Experimental Study On The Thermoacoustic Characteristics Of Multi-Nozzles Swirl-Stabilized Lean Premixed Model Combustor Under Different Fuel- Mixing Distance

Abstract This study investigated the effects of varying fuel-mixing distances on flame structure and self-excited thermoacoustic oscillations in a premixed model combustion chamber equipped with multi-swirl nozzles, operating under atmospheric pressure with methane fuel at an adiabatic flame temperature of 1873 K. Dynamic pressure sensors were used to acquire pressure signals, while a combination of analytical techniques —including Fast Fourier Transform (FFT), Proper Orthogonal Decomposition (POD), and phase-space reconstruction—was applied to comprehensively characterize the pressure pulsations within the combustion chamber and the coherent structures in the reaction zone. High-speed OH* chemiluminescence imaging was employed to capture time-resolved data of the heat release region, enabling insight into how mixing distance influences flame dynamics. The results show that increasing the mixing distance between nozzles induces periodic transition in thermoacoustic instability, following a sequence of oscillation, stabilization, re-oscillation and eventual attenuation. The asymmetry introduced by differential mixing distance alters the primary location of heat release, and the axial and azimuthal centers of intensity exhibit distinct responses to changes in mixing distance. These spatial shifts create a time-delay effect between convective and acoustic responses, which can be leveraged to suppress thermoacoustic oscillations. This control strategy demonstrates locally optimal performance, offering valuable guidance for mitigating thermoacoustic instabilities in similar multi-swirl combustor configurations