Effect of H2O on macroscopic flame behaviors and combustion reaction mechanism of 1,1-difluoroethane (R152a)

1,1-difluoroethane (R152a) is one of the most prospective low GWP refrigerants but may trigger fires and explosions once it leaks. Understanding the flame propagation process and combustion mechanisms at different relative humidity conditions is essential to use flammable refrigerants safely. In this study, a high-speed camera has recorded the flame propagation of R152a combustion near the flammability limit. Combining with macroscopic experimental phenomena, we revealed the effect of H₂O on the microscopic mechanism of R152a combustion by using reactive force field molecular dynamics simulations with a reliable force field. The promotion effects of H₂O on the oxidation of R152a were revealed from an atomistic perspective. The differences of oxidation intermediates and products in different environments were analyzed for the first time. The H₂O/O₂ environment was the most potent promoter of R152a decomposition, followed by the O₂ and the pyrolysis environment. The O₂/H₂O environment reduced the apparent activation energy of R152a, significantly enhanced the consumption rate of R152a, and enriched the number of species. O₂ reacts with H₂O or H to form OH to accelerate the reaction process. The H₂O could provide more OH active fragments for the reaction. Moreover, it promotes the formation of HF and H_2, H₂O + F→HF + OH, H₂O + H→H₂ + HO. This study aims to provide a guiding theory for the safe application and disaster prevention of flammable refrigerants.