The Fundamental Flammability Characteristics Of HFO-1243zf And Its Mixture

With the introduction of new refrigerant regulations,refrigerants with high global warming potential（GWP）have been included in the phase out plan,and the researches on eco-friendly refrigerants have become a hot spot in the industry.HFO-1243zf is regarded as a potential substitute for traditional refrigerants as R-134a in air conditioning and refrigeration systems due to its non-ozone depleting nature,short atmospheric lifetime,extremely low GWP,and its ability to meet the requirements of environmental regulations on refrigerants.However,the flammability of HFO-1243zf,which is classified as Class 2 in the refrigerant flammability classification,has hindered the practical application of HFO-1243zf to a certain extent.In order to accurately evaluate the flammability risk of HFO-1243zf and its mixtures,this study measured the flammability limits and flame propagation velocities of HFO-1243zf and its mixtures,and analyzed the influence law and mechanism of temperature,humidity,reaction vessel,flammable refrigerant and flame retardant on the flammability limit and burning velocity of HFO-1243zf.Referring to ASHRAE 34 and ISO 817,the comprehensive experimental system for flammability limit measurement and flame propagation velocity measurement was designed and established.The flammability limit and burning velocity of HFO-1243zf and the relationship between the flammability limit and the environment have been explored,and the estimated value closest to the experimental value of the flammability limit was obtained by Jones’method.The increase of temperature can promote the combustion of HFO-1243zf,while the increase of humidity has a weak effect.The flammability range of HFO-1243zf measured by the glass tube is smaller than that measured by the spherical glass flask.The flammability limits and burning velocities of HFO-1243zf/R-E170 mixture were studied.The addition of HFO-1243zf reduces the flammability risk of R-E170 for HFO-1243zf/R-E170 mixture.The flammability limits of HFO-1243zf/R-E170 can be estimated by using the Le Chatelier’s formula,and the estimated value is in good agreement with the experimental value.The burning velocities of HFO-1243zf/R-E170 are related to the mixture concentration,showing a changing trend of first increasing and then decreasing.The allowable maximum charge amount of the HFO-1243zf/R-E170 refrigerants in an air conditioner for human comfort in a room under different conditions was predicted based on the measured results and ISO Standard 5149.The flammability inhibition of HFO-1243zf can effectively reduce the flammability risk,the inhibition effects of R-744,R-227ea,R-125,and R-134a on the flammability of HFO-1243zf were measured and analyzed.The measured critical suppression ratios of the four flame retardants are in the order:R-744（3.1）>R-134a（1.42）>R-125（0.68）>R-227ea（0.58）,indicating that R-227ea has the highest flammability inhibition efficiency.The differences between the critical suppression ratios and estimation results by the group contribution method were compared.Finally,the mechanism of different inhibition effects of R-744,R-227ea,R-125,and R-134a on the flammability of HFO-1243zf was analyzed from the aspects of dilution of combustibles and oxidants,isolation of combustibles and oxidants,generation and consumption of free radicals.The greater the R_F/H（amount ratio of the fluorine atoms to hydrogen atoms）and the more inhibiting free radicals as CF₃ and CF₂ produced during the thermal decomposition,the better the flammability inhibition effect of the flame retardant on HFO-1243zf.