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Title of article :
Direct numerical simulation of lean premixed CH4/air and H2/air flames at high Karlovitz numbers
Author/Authors :
Carlsson، نويسنده , , Henning and Yu، نويسنده , , Rixin and Bai، نويسنده , , Xue-Song، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2014
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Abstract :
Three-dimensional direct numerical simulation with detailed chemical kinetics of lean premixed CH4/air and H2/air flames at high Karlovitz numbers (Ka ∼ 1800) is carried out. It is found that the high intensity turbulence along with differential diffusion result in a much more rapid transport of H radicals from the reaction zone to the low temperature unburned mixtures (∼500 K) than that in laminar flamelets. The enhanced concentration of H radicals in the low temperature zone drastically increases the reaction rates of exothermic chain terminating reactions (e.g., H + O2+M = HO2 + M in lean H2/air flames), which results in a significantly enhanced heat release rate at low temperatures. This effect is observed in both CH4/air and H2/air flames and locally, the heat release rate in the low temperature zone can exceed the peak heat release rate of a laminar flamelet. The effects of chemical kinetics and transport properties on the H2/air flame are investigated, from which it is concluded that the enhanced heat release rate in the low temperature zone is a convection–diffusion-reaction phenomenon, and to obtain it, detailed chemistry is essential and detailed transport is important.
Keywords :
Turbulent premixed combustion , detailed chemistry , High Karlovitz number , direct numerical simulation , Differential diffusion
Journal title :
International Journal of Hydrogen Energy
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