To investigate the combustion instability of the premixed swirling tubular flame

the responses characteristics of methane/air premixed flames to longitudinal acoustic field was experimentally studied with different air volume flow rates and methane equivalent ratios. The dynamic response range of flame to different acoustic frequencies was revealed

and the variation of flame structure

acoustic pressure and OH* fluctuations under acoustics perturbation were studied. The results showed that the flame presented the low-pass filtering characteristic

demonstrating very weak response to the high acoustic frequency. For middle and low acoustic frequency

the flame was forced to oscillate at the same frequency

and even quenched at a lower acoustic frequency. In addition

the low-pass filtering behaviors were slightly affected by the flow rate and equivalent ratio. According to the calculated extinction strain rate

near lean extinction limit (eg

equivalence ratio equaling to 065)

the flame was much sensitive to middle acoustic frequency owing to low extinction strain rate

generally presenting flame lift-off.