Swirling flow and spray atomization interactions in a swirl cup airblast fuel injector: Outer and inner swirlers mass flow ratio

The swirl cup airblast fuel injector is widely used in modern low-emission gas turbine combustors. It is important to understand the underlying physics in the interaction between fuel spray and complex swirling airflow. This study systematically investigated the dynamics of swirling flow and spray atomization, examining the influence of the mass flow ratios (Φ) of outer and inner swirlers on spray characteristics. Various laser-based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer (PDPA), and high-speed particle imaging velocimetry (PIV), were employed for this purpose. This study revealed significant interactions between the central toroidal recirculation zone and the swirling jet zone. These interactions altered spray angle, Sauter mean diameter, and droplet velocity, with the inner swirler's impact being more pronounced at lower fuel mass rates (mf=2.0 kg/h). At higher rates (mf=4.0 kg/h), the influence of both swirlers diminished. PDPA-measured droplet velocities were lower than PIV results for smaller droplets, especially at high rates, emphasizing the role of collision-coalescence dynamics in spray distribution.