Direct numerical simulation of lean premixed CH4/air and H-2/air flames at high Karlovitz numbers

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Direct numerical simulation of lean premixed CH4/air and H-2/air flames at high Karlovitz numbers. / Carlsson, Henning; Yu, Rixin; Bai, Xue-Song.

I: International Journal of Hydrogen Energy, Vol. 39, Nr. 35, 2014, s. 20216-20232.

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

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T1 - Direct numerical simulation of lean premixed CH4/air and H-2/air flames at high Karlovitz numbers

AU - Carlsson, Henning

AU - Yu, Rixin

AU - Bai, Xue-Song

PY - 2014

Y1 - 2014

N2 - Three-dimensional direct numerical simulation with detailed chemical kinetics of lean premixed CH4/air and H-2/air flames at high Karlovitz numbers (Ka similar to 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 (similar to 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 + O-2+M = HO2 + M in lean H-2/air flames), which results in a significantly enhanced heat release rate at low temperatures. This effect is observed in both CH4/air and H-2/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 H-2/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. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

AB - Three-dimensional direct numerical simulation with detailed chemical kinetics of lean premixed CH4/air and H-2/air flames at high Karlovitz numbers (Ka similar to 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 (similar to 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 + O-2+M = HO2 + M in lean H-2/air flames), which results in a significantly enhanced heat release rate at low temperatures. This effect is observed in both CH4/air and H-2/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 H-2/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. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

KW - Turbulent premixed combustion

KW - Direct numerical simulation

KW - High

KW - Karlovitz number

KW - Detailed chemistry

KW - Differential diffusion

U2 - 10.1016/j.ijhydene.2014.09.173

DO - 10.1016/j.ijhydene.2014.09.173

M3 - Article

VL - 39

SP - 20216

EP - 20232

JO - International Journal of Hydrogen Energy

JF - International Journal of Hydrogen Energy

SN - 1879-3487

IS - 35

ER -