Effects of curvature on extinction of premixed flames stabilized in stagnation flow

Abstract

Characteristics of laminar premixed flames convex to uniform stream of unburned mixture, which were established in the stagnation region of a jet and the uniform stream opposing each other, were studied experimentally. The effects of flame curvature and the combined effects of the curvature and the Lewis number (Le) on the extinction of the convex flame were discussed, and the results were contrasted with those obtained from premixed flat flames established in the stagnation flow. The main conclusions obtained are summarized as follows: (1) In the lean methane flames of Le=1.0, the convex flames are extinguished close to the stagnation point in the same manner as the flat flames. In the lean propane flames of Le<1.0, the convex flames are extinguished further away from the stagnation point compared with the flat flames. (2) In the lean methane flames of Le=1.0, the flame temperature of the convex flames at the extinction limits is nearly equal to that of the flat flames. In the lean propane flames of Le <1.0, the flame temperature of the convex flames at the extinction is higher than that of the flat flames. (3) In the methane convex flames of Le=1.0, the flame curvature promotes further the incomplete combustion at the head of the convex flame compared with the flat flames, as the flame approaches the extinction limits. In the propane conves flames of Le <1.0, the outflow of heat from the flame is relatively so increased that the flame curvature plays a role to decrease apparently the Lewis number, approaching the extinction.