Simultaneous OH PLIF/Chemiluminescence and stereoscopic PIV measurements of combustion oscillation onset in turbulent swirling lean premixed flames

Abstract

To yield an effective control to impede the progress of combustion oscillation and to lead to the development of completely stable combustors, it is necessary to reveal the mechanism of the destabilization. For revealing the destabilization characteristics of combustion oscillation, methane-air turbulent lean premixed flames in a swirl-stabilized combustor were investigated by high-speed simultaneous measurements of stereoscopic particle image velocimetry (SPIV) arranged side by side, OH planar laser induced fluorescence (OH PLIF), OH chemiluminescence and pressure fluctuation. The transition process from stable state to unstable state of combustion oscillation is defined based on the root-mean-square (rms) values of pressure fluctuation p’rms. Experimental condition was set as the swirl number of 1.14, equivalence ratio of 0.69 and total flow rate of 350 L/min where the transition process is observed. In the transition process, magnitudes of fluctuating properties gradually gain. Pressure fluctuation phase-based analyses clarified that, as the transition process advances, intermittent large-scale vortical motion in the outside of sheer layer expands and approach the inlet, which has a close affinity with the growth of oscillation with making burnt regions involve unburnt regions. The transition process holds well for the Rayleigh criteria in that heat release fluctuates approximately the same phase of pressure fluctuation. On the other hand, in-flow velocity fluctuates in the antiphase of pressure fluctuation.