Inhibition mechanism of CF3CHCl2 (HCFC-123) on H2–O2 combustion based on reactive molecular dynamics simulation

To reduce the risk of hydrogen explosion, CF₃CHCl₂ is considered as a promising flame inhibitor. However, the inhibitory kinetic mechanisms and reaction pathways at the microscopic scale are not yet completely understood. In this study, reactive molecular dynamics simulations (ReaxFF-MD) were conducted to investigate the effects of CF₃CHCl₂ on H₂–O₂ oxidation reaction. The simulations were performed at an initial temperature of 2000 K with CF₃CHCl₂ from 0 % to 10 %. It was revealed that the system temperature dropped and the consumption rate of H₂ and O₂ also decreased due to the dilution effect of CF₃CHCl₂. The initial chain reactions (H₂+O₂→HO₂+H, H+O₂→HO₂, and HO₂+H→H₂O₂) were inhibited after adding CF₃CHCl₂, there by postponing the formation of HO₂ and H₂O₂ radicals. As the reaction progressed, the F and Cl radicals produced from CF₃CHCl₂ combined with H₂, H and OH to form stable HF and HCl molecules through key reactions such as H₂+Cl→HCl+H, H+F→HF and Cl+OH→HCl+O. These reactions competed with the H₂–O₂ chain reactions and reduced the concentration of free radicals (H, OH and O). As CF₃CHCl₂ increased from 0 % to 10 %, the ignition delay time of H₂–O₂ combustion increased from 150 ps to 550 ps, and the activation energy of the one-step oxidation reaction increased from 33.77 kcal/mol to 37.68 kcal/mol. This study demonstrates that CF₃CHCl₂ could be served as a promising inhibitor for hydrogen flame propagation.