This paper describes an alternative approach to ASTM E 681 for identifying the limits of flammability of refrigerants, employing a premixed counterflow flame. By decreasing the fuel/air ratio of an established flame while maintaining the flow velocity constant, an unambiguous extinction point can be determined. The extinction mole fraction of refrigerant can be measured for decreasing flow velocities, so that the mole fraction at zero flow can be determined by extrapolation. Using this method, a distinct flammability limit can be determined even for weak fuels. The theory of operation and the experimental facility designed specifically for the new generation of refrigerants is described. The uncertainties of the measurements are presented and the results compared to data in the literature taken in the ASTM E 681 apparatus. Measurements of the critical flammability ratio of R-125/ R-32 (C ₂ HF ₅ /CH ₂ F ₂ ) are discussed as an example.

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