Influence of air swirl orientation on the spray characteristics of a micro-channel-based rotary (MCR) atomizer

Abstract

In this work, we investigate the atomization and spray characteristics of a novel rotary atomizer with micro-channel grooves, using optical diagnostics. Micro-jets emanate from the grooves provided in the rotating injector. The spiraling liquid jets interact with the surrounding high-speed swirling air flow, resulting in the creation of a well-dispersed fine spray. Attention is focused on the effects of air swirler orientation with respect to that of injector rotation. Accordingly, the co- and counter-swirl cases are investigated. The primary jet breakup process is visualized using back-lit illumination technique, which also provides the measurement of jet breakup length. The jet break-up modes are identified for different air swirl strength and orientation and injector rotational speed. The size, number density and velocity components of the spray droplets are measured using PDPA technique at different axial and radial locations. Air velocity is also measured (in the absence of liquid injection) using the LDV technique. In addition, Laser Sheet Imaging (LSI) is employed to investigate the overall spray structure. Results show that the droplet size significantly reduces when air swirl strength or injector rotational speed is increased. Though not much difference is observed in the characteristic droplet size between the co- and counter-swirl cases, the droplet size distribution is narrower and droplet dispersion is improved for the latter. The current findings demonstrate the potential of the rotary injector to dynamically control the spray characteristics as per requirement.