refrigerant flammability, burning velocity, HFC, HFO
Due to their high global warming potentials, many existing working fluids for heating, cooling and refrigeration equipment are being phased out. Their replacements will often be flammable or slightly flammable, and the burning velocity of refrigerant-air mixtures is being used as a metric to rank their flammability. To allow industry to estimate the flammability of new blends of agents, predictive tools for the burning velocity of refrigerants are being developed, and calculating burning velocity requires a kinetic mechanism. The National Institute of Standards and Technology hydrofluorocarbon (HFC) mechanism was developed 20 years ago to describe hydrocarbon-air flames with added trace amounts of hydrofluorocarbon fire retardants (primarily CH2F2, CF3H, CF4, C2H2F4, C2HF5, and C2F6). In the present work, the mechanism has been updated slightly to include new HFC compounds, more recent rate data, and rate data for new species. The modified mechanism is used to predict steady, planar, 1D, unstretched burning velocities for mixtures of air with each of the one- and two-carbon saturated HFC compounds R41 (CH3F), R32 (CH2F2), R161 (C2F5H), R152 (CH2F-CH2F), R152a (CH3-CHF2), R143 (CH2F-CHF2), R143a (CH3-CF3), R134 (CHF2-CHF2), and R134a (CH2F-CF3), for which existing experimental data were available. Simulation results are present for a range of fuel-air equivalence ratio ϕ, for comparison with the available experimental data. Agreement is reasonable, and major kinetic pathways and radical populations are explored to uncover the general reaction properties of these new flames.