Experimental Investigation on the Effect of Inlet Temperature on Thermoacoustic Oscillation in a Centrally-Staged Combustor

Self-excited thermoacoustic oscillations frequently manifest in lean premixed prevaporized (LPP) centrally-staged combustors, impacting the dynamic characteristics of flames and potentially causing damage to combustor components. Due to the susceptibility of thermoacoustic oscillations to passive control factors, this study explores the influences of the combustor inlet air temperature on these oscillations. The two investigated schemes in this study exhibit thermoacoustic oscillations at 400 K, and as the inlet temperature increases, the overall oscillation amplitude of the system decreases, reaching approximately 50 Pa at 600 K. A noteworthy observation is that at 450 K, the oscillation amplitude of the counter-swirl (CNS) scheme exceeds that observed at 400 K. Furthermore, the shapes and CH* chemiluminescence intensities of the flame are determined through time-averaged and Abel-inverted transform methods, allowing for the characterization of the dynamic features of the flame. By combining insights from the local Rayleigh map, it is found that the driving thermoacoustic oscillation occurs at the inner/out shear layer and the region where the main and pilot flames intersect. A stronger thermoacoustic oscillation in a region indicates a more pronounced coupling between pressure and heat release fluctuations. Hence, exploring the mechanism through which the inlet temperature influences thermoacoustic oscillations is beneficial for the design and optimization of the combustor.