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Title: Experimental investigation of the response of turbulent premixed flames to acoustic oscillations
Author: Balachandran, R.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2005
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The first part of the thesis describes an experimental investigation of forced lean fully premixed turbulent flames with special emphasis placed on the amplitude dependence of their response. The heat release rate estimates from HO*/CH* chemiluminescence, flame surface density (FSD) from OH Planar Laser Induced Fluorescence (PLIF), and reaction rate (RX) imaging using simultaneous CH2O and OH PLIF were used. The heat release response became non-linear after inlet velocity amplitudes of around 15% of the bulk velocity. This value depended on the forcing frequency and the equivalence ratio. The non-linearity was found to occur when the shear layers rolled-up into vortices. These vortices not only generated flame area when the flame wrapped around them, but also caused large-scale flame annihilation events. The results suggest that the flame kinematics play the major role in the saturation mechanism in these flames. The second part of the thesis describes the experimental investigation of the response of imperfectly premixed flames to acoustic oscillations. The results suggest that the flame response was controlled by two mechanisms, namely equivalence ratio perturbations and flame kinematics. The former mechanism dominated in low frequency conditions, under which the flame was compact, resulting in nonlinear amplitude dependence. The flame kinematics seemed to play an important role only when the flame length was comparable to the acoustic wave-lengths. The forced flame measurements were finally compared successfully with the response to self-excited flames which suggests that the mechanism of heat release variation investigated in the forced response studies is representative of the true limit-cycle behaviour of self-excited flames.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available