Laminar premixed flame propagation using large axial velocity variation

Abstract

A stabilization condition for the premixed flame in a tube was investigated, and then a mean velocity variation larger than the burning velocity was introduced to the stabilized flame for a period longer than the reaction time scale in order to examine the unsteady behavior of flame propagation. The stabilized flames were classified into two regimes, a one-dimensional regime and a two-dimensional regime, by both the shape and the mass consumption rate. The magnitude and period of the mean velocity variation were treated as experimental parameters. When the large velocity variation was introduced in the same direction as the initial mean velocity, the extinction behaviors were observed and systematically classified into two groups: extinction by boundary layer and extinction by acoustic instability. We found out that there exists a critical velocity change and a critical time above which the extinction region develops to the center of the tube and extinguishes the flame. With the velocity variation in the opposite direction of the initial mean velocity, the flame was not extinguished near the wall, and the characteristics of the flame propagation were similar to those of earlier studies on flame propagation. The mechanism of the extinction near the wall is explained by the flame stretch theory, which provides a clue to the stretch effects on the finger flame.