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A consistent flamelet formulation for a reacting char particle considering curvature effects

Xu, H. and Hunger, F. and Vascellari, M. and Hasse, C. (2013):
A consistent flamelet formulation for a reacting char particle considering curvature effects.
In: Combustion and Flame, pp. 2540-2558, 160, (11), ISSN 0010-2180, DOI: 10.1016/j.combustflame.2013.06.006, [Online-Edition: http://dx.doi.org/10.1016/j.combustflame.2013.06.006],
[Article]

Abstract

Abstract In the present work, the combustion of a single char particle in quiescent and convective environments is investigated numerically. Fully resolved {CFD} calculations are carried out considering heterogeneous reactions at the particle surface and detailed homogeneous reactions in the gas phase. Unity and non-unity Lewis number diffusion modeling approaches are employed and compared to each other. The flame shape of the particle in a quiescent atmosphere shows full symmetry whereas the particle in the convective environment exhibits a stagnation region upstream of the particle and a wake region downstream of the particle. The detailed {CFD} results are used to analyze the flame structure around the char particle and corresponding flamelet simulations are carried out. For the presently investigated case, curvature effects of mixture fraction, species and temperature are found to be significant in almost all the cases. These curvature effects correspond to diffusion tangential to iso-surfaces of mixture fraction. To describe these processes, new extended flamelet equations are derived. The individual terms in the flamelet equations are analyzed for both the quiescent and the convective environment based on the {CFD} data and the results confirm the importance of tangential diffusion. Except for the quiescent environment and unity Lewis numbers, curvature cannot be neglected for the investigated char combustion case. For all other cases, significant differences between the standard flamelet model and the detailed {CFD} results are found. On the other hand, applying the extended flamelet equations yields very good agreement with the {CFD} results.

Item Type: Article
Erschienen: 2013
Creators: Xu, H. and Hunger, F. and Vascellari, M. and Hasse, C.
Title: A consistent flamelet formulation for a reacting char particle considering curvature effects
Language: English
Abstract:

Abstract In the present work, the combustion of a single char particle in quiescent and convective environments is investigated numerically. Fully resolved {CFD} calculations are carried out considering heterogeneous reactions at the particle surface and detailed homogeneous reactions in the gas phase. Unity and non-unity Lewis number diffusion modeling approaches are employed and compared to each other. The flame shape of the particle in a quiescent atmosphere shows full symmetry whereas the particle in the convective environment exhibits a stagnation region upstream of the particle and a wake region downstream of the particle. The detailed {CFD} results are used to analyze the flame structure around the char particle and corresponding flamelet simulations are carried out. For the presently investigated case, curvature effects of mixture fraction, species and temperature are found to be significant in almost all the cases. These curvature effects correspond to diffusion tangential to iso-surfaces of mixture fraction. To describe these processes, new extended flamelet equations are derived. The individual terms in the flamelet equations are analyzed for both the quiescent and the convective environment based on the {CFD} data and the results confirm the importance of tangential diffusion. Except for the quiescent environment and unity Lewis numbers, curvature cannot be neglected for the investigated char combustion case. For all other cases, significant differences between the standard flamelet model and the detailed {CFD} results are found. On the other hand, applying the extended flamelet equations yields very good agreement with the {CFD} results.

Journal or Publication Title: Combustion and Flame
Volume: 160
Number: 11
Uncontrolled Keywords: Char combustion, coal, Non-premixed flamelet, Differential diffusion, Curvature, Tangential diffusion
Divisions: 16 Department of Mechanical Engineering > Simulation of reactive Thermo-Fluid Systems (STFS)
16 Department of Mechanical Engineering
Date Deposited: 30 Nov 2017 13:36
DOI: 10.1016/j.combustflame.2013.06.006
Official URL: http://dx.doi.org/10.1016/j.combustflame.2013.06.006
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