Flammability assessment of CH2CFCF3: comparison with fluoroalkenes and fluoroalkanes

Minimum ignition energies and laminar burning velocities of ammonia, HFO-1234yf, HFC-32 and their mixtures with carbon dioxide, HFC-125 and HFC-134a

Given the safety issues associated with flammability characteristics of alternative environmentally-friendly refrigerants, it is vital to establish measurement systems to accurately analyse the flammability of these mildly flammable refrigerants. In this study, we used a customised Hartmann bomb analogue to measure the minimum ignition energy (MIE) and laminar burning velocity (BV) for refrigerant/air mixtures of pure ammonia (R717), R32, R1234yf and mixtures of R32 and R1234yf with non-flammable refrigerants of R134a, R125 and carbon dioxide (R744). The MIEs of R717, R32, and R1234yf were measured at an ambient temperature of 24 °C to be (18.0 ± 1.4), (8.0 ± 1.5) and (510 ± 130) mJ at equivalence ratios of 0.9, 1.27 and 1.33, respectively. Adding the non-flammable refrigerants R134a, R125 and R744 along with R32 at volumetric concentrations of 5% each to R1234yf reduced the latter compound's flammability and increased its MIE by one order of magnitude. The laminar burning velocities of pure R717 and R32 were measured at an equivalence ratio of 1.1 using the flat flame method and found to be 8.4 and 7.4 cm/s, respectively. Adding 5% R1234yf to R32 decreased the laminar burning velocity by 11%, while a further 5% addition of R1234yf resulted in a decrease of over 30% in the laminar burning velocity.

Thermodynamic analysis of low-GWP blends to replace R410A for residential building air conditioning applications

The Kyoto Protocol has stipulated array of national policies to combat the climate change. To tackle the global warming, governments embraced Paris Agreement and Kigali Amendment which deal with the reduction of greenhouse gas emission. For example, the European F-gas regulation and the Japan METI now enforce refrigerants below 150 GWP for automobile industry and below 750 GWP for the residential air-conditioning applications. To invent a perfect refrigerant that meets performance requirement, environmental requirements, and safety standards is considered extremely difficult. On the other hand, some existing refrigerants exhibit excellent performance with safe operation but record high-GWP while refrigerants such as R1234yf and R744 possess almost 0 GWP. Thus, these refrigerant blends might serve as urgent solutions with minimum performance compromise. This paper evaluates the performance of binary and ternary blends using several promising refrigerants. Exploiting the excellent performance of R32 as the base refrigerant, R1123, R1234yf, R1234ze(E), and R744 are utilized in the blends. The performance indicators employed here are (i) GWP, (ii) temperature glide, (iii) volumetric capacity, and (iv) coefficient of performance. The advantages to reduce the irreversible heat loss by glide matching and energy saving potential for the blends are also discussed. Results showed that some refrigerant blends considering GWP 200 and 300 could successfully replace the widely used R410A in a residential air conditioner. Thermodynamic cycle and performance of zeotropic blend.

Structures and Properties of trans-1,3,3,3-Tetrafluoro- propene (HFO-1234ze) and 2,3,3,3-Tetrafluoropropene (HFO-1234yf) Refrigerants

The refrigerant trans-1,3,3,3-tetrafluoropropene (HFO-1234ze) is used as a replacement for former cooling agents that have been phased-out due to their global warming potential or ozone depleting potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO-1234ze are known. We report structure determinations based on low-temperature single-crystal X-ray diffraction data as well as gas-phase diffraction data of HFO-1234ze and HFO-1234yf (2,3,3,3-tetrafluoropropene). Furthermore, vibrational spectra of HFO-1234ze in all phases are described. The results are discussed together with quantum-chemical calculations on the PBE0/cc-pVTZ level of theory. Combustion experiments of HFO-1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products.

Kinetic Mechanism of 2,3,3,3-Tetrafluoropropene (HFO-1234yf) Combustion

A kinetic model for 2,3,3,3-tetrafluoropropene (HFO-1234yf) high temperature oxidation and combustion is proposed. It is combined with the GRI-Mech-3.0 model, the previously developed model for 2-bromo-3,3,3-trifluoropropene (2-BTP), and the NIST C1-C2 hydrofluorocarbon model. The model includes 909 reactions and 101 species. Combustion equilibrium calculations indicate a maximum combustion temperature of 2076 K for an HFO-1234yf volume fraction of 0.083 in air for standard conditions (298 K, 0.101 MPa). Modeling of flame propagation in mixtures of 2,3,3,3-tetrafluoropropene with oxygen-enriched air demonstrates that the calculated maximum burning velocity reproduces the experimentally observed maximum burning velocity within about %reasonably well. However, the calculated maximum is observed in lean mixtures in contrast to the experimental results showing the maximum burning velocity shifted to the rich mixtures of HFO-1234yf.

Thermal Decomposition of 2,3,3,3- and trans-1,3,3,3-Tetrafluoropropenes

The thermal decomposition reactions of 2,3,3,3- and trans-1,3,3,3-tetrafluoropropenes (TFPs) have been studied both experimentally and computationally to elucidate their kinetics and mechanism. The experiments were performed by observing the temporal profiles of HF produced in the decomposition of the tetrafluoropropenes behind shock waves at temperatures of 1540-1952 K (for 2,3,3,3-TFP) or 1525-1823 K (for trans-1,3,3,3-TFP) and pressure of 100-200 kPa in Ar bath. The reaction pathways responsible for the profiles were explored based on quantum chemical calculations. The decomposition of 2,3,3,3-TFP was predicted to proceed predominantly via direct 1,2-HF elimination to yield CHCCF₃, while trans-1,3,3,3-TFP was found to decompose to HF and a variety of isomeric C₃HF₃ products including CHCCF₃, CF₂CCHF, CCHCF₃, and CF₂CHCF. The C₃HF₃ isomers can subsequently decompose to either CF₂ + CHCF or CF₂CC + HF products. Multichannel RRKM/master equation calculations were performed for the identified decomposition channels. The observed formation rates and apparent yields of HF are shown to be consistent with the computational predictions.

Understanding overpressure in the FAA aerosol can test by C3H2F3Br (2-BTP)

Thermodynamic equilibrium calculations, as well as perfectly-stirred reactor (PSR) simulations with detailed reaction kinetics, are performed for a potential halon replacement, C₃H₂F₃Br (2-BTP, C₃H₂F₃Br, 2-Bromo-3,3,3-trifluoropropene), to understand the reasons for the unexpected enhanced combustion rather than suppression in a mandated FAA test. The high pressure rise with added agent is shown to depend on the amount of agent, and is well-predicted by an equilibrium model corresponding to stoichiometric reaction of fuel, oxygen, and agent. A kinetic model for the reaction of C₃H₂F₃Br in hydrocarbon-air flames has been applied to understand differences in the chemical suppression behavior of C₃H₂F₃Br vs. CF₃Br in the FAA test. Stirred-reactor simulations predict that in the conditions of the FAA test, the inhibition effectiveness of C₃H₂F₃Br at high agent loadings is relatively insensitive to the overall stoichiometry (for fuel-lean conditions), and the marginal inhibitory effect of the agent is greatly reduced, so that the mixture remains flammable over a wide range of conditions. Most important, the flammability of the agent-air mixtures themselves (when compressively preheated), can support low-strain flames which are much more difficult to extinguish than the easy-to extinguish, high-strain primary fireball from the impulsively released fuel mixture. Hence, the exothermic reaction of halogenated hydrocarbons in air should be considered in other situations with strong ignition sources and low strain flows, especially at preheated conditions.

Case Study of R-1234yf Refrigerant: Implications for the Framework for Responsible Innovation

Safety and care for the natural environment are two of the most important values that drive scientific enterprise in twentieth century. Researchers and innovators often develop new technologies aimed at pollution reduction, and therefore satisfy the strive for fulfilment of these values. This work is often incentivized by policy makers. According to EU directive 2006/40/EC on mobile air conditioning since 2013 all newly approved vehicles have to be filled with refrigerant with low global warming potential (GWP). Extensive and expensive research financed by leading car manufacturers led to invention of R-1234yf refrigerant with GWP < 1, which was huge improvement. For the proper understanding of this case it will be useful to refer it to the idea of responsible innovation (RI), which is now being developed and quickly attracts attention. I proceed in the following order. Firstly, I present the relevant properties of R-1234yf and discuss the controversy associated with its marketing. Secondly, I examine framework for responsible innovation. In greater detail I discuss the notions of care for future generations and collective responsibility. Thirdly, I apply the offered framework to the case study at hand. Finally, I draw some conclusions which go in two directions: one is to make some suggestions for improving the framework of RI, and the second is to identify missed opportunities for developing truly responsible refrigerant.