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Title: The burning rate of premixed turbulent flames in divergent flows

Abstract

This study presents a means of determining the burning rate of non-one-dimensional premixed turbulent flames based on fundamental principles, which breaks with the convention of using a cold boundary mass flux. The approach is through direct analytical integration of the balance equation for the mean progress variable, [tilde c]. A relationship is derived that shows the importance when calculating the burning rate of considering mean velocity gradients and turbulent transport transverse to the mean turbulent flame and mean flame shape. A position in the flame zone can be identified where the local mass flux normal to the mean flame zone equals the mean rate of creation of products through the turbulent flame. Only at this position can the mass flux be related to a one-dimensional turbulent burning velocity and identified with the mass burning rate. Furthermore, all the quantities necessary to determining the burning rate are readily accessible to experimental measurement. The analysis is valid generally but is applied in detail to stagnation flames because of their relatively simple flow geometry. Under conditions of zero turbulent transport transverse to the mean flame orientation, the burning rate of the flame per unit area is the local mass flux weighted by amore » local gradient in [tilde c] integrated through the flame. Further analysis shows that ignoring nongradient transport would lead to an underestimation of the burning rate. Two special cases of stagnation flows are considered that allow even greater simplifications in calculating the burning rate. Results of a numerical simulation of stagnation flames stabilized in two opposed reactant streams are used to compare the burning rate determined from the above analysis with the value estimated from the cold boundary mass flux. Large differences are observed, especially when [tilde c] < 1 at the stagnation surface.« less

Authors:
;  [1]
  1. Lawrence Berkeley Lab., CA (United States)
Publication Date:
OSTI Identifier:
5181931
Resource Type:
Journal Article
Journal Name:
Combustion and Flame; (United States)
Additional Journal Information:
Journal Volume: 96:4; Journal ID: ISSN 0010-2180
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COMBUSTION KINETICS; MATHEMATICAL MODELS; ONE-DIMENSIONAL CALCULATIONS; STAGNATION POINT; TURBULENT FLOW; CHEMICAL REACTION KINETICS; FLUID FLOW; KINETICS; REACTION KINETICS; 400800* - Combustion, Pyrolysis, & High-Temperature Chemistry

Citation Formats

Shepherd, I G, and Kostiuk, L W. The burning rate of premixed turbulent flames in divergent flows. United States: N. p., 1994. Web. doi:10.1016/0010-2180(94)90105-8.
Shepherd, I G, & Kostiuk, L W. The burning rate of premixed turbulent flames in divergent flows. United States. doi:10.1016/0010-2180(94)90105-8.
Shepherd, I G, and Kostiuk, L W. Tue . "The burning rate of premixed turbulent flames in divergent flows". United States. doi:10.1016/0010-2180(94)90105-8.
@article{osti_5181931,
title = {The burning rate of premixed turbulent flames in divergent flows},
author = {Shepherd, I G and Kostiuk, L W},
abstractNote = {This study presents a means of determining the burning rate of non-one-dimensional premixed turbulent flames based on fundamental principles, which breaks with the convention of using a cold boundary mass flux. The approach is through direct analytical integration of the balance equation for the mean progress variable, [tilde c]. A relationship is derived that shows the importance when calculating the burning rate of considering mean velocity gradients and turbulent transport transverse to the mean turbulent flame and mean flame shape. A position in the flame zone can be identified where the local mass flux normal to the mean flame zone equals the mean rate of creation of products through the turbulent flame. Only at this position can the mass flux be related to a one-dimensional turbulent burning velocity and identified with the mass burning rate. Furthermore, all the quantities necessary to determining the burning rate are readily accessible to experimental measurement. The analysis is valid generally but is applied in detail to stagnation flames because of their relatively simple flow geometry. Under conditions of zero turbulent transport transverse to the mean flame orientation, the burning rate of the flame per unit area is the local mass flux weighted by a local gradient in [tilde c] integrated through the flame. Further analysis shows that ignoring nongradient transport would lead to an underestimation of the burning rate. Two special cases of stagnation flows are considered that allow even greater simplifications in calculating the burning rate. Results of a numerical simulation of stagnation flames stabilized in two opposed reactant streams are used to compare the burning rate determined from the above analysis with the value estimated from the cold boundary mass flux. Large differences are observed, especially when [tilde c] < 1 at the stagnation surface.},
doi = {10.1016/0010-2180(94)90105-8},
journal = {Combustion and Flame; (United States)},
issn = {0010-2180},
number = ,
volume = 96:4,
place = {United States},
year = {1994},
month = {3}
}