Spray morphology and droplet characteristics in gas centered swirl coaxial GCSC atomizers

Abstract

Studies on liquid atomization and spray formation in coaxial type atomizers are necessary to improve the performance of liquid propellant rocket engines. Recess ratio, expressed as the ratio of orifice recess length to inner orifice diameter, is one of the geometrical parameters that influences the characteristics of sprays discharging from coaxial atomizers. The present thesis reports an experimental investigation on the atomization and spray formation processes in recessed gas-centered swirl coaxial (GCSC) atomizers through the analysis of spray morphologies and measurements of size and velocity characteristics of spray droplets. A GCSC atomizer discharges a swirling liquid film and a gas jet via its annular and central orifices, respectively. Specific attention is given to elucidate the role of atomizer recess ratio of the GCSC atomizer on the characteristics of the spray that results from the breakup of the annular swirling liquid sheet by the central gas jet. The experiments are carried out in a spray test facility using water and air as the experimental fluids. The measurements of pressure drop across the atomizer orifices and fluid flow rates are made in the test facility. The images of sprays at different flow conditions are captured using the technique of backlighted shadowgraphy. Laser-based optical diagnostic systems (Phase Doppler Interferometry and Spraytec) are used to measure the size and velocities of spray droplets at different spatial locations of the spray below the atomizer exit. In the present study, the spray condition from the GCSC atomizers is expressed in terms of the gas-to-liquid momentum flux ratio, J. The quantitative variations of the spray cone angle and the streamwise breakup length of the annular liquid sheet, with the atomizer recess ratio, RR are presented for different GCSC atomizer flow conditions. An increase in RR of the GCSC atomizer results in a smaller spray cone angle and a longer sheet breakup length...