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Inhibition of Premixed Methane-Air Flames by Fluoroethanes and Fluoropropanes.


pdf icon Inhibition of Premixed Methane-Air Flames by Fluoroethanes and Fluoropropanes. (1585 K)
Linteris, G. T.; Burgess, D. R. F., Jr.; Babushok, V. I.; Zachariah, M. R.; Tsang, W.; Westmoreland, P. R.

Combustion and Flame, Vol. 113, No. 1/2, 164-180, April 1998.

Keywords:

chemical inhibition; flame chemistry; flame models; flame retardants; flame speed

Abstract:

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 fluoroporpanes C3HF7 and C3F8. The modeling results are in good agreement with the measurements. At high inhibitor mole fractions, the calculated burning velocities are very sensitive to the values of the specific reaction rate constant for initial inhibitor reaction, whereas at low mole fraction, the flame speed is only moderately sensitive to the rate constants used for reactions of the inhibitor fragments. 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 stiochiometric flames mostly by raising the effective equivalence ratio and lowering the adiabatic flame temperature. For lean flames, the inhibition is primarily kinetic, since inhibitor reaction helps 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.