Influences of stretch and curvature on the temperature of stretched cylindrical diffusion flames

The structure of a counterflow-type cylindrical diffusion flame was studied experimentally to determine the effect of stretch and curvature. The cylindrical flame used in this study had a concave curvature with respect to the fuel stream. The fuels used were propane and methane, diluted with nitrogen, argon or helium. Diluent gases were used to change the Lewis number, Lef, of the fuel. Our results indicated that (1) the fuel was preheated to a high temperature by the concentric inward heat flow from the flame because the flame shape is concave curvature with respect to the fuel flow; (2) at constant flame stretch, flame temperature increased with a decrease in flame radius when Lef > 1, but decreased when Lef < 1; and (3) at constant flame radius, flame temperature decreased with increased flame stretch rate when Lef > 1, but increased when Lef < 1.