Experimental study on spray atomization and liquid film impingement characteristics of an annular injector

As a novel underwater propulsion system, the water-ramjet engine relies on the atomization performance of its injector, which directly affects the combustion efficiency and thrust of the engine. This paper experimentally investigates the effects of injection pressure (1.0–2.5 MPa), divergence angles (30°–120°), and nozzle number (4 and 8) on the atomization and liquid-film impingement characteristics of single nozzles and annular multi-nozzle injectors. The results show that the flow coefficient of a single nozzle is jointly affected by the nozzle orifice diameter and divergence angle, whereas the spray cone angle β is mainly determined by the divergence angle, and the Sauter mean diameter decreases with increasing Weber number. The overall flow coefficient of the injector decreases as the nozzle number increases, which indicates a significant superposition effect of flow resistance. As the divergence angle increases, the impingement angle increases monotonically, whereas the impingement distance decreases significantly. In contrast, increasing the injection pressure does not change the evolution stages of the liquid film but shortens the duration of each stage.