Reconsidering the flammability diagram for CH4/O2/N2 and CH4/O2/CO2 mixtures in light of combustion-induced Rapid Phase Transition

n recent works, we have demonstrated both experimentally and theoretically the occurrence of strong pressure shocks due to Rapid Phase Transition of water produced by combustion, if oxygen-enriched fuel mixtures are exploded in a non-adiabatic reactor. Indeed, peaks of hundreds of bars, although with very short duration, are observed if ultra-high-frequency acquisition system is adopted.In this work, experimental tests were performed, in a non-adiabatic 5dm3 cylindrical vessel, for methane explosion in oxygen varying fuel concentration and inert concentration and type (CO2, N2). Both flammability limits, following the classical definition, and limits of fuel concentration for the combustion-induced Rapid Phase Transition (cRPT) phenomenon have been found experimentally and justified theoretically. Results are relevant to a range of applications and surely to mitigation/prevention measures. Reconsidering fuel hazards in real process is also mandatory.