EFFECT OF DESIGN PARAMETERS ON SPRAY CHARACTERISTICS OF ADDITIVELY MANUFACTURED BISWIRL COAXIAL INJECTORS

This study aims to achieve the axisymmetric spray characteristics of biswirl coaxial injectors fabricated via additive manufacturing (AM) and investigates the effects of nozzle length, contraction angle, and tangential inlet height on the discharge coefficient, spray-cone angle, and breakup length. Ten injectors were additively manufactured using UNS S31603 powder and tested using water as a simulant propellant. Shorter nozzle lengths resulted in higher discharge coefficients, larger spray-cone angles, and shorter breakup lengths. The contraction angle had minimal impact, whereas variations in the tangential inlet height influenced the spray characteristics through changes in the swirl injector geometric constant. The experimental results confirmed that the injectors produced highly axisymmetric sprays, thereby validating the applicability of conventional swirl injector theories to AM. Furthermore, a new empirical model incorporating a normalized nozzle length is developed to improve the breakup-length predictions. These findings highlight the potential of AM to optimize high-performance bipropellant thrusters.