Theoretical investigation of flame propagation through compositionally stratified methane-air mixtures

Flame propagation speeds in compositionally stratified methane-air mixtures were theoretically calculated as a function of the equivalence ratio distribution in the unburnt mixture and compared with experimental results. A solution of non-adiabatic flame propagation under a quasi-steady approximation was able qualitatively to describe the experimentally observed characteristics of flame speeds in stratified mixtures, which were flame speed increase in the vicinity of the flammability limits as well as for high equivalence ratio gradients. However, this analysis failed to provide quantitative agreement with the experimental results. In order to address this, the cumulative heat support effects on flame temperature, depending on the history of flame propagation, had to be accounted for. Quantitative agreement with the experiments was achieved, especially for propagation in lean mixtures.