Lean flammability limit as a fundamental refrigerant property: Phase 2. Interim technical report, 1 April 1995--30 March 1996

Abstract

The flammability of alternative, non-ozone depleting refrigerants is an issue of growing importance to the air-conditioning and refrigeration industry. Test methods developed decades ago are being stretched to their limits when measuring the combustion behavior of weakly flammable refrigerants. This work is Phase 2 of a three part project to determine the feasibility, accuracy, and applicability of a premixed opposed-flow burner as an alternative means of measuring lean flammability limits. In this work, the Phase 2 burner demonstrates the precision available to the opposed-flow technique for evaluating the lean flammability limit of weak fuels. Using opposed, converging nozzles, two jets support a premixed twin flame at different global strain rates and permit evaluation of the corresponding fuel concentration at the extinction point. Comparisons with published data support that the LFL{sub 0}, a lean flammability limit value defined by the extrapolation of the extinction conditions to zero global strain, yields a consistent value. Using a computer simulation to analyze the uncertainty, the lean flammability limit of refrigerants in dry air is found. Concurrent computational modeling of the combustion of refrigerants in air, individually and in mixtures has been performed with the chemical kinetics code CHEMKIN. Estimates of the impact of the initial conditions (equivalence ratio, fuel composition, temperature, and relative humidity) on the magnitude of the laminar flame speed of a zero strain flame are made.