Characterizing the spray under varying ambient pressures for internal-mixing gas-liquid injector

This study investigates the spray dynamics of an internal-mixing gas-liquid injector under elevated backpressure, relevant to engine combustors. Experiments combining high-speed imaging, shadowgraphy, and proper orthogonal decomposition reveal how gas-liquid momentum ratio ( GLMR ), backpressure ( P _b), and gas Weber number ( We _g) govern the flow and spray characteristics. Critical GLMR for separating aerodynamic and impact fragmentation regimes is predicted by theoretically deriving the liquid jet trajectories. The results demonstrate that increasing GLMR raises the gas discharge coefficient but lowers the liquid one. While We_g enhances the spray angle, P _b reduces it. Increasing We_g also enhances the penetration distance, with a slight increase observed under higher P _b. P _b significantly reduces droplet velocity—a consequence of attenuated kinetic energy of atomized droplets—and generally increases droplet size, whereas We_g tends to reduce it. Furthermore, P _b suppresses spray oscillation instability. These findings elucidate the mechanisms of backpressure influence and provide direct insights for optimizing injector performance in high-pressure environments.