Explanation of the blowoff of inverted flames by the area-increase concept

Abstract

An experimental study of a laminar, two-dimensional inverted flame established in the wake of a thin plate inserted into the interior of the premixed gas stream was performed, and the effects of the radius of curvature of the very base of the flame on the blowoff limit were examined in detail. Experimental results show that as the boundary velocity gradient at the trailing edge of the plate is increased, the distance from the trailing edge to the flame base increases, whereas the radius of curvature of the flame base decreases. The critical radii of curvature at the blowoff limits tend to approach a constant value independent of the plate thickness when it is small. A single curve for the critical area-increase factors-namely, for the fractional area increases from the ignition plane to the front edge of the preheat zone for the flame base at the blowoff limits-can be drawn through the data points except for the thicker plate, and the blowoff is more directly correlated to the factor based on the area-increase concept than to the socalled Karlovitz number that has been used so far.