Acoustic excitation effects on combustion evolution and soot suppression in jet diffusion flames

This study investigates the multi-scale coupling mechanisms of acoustically modulated soot suppression in non-premixed jet flames using experimental measurements, numerical simulations, and flame transfer function (FTF) analysis. Macroscopically, 500 Hz forcing outperforms 200 Hz in soot suppression; however, both frequencies exhibit pronounced marginal attenuation at high fluctuation amplitudes. Microscopically, the short convective wavelength of 500 Hz excitation induces high-frequency wrinkling and periodic shear vortices. This forced convection elevates the scalar dissipation rate and radially compresses the fuel-rich zone, drastically curtailing the residence time of soot precursors. Flame transfer function analysis elucidates the dynamic origins of the high amplitude attenuation: under intense perturbations, the system exhibits nonlinear gain saturation, and the local phase abruptly shifts toward zero. This phase shift causes the flame response to degenerate from a convection shear dominated mode into an inefficient “bulk piston like pulsation,” dismantling the convective time delay essential for micro mixing. Ultimately, this study establishes the decisive roles of phase coherence and high-frequency wrinkling in optimizing active combustion control.