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A new approach to model turbulent lifted CH4/air flame issuing in a vitiated coflow using conditional moment closure coupled with an extinction model

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Title A new approach to model turbulent lifted CH4/air flame issuing in a vitiated coflow using conditional moment closure coupled with an extinction model
 
Creator ROY, RN
KUMAR, S
SREEDHARA, S
 
Subject Conditional moment closure
Flame lift-off height
Methane flame
Extinction model
JET FLAMES
SCALAR DISSIPATION
DIFFUSION FLAMES
STABILIZATION MECHANISMS
MIXTURE FRACTION
CMC SIMULATIONS
COMBUSTION
1ST-ORDER
LIFTOFF
VELOCITY
 
Description In this article, conditional moment closure model (CMC) with detailed chemistry is used to model lifted turbulent methane flame in a high temperature and vitiated coflow and to predict flame lift-off height. The flow and mixing field are predicted by a 2D in-house code employing a k-epsilon turbulence model (RANS) with modified constant C-epsilon 2. The first-order CMC model on its own could not capture the behavior of the lifted flame. Large eddy simulations (LES) coupled with second-order CMC model would be a promising alternative but the objective here was to improve low-cost simulations based on RANS and first-order CMC to address realistic problems. Hence, an extinction model has been incorporated in the first-order CMC to improve its predictions and is referred in this paper as CMCE. In the CMCE model, flame is assumed to be extinguished when the ratio of flow time scale to the chemical time scale falls below a critical value. Predicted lift-off height by the CMCE model agrees very well with the experimental results. There is a significant improvement in temperature and species distributions in both axial and radial directions with the implementation of the CMCE model. Further, the model is extended to predict the flame lift-off height for various coflow temperatures and jet velocities by using scaling ratios. With these modifications, the lift-off heights predicted by the CMCE model match well with the experimental results for a wide range of jet velocities and coflow temperatures. Results from both CMC and CMCE models are compared against the experimental data to show the importance of the extinction model. Flame stabilization process indicates that flame stabilizes on the contour of mean stoichiometric mixture fraction where axial mean velocity equals the turbulent burning velocity. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
 
Publisher ELSEVIER SCIENCE INC
 
Date 2014-12-28T14:10:47Z
2014-12-28T14:10:47Z
2014
 
Type Article
 
Identifier COMBUSTION AND FLAME, 161(1)197-209
0010-2180
1556-2921
http://dx.doi.org/10.1016/j.combustflame.2013.08.007
http://dspace.library.iitb.ac.in/jspui/handle/100/16718
 
Language English