The extinction characteristics of diffusion flames of methane and butane in counterflow jets under opposing rigid-body rotation are investigated. It is found that the critical volumetric concentration of fuels in nitrogen corresponding to flame extinction decrease to a minimum value and increase thereafter as the jet angular velocity increases. This tendency could be described on the basis of variation of the rate of stretch and eventual breakdown of laminar flow caused by the angular velocity. An absolute mimimum fuel concentration corresponding to local extinction for diffusional burning is identified showing favorable agreement with the existing data. It is established that as the angular velocity of the jets increase, the unbalanced pressure gradients result in radially inward secondary flows. This leads to the development of recirculation zones on both sides of the stagnation plane whose thickness increase with angular velocity. Also, when oxygen enriched air is used, the jet vorticity may result in the formation of a soot layer on the fuel side of diffusion flames. The implications of the study to the modeling of turbulent diffusion flames and soot formation in such flames are discussed.
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