Experimental and Numerical Investigations of the Local Behavior Under Thermoacoustic Instability in Spray Swirling Flames

We conducted experiments and numerical simulations of a laboratory-scale spray swirl-stabilized burner to evaluate the local flame behavior under thermoacoustic instability and gain insights into the coupling mechanisms between the flow, spray, and flame near the injection region. Comparison with experimental data shows that the numerical simulation achieves good quantitative agreement in predicting the velocity fields under non-reacting conditions and the main structure of the swirling flame under steady combustion. Phase-averaged results from simulations of flow, spray, and flame dynamics during thermoacoustic instability also exhibit good qualitative agreement with experimental observations. Both experiments and Large Eddy Simulation results indicate a strong in-phase correlation between flame motion and flow aerodynamics during oscillations, while the spray injection remains unchanged. A detailed analysis of local flame behavior under thermoacoustic instability is performed by using the Rayleigh index, the liquid fuel-pressure fluctuation index and the evaporation-pressure fluctuation index. The results reveal that evaporation fluctuations are strongly correlated with the coupling between droplet behavior and thermoacoustic instability, whereas the injection process itself appears to play an inert and damping role in the thermoacoustic instability. Moreover, vortex motion and interactions among evaporation, mass exchange, and reaction processes near the injection zone significantly influence flame oscillations, particularly in the inner branch of the flame. This mechanism highlights the need for further investigation into the complex spray-flame interactions that trigger and control thermoacoustic oscillations at the local level.