Two-fluid coaxial atomization in a high-pressure environment

We study the dynamics of atomization of a liquid column by a coaxial gas flow with varying gas pressures. Specifically, we analyse how the gas density increase associated with elevated gas pressures in the ambient and co-flowing gas jet influences the liquid destabilization and breakup process, as well as the resulting droplet formation and dispersion. We present new experimental results for a coaxial liquid-gas atomizer operating in a high-pressure environment, with gas-liquid momentum ratio in the range M = 5-56 and pressurized gas densities rho(g) /rho(0) = 1-5, where rho(0) is the ambient gas density at standard conditions. High-speed shadowgraphy images are used to quantify the spatially and temporally varying liquid-gas interface in the spray near-field. Liquid core lengths, spreading angles and other spray metrics are presented, and the influence of gas density is identified from the comparison with atomization at atmospheric conditions. In the spray mid-field, phase Doppler interferometry is used in conjunction with laser Doppler velocimetry to quantify the droplet size and velocities, as well as their radial variations across the spray. Results show an increase in droplet size at elevated ambient pressures, when keeping the gas-liquid momentum ratio constant. Finally, we show that these observations are in line with predictions from the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, both of which are relevant to the gas-liquid atomization process.