Type of Document Master's Thesis Author Carson, J. Matthew URN etd-12182001-171041 Title Subharmonic and Non-Subharmonic Pulsed Control of Thermoacoustic Instabilities: Analysis and Experiment Degree Master of Science Department Mechanical Engineering Advisory Committee
Advisor Name Title Saunders, William R. Committee Chair Baumann, William T. Committee Member Leo, Donald Committee Member Keywords
- Thermo-acoustic Instabilities
- Active Combustion Control
- Linear Phase Shifter
- Subharmonic Control
- Pulsed Control
Date of Defense 2001-12-13 Availability unrestricted AbstractThermoacoustic instabilities are a problem in modern pre-mixed combustors causing reduced
performance and leading in the extreme to combustor failure from excessive pressure cycles.
Much work has been done using linear controllers to eliminate these instabilities. Many
experimenters in the field have used pulsed and subharmonic fuel controllers to eliminate
these instabilities, but very little investigative work has been done on these controllers.
The goal of this work is to explain the mechanism of control behind pulsed controllers. It
is shown that the combustion system can be treated as a linear system, thus meaning that
frequency components of the control signal at the desired instability frequency are the
dominant means of control, with nonlinear effects only serving to slightly reduce the gain
necessary for control. Fourier analysis is thus performed on pulsed signals and the
components analyzed, showing that there will indeed be a component of a pulsed signal at the
frequency of the instability, aside from a few select cases. It is then proven that this
frequency component is largely responsible for control of the thermoacoustic system using
proportional height pulse train signals, which will change pulse height based on the
amplitude of the instability. This analysis is then used to predict the height of
instabilities resulting from the use of fixed height pulse control signals. Finally,
numerical simulations and experimental observations support the analytical constructs.
Acoustic control is mainly used for these experiments, although some preliminary work with
liquid fuel controllers is also presented.
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