This paper describes an experimental investigation of Flame Transfer Function (FTF) behavior where the response of a swirl-stabilized, natural gas fueled combustor is measured for partially premixed conditions. Controlled perturbations of the combustor inlet flows are produced using a siren and the combustor response is observed using several measurement techniques. The fuel/air equivalence ratio fluctuation is measured using a diode laser absorption sensor operating near 1.6 μm. Measurements of global heat release perturbations are obtained using a three-color optical emission technique and velocity measurements are obtained using the two-microphone method. FTFs are derived from these measurements for a frequency range commensurate with field-observed tones. Typical experimental investigations of dynamic signals involve the use of Fourier methods to obtain average signal amplitudes and phase. In this investigation, standard Fourier techniques are used to verify the driving frequencies, but they are coupled with a homodyne detection algorithm to measure time-dependent gain and phase behavior of a FTF.

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