Inhibition of premixed methane-air flames by fluoroethanes and fluoropropanes

This paper presents experimental and modeling results for laminar premixed methane-air flames inhibited by the fluoroethanes C2F6, C2HF5, and C2H2F4, and experimental results for the fluoropropanes C3F8 and C3HF7. The modeling results are in good agreement with the measurements with respect to reproducing flame speeds. For the fluoroethanes, calculated flame structures are used to determine the reaction pathways for inhibitor decomposition and the mechanisms of inhibition, as well as to explain the enhanced soot formation observed for the inhibitors C2HF5, C2H2F4, and C3HF7. The agents reduce the burning velocity of rich and stoichiometric flames primarily by raising the effective equivalence ratio and lowering the adiabatic flame temperature. For lean flames, the inhibition is primarily kinetic, since inhibitor reactions help to maintain the final temperature. The peak radical concentrations are reduced beyond that due to the temperature effect through reactions of fluorinated species with radicals. (C) 1998 by The Combustion Institute.