Swirling flow and spray atomization interactions in a swirl cup airblast fuel injector: Outer swirler effect

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. The present study investigates a swirl cup airblast fuel injector's swirling flow and spray atomization characteristics. Various laser-based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer, and high-speed particle imaging velocimetry, were employed for this purpose. The swirl cup airblast fuel injectors, featuring different outer swirler swirl numbers (0.8<SN<1.8) and inner–outer relative swirling directions, were investigated in an air Reynolds number ranging from 0.77 × 106 to 1.16 × 106 and a 2 kg/h constant kerosene mass flow rate. The results showed that, since the swirler relative direction showed a significant influence on the inner swirler induced central toroidal recirculation zone and outer swirler induced swirling jet zone, the interaction between spray and swirling airflow was changed. Therefore, spray angle, Sauter mean diameter, and droplet velocity were changed by the swirler relative direction. Moreover, the effect of swirl number on the spray characteristics was found to be different for co- and counter-direction swirler configurations.