الفهرس 
LITERATURE SURVEY.Only 14 pages are availabe for public view
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Abstract
The problem of active control of thermoacoustic
instability that appears in the context of NDx control is
approached by understanding the basic mechanism of
thermo acoustic instability in combustion systems, obtaining
models that describe the behavior of the combustion system
and designing the required stabilizing compensator using the
developed dynamic models.
Experimental verifications of Rayleigh’s criterion, which
is the first attempt to interpret the thennoacoustic instability,
are reviewed and analyzed. Rigorous theoretical derivations
and analytical verifications of Rayleigh’s criterion are
reviewed and extended to include the effect of mass addition
in three dimensions with general boundary conditions.
Combustion modifications for NDx reduction are shown
to be represented by multiple heat and mass sources. A
model that shows how the multiple heat and mass sources
can lead to thermo acoustic instability has been developed.
The model is used to show the conditions under which the
instability can occur in a boiler.
A model that describes the response of the class of
laminar premixed flames to an oscillating flow field has
been developed from first principles. The developed flame dynamics model, has been shown to verify the sensitive time lag model. Then the flame dynamics was transformed into a
transfer function that is suitable for controller design.
Using Galerkin method, the longitudinal acoustic field in
a duct combustor has been modeled in a form of a finite
dimensional dynamic model. Using the acoustics dynamics
and the flame dynamics model, the thermoacoustic
instability is shown to occur due to an unstable feedback
between the unsteady heat release and the acoustic field.
The developed feedback model is used to predict the growth
rate and the frequency of the pressure oscillations at the
onset of instability in a previously published experiment.
A rigorous active control methodology for the class of
laminar premixed combustors has been implemented for
active control of thermo acoustic instability . Using this
methodology, a control system which consists of a microphone,
a loudspeaker and a compensator, has been
designed for stabilizing a laminar premixed combustor.
Compensator design is shown to depend mainly on the
relative positions of the sensor and the actuator with respect
to the acoustic field and the heat source.