On non-Huygens flame configuration in stagnation flow

Abstract

The stagnation flow has been extensively used for stretched flame analysis because the flow field is defined by a single parameter, namely the stretch rate. Thus when the flame exists in the planar configuration the effects of stretch on the flame response can be studied without complications due to flame curvature. However, a recent theoretical study has demonstrated that several nonplanar configurations are also possible in such a flow. The analysis further shows the presence of flame surface discontinuities in the form of sharp edges. This discontinuous behavior is in variance with experimental observations that these edges, while appearing sharp, are smooth. It is reasonable to expect that such discontinuities are caused by the Huygens assumption of a constant flame speed over the flame surface, and they would be rounded off when flame stretch effects are accounted for. The objective of this communication is to extend the Huygens limit analysis of these stagnation flame configurations to include the effect of stretch. In particular the authors shall show that the inner structure of these edges is identical to that of the Bunsen flame tip, hence providing a unified understanding of the properties of these sharply curved flames.