Experimental Investigation of Thermoacoustic Oscillations in Syngas Premixed Multi-Swirler Model Combustors

This paper presents the experimental results of the thermoacoustic oscillations in several premixed syngas multi-swirler model combustors. Multi-swirler lean premixed combustion technology has been successfully applied to achieve an anticipative stability, lower noise and high efficiency in industrial gas turbines that burn natural gas or distillated oil. However, some critical operational issues, including combustion oscillations, flashback, blowout and autoignition, should be considered and balanced when burning the coal-derived syngas mainly composed of H₂ and CO. In this paper several multi-swirler combustors are tested on an atmospheric-pressure downscaled test rig. Each multi-swirler combustor includes several elemental swirling nozzles with the equal Swirl Number and different array of port configurations. The dynamic pressure, dynamic heat release and critical flashback equivalence ratio are tested in these model combustors burning several kinds of simulated syngases with a similar low heat value. Firstly, the critical equivalence ratios of flashback are shown and compared with those in single-swirler combustors. Secondly, the paper presents the analysis of the temporal and spectral features of dynamic pressure oscillations using many data-processing methods. Thirdly, we describe the bifurcation and retardation phenomenon when the combustion transforms between stable and unstable operations. We also discuss how the equivalence ratio, the fuel composition and the combustor inlet velocity play important roles in determining the amplitudes, the frequencies, the bifurcation and retardation of the thermoacoustic oscillations. Finally, we use a wavelet transformation with a higher resolution in time domain than that with a PSD estimation by the AR model. The processes of amplitude “jump” and flashback are analyzed in details. The results in this paper could improve the current understanding of the nonlinear self-excited and combustion driven thermoacoustic oscillations in gas turbines and give us some references to the development of lean premixed syngas turbines for coal-based IGCC and co-generation systems.