The effect of the flame front structure on flame propagation in premixed gases

Abstract

It is well known that the surface of a premixed turbulent flame changes its appearance very quickly and is made of a series of numerous different curvatures. For this reason a so-called “turbulent burning velocity” has been defined as “the ratiobetween the mean volumetric flow rate of the cold mixture and a mean surface around which the burning surface fluctuates”. Final, the turbulent burning velocity depends on the laminar burning velocity as well as on, the way in which the wave is folded. Therefore, the turbulent burning velocity does not indicate anything about the laminar burning velocity in a turbulent flame. In this work experimental data of a pneumatically excited, non-steady laminar flame frontof a methane-air mixture showed that an increasing disturbance of the wave induces an increasing surface, combined with a decreasing laminar burning velocity. It has also been found out that flame stretching, as first described by Karlovitz [2] has been the most important factor of influence on the laminar burning velocity apart from temperature and diffusion effects. Under these aspects further investigations were made in curved stationary premixed flames. They have delivered data on the interaction between flame stretching and laminar burning velocities.