Regime and morphology of polyhedral bunsen flames

Abstract

Intrinsic flamefront cellular instabilities wrinkle, otherwise smooth, laminar flamefronts leading to excess surface area and, thus, burning rate. Since such instabilities increase flame propagation speed and burning rate without any external influence, such as turbulence, they are of both fundamental and practical interest. While extensively studied for freely propagating expanding or planar flames, cellular instabilities can also occur in burner-stabilized premixed flames. In this study, we present an experimental investigation of flamefront polyhedral instability occurring in premixed Bunsen flames for practically relevant lean hydrogen mixtures. Through systematic experiments, we delineate the effect of flame temperature, Lewis number, and flow rate on the stability and morphology of such flames. The results are presented as regime maps to clearly identify the conditions for which the flame manifests the instabilities and further illustrate how the transitional boundaries shift due to changes in experimental conditions. Moreover, the morphology of the flames was also investigated by identifying changes in the polyhedral structure as a function of operating conditions. Finally, we explain the observed dynamics of the polyhedral flames with the aid of analyzes of dispersion relation and residence time.