Experimental and modeling study of the effect of CF3CHFCF3 on the chemical structure of a methane-oxygen-argon flame

The chemical structure of stoichiometric methane-oxygen-argon flames seeded or not with 1% heptafluoropropane (CF3CHFCF3) was measured by the molecular beam-mass spectrometry technique. Both flames were stabilized on a water-cooled flat-flame burner under low pressure (4.2 kPa). Mole fraction profiles were computed by a simulation code as well. Modeling of the unseeded flame was performed with an updated version of a mechanism issued from Warnatz. Two submechanisms were considered to model the chemistry of fluorinated species: (i) a mechanism proposed by Westbrook to model flame inhibition by CF3Br, (ii) a modified version of (i) validated recently by Sanogo in a modeling study of the effect of C2F6 on a methane flame. Both submechanisms were compared on the basis of their reaction pathways. They have in common a key role played by CF2 in the consumption of the fluorinated additive. The consumption of this radical forms CF that is consumed very slowly with Westbrook mechanism, in contradiction with experimental results. A better agreement is obtained with the modified version so that this study extends and confirms its validation.