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

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Abstract

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.

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Fluid Mechanics and Acoustics

Keywords

  • Turbulent premixed combustion, Direct numerical simulation, High, Karlovitz number, Detailed chemistry, Differential diffusion
Original languageEnglish
Pages (from-to)20216-20232
JournalInternational Journal of Hydrogen Energy
Volume39
Issue number35
Publication statusPublished - 2014
Publication categoryResearch
Peer-reviewedYes