Experimental study of spray characteristics of a pressure-swirl atomizer based on air core dynamics

The performance of combustion is heavily influenced by the quality of fuel injection, with pressure-swirl atomizers frequently used in engines due to their simplicity, cost-effectiveness, and reliability. Although extensive experimental research exists on pressure-swirl atomizer sprays, a comprehensive predictive mathematical model and consensus on an accurate droplet size distribution function are still lacking. This study aims to address these gaps by experimentally analyzing key spray characteristics – discharge coefficient, spray cone angle, breakup length, and droplet size distribution – using the imaging technique across a broad range of Reynolds numbers (1250–8500), covering the laminar, transition, and atomization regimes. Results showed that during the transition stage, the discharge coefficient decreased before increasing steadily in the atomization regime, where it eventually stabilized. A similar trend was observed in the spray cone angle throughout the transition and atomization phases based on air core dynamics. In examining droplet size distribution, the Rosin-Rammler function was found to be an inadequate fit. Instead, the gamma distribution effectively described droplet sizes near the primary breakup region, while the log-normal distribution was more accurate for droplets farther from the liquid sheet disintegration point, where secondary breakup dominates. The study also identified a positive correlation between the Reynolds number and the shape parameter of the gamma function in the atomization regime, suggesting smoother ligaments at higher Reynolds numbers. These findings provide critical insights into the influence of flow dynamics on pressure-swirl atomizer spray behavior and offer refined mathematical functions for predicting droplet size distribution. This research has implications for optimizing atomizer design in various applications requiring controlled liquid dispersion, including combustion.