الفهرس 
LITERATURE SURVEYOnly 14 pages are availabe for public view
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Abstract
Thermoacoustic instability occurs due to the interaction between the
unsteady heat release from a flame and the acoustic field in combustion systems. In the present
investigation this phenomenon has been studied both experimentally and theoretically with the
objective of gaining more insight into and understanding. of the physical parameters inducing
instability, modeling of the phenomenon and designing a robust and active control system in order
to stabilize such combustors.
A test rig which employs a model combustor consisting of a bunsen burner and a long tube and
together with all the necessary measuring equipment has been set up to study and investigate the
phenomenon of thermoacoustic instability in laminar premixed flames. Measurements carried out at
different locations of the flame over the bottom quarter of the tube have shown that the noise,
pressure oscillations, due to the inception of instability consists mainly of the fundamental
frequency of the tube, which oscillates around 300 Hz.
A theoretical model describing the coupling between the unsteady heat release and the pressure
oscillation in laminar premixed combustors has been solved numerically. The model assumes the flow
to be one dimensional and neglects the transport properties of the fluid. Good agreement has been
obtained between experimental results and numerical predictions. Numerical results obtained using
the verified theoretical model have shown that the growth rate of thermoacoustic instability is
influenced by the flame location with respect to the mode shape, and by the frequency in the tube.
For flame located at the lower quarter of the tube the pressure oscillation grows, and for flame
located at the upper half of the tube the pressure oscillation decays.
The mathematical model of the premixed combustor has been obtained by experimental
identification to design a robust and economical
compensator. To obtain this mathematical model, the frequency response of the combustor with a
stabilizing controller has been measured.
The controller, which was used to stabilize the combustor has been built using the principle of
”antisound”. Therefore, the controller consists of: (1) a microphone to pick up the sound of the
combustor, (2) a compensator contains a band pass filter to pass frequencies in the range
corresponding to the fundamental frequency producing instability, and an amplifier and phase
shifter to provide the required gain and phase shift respectively, (3) and a loudspeaker to convert
the electrical signal to a sound out of phase with the original sound.
The experimental identification has been carried out by measuring the frequency response of the
stabilized combustor and the compensator. Measuring these responses has been carried out by
exciting each of them with a sinusoidal signal from a wave generator. The gain and phase shift was
measured · off the oscilloscope screen. Knowing the frequency response of the compensator and the
feed back system, the frequency response and hence the mathematical model of the combustor has been
obtained.
The mathematical model of the premixed combustor has been used to design a compensator by using the
linear quadratic regulator (LQR) method. A Comparison between the response of the combustor when
it was stabilized by the compensator which was built by trial and error, and when the combustor is
stabilized with the compensator which is designed using the mathematical model, has shown that the
performance of the latter compensator is superior to that of the first compensator, in the settling
time and the control effort.
To conclude, active control of the thermoacoustic instability in combustor due to the excitation of
fundamental frequency has been successfully carried out. The mathematical model which enable the
designer to design the proper compensator for such combustors has been deduced using identification
techniques. It has been shown that the model can be used to design the optimum active control
system for such category of combustors.