Measurement of flame transfer functions in swirl-stabilized, lean-premixed combustion

Results of ongoing experimental measurements of lean-premixed combustion flame dynamics, necessary to further predictive capabilities of models for combustion instabilities, was studied. Two possible mechanisms were considered for the study, including coupling through velocity and equivalence ratio oscillations. Experiments were carried out on a rig specifically designed for gaseous, premixed, turbulent combustion experiments. Swirl was generated by a fixed-vane swirler with vanes at a 30 deg angle to the flow axis. Fuel flows were specified to provide mean equivalence ratios for both natural gas and propane. The flame output was measured relative to each of these perturbations, resulting in the FTF. Low-frequency gain exhibited an increasing trend with respect to mean equivalence ratio for the case of velocity perturbations, but remained practically constant for the case of equivalence ratio perturbations. Time delay was slightly shorter for equivalence ratio perturbations, however, no significant variation in the delay is observed between fuels.