Analysis of flame instability in low-emission tower-type gas turbine combustor with multi-stage methane injection

Abstract

A low-emission tower-type coaxial-staged combustor with a pilot stage, first main stage and second main stage is simulated in this study. The flow field, flame structure, vortex-mixing interaction, and flame instabilities are predicted with large eddy simulation and partially stirred reactor model. Heat radiation is not considered in the simulations. The results show that the maximum of the averaged length and width of the inner recirculation zone are approximately 249.8 and 71.3 mm, respectively. The distributions of the fuel from various stages in the combustor are analyzed based on the respective mixture fractions. The pressure and heat release rate (HRR) in the combustor fluctuate periodically with a frequency of about 373 Hz. Both HRR and pressure fluctuations increase and then decrease with time, and there is a phase difference of 46.1° between them. Due to the combustion instabilities, the flame structures change periodically, including attached flame and lifted V-shaped flame, in one HRR oscillation cycle. Moreover, the swirling flame length also varies periodically with time. As the pilot stage and first main stages are turned-off, the frequency of HRR fluctuations and pressure fluctuations, as well as the flame root dynamics, are significantly affected. It is also found that the effects of the fuel ratio of the first and second main stages have a significant influence on the flame root dynamics, e.g., different degrees of flashback observed in different cases.