Inhibition effectiveness of halogenated compounds (original) (raw)
Related papers
Inhibition of Premixed C 3 H 6-AIR Flames by CH 2
2006
The effect of gaseous CH2BrCl addition upon the characteristic parameters of combustion propagation in propyleneair mixtures in a closed vessel was investigated, at various initial pressures within 0.3-1.3 bar and various [C3H6] : [O2] and [C3H6] : [CH2BrCl] ratios. Small concentrations of added CH2BrCl (0.5-1.0 vol %) to propylene – air mixtures do not influence much the peak explosion pressures, as CH2BrCl contributes to the total amount of released heat. An important inhibiting effect of the additive is observed by means of normal burning velocities and rates of pressure rise, directly influenced by the overall reaction rate in the flame front.
Chemical and Physical Influences of Halogenated Fire Suppressants
The specific mechanisms by which fire suppressants influence flame properties have been determined on the basis of computer simulations. Attention is focussed on the relative contributions from physical and chemical processes. Chemical effects are most strongly manifested at low concentrations of suppressants. As their concentrations are increased, the chemical effects reach a maximum value, while the physical effects continue to increase. The use of a composite inhibitor composed of a mixture of an effective chemical inhibitor with a high heat capacity diluent may be beneficial. The relative contributions towards fire suppression from physical and chemical mechanisms are estimated near the flammability limits. Halon Options Technical Working Conterence 6.
Inhibition of Premixed Methane–Air Flames by Fluoroethanes and Fluoropropanes
Combustion and Flame, 1998
This paper presents experimental and modeling results for laminar premixed methane-air flames inhibited by the fluoroethanes C 2 F 6 , C 2 HF 5 , and C 2 H 2 F 4 , and experimental results for the fluoropropanes C 3 F 8 and C 3 HF 7. The modeling results are in good agreement with the measurements with respect to reproducing flame speeds. For the fluoroethanes, calculated flame structures are used to determine the reaction pathways for inhibitor decomposition and the mechanisms of inhibition, as well as to explain the enhanced soot formation observed for the inhibitors C 2 HF 5 , C 2 H 2 F 4 , and C 3 HF 7. The agents reduce the burning velocity of rich and stoichiometric flames primarily by raising the effective equivalence ratio and lowering the adiabatic flame temperature. For lean flames, the inhibition is primarily kinetic, since inhibitor reactions help to maintain the final temperature. The peak radical concentrations are reduced beyond that due to the temperature effect through reactions of fluorinated species with radicals.
Inhibition of premixed C3H6-air flames by CH2BrCl
Revue Roumaine de Chimie
The effect of gaseous CH 2 BrCl addition upon the characteristic parameters of combustion propagation in propyleneair mixtures in a closed vessel was investigated, at various initial pressures within 0.3-1.3 bar and various [C 3 H 6 ] : [O 2 ] and [C 3 H 6 ] : [CH 2 BrCl] ratios. Small concentrations of added CH 2 BrCl (0.5-1.0 vol %) to propylene -air mixtures do not influence much the peak explosion pressures, as CH 2 BrCl contributes to the total amount of released heat. An important inhibiting effect of the additive is observed by means of normal burning velocities and rates of pressure rise, directly influenced by the overall reaction rate in the flame front.
Journal of Loss Prevention in the Process Industries, 2017
After the restriction on several ozone-depleting compounds, including the high efficiency fire suppressant Halon 1301(CF 3 Br), several alternatives have been proposed. Among them, HFC-227-(C 3 HF 7) and HFC-125 (C 2 HF 5) represent two of the most-used fire suppressants in the industry because of their environmentally favorable properties. Due to their increasing demand, it is very important to understand their combustion properties to optimize their applications and to prevent undesirable events. To this end, the present work examined the effect of C 2 HF 5 and C 3 HF 7 on CH 4 and C 3 H 8 laminar flame speeds and ignition delay times. The experimental techniques included freely propagating flames to obtain unstretched, laminar flame speed and a shock tube for the ignition delay times in fuel-O 2-suppressant mixtures highly diluted in Ar (~98%) using OH* emission near 307 nm. The laminar flame speed experiments were performed at 1 atm over a range of equivalence ratios from 0.7 to 1.3, and the shock-tube tests were done near 1.5 atm over a 1350e2200 K temperature range. A chemical kinetics mechanism was assembled using a HFC set of reactions together with a recently updated C 0-C 5 hydrocarbon mechanism and OH* chemistry. The results suggest that the tested agents may not be good alternatives as ignition preventers, although they can reduce the laminar flame speed, as a proof that they can be used as fire extinguishers. Comparisons between modeled and experimental data show that the HFC submechanism behaves well, however it can be improved. Surprisingly, a sensitivity analysis shows that many of the top reactions containing fluorinated compounds are classified as ignition-promoters, especially for the experiments with CH 4. This work presents some of the first fundamental ignition delay time and flame speed data for HFC-227 and-125, and the results can be used as the basis for future HFC-based chemical kinetics mechanism improvements and to further understand their impact on the combustion process.
Theoretical analysis and simulation of methane/air flame inhibition by sodium bicarbonate particles
Combustion and Flame, 2018
The capacity of sodium bicarbonate (NaHCO 3) s powder to chemically reduce flame speeds and mitigate the effects of accidental explosions is well established. The inhibition of premixed hydrocarbon/air flames by monodisperse (NaHCO 3) s solid particles is investigated, here, using theory and numerical simulations. First, an analytical solution for the temperature history of a solid (NaHCO 3) s particle crossing a flame shows that the size of the largest (NaHCO 3) s particle which can decompose inside the flame front, and act on chemical reactions efficiently, strongly depends on the flame speed. For various fuels and a wide range of equivalence ratios, particles with a strong potential for flame inhibition are identified: hence a criterion, on the maximum particle size, for efficient inhibition is proposed. Thereafter, a one-dimensional methane/air flame traveling in a premixed gas loaded with sodium bicarbonate is simulated using a chemical mechanism based on GRI-Mech, extended to include inhibition chemistry and reduced to 20 species with a DRGEP method (Pepiot-Desjardins and Pitsch, 2008). Inhibitor particle size and mass loading are varied to study the flame response to inhibition by (NaHCO 3) s powders. Finally, two-dimensional simulations of a planar flame traveling in a flow with a non-uniform inhibitor mass loading distribution are analyzed. In the case of strong particle stratification, an acceleration of the flame is observed, instead of a mitigation. This fundamental mechanism may limit the actual potential of inhibition powders in real configurations.
1998
C3F7H (FM-200) has recently been introduced as an alternative for Halon 1301 (CF3Br) fire suppression agent. In this paper, as part of an effort to study the effects of C3F7H on high temperature ignition of gaseous fuels, we are expanding on our earlier evaluations of ignition inhibition characteristics of C3F7H. Of particular interest is a better or improved understanding of the fundamental mechanisms by which C3F7H functions as an inhibitor. We found that the ignition delay is primarily controlled by the initial C3F7H decomposition kinetics, which releases active species into the system. At low temperatures (below1000 K) these active species increase the overall reaction rate by initiating new chain reactions. However, at higher temperatures, due to competition between the main chain branching reaction of CH4 combustion and reactions involving C3F7H derivatives (e& C3F7 and C3F& the heat release rate of the overall combustion reaction is substantially decreased leading to a longer ignition delay time.
Fire Safety Journal, 2017
Computations of cup-burner flames in normal gravity have been performed using propane as the fuel to reveal the combustion inhibition and enhancement by the CF3Br (halon 1301) and potential alternative fireextinguishing agents (C2HF5, C2HF3Cl2, and C3H2F3Br). The time-dependent, two-dimensional numerical code used includes a detailed kinetic model (up to 241 species and 3918 reactions), diffusive transport, and a gray-gas radiation model. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of agent in the coflow increases gradually, the premixed-like reaction kernel weakens, thus inducing the flame base detachment from the burner rim and blowoff-type extinguishment eventually. The two-zone flame structure (with two heat-release-rate peaks) is formed in the trailing diffusion flame. The H2O formed in the inner zone is converted further, primarily in the outer zone, to HF and CF2O through exothermic reactions most significantly with the C2HF5 addition. The total heat release of the entire flame decreases (inhibiting) for CF3Br but increases (enhancing) for the halon alternative agents, particularly C2HF5 and C2HF3Cl2. Addition of C2HF5 results in unusual (non-chain branching) reactions.