Thermoacoustic instability and lean blowout (LBO) are investigated experimentally in an atmospheric swirl-stabilized combustor fueled with gaseous propane. Factors affecting combustion instability are identified. Sinusoidal or steady air forcing of either the swirling air shear layer or the fuel line, with less than 1.0% of combustion air, can reduce pressure oscillations amplitude by more than 20 dB. Phase-shifted close-loop air forcing of the flame can reduce the pressure oscillations amplitude by 13 dB. For a constant air flow rate and air inlet temperature, initially smooth turbulent combustion exhibits relatively intense heat release oscillations with decreasing equivalence ratio, followed by a quiet state before blowout. High outer swirl intensity and a rich burning flame stabilization region can effectively extend the LBO limit.
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