Harnessing Flame Acoustic-Phase Dynamics to Control Thermoacoustic Instabilities in Non-premixed Combustors

Thermoacoustic instabilities pose significant challenges to the safety and efficiency of modern aero-engines, often triggered by complex inlet conditions and flame dynamics. This study explores how the acoustic-phase relationship at the flame location influences the onset and suppression of self-sustained oscillations within a scaled model combustor featuring a bluff-body flameholder. By systematically adjusting the flame’s axial position, we examine its effect on the development of longitudinal acoustic modes. Combining high-speed chemiluminescence imaging with pressure measurements, we reveal how variations in the flame’s acoustic phase modulate the energy transfer mechanisms responsible for oscillation growth. Complementary acoustic simulations, integrating a flame-response model with the Helmholtz equation, identify the precise conditions under which the flame’s acoustic characteristics resonate with the combustor’s natural modes. Our findings demonstrate that repositioning the flame alters the acoustic impedance experienced by the flame—a key factor influencing oscillation amplitude and stability. Specifically, the magnitude of the impedance governs the pressure oscillation strength, while its phase determines the likelihood of instability onset and mode coupling. Detailed acoustic field analyses provide valuable insights into the mechanisms underlying thermoacoustic oscillation initiation and offer pathways for targeted control strategies. Ultimately, this research underscores the critical role of flame acoustic-phase management in advancing stable, high-performance combustion systems.