TY - JOUR

T1 - Measurement of the resolved flame structure of turbulent premixed flames with constant reynolds number and varied stoichiometry

AU - Soika, Armin

AU - Dinkelacker, Friedrich

AU - Leipertz, Alfred

N1 - Funding Information: The authors gratefully acknowledge financial support for this research by the Deutsche Forschungsgemeinschaft (DFG).

PY - 1998

Y1 - 1998

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=0032270823&partnerID=8YFLogxK

U2 - 10.1016/S0082-0784(98)80473-6

DO - 10.1016/S0082-0784(98)80473-6

M3 - Conference article

AN - SCOPUS:0032270823

VL - 27

SP - 785

EP - 792

JO - Symposium (International) on Combustion

JF - Symposium (International) on Combustion

SN - 0082-0784

IS - 1

T2 - 27th International Symposium on Combustion

Y2 - 2 August 1998 through 7 August 1998

ER -