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[Display omitted] • The change laws of flammability limits with ignition energy for flammable working fluids are studied. • The influence laws of ignition energy on flame propagation are acquired. • The burning velocity in stable propagation stage is independent of ignition energy. • The influence mechanism of ignition energy on combustion characteristics is obtained. Working fluids with low global warming potential (GWP) will play an important role in the research and development of alternative working fluids for organic Rankine cycles and refrigeration cycles. However, the flammability of low GWP working fluid limits their development, and the energy of typical fire sources has a significant impact on their safe application. At present, there is a lack of relevant research on the effect of ignition energy on their flammability. In this paper, the effect of ignition energy on the combustion characteristics for propane (R290), fluoroethane (R161), 1,1-Difluoroethane (R152a), and 3,3,3-Trifluoropropene (R1243zf) was studied using a variable ignition energy system. The initial flame propagation process, flammability limit, and burning velocity were tested and analyzed in the range of 50 mJ to 20 J. The results showed that with the increase of ignition energy, the lower flammability limit (LFL) decreased and the upper flammability limit (UFL) increased, but their rate of change decreased with the increasing ignition energy. The effect of ignition energy on the flammability limit of R1243zf was significantly greater than that of the other three working fluids. In addition, the effect of ignition energy on flame propagation was mainly limited to the initial stage, and the burning velocity was independent of ignition energy. The mechanism of ignition energy on combustion characteristics was obtained. The research results have guiding significance for the safe application of flammable working fluids. [ABSTRACT FROM AUTHOR]

• The flammability limits and burning velocities of R1234yf mixtures were measured. • The relationship between flammability limit ranges and the n F /n H was analyzed. • The factors affecting the burning velocity were explored in the molecular structure. In response to the pressure of environmental protection, a series of environment-hazardous refrigerants will be phased out. And the selection of the substitutions for the future will need to balance thermodynamic property, safety and sustainability. Thus, the mixed refrigerants are receiving increasing attentions for their special performances. In this paper, the flammability characteristics of the commonly used mixtures R32/R1234yf and R152a/R1234yf were experimentally researched. The flammability limits of the two binary mixtures at different proportions of R1234yf were measured in a 12L spherical glass vessel. And the burning velocities of the two mixtures at different equivalence ratios were measured in a cylindrical quartz vertical tube. It can be found that the flammability limit curves of R32/R1234yf were different from that of R152a/R1234yf. The ratio of F atoms to H atoms (n F /n H) for the two mixtures had a close relationship with the flammability limit ranges. The maximum burning velocity for R32/R1234yf and R152a/R1234yf tended to decrease with the increase of the R1234yf proportion, and also decreased with the increasing of the n F /n H. But the n F /n H was not the only impact on the burning velocity. The number of C–H bonds and the molecular structure reflected in the heat of combustion would be correlated with the burning velocities of the mixtures. The results will provide a guidance for the development and safe application of R1234yf mixtures. [ABSTRACT FROM AUTHOR]