Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7717681 | International Journal of Hydrogen Energy | 2014 | 17 Pages |
Abstract
Three-dimensional direct numerical simulation with detailed chemical kinetics of lean premixed CH4/air and H2/air flames at high Karlovitz numbers (Ka â¼Â 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 (â¼500 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
Related Topics
Physical Sciences and Engineering
Chemistry
Electrochemistry
Authors
Henning Carlsson, Rixin Yu, Xue-Song Bai,