The Effect of Volume Expansion on the Propagation of Wrinkled Laminar Premixed Flame

Abstract

Past studies using G-equation successfully described the effect of flame stretch on the laminar flame propagation. In those studies, flames were regarded as a passive interface that did not influence the flow field. The experimental evidences, however, suggested that flow field was significantly modified by the flames as the burned gas expanded at the flame. A method using G-equation and Biot-Savart law to approximate induced velocity field is described to estimate the effect of volume expansion. Present method was applied to initially wrinkled and planar flames propagating in an imposed velocity field and the average flame speed was evaluated from the ratio of simulated flame surface area and projected area of unburned stream channel. It was found that the initial wrinkling of flame could not sustain itself without velocity disturbance but decayed into planar flame. The rate of decay of the wrinkles increased as the volume expansion ratio increased. The asymptotic change in the average burning speed occurred only in a disturbed velocity field. The average burning speed was always affected by the volume expansion that directly influenced the velocity field. With relatively small expansion ratio of 3, the average flame speed increased 10%. The comparison of the relative significance of volume expansion and flame stretch suggested that the effect of volume expansion was no less important than that of flame stretch and warranted that both of the effects should be taken into account in the simulation of flame propagation.