Influence of heat loss, preferential diffusion, and stretch on a conical flame in an impinging jet flow

Abstract

In this study, we aim at studying the structure of a negatively stretched conical methane/air flame in a positively stretched flow under the influence of preferential diffusion, curvature stretch, flow stretch, and external heat loss by using large activation energy asymptotics. Parameters for the open and closed flame tips in the analysis consist of the curvature stretch and aerodynamic straining coupled with Lewis number (Le). The curvature stretch, which is negative stretch or compression, strengthens and weakens the burning intensity of the and conical flame, respectively. The opposite holds for aerodynamic straining, which is positive stretch. Additionally, irrespective of or , the external heat loss weakens the burning intensity and has a significant influence on the structure of conical flame tips. For rich methane/air conical flames (), closed tip solutions are obtained. Furthermore, the burning intensity is enhanced with increasing curvature stretch or decreasing flow stretch. Conversely, the curvature stretch weakens the burning intensity of the lean methane/air conical flames () and eventually leads to tip opening, that is, local flame extinction. The burning intensity is further reduced with the increase of curvature stretch or external heat loss, or with the decrease of flow stretch. Note that the openings become wider for open-tip conical flames when the external heat loss increases or flow stretch decreases.

Keywords:

• conical Bunsen flame
• external heat loss
• impinging jet flow
• Lewis number
• preferential diffusion

Acknowledgments

The authors would like to thank the National Science Council, Taiwan, ROC, for financially supporting this research under contracts NSC91-2212-E-168-014 and NSC98-2221-E-168-036-MY2.