Influence of water vapor on hydrocarbon combustion in the presence of hydrofluorocarbon agents

The effect of water vapor on hydrocarbon combustion (CH4, C2H4, C3H8) was studied in the presence of an HFC agent (HFC-125). The effect depends on the F/H ratio of the initial mixture. A promotion effect was observed in mixtures with the F/H ratios ranging approximately from 0.9 to 2. The calculated maximum increase in peak flame temperature was in the range of 100-150 K, and in burning velocity, in the range of 1-2 cm/s. The change of the ratio from F/H ratio <1 to the conditions with the F/H ratio >1 corresponds to the disappearance of H2O and a substantial increase of CF2O in the combustion products. Thermodynamic and laminar premix flame calculations demonstrate that “extra” fluorine, which is in excess of hydrogen (F/H > 1), reacts with added H2O forming HF molecules. Calculations demonstrate that the equilibrium volume fractions of the fluorine atom can be as large as 0.5-3% for mixtures with an F/H > 1. The main reaction of H2O conversion to HF is the F + H2O = HF + OH reaction. Dependencies of the F/H ratio as a function of HFC-125 (C2F5H) concentration and showing the possible range of mixture compositions for a promotion effect, were generated for methane, ethylene and heptane at different equivalence ratios.