Study on the effect of injection temperature and nozzle geometry on the flashing transition of liquid ammonia spray

•The transition to flashing was observed for liquid ammonia.•Existing criteria approximated flashing transition but did not catch geometry effect.•Spray angles and flow rates were measured and can be used for modeling validation.•Two-phase flow could be observed in glass nozzles. Ammonia is a promising alternative fuel for carbon emission reduction in industry, transport, and power generation. For high-pressure combustion environment applications, direct injection of liquid ammonia (LNH3) is considered. Because of its thermophysical properties, and dependence on the injection and combustion environment conditions, the direct injection of ammonia in its liquid state can lead to flash-boiling, changing drastically the spray characteristics. In this study, we characterized the effect of injection temperature and nozzle geometry on the spray characteristics and transition to flashing using backlit imaging. Flow rates pressure curves and spray angles were obtained in a well-controlled environment and can be used as a database for simulation. Finally, some practical considerations on the design of nozzles are highlighted in the present work.