Improved atomization using variable aspect ratio air swirlers

In this paper, novel designs of air swirlers having variable aspect ratio (VAR) with variation in hub/tip diameter from swirler inlet to exit are proposed and the performance of VAR swirlers with respect to spray atomization and dispersion is experimentally investigated. A laser Doppler velocimeter is used to track the air velocity field, and high-speed imaging and phase Doppler interferometer are used to measure the spray characteristics. Airflow rate is varied from 0 to 2400 lpm, and liquid injection pressure is varied between 0.1 bar to 3 bar (gauge). The reduction in aspect ratio and flow area in the flow direction leads to acceleration of airflow toward the exit. In addition, higher magnitudes of tangential and radial air velocities are induced near the orifice, which improves spray atomization. The size of the air recirculation zone is also larger for VAR swirlers. At very low liquid injection pressures, with a conventional air swirler, the spray does not open up; also, the radial dispersion of the spray is poor and the variation of average droplet size is very significant. However, a fully developed open spray with finer atomization, better dispersion, and milder spatial variation of droplet size is observed when VAR air swirlers are employed.