Near-field spray characteristics and steadiness of a novel twin-fluid injector with enhanced primary atomization

The present study investigates the effect of the internal swirling atomizing air on the injector near-field spray characteristics and spray stability of a novel twin-fluid injector named swirl burst (SB) injector by incorporating an internal swirl. It involves primary atomization by internal bubbling and bubble bursting, and external secondary atomization by shear layer instabilities. A previous design integrated an external swirl and successfully enhanced the secondary atomization. It generated fine droplets immediately, rather than a typical jet core/film of conventional airblast or pressure swirl atomizers. It thus resulted in compact and ultra-clean lean-premixed combustion of distinct fuels, potentially enabling small-core fuel-flexible combustors. The current work aims to further enhance the primary atomization. The near-field flow patten and droplet size distribution and dynamics are investigated using high-speed laser-driven shadowgraph imaging accompanied by the internal bubble visualization. Results reveal that the internal swirl leads to more uniform, smaller and faster-moving bubbles that concentrate at the internal liquid tube tip regardless of the increased flow rates, generating ultra-stable and finer sprays with a wider working range, compared to the injector without the internal swirl. The frequency spectrum analysis of droplet sizes consistently substantiates the significantly improved spray steadiness, enhancing clean spray combustion stability.