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

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Author

Summary, in English

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.

Publishing year

2014

Language

English

Pages

20216-20232

Publication/Series

International Journal of Hydrogen Energy

Volume

39

Issue

35

Document type

Journal article

Publisher

Elsevier

Topic

  • Fluid Mechanics and Acoustics

Keywords

  • Turbulent premixed combustion
  • Direct numerical simulation
  • High
  • Karlovitz number
  • Detailed chemistry
  • Differential diffusion

Status

Published

ISBN/ISSN/Other

  • ISSN: 1879-3487