Experimental study on the effects of transverse standing wave frequency and amplitude on oscillation and mode transition of partially premixed flame

Reasonable matching of the acoustic and the combustion field can effectively boost burner power density. This study investigates the oscillation modes of the flame and the mechanism of mode transition under periodic acoustic excitation at different frequencies and amplitudes. Visualize the reaction zone by capturing OH* chemiluminescence images with a 307.15 nm filter and an ICCD camera. The intensity fluctuation of OH* and modal transitions of flame are analyzed using Fast Fourier Transform (FFT) and Proper Orthogonal Decomposition (POD) methods. The results show that flame disturbances from transverse standing waves depend on both the strength and duration of the acoustic field. A displacement oscillation factor (p*/St²) is used to describe how the acoustic field affects the flame front. When p*/St2 is low, the acoustic field causes small-amplitude transverse symmetrical oscillations at the flame's edges. As p*/St² increases, vertical oscillations appear at the flame head, and the oscillation frequency of the flame matches the excitation frequency. High-intensity OH* chemiluminescence region is observed near the oscillation center. When p*/St² is excessive, the acoustic excitation creates macro flow that causes the flame into transverse oscillation, causing local blowout, periodic disruption, and a decrease in OH* intensity. The flame heat release intensity, indicated by OH* brightness, peaks near the condition of flame mode transitions from vertical to transverse oscillation.