Atomization dynamics and heat release of a horizontal oil spray flame under pressurized micro-leakage conditions

Oil spray flames under pressurized micro-leakage frequently occur in industrial and power systems, often resulting in significant economic losses. Previous studies have primarily focused on horizontal spray combustion under confined-space conditions, where suppressed spray–flame interactions lead to an underestimation of heat release, causing predictive models developed under such conditions exhibit significant bias when applied to open-space scenarios. However, the interaction between pre-combustion atomization and heat release characteristics of horizontal spray flames remains largely unexplored. This study experimentally reproduced pressurized micro-leakage using pressure-swirl nozzles of different diameters to investigate the spray morphology and heat release of horizontal flames fueled by 25# transformer oil. High-speed camera, image processing technique, and oxygen depletion calorimetry were employed to capture the temporal evolution of spray morphology, droplet breakup, and heat release rate (HRR). A predictive model for the spray cone angle was systematically developed as a function of nozzle diameter, Reynolds, and Weber numbers. The spray cone angle, a key macroscopic parameter, strongly influences the air entrainment and combustion. To establish the correlation between atomization and flame behaviors, dimensionless parameters governing the spray were integrated with the combustion characteristics to derive a theoretical pre-combustion atomization index, which was then correlated with the measured HRR. A dimensionless HRR prediction model was proposed as Q*=210.6We0.5Re1.47[d32d0]0.67. The results show that pre-combustion atomization and dimensionless spray parameters govern heat release, providing a mechanistic basis for assessing hazards of horizontal spray flames from pressurized micro-leakage.