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Air Humidity Influence on Combustion of R1234yf (CF3CFCH2), R1234ze(E) (trans-CF3CHCHF) and R134a (CH2FCF3) Refrigerants



Gregory T. Linteris, Valeri I. Babushok


The influence of air humidity on flame propagation in mixtures of hydrofluorocarbons (HFCs) with air was studied through numerical simulations and comparison with measurements from the literature. The addition of water vapor to the air in mixtures of fluorine rich hydrofluorocarbons (F/H≥1) can be considered as a fuel additive that increases the production of the radicals (H, O, OH) and increases the overall reaction rate. The hydrofluorocarbon flame is typically a two-stage reaction proceeding with a relatively fast reaction in the first stage of the process with the following transition to a very slow reaction proceeding in the second stage leading to the combustion equilibrium products. The transition to the second stage is determined by the consumption of hydrogen-containing species and formation of HF. Despite a relatively small effect of water on the adiabatic combustion temperature, its influence is significant on the reaction rate and on the temperature increase in the first stage of the combustion process leading to the increase in burning velocity. The main reaction for converting H2O to hydrogen-containing radicals and promoting combustion is H2O+F=HF+OH, as demonstrated by reaction path analyses for the fluorine rich hydrofluorocarbons R-1234yf, R-1234ze(E), and R-134a (F/H = 2). The calculated dependency of burning velocities on the equivalence ratio  agree reasonably well with available experimental measurements for R1234yf and R-1234ze(E) with and without the addition of water vapor. In agreement with experimental data, the maximum of burning velocity over  is shifted to the lean mixtures (near  = 0.8).
Combustion and Flame


Refrigerant flammability, Burning velocity, Low-GWP refrigerants, Kinetic model, Hydrofluorocarbons, Humidity, Moist air, R-1234yf, R-1234ze(E), R-134a


Linteris, G. and Babushok, V. (2024), Air Humidity Influence on Combustion of R1234yf (CF3CFCH2), R1234ze(E) (trans-CF3CHCHF) and R134a (CH2FCF3) Refrigerants, Combustion and Flame, [online],, (Accessed April 19, 2024)
Created February 23, 2024, Updated February 28, 2024