Measurement of the resolved flame structure of turbulent premixed flames with constant reynolds number and varied stoichiometry

authored by: Armin Soika, Friedrich Dinkelacker, Alfred Leipertz
Abstract: Wire-stabilized premixed methane-air flames have been studied in a grid-generated homogeneous turbulent flow field in order to identify different burning regimes. The planar Rayleigh scattering technique was used with two parallel laser light sheets, which allows the detection of three-dimensional temperature gradients. For a detailed investigation of the flame structure and topology, the modification of the local temperature gradients at different progress variables c due to the turbulent motion was studied by varying the flame stoichiometry and thereby the Karlovitz number Ka while keeping the turbulent Reynolds number Re_t constant at 87 or 134. Because of a nearly Gaussian shaped statistical distribution of the thermal gradients, the 50% median and the width of the distribution are suitable measures used to characterize the flame response. Compared with laminar unstrained calculations, especially very lean flames (φ < 0.55) marked with the highest Karlovitz number (Ka = 4.6) revealed a reduction of the flame thickness of about 30%. This is in contrast to the expected burning regime but fits well with laminar strained calculations. Subsequently, detailed investigations were made to examine the influence of curvature on local thermal gradients. It was found that negatively curved cusps (concave toward the reactants) show a steepening of the flame-temperature profile, while positively curved flame elements can be identified by a retardation of the overall reaction process. In terms of a statistical examination, the widths of the thermal gradient distribution conditioned at different reaction progress variables c were regarded, finding a decrease of the spread with increasing Ka independent of Re_t and c. Based on different curvature radii and perturbation frequencies of the detected flames, we assume that in our experiments the flame response depends more on flame curvature than on effects caused by modification of Ka.
External Organisation(s): Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU Erlangen-Nürnberg)
Type: Conference article
Journal: Symposium (International) on Combustion
Volume: 27
Pages: 785-792
No. of pages: 8
ISSN: 0082-0784
Publication date: 1998
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: General Chemical Engineering, Fuel Technology, Energy Engineering and Power Technology, Mechanical Engineering, Physical and Theoretical Chemistry, Fluid Flow and Transfer Processes
Electronic version(s): https://doi.org/10.1016/S0082-0784(98)80473-6 (Access: Unknown)

BibTeX

@article{56a839a0a1b14d3f9e1f41d5c2521992,
title = "Measurement of the resolved flame structure of turbulent premixed flames with constant reynolds number and varied stoichiometry",
abstract = "Wire-stabilized premixed methane-air flames have been studied in a grid-generated homogeneous turbulent flow field in order to identify different burning regimes. The planar Rayleigh scattering technique was used with two parallel laser light sheets, which allows the detection of three-dimensional temperature gradients. For a detailed investigation of the flame structure and topology, the modification of the local temperature gradients at different progress variables c due to the turbulent motion was studied by varying the flame stoichiometry and thereby the Karlovitz number Ka while keeping the turbulent Reynolds number Ret constant at 87 or 134. Because of a nearly Gaussian shaped statistical distribution of the thermal gradients, the 50% median and the width of the distribution are suitable measures used to characterize the flame response. Compared with laminar unstrained calculations, especially very lean flames (φ < 0.55) marked with the highest Karlovitz number (Ka = 4.6) revealed a reduction of the flame thickness of about 30%. This is in contrast to the expected burning regime but fits well with laminar strained calculations. Subsequently, detailed investigations were made to examine the influence of curvature on local thermal gradients. It was found that negatively curved cusps (concave toward the reactants) show a steepening of the flame-temperature profile, while positively curved flame elements can be identified by a retardation of the overall reaction process. In terms of a statistical examination, the widths of the thermal gradient distribution conditioned at different reaction progress variables c were regarded, finding a decrease of the spread with increasing Ka independent of Ret and c. Based on different curvature radii and perturbation frequencies of the detected flames, we assume that in our experiments the flame response depends more on flame curvature than on effects caused by modification of Ka.",
author = "Armin Soika and Friedrich Dinkelacker and Alfred Leipertz",
note = "Funding Information: The authors gratefully acknowledge financial support for this research by the Deutsche Forschungsgemeinschaft (DFG).; 27th International Symposium on Combustion ; Conference date: 02-08-1998 Through 07-08-1998",
year = "1998",
doi = "10.1016/S0082-0784(98)80473-6",
language = "English",
volume = "27",
pages = "785--792",
journal = "Symposium (International) on Combustion",
issn = "0082-0784",
publisher = "Elsevier Ltd.",
number = "1",
}