Investigation on the Instability of Methane/Oxygen Combustion Under High Oxygen Concentration

An inherently safe technique of rapidly mixed type tubular flame combustion was employed to investigate the instability of oxy-fuel combustion of methane with oxygen mole faction of 0.67. The flame structures were analyzed based on CH* images, which were taken by a high speed video camera. Periodical variation was observed, and its frequency was equal to the frequency of acoustic pressure simultaneously measured by an acoustic pressure sensor. The result showed that the pulsation frequency of the combustion heat release rate was almost equal to the frequency of the sound pressure oscillation, this meant thermo-acoustic coupling had taken place in the combustion chamber. Oxy-fuel combustion oscillation mode in the combustor was verified to belong to the axial acoustic resonant mode by calculation and analysis of the sound pressure oscillation frequency. As the equivalence ratio of mixed gas increasing from 0.6 to 1.0, thermo-acoustic coupling in chamber was enhanced by the increasing exothermic energy, the amplitude of low frequency sound pressure oscillation decreased, the amplitude of high frequency sound pressure oscillation increased, and the energy of low frequency vibration was converted to that of high frequency vibration, in which the oscillation cycle of oxy-fuel combustion transferred from double cycle to single.