Inhibition of premixed methane-air flames with CF₃I

This paper presents a systematic computational study of the inhibition of premixed flames of short chain hydrocarbons with CF₃I, focusing on sensitivity analysis of the (normalized) burning velocity and reaction pathway analysis using the "iodine-flux" approach. A comprehensive kinetic mechanism was obtained by combining the GRI, hydrofluorocarbon and CF₃I sub-mechanisms, and updating the rates of some of the elementary reactions. Calculations were performed using the PREMIX computer code in the CHEMKIN suite of computer codes. The updated mechanism yielded estimates of the normalized laminar burning velocities which concurs closely with published measurements. The sensitivity analysis resulted in a positive coefficient for CF₃I + M → CF₃ + I + M, confirming the promoting effect of CF₃I on the laminar flame velocity and is consistent with previous studies. Reaction pathways were drawn for stoichiometric, fuel-lean and fuel-rich flames doped with 1 and 2% of CF₃I at atmospheric pressure. The reaction pathway analysis served to identify four major inhibition cycles, denoted as HI → I → HI, HI → I → I₂ → HI, HI → I → CH₃I → HI and HI → I → C₂H₅I → HI. Furthermore, the paper developed a linear expression linking the normalized rate of heat release with the ratio of laminar burning velocities of mitigated and non-mitigated flames, and verified the efficacy of this expression for flames inhibited with CF₃I