Low global-warming-potential refrigerant CH2F2 (R-32): Integration of a radiation heat loss correction method to accurately determine experimental flame speed metrics

Abstract

Due to their high global warming potential (GWP), hydrofluorocarbon refrigerants are systematically being phased out. Replacements with low GWP exist, but give rise to safety hazards as they are found to be mildly flammable. The assessment of the safety hazards of such fluids is typically based on their laminar flame speeds. Typical laminar flame speeds are below 10 cm/s, and hence are challenging to measure. Flames propagating at this speed are strongly affected by radiation heat loss and have to be corrected if considered for kinetic model validation. In the present study, the laminar flame speed of the representative refrigerant difluoromethane (CH2F2, R-32) is measured experimentally in an outwardly propagating flame configuration at elevated pressure and temperature. To assess radiation heat loss effects, detailed simulations using a recent kinetic model for CH2F2 are conducted. Flame speed reductions due to radiation are found to be in the order of 15%. An analytical radiation correction model, as discussed by Santner et al. (2014), is adopted and its suitability for refrigerant/air flames is demonstrated based on simulation. After subsequent correction of experimental results, the predictability of the model is evaluated, showing good agreement.