The explosion characteristics of methane, hydrogen and their mixtures: A computational study

The maximum pressure rise rate during gas explosions in enclosures and the deflagration index are important explosion characteristics of premixture. They can be used to quantify the potential severity of an explosion. However, there are large discrepancies in the deflagration index measured by different researchers for the same methane/air or hydrogen/air mixture. In this study, outwardly propagating spherical flames in a closed vessel are simulated by considering detailed chemistry as well as temperature-dependent thermal and transport properties. From simulation, the maximum pressure rise rate and deflagration index of methane, hydrogen and their mixtures are obtained. The influence of equivalence ratio, initial temperature and initial pressure on the maximum pressure rise rate and deflagration index is examined. It is found that the deflagration index has not been accurately measured in previous experiments, and that experiments conducted in cylindrical vessels have under-predicted greatly the deflagration index. For hydrogen/methane mixtures with hydrogen blending level above 70%, the deflagration index is observed to increase exponentially with hydrogen blending level. Moreover, the deflagration index is found to be greatly affected by initial pressure; while the initial temperature has little influence on deflagration index. Finally, based on theoretical analysis we propose a correlation to calculate the maximum pressure rise rate and deflagration index of methane at a broad range of initial pressure. The performance of this correlation is examined and it is demonstrated to provide accurate prediction.