Experimental study of spherical-flame acceleration mechanisms in large-scale propane-air flames

Large-scale experiments examining spherical-flame propagation of propane-air flames up to a diameter of 1.2 m were performed. Throughout these experiments, the growth of the Darrieus-Landau instability was directly observed and detailed measurements show that the increase of flame velocity follows a pattern of self-similar oscillatory growth that has not been previously reported. These oscillations are found to be the result of periodic growth and saturation of a narrow range of length scales that follows each generation of cell formation. Based on these observations, a new method to estimate the fractal-acceleration exponent is proposed based on the amplitude and frequency of these oscillations. Comparisons between the fractal exponents derived by this method and a direct power law fit show reasonable agreement with one another, as well as with values reported by previous studies. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.