Subharmonic and Non-Subharmonic Pulsed Control of Thermoacoustic Instabilities: Analysis and Experiment

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.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Mechanical Engineering

Department dc:contributor.department

Mechanical Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2001

Author dc:creator

• Carson, J. Matthew

Chair dc:contributor.committeechair

• Saunders, William R.

Committee members dc:contributor.committeemember

• Leo, Donald
• Baumann, William T.

• Thermo-acoustic Instabilities
• Active Combustion Control
• Linear Phase Shifter
• Subharmonic Control
• Pulsed Control

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-12182001-171041

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/36261