The present work discusses the role of orifice recess on the drop size characteristics of sprays discharging from gas centered swirl coaxial (GCSC) injectors used in liquid propellant rocket engines. Four GCSC injectors (one coplanar and three recessed) are considered. The experiments are conducted in a spray test facility with water and air as experimental fluids. The measurements of spray drop size are obtained using laser diffraction based Spraytec. The spray flow is characterized in terms of the gas-to-liquid momentum flux ratio, J. For a given GCSC injector, the measured SMD for sprays discharging from the injector decreases with increasing J. The sprays discharging from the coplanar CGCS injector exhibit typical uni-modal drop size distribution. However, the sprays discharging from the recessed GCSC injectors exhibit a bi-modal drop size distribution and the existence of bi-modality gets stronger with increasing J. Detailed analysis is made to shed lights on the mechanisms of spray formation in recessed GCSC injectors.
