Active Instability Control (AIC) of Spray Combustors by Modulation of the Liquid Fuel Flow Rate

Abstract

Abstract Existing papers on active control of combustion instabilities (AIC) mainly deal with combustion systems for gaseous fuel, with loudspeakers serving as interference sources in the combustion process. In this paper, an actuator for liquid fuel is described, which makes it possible to influence combustion actively within a broad frequency range. The structure and function of this control element, called piezo actuator, is described more closely. In particular, the transfer function between excitation of the actuator and the modulation of the fuel flow rate is dealt with, because it provides clues as lo how the modulated fuel flow rate can be used for attenuating oscillations by active control. The additional use of the acoustic resonance in the fuel supply leads to an enhanced effectiveness of the piezo actuator. The performance of the actuator is demonstrated on a diesel-oil-based turbulent laboratory burner exhibiting strong self-excited combustion oscillations. A reduction in the sound pressure amplitude of up to 40 dB is obtained.