiling region, spray tip penetration and velocity increases generally with the increase of RP, while that in the transition flash boiling region in versus. Furthermore, the microscopic droplet statistics clearly demonstrate show that the most probable droplet diameter moves to a larger value with the increase of RP. The peak probability of droplet size and the droplet number density decreases at larger RP cases, resulting in a more uniformly distributed droplet sizes and an increased Sauter Mean Diameter. Finally, the ambient temperature show limited influence on the macroscopic spray penetration behaviors or the microscopic droplet size distribution, but evaporation is significantly enhanced since at highest ambient temperature, there are minimized droplet number density in some of the test locations.

Automated summary

This study experimentally investigated the macroscopic and microscopic characteristics of liquid ammonia spray under different pressure ratios and ambient temperatures. It was found that the spray morphology and droplet size distribution vary significantly with different pressure and temperature conditions. The spray expands in the radial direction in the flare flash boiling region, while it contracts in the penetration direction in the transition flash boiling region. The droplet size and number density change with the increase of pressure, leading to a more uniform droplet size distribution. The ambient temperature has limited influence on the spray penetration and droplet size distribution.