Stabilization process of a lifted flame tuned by acoustic excitation

Abstract

Acoustically tuned lift-off flame with good repetition of the global flame stabilization process is used for detailed measurements and analysis using the line Raman spectroscopy and laser-induced fluorescence techniques, which are usually single shot with low repetition, to delineate the stabilization process and to verify the various theories and findings concerning the lift-off flame stabilization mechanism. The laser diagnostic results show that the flame base is found to locate in lean mixtures for all the phase angles, and water vapor of combustion products are found upstream of the flame base. These results support Broadwell, Dahm, and Mungal's (1984) large-scale re-entrainment model. The current Raman results of mixture fraction and scalar dissipation rate on lifted flames can further substantiate Everest, Feikema, and Driscoll's (1996) cold flow results and Ashurst and Williams' (1990) simulation, and extend Everest, Feikema, and Driscoll's stabilization model. The stabilization process of the flame propagation and recession of a lifted flame in an oscillation cycle is described by the evolution of the upstream large-scale vortex and the induced strain and dissipation rate on the flammable layer and the flame base.