Quantitative SLIPI-PIV-PDPA analysis of flow-blurring sprays in a swirling coflowing air stream

This study investigates the effects of coaxial swirling air on flow-blurring (FB) atomization of ethanol sprays using advanced planar and volumetric diagnostics. Structured Laser Illumination Planar Imaging (SLIPI) delivers spatially resolved Sauter Mean Diameter (SMD) and liquid volume fraction (LVF) maps, quantitatively calibrated by phase Doppler particle analyzer, complemented by particle image velocimetry for velocity field characterization. A higher air-to-liquid ratio (ALR) enhances atomization performance by increasing air–liquid momentum exchange and intensifying primary breakup within the FB atomizer. This yields a more concentrated axial spray core and finer droplets, reducing the SMD by up to 50%. Conversely, increasing the swirl airflow rate (SAFR) imparts tangential momentum that broadens the spray cone angle, promotes radial liquid dispersion, and homogenizes both SMD and LVF distributions via aerodynamic shear-induced secondary breakup. A novel non-dimensional SMD correlation, incorporating ALR, Laplace number, swirl-air fraction, and non-dimensional axial/radial positions, accurately predicts SLIPI-derived measurements with a mean absolute percentage error of < 2 0 % across all conditions. Reconstructed three-dimensional droplet fields reveal swirl-enhanced spatial homogeneity. An optimum ALR with moderate-to-high SAFR achieves fine atomization, wide dispersion, and uniform fuel-air mixing, critical for low-emission swirl-stabilized combustors.