University of Cambridge > > Hopkinson Seminars > The forced heat release response of stratified flames to acoustic velocity fluctuations

The forced heat release response of stratified flames to acoustic velocity fluctuations

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Combustion instability has long been the primary obstacle to the development and application of advanced GT engines. Flames under nonuniform stoichiometric conditions leave the combustion system more susceptible to the instability. The forced heat release responses of stratified lean-premixed flames to acoustic velocity fluctuations are investigated. A laboratory-scale burner and its boundary conditions were designed to generate high-amplitude acoustic velocity fluctuations in flames subject to well-defined radial equivalence ratio distributions created via a split annular fuel delivery system with a swirling stabilizer. A quartz tube was used as a combustor to generate forced flames. Simultaneous measurements on the oscillations of inlet velocity and heat release rate were carried out. A high speed CMOS camera was used to capture the chemiluminescence images. The measurements show that the flame responses vary significantly depending on the parameters of forcing frequency, equivalence ratio split and velocity fluctuation, for a given mean global power. The modification of the flame structure by stratification changes the nonlinear response of flames to both low and high-amplitude acoustic forcing. The gain of the flame transfer function is larger for the cases of inner flow enrichment under high forcing frequencies. The results confirm previous findings that increasing stratification towards the inner zone increases the gain and susceptibility to instabilities. The reasons are still being investigated, but involve the interaction of the location of the centroid of heat release and the speed of propagation of the perturbation of the velocity along the shear region near the stabilization point.

This talk is part of the Hopkinson Seminars series.

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