Tip opening of premixed bunsen flames: Extinction with negative stretch and local Karlovitz number
KAUST DepartmentClean Combustion Research Center
Physical Sciences and Engineering (PSE) Division
Mechanical Engineering Program
Combustion and Laser Diagnostics Laboratory
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AbstractThe characteristics of tip openings in premixed bunsen flames have been studied experimentally by measuring OH radicals from laser-induced fluorescence and tip curvatures from chemiluminescent images. Results showed that the tip opening occurred at a constant equivalence ratio and was independent of the jet velocity in propane/air mixtures. The observation of a local extinction phenomenon of the negatively stretched flame due to the flame curvature could not be consistently explained based on flame stretch or the Karlovitz number, since they varied appreciably with the jet velocity. The concept of the local Karlovitz number (KaL) was introduced, which is defined as the ratio of the characteristic reaction time in the normal direction for a stretched flame to the characteristic flow time in the tangential direction for the stretched flame. The local Karlovitz number maintained a constant value under tip opening conditions, irrespective of the jet velocity. Tip opening occurred at a reasonably constant local Karlovitz number of about ~1.72 when the nitrogen dilution level in propane and n-butane fuels was varied.
SponsorsResearch reported in this publication was supported by Competitive Research Funding from King Abdullah University of Science and Technology (KAUST).
JournalCombustion and Flame