The combined effects of chemical reaction order and stoichiometry on nonpremixed edge flames

Abstract

We examined in this work the combined effects of chemical reaction order n and the stoichiometric mixture fraction $Z_s$ on the propagation of nonpremixed edge flames in a counterflow configuration. We began by formulating the problem mathematically using the constant density thermo-diffusive model. The problem was then solved numerically using the finite element method. It has been shown that the reaction order and stoichiometry have an interchangeable role in modifying flame propagation. The study has shown that triple flames exist only for a limited range of values of both the chemical reaction order n and the stoichiometric mixture fraction $Z_s$. Over such values, modifying n and $Z_s$ were found to have a great impact on many characteristics related to the flame structure, such as the flame location, the extent of both the premixed flame wings and the trilling diffusion flame, and the flame curvature. In addition, the flame location was found to vary subjected to the value of the reaction order in a manner similar to that observed by varying the mixture fraction. The study also identified the influence of the fuel Lewis number ${\mathrm{L}\mathrm{e}}_{\mathrm{F}}$ on the flame propagation and was found that the effect of ${\mathrm{L}\mathrm{e}}_{\mathrm{F}}$ is more pronounced when the reaction order differs from unity. Finally, the study has examined the role of the strain rate on the flame propagation and concluded that the effect of the chemical order n is negligible for stoichiometric mixtures but tends to be significant for off-stoichiometric mixtures.

Keywords:

• triple flames
• non-unity Lewis numbers
• counterflow
• stoichiometry
• reaction order

Acknowledgments

The first author would like also to thank the University of Southern California (USC) at the US for hosting him during his sabbatical leave.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The first author would like to thank Taif University for supporting this paper under the Taif University Researchers Supporting Project number (TURSP-2020/118), Taif University, Taif, Saudi Arabia.