| Summary: | 碩士 === 淡江大學 === 機械工程學系 === 84 === This research is concerned with the experimental
investigations of self-excited oscillations in a combustor with
premixed flames stabilizedon a burner surface located at one end
of a rectangular duct. These studieswere conducted by using
photomultiplier tube for the flame radiation measurements, Laser
Doppler Velocimetry(LDV) for the oscillatory
velocitymeasurements and pressure transducer for the oscillatory
pressure measurements.The obtained data were analyzed by the
methods of Rayleigh criterion andacoustic admittance. Results of
this study show that self-excited flame oscillations were
observed at certain flow velocities and equivalence ratios,which
depend on the duct configurations and the burner assemblies.
Velocitymeasurements show that flow recirculation occur at
downstream of the flame.However, no vortex shedding were
observed, indroting that the self-excited flame oscillation is
not caused by the hydrodynamic instability. Results of the flame
radiation studies indicated that the flame induce higher
intensity of pressure oscillation with lager values of the
Rayleigh integral, whichfulfills the Rayleigh criterion. In
addition, The intensity of pressure oscillation depends on the
flow velocities and the equivalence ratios. The admittance
studies show that the imaginary part of the cold admittance
playsan important role in the self-excited flame oscillation.
The necessary condition for the flame exhibiting self-excited
oscillation is with positiveimagiray part of the cold
admittance. The frequency of the self-excited flameoscillation
does not always occur at the frequency where the flame provides
the maximum amount energy to the acoustic field. The natural
frequencies of the experimental duct are also important in the
flame and pressure oscillation.
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