Title page for ETD etd-12182001-171041

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
  • Thermo-acoustic Instabilities
  • Active Combustion Control
  • Linear Phase Shifter
  • Subharmonic Control
  • Pulsed Control
Date of Defense 2001-12-13
Availability unrestricted
Thermoacoustic 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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