Stability of propane-air flames in vortex flow

A. E. Potter, Jr., E. L. Wong, A. L. Berlad
naca-tn-4210
Feb 1958


A vortex burner in which the vortex strength could be varied at constant flow rate was used for a study of propane-air vortex flames. The effect of weak vortices on a Bunsen flame was to distort the flame shape slightly. Strong vortices caused the flame to assume an inverted cone shape. Since this flame did not touch the burner, it was stabilized by a different mechanism from an ordinary Bunsen flame. The stability limits of propane-air flames in strong vortices were measured. The blow-off velocity varied to the 0.73 power of vortex strength and increased slightly with fuel concentration at constant vortex strength. Reverse flow was observed in both cold flow and in flames. It appears that flames in strong vortices are stabilized by a stagnation or near-stagnation region induced by a pressure defect at the vortex center. When the vortex strength was made large, the pressure defect at the vortex center drew ambient air into the flame. This causes partial quenching of lean flames. Hydrogen peroxide, formaldehyde, higher aldehydes, methanol, hydrogen, and carbon monoxide were found in the combustion products of lean flames in strong vortices.

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