Structure of Turbulent Jet Flames Stabilized in Annular Air Jet

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Abstract
—Flame features and combustion process of fuel rich double concentric turbulent jet flames were experimentally examined. Flame appearances are very different by the velocity of the annular air jet Uam (or mass velocity ratio λ). The flames of λ = 0.25 and 0.50 for small values of Uam appear to be the conventional wrinkled laminar flames, however, for λ more than 0.74, the crowded flame appears as the result of the unburnt fuels being torn by the strong shear stress of the annular air jet and the torn–unburnt fuel crowds are intermittently ejected from the recirculation wake zone. This fact was verified by the analyses of the motion pictures and also supported by calculations of the combustion process using experimental results. Moreover, from measurements of the temperature fluctuation of the crowded flame in λ = 1.00, it was found that a comparatively high frequency fluctuation of 200∼300 Hz was superimposed on the low frequency fluctuation of 20∼50 Hz. The former corresponds with that of the motion pictures and the latter is caused by the unsteady motion of the merging point which affects the whole downstream region.