Heat release rate responses to inlet fuel modulations, i.e. the flame transfer function (FTF), are measured for a turbulent, liquid-fueled, swirl-stabilized, LDI combustor. Fuel modulations are achieved using a motor-driven rotary fuel valve designed specially for this purpose, which is capable of fuel modulations up to 1 kHz. Small-amplitude fuel modulations, typically below 2.0% of the mean fuel, are applied in this study. There is almost no change in FTFs at different fuel modulation amplitude, implying that the derived FTFs are linear and that the induced heat release rate oscillations mainly respond to variations in the instantaneous fuel flow rate rather than in the droplet size and distribution. The gain and phases of the FTFs at different air flow rates and preheat temperature are examined. The instantaneous fuel flow rate is determined from pressure measurements upstream of a fuel nozzle. Applications of the FTF to modeling and control of combustion instability and lean blowout are discussed. Near-LBO stability enhancement using small-amplitude fuel modulation based on the output of a LQG controller is numerically demonstrated.

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