An assessment of stretch effects on a flame tip using the thin flame and thick flame formulations

The tip of a rich laminar premixed methane flame stabilized on a Wolfi slot burner was numerically simulated to study the effects of flame stretch on flame speed. The flame stretch was computed using two different formulations. In the first formulation, the conventional definition of flame stretch, which assumes an infinitesimally thin flame, was employed. The other formulation modeled the flame as a zone of finite thickness and stretch was computed on a surface within that finite volume. For the premixed flames, the flame was well presented by contours of temperature. The flame displacement speed for the stationary flame was obtained as the normal component of the local velocity at the flame surface. The two formulations predicted quantitatively different responses at the flame stretch. The stretch due to variation of flame thickness along the flame surface was the major contributor to this difference.