Atomization characteristics of self-excited oscillation nozzles based on a gas–liquid two-phase premixed inlet

This study investigates the atomization characteristics of a Coanda-effect-based self-excited oscillation nozzle integrated with air–fuel premixing to mitigate oxidative coking in high thermal load combustion chambers. Three-dimensional unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations using Fluent 2021 R1, coupled with Volume of Fluid (VOF) and Discrete Phase Model (DPM) methods, were conducted to analyze gas–liquid interaction mechanisms. The effects of air–fuel ratio (AFR) and nozzle geometry were examined by an experimental setup comprising a pre-mixing cavity and self-excited oscillation nozzle. Results reveal that increasing AFR reduced velocity gradient extremes in the mixing cavity, decreased jet deflection and low-pressure zones in the external field, and promoted axial droplet aggregation, thereby suppressing spray cone angle expansion. Nozzle size significantly influences behavior: small nozzles (D1.8H1.8, indicating a throat diameter and height both measuring 1.8 mm) stabilize self-excited oscillation frequency at 600 Hz with a maximum deflection angle of 17°, while high shear forces enhance liquid film breakup. Larger nozzles (D4.5H4.5) exhibit slower oscillation frequency increases, decreasing deflection angles, and a higher liquid phase concentration near edges. Atomization analysis shows that under low AFR (<30 %), Sauter Mean Diameter (SMD) reduces by up to 45 %, stabilizing beyond 60 % AFR. Spray cone angle decreases with higher AFR and fuel flow rates. Elevated temperatures lead to a significant reduction in SMD within low AFR ranges (10 %–50 %), with a decrease of 65 μm observed at an AFR of 20 % under a temperature increase of 100 K. In contrast, within high AFR ranges (>50 %), SMD remains stable and exhibits minimal sensitivity to rising air temperatures.