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Burning Velocities of Marginally Flammable Refrigerant-Air Mixtures



Gregory T. Linteris


Refrigerant working fluids have been predicted to be large contributors to the increase in radiative forcing of the earth. Consequently, existing compounds will soon be phased out. Low- GWP replacements exist, but they tend to be mildly flammable, and there is a need to understand their flammability properties so that effective building codes and standards can be written to address their application. The burning velocities of interest are in the range of 1 cm/s to 10 cm/s, and hence are challenging to measure. To understand the challenges and properties of the new agents, experimental measurements and numerical predictions have been made for representative refrigerant-air mixtures. Burning velocities were measured using a constant pressure spherical chamber with high-speed imaging of the shadowgraph image of the propagating spherical flame. The flame propagation rate as a function of flame radius was used to estimate the effects of stretch, and to determine the un-stretched laminar burning velocity. For comparison, the burning velocity was also predicted numerically using a detailed kinetic mechanism for hydrofluorocarbon combustion developed at the National Institute of Standards and Technology (NIST).
Technical Note (NIST TN) - 1988
Report Number


Refrigerant flammability, R32, difluoromethane, burning velocity, low-GWP refrigerant, Markstein length.


Linteris, G. (2018), Burning Velocities of Marginally Flammable Refrigerant-Air Mixtures, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 21, 2024)
Created May 1, 2018, Updated November 10, 2018