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Stability of premixed flames is important in applications involving industrial and domestic impingement heat transfer processes, gas turbine combustion chamber and others. Blowoff limits of premixed methane-air flames stabilised on an uncooled Bunsen type burner is considered in the present experimental work. The effect of burner material, wall thickness and burner exit shape on the blowoff limits is presented. Burner materials covered in this study are stainless steel, brass and pyrex. Wall thicknesses considered are 1 mm, 2 mm and 3 mm for pyrex tubes of 10 mm inside diameter. The burner exit shapes covered in this study are circle, triangle, square and hexagon. The operating mixture Reynolds number range is 800 - 4000. It is found that the burners with low thermal conductivity, larger wall thickness and minimal sided polygon shapes provide better lean blowoff stability. Critical velocity gradient parameter defined on the basis of hydraulic diameter collapses the blowoff limits for all shapes covered in the present study. Correlations for Karlowitz number (Ka) are suggested for the blowoff stability for the various cases studied. The Karlowitz number is found to increase steeply with increase in fuel richness when equivalence ratio (φ) is greater than 1. This is attributed to the secondary reaction zones that provide additional heating of the tube at the stabilisation region. For equivalence ratio less than 1, the dependence of Karlowitz number with equivalence ratio is relatively weak. For turbulent flow, the Karlowitz number is found to be independent of the tube material, thickness and shape. [ABSTRACT FROM AUTHOR]