Search

• The scientific law of burning velocities of working fluids was found. • The effect of flame retardants on combustion characteristics was acquired. • The relationship between LFL/UFL and burning velocities was researched. • The inhibition mechanism of retardants on combustion characteristics was obtained. Despite its good environmental properties, the application of 1,1-Difluoroethane (R152a) is hindered by its flammability. So, an accurate instrument is required to solve the safety issues of R152a. In this study, the combustion characteristics of R152a mixtures with non-flammable CF 3 I/C 3 F 6 were measured using the vertical tube method by ISO-817. It could be found that the maximum burning velocity (S u, max) of R152a decreased from 21.163 cm/s to 7.805 cm/s (with R13I1) or 7.675 cm/s (with R1216) at concentration of 15.403%(with R13I1) and 11.508%(with R1216) at an ambient temperature. By adding non-flammable retardants to R152a from volumetric concentration of 10% – 40%, the flammability of the mixtures was lowered. And S u, max of both were reduced by more than 60%, leading the mixture to reach A2L. According to the S u, max data, the dilution effect of the three refrigerants is: R1216 > R13I1 > R227ea. Meanwhile, the density functional analysis theory was used to study the relationship between the molecular bonds of these refrigerants. The results showed that the refrigerants containing higher F/H ratio and the molecules with -CF 3 and -I groups were more prone to inhibit combustion. [ABSTRACT FROM AUTHOR]

• The schematic mechanism for R1234yf combustion were revealed in unimolecular lysis reactions, colliding reactions with oxygen molecules, collision reaction with active radicals (H and OH radicals). • The new chemical reaction equations for the combustion of R1234yf were proposed. • This paper provided an effective method to establish the combustion mechanism of flammable hydrofluoroolefins. To describe the combustion process of hydrofluoroolefins (HFOs) 2,3,3,3-tetrafluroropropene (R1234yf), a kinetics mechanism was developed. On the M06–2X/6–311++ G (d,p) level, dynamic calculations have been performed using the density function theory (DFT) method. Proposed R1234yf kinetic reactions included unimolecular decomposition and intermolecular reactions, such as collisions with O 2 , OH, and H radicals. The results indicated that R1234yf combustion is a step-by-step chain reaction involving chain initiation (unimolecular lysis and collision reaction with oxygen), chain transmission (collision reactions with free radicals), and chain termination. In conjunction with the priority rule of kinetics reactions, a schematic diagram of the primary microscopic combustion pathways for R1234yf was created at 298.15 K and 1 atm. All the simulation results could provide a data basis to establish the kinetic model of hydrofluoroolefin pyrolysis and combustion. In addition, to verify the product direction of the reaction path, experiments were conducted to determine the properties of the R1234yf combustion products. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen enriched with compressed natural gas is an efficient and environment-friendly gaseous fuel. However, the safety issues of mixture and the method to control or weaken their combustion are highly concerned. To explore the inhibition effect of halogenated fire suppressants on the mixture, the effect of HFC-227ea on the laminar premixed methane/air flames, with different fractions of H 2 , have been studied. Burning velocities have been measured with constant-volume combustion chamber and kinetically modelled a recently assembled kinetic mechanism. The fractions of H 2 influence the enhancement and inhibition effect of HFC-227ea, and it is less effective with the lean mixture. In stoichiometric condition, HFC-227ea showed good inhibition effect on the mixture flames. The HFC-227ea increased the burning velocities of CH 4 -0% H 2 -air and CH 4 -10% H 2 -air flames at leanest condition, whereas the increased burning velocity arising from HFC-227ea not occurred as the addition of H 2 above 20%. Experimental results coincided well with numerical results, however the agreement was poor for the leanest flames at low agent loading. Lastly, kinetic mechanism analysis was used to interpret the combustion enhancement and inhibition effect of hydrogen-doped methane flame by HFC-227ea. • Effect of HFC-227ea on methane flames with different fractions of H 2 were studied. • The burning velocity and kinetic mechanism were obtained and analyzed. • The fractions of H2 influence the enhancement and inhibition effect of HFC-227ea. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) is an effective way to improve energy efficiency, and 2,3,3,3-tetrafluoropropene (R1234yf) is considered as a promising working fluid for ORC. However, the development of R1234yf in ORC is limited by its flammability, and the addition of 1,1,1,2-tetrafluoroethane (R134a) is an effective method to inhibit its flammability. In this paper, the combustion and interaction mechanism of R1234yf/R134a were investigated. Firstly, the combustion products of R1234yf/R134a were measured using an improved experimental device, the results showed a substantial reduction in the concentrations of CO, CO 2 , and HF with an increasing proportion of R134a. Then, the combustion mechanism of R1234yf/R134a was studied by ReaxFF-MD simulation. The initial decomposition time of R134a was found to be later than that of R1234yf, and a reduction in the production rate of combustion products was achieved with the addition of R134a. Furthermore, the combustion reaction was promoted by the increase in temperature. Finally, the main reaction pathways of working fluids were analyzed. The abstraction reaction of R134a with radicals and the scavenging of active radicals by flame retardant radicals were the key to inhibit the combustion reaction. The results have universal guiding significance for the safe application of R1234yf/R134a. • The combustion and interaction mechanism of R1234yf/R134a was investigated. • The combustion products of R1234yf/R134a with different proportions were measured. • The inhibitory effect of R134a on the combustion of R1234yf was studied. • The main reaction pathways of R1234yf/R134a were analyzed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Gas disturbance changes the flammable characteristics of flammable refrigerants. • Effect of different disturbance on LFLs of flammable refrigerants was studied. • Specific low disturbance may contribute to combustion of nature refrigerants. • A multi angle method to determine the LFLs of the flammable gases was proposed. Abstract Refrigerants with low global warming potential (GWP), will play an important role in the research of alternative refrigerants and the development of new refrigerants, but most of them are flammable. And the actual environment of the refrigeration system varies with different factors, especially gas disturbance. In this paper, the combustion characteristics of four refrigerants, i.e., isobutane (R600a), ethylene (R1150), propane (R290), and 2,3,3,3-Tetrafluoroprop-1-ene (R1234yf) under the conventional static and the gas disturbance were studied. Firstly, the flame characteristics and lower flammability limits (LFLs) of the refrigerants were investigated. Then the special combustion phenomena were observed and analyzed in the presence of the gas disturbance, and an improved method for better defining the LFLs of the flammable gases under the disturbance was proposed. Finally, the experimental results show that the LFLs of the three natural refrigerants under specific low disturbance are lower than that in normal conditions, but except for R1234yf. It was found that the specific disturbance may enhance the combustion intensity by comparing the burning time of visible flame under the two conditions. The results have guiding significance for the safe application of flammable refrigerants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fire extinguishing experiments of R123 and R125 were performed using the cup burner. • The MEC of R123 is lower than R125. • From the change of flame height and width, the suppression effect of R123 is better than that of R125. • The addition of R123 did not cause a significant temperature change in the flame. • The reaction pathways of thermal decomposition and R123 with H and OH radicals were calculated by DFT. Fire extinguishing performance and mechanism of C 2 HF 3 Cl 2 (R123) were studied by experimental and theoretical methods. The minimum extinguishing concentration (MEC) of R123 in methane/air flames is 7.31 %. The addition of R123 to flame increased first and then decreased the flame height, due to the effect of R123 on the movement of the reaction kernel. Theoretical calculations indicated that R123 and pyrolysis products affect the combustion reaction, the generated fluorine or chlorine-containing groups improved the suppression of combustion chain reactions. The in-depth experimental and theoretical study of R123 boost the development of ideal halon replacement in aircraft cargo compartment. [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]

The combustion mechanism of trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(E)) has been investigated theoretically and experimentally. Firstly, The theoretical model of R1234ze(E) combustion was revealed in unimolecular decomposition, collision with oxygen, and addition with radicals (hydrogen and hydroxyl radical). All the reaction pathways were calculated by density function theory method on M06-2X/6–311 + G (d, p) level. Then, combustion experiments were performed to verify the transformation law of volume fractions of R1234ze(E), CO, CO 2 and O 2 as the volume fractions of R1234ze(E) were changed from 8.4% to 13.6%. Combined with the theoretical calculation model, a mechanism map was established for the combustion reaction of R1234ze(E) into stable products (electric spark ignition, 298.15 K, 1 bar). Furthermore, new chemical reaction equations were proposed to describe the stoichiometric combustion of R1234ze(E) in different conditions. • A theoretical calculation model for the R1234ze(E)–air combustion system was established. • The combustion reaction measurement of R1234ze(E) were conducted. • The schematic mechanism for the combustion of R1234ze(E) were described. • The new chemical reaction equations for the stoichiometric combustion of R1234ze(E) were proposed. [ABSTRACT FROM AUTHOR]