Evaluation of limits for effective flame acceleration in hydrogen mixtures

Results of experiments and data analysis on turbulent flame propagation in obstructed channels are presented. The data cover a wide range of mixtures: H-2/air, H-2/air/steam (from lean to rich) at normal and elevated initial temperatures (from 298 to 650 K) and pressures (from 1 to 3 bar); and stoic hiometric H-2/O-2 mixtures diluted with N-2, Ar, He and CO2 at normal initi al conditions. The dataset chosen also covers a wide range of scales exceed ing two orders of magnitude. It is shown that basic flame parameters, such as mixture expansion ratio sigma, Zeldovich number beta and Lewis number Le , can be used to estimate a priori a potential for effective flame accelera tion for a given mixture. Critical conditions for effective flame accelerat ion are suggested in the form of correlations of critical expansion ratio s igma* versus dimensionless effective activation energy. On this basis, limi ts for effective flame acceleration for hydrogen combustibles can be estima ted. Uncertainties in determination of critical sigma* values are discussed . (C) 2001 Elsevier Science Ltd. All rights reserved.