Effects of preferential transport in turbulent bluff-body-stabilized lean premixed CH4/air flames

被引:145
作者
Barlow, Robert S. [1 ]
Dunn, Matthew J. [1 ]
Sweeney, Mark S. [2 ]
Hochgreb, Simone [2 ]
机构
[1] Sandia Natl Labs, Combust Res Facil, Livermore, CA 94550 USA
[2] Univ Cambridge, Dept Engn, Cambridge CB2 1PZ, England
基金
美国能源部; 英国工程与自然科学研究理事会;
关键词
Turbulent premixed flames; Bluff-body flames; Differential diffusion; Preferential transport; Multiscalar diagnostics; DIFFERENTIAL DIFFUSION; LASER DIAGNOSTICS; LEWIS NUMBER; COMBUSTION; TEMPERATURES;
D O I
10.1016/j.combustflame.2011.11.013
中图分类号
O414.1 [热力学];
学科分类号
摘要
Preferential species diffusion is known to have important effects on local flame structure in turbulent premixed flames, and differential diffusion of heat and mass can have significant effects on both local flame structure and global flame parameters, such as turbulent flame speed. However, models for turbulent premixed combustion normally assume that atomic mass fractions are conserved from reactants to fully burnt products. Experiments reported here indicate that this basic assumption may be incorrect for an important class of turbulent flames. Measurements of major species and temperature in the near field of turbulent, bluff-body stabilized, lean premixed methane-air flames (Le = 0.98) reveal significant departures from expected conditional mean compositional structure in the combustion products as well as within the flame. Net increases exceeding 10% in the equivalence ratio and the carbon-to-hydrogen atom ratio are observed across the turbulent flame brush. Corresponding measurements across an unstrained laminar flame at similar equivalence ratio are in close agreement with calculations performed using Chemkin with the GRI 3.0 mechanism and multi-component transport, confirming accuracy of experimental techniques. Results suggest that the large effects observed in the turbulent bluff-body burner are cause by preferential transport of H-2 and H2O through the preheat zone ahead of CO2 and CO, followed by convective transport downstream and away from the local flame brush. This preferential transport effect increases with increasing velocity of reactants past the bluff body and is apparently amplified by the presence of a strong recirculation zone where excess CO2 is accumulated. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
引用
收藏
页码:2563 / 2575
页数:13
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