Flame retardant effect of the halohydrocarbons on the mildly flammable refrigerant difluoromethane

R-32 (difluoromethane) has got much attention as an alternative for R-22 (chlorodifluoromethane) or R-410A with excellent thermodynamic property. However, R-32 is flammable, and also has been listed in the Kigali Amendment for relatively high global warming potential (GWP). To make up for the shortcomings, it is necessary to research the reduction of the flammability and GWP of R-32 by developing the mixtures of R-32. In this paper, the flammability characteristics of R-32 mixed with R-134a (1,1,1,2-tetrafluoroethane), R-1234ze(E) (trans-1,3,3,3-tetrafluoroprop-1-ene) and R-13I1 (trifluoroiodomethane) were experimentally studied. The flammability limits of the three mixtures were measured in a 12 L spherical glass flask according to ASHRAE method, and the flame-retarding effect of the three retardants was researched. The test results showed that the flame inhibition effect of R-13I1 was better than that of R-134a and R-1234ze(E). The inhibition effect of R-1234ze(E) was the worst, which would not completely suppress the flammability of R-32. The minimum inerting concentrations of R-134a and R-13I1 on R-32 were about 28.6% and 13.8%, respectively. Besides, the chemical inhibition mechanism of the three flame-retards was analyzed. The results will provide a comprehensive understanding of R-32 and its mixtures in combustibility hazard, flame retardant mechanism and environmental protection.