Premixed Flame Combustion Instability And Its Active Control

NOx emission can be reduced with premixed combustion for it reduces the temperatures of gas turbine combustors. But it is easy for premixed combustion to introduce instability to combustion. The purpose of this thesis is to research characteristics of premixed flame combustion instability and to develop active control technology.Active control of combustion instability is tested on a cold model. Pressure oscillation can be attenuated by the active control system and main frequencies of pressure oscillation can be changed by the active control system.The influence of acoustic perturbation on premixed conical flame is theoretically and experimentally analyzed. A predigested model of flame temperature fluctuation is deduced, and it is predicted that flame temperatures fluctuate at the frequencies of perturbation acoustic. The harmonic, sub-harmonic and multi-harmonic responses of a premixed flame to acoustic perturbation are observed in the experiments.The influence of acoustic perturbation on the wrinkle of premixed V-shape flame is theoretically and experimentally analyzed. Frequencies of the flame wrinkle are the same as the perturbation acoustic, and the amplitudes are smaller as the frequencies rise.The influence of acoustic perturbation on the pressure oscillation of a premixed conical flame combustor is experimentally investigated. The frequencies of pressure oscillation are the same as perturbation acoustic, and the amplitudes rise with the increase of perturbation intensity.Combustion instability related strongly to equivalent rates of fuel/air. The main frequencies of pressure oscillation decrease with the increase of the equivalent rates, and with the increase of the mean pressures of a combustor. The relationship between oscillation frequency and premixed gas flux is complex.To a typical instable combustion, a active control is experimentally investigated. The pressure oscillation is amplified when it oscillates in phase with heat release rate fluctuation, and it is reduced when it oscillates out phase with heat release rate fluctuation.