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• Flammability characteristics of R1216 mixed with R32 and R152a were investigated. • The suppression effect of R1216, R134a, R1233zd(E), and R13I1 was compared. • The flame inhibition mechanism of R1216 was analyzed. R1216 (1,1,2,3,3,3-hexafluoro-1-propene), which has a low global warming potential, is regarded as the new generation of environmentally friendly working fluid in ORCs (organic Rankine cycle) and refrigeration systems. Besides, it also has the advantage of nonflammable property. Thus, R1216 can be mixed with some flammable working fluids to develop new mixed alternatives, which can possess a combination of chemical, environmental, thermodynamic, and safety properties. In this work, the flammability limits of R1216/R32 and R1216/R152a were measured in a 12L spherical glass vessel according to the method of ASTM E681. And the critical flammable volumetric ratios of R1216 on R32 and R152a were about 0.15 and 1.1, respectively. This study also found that the ratio of F atoms to H atoms for the two mixtures had a close relationship with the flammability limit ranges. Finally, the flame inhibition performances of R1216 were compared with other commonly used flame retardants, such as R134a, R13I1 (trifluoroiodomethane), and R1233zd(E) (trans -1-Chloro-3,3,3-trifluoro-propene). It can be concluded that the rank of the inhibition effects was R1216 > R13I1 > R134a > R1233zd(E). And a flame retardant, which contained a higher F/H ratio and much more Cl, I, and CF 3 radicals, can possess a higher flammability inhibition efficiency. [ABSTRACT FROM AUTHOR]

2-BTP (2-Bromo-3,3,3-trifluoropropene) is a promising environment-friendly flame retardant showing high effectiveness. Because of the good mutual solubility with polyol ester oil, 2-BTP was selected as a lubricant additive in this work. The flame inhibition performance of lubricating oil with 2-BTP on the combustion of R152a (1,1-difluoroethane) and R1234yf (2,3,3,3-tetrafluoroprop-1-ene) was investigated, which was expected to enhance the safety level of accidental leaks of flammable working fluids. To assess the suppression capability, experiments were conducted using a 12 L spherical flask according to the test method of ASTM E681. The results indicated that the lower flammable limit of R152a was increased from 4.8% to 5.0% in volumetric concentration as the mass fraction of 2-BTP contained in the POE oil was 20%. As to R1234yf, the lower flammable limit was increased from 7.2% to 10.3%, and the upper flammable limit was decreased from 13.0% to 10.3%. Besides, with the addition of 2-BTP, the combustion intensity of R152a and R1234yf was weakened. Both of the flame diameter and duration were reduced. And the maximum flame transient temperature of R152a also had a decrease. The inhibition effect of lubricating oil with 2-BTP on the mildly flammable working fluid R1234yf was much better. [ABSTRACT FROM AUTHOR]

• Initial oxidative decomposition path and energy change of fluoroethane are obtained. • Energy changes of reactions of six active radicals with fluoroethane are compared. • Fluoroethane generates more than 20 products through two main radicals ·CH3 and ·CH2F. • Intermediates are easy to combine to form products rather than continue to decompose. Fluoroethane is a potential fluid or component of new environmentally friendly working fluids, but its flammability affects its direct application. The oxidative decomposition mechanism of the working fluid is the key to further study its flammability or stability. Therefore, the oxidative decomposition mechanism of fluoroethane was researched by density functional theory. Firstly, seven initial thermal decomposition paths of fluoroethane and four oxidative decomposition paths involving oxygen were obtained, among which the main initial decomposition products were CH 2 =CH 2 and HF, and the free radicals were ·CH 3 , ·CH 2 F, H·, HOO·, etc.; Secondly, the main reaction process of six typical active radicals generated by the chain reaction and fluoroethane was also studied, and it was found that the energy barrier of the hydrogen-extraction reaction was lower than that of the fluorine-extraction reaction, and most of the reactions were exothermic reactions; Finally, the subsequent reaction processes of the main radicals ·CH 3 and ·CH 2 F in the decomposition of fluoroethane were analyzed, and more than 20 possible products and their energy changes were obtained. The relevant results have guiding significance for weakening the flammability of fluoroethane, improving its thermal stability and evaluating its oxidative decomposition products from the deep mechanism. [ABSTRACT FROM AUTHOR]

CO 2 /C 3 H 6 mixture has a wide range of applications in refrigeration systems, heat pumps and Organic Rankine Cycle (ORC) systems, but its flammability safety needs to be considered. An experimental and computational investigation has been conducted on the determination of the flammability limits of CO 2 /C 3 H 6 and on the understanding of associated limit phenomena in general. We tested the flammable zone of CO 2 /C 3 H 6 at variable initial temperature. The accuracy of the prediction model of calculation adiabatic flame temperature were verified based on the experimental data. Meanwhile, a high-speed camera was used to record the process of CO 2 suppression of flame propagation near flammability limit. Furthermore, based on kinetic numerical calculation, the effect of CO 2 chemical and thermal on the flammability limit of C 3 H 6 were analyzed. The results show that the thermal effect of CO 2 is greater than that of chemical effect near the flammability limit. The theory of chemical reactivity inhibition reduces the yield and molar ratio of key radicals. The addition of CO 2 can inhibit the activity of the dominant chain and increase the activity of the dominant chain termination reaction in the global combustion kinetics. Results of this study provide theoretical guidance for the safe application of CO 2 /C 3 H 6 mixture. • The higher the ambient temperature, the larger the CO 2 /C 3 H 6 flammable zone is. • Validation of the accuracy of calculated adiabatic flame models. • Introducing innovative computational strategies to clarify CO 2 suppression theory. • The thermal inhibition effect of CO 2 is more significant than the chemical effect. [ABSTRACT FROM AUTHOR]