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To cope with the problem of global warming caused by greenhouse gases, an environmentally friendly working fluid with low global warming potential (GWP) value was proposed to replace R507A which has a higher GWP value. This paper evaluated the thermodynamic properties and cycle performance of the alternative named RTB1. Firstly, the thermodynamic properties of RTB1 were investigated experimentally, including saturated vapor pressure and miscibility with polyol ester (POE) lubricating oil. The results showed that the saturated vapor pressure of RTB1 is 7.14% higher than that of R507A on average, and RTB1 has good miscibility with POE 32. Secondly, the flammability of RTB1 was tested by the flammability limits test system, and the experimental results showed that RTB1 was a non-flammable working fluid. Finally, the cycle performance of RTB1 and R507A under different operating conditions was compared. RTB1 is better than R507A in terms of cooling capacity per unit volume and coefficient of performance, however, the discharge temperature of RTB1 is higher than that of R507A. This work is of great significance to promote the elimination process of high-GWP working fluids and reduce emissions of greenhouse gases. [ABSTRACT FROM AUTHOR]

[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]

• 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]

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]

[Display omitted] • Flammability limits of the new binary mixture R1234ze(E)/R32 was measured. • Oxidative decomposition and interaction mechanisms of R234ze(E)/R32 were studied. • R32 decomposes preferentially and R1234ze(E) is more likely to react with radicals. • CF 3 plays an important role in R1234ze(E) inhibiting flammability of R32. At present, mixed working fluids have received increasing attention due to their excellent comprehensive performance. Among them, R1234ze(E) (trans -1,3,3,3-tetrafluoropropene) and the R32 (difluoromethane) with excellent thermal properties can form a safe and environmentally friendly new mixture through advantageous complementarity. In this paper, the flammability of the binary mixture R1234ze(E)/R32 mentioned above was studied. Firstly, the flammability limits and critical concentration inhibition ratio of R1234ze(E)/R32 were tested at different ratios. Then, based on density functional theory (DFT), the interaction mechanism between the two components in the mixture was analyzed. The results show that with the increase of R1234ze(E), the flammable limit range becomes narrower. In the early stage of the reaction between R1234ze(E)/R32, R32 preferentially breaks the bond to generate H and F radicals, but the reactions between R1234ze(E) and free radicals are dominant. CF 3 radical is an important free radical for R1234ze(E) to inhibit the flammability of R32. The research results will have guiding significance for the internal interaction mechanism of the flammability of new binary mixtures and their safe applications. [ABSTRACT FROM AUTHOR]