Methodology Development for the Measurement of Refrigerant Flammability Limits

Flammability has emerged as a challenge to the adoption of refrigerants with low global warming potential (GWP) and zero ozone depletion potential (ODP). Among the flammability criteria considered in safety standards, the concentration limits of flammability (i.e., flammability limits) require further empirical study. Existing methodologies can benefit from improved precision and reproducibility, particularly for refrigerants, and the reported data for current and next-generation refrigerants remains limited. In this study, an experimental apparatus following the ASTM E681–09 test method was developed that enabled precise control of temperature, pressure, humidity, and ignition strength. Reproducibility and comparison with literature measurements was investigated using mixtures of difluoromethane (HFC-32) and air. The lower and upper flammability limits (LFL and UFL) for HFC-32 were observed at 14.2 ± 0.2 and 26.8 ± 0.2 vol %, respectively, under average conditions of 23.0 ± 2.2 °C, 8.8 ± 0.5 g water/kg dry air, and 960.3 ± 1.0 mbar.