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The extinguishment of propane cup-burner flames by a halon-replacement fire-extinguishing agent C6F12O (Novec 1230) added to coflowing air in normal gravity has been studied computationally and experimentally. The time-dependent, axisymmetric numerical code with a detailed reaction mechanism (up to 141 species and 2206 reactions), molecular diffusive transport, and a radiation model, is used to reveal a unique two-zone flame structure. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing diffusion flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of the agent in the coflow is increased gradually, the total heat release increases up to three times due to unwanted combustion enhancement by exothermic reactions to form HF and CF2O in the two-zone trailing flame; whereas at the base, the flame-anchoring reaction kernel weakens (the local heat release rate decreases) and eventually the flame blows off. A numerical experiment, in which the C6F12O agent decomposition reactions are turned off, indicates that for addition of inert C6F12O, the maximum flame temperature decreases rapidly due to its large molar heat capacity, and the blow-off extinguishment occurs at ≈1700 K, a value identical to that for inert gases previously studied, while the reaction kernel is still burning vigorously. The calculated minimum extinguishing concentration of C6F12O in a propane flame is 4.12 % (with full chemistry), which nearly coincides with the measured value of 4.17 ± 0.30 %.

A kinetic model is presented for high-temperature oxidation and combustion of the refrigerants: 2,3,3,3-tetrafluoropropene (R-1234yf), 1,3,3,3-tetrafluoropropene (R-1234ze(E)), and 3,3,3-trifluorop...

This work entails characterizing the flammability of the refrigerant R-32 (CH2F2) by both experimental measurements and modeling. Burning velocities Su were measured using a constant-volume spherical-flame method for R-32/O2/N2 mixtures with O2/N2 ratios ranging from 21% (synthetic air) to 40%, pressures of (1 to 3) bar, and equivalence ratios ϕ of (0.8 to 1.3). Based on a critical assessment of available data, and extended by our own calculations, a detailed chemical kinetic model was developed and key reactions determined using reaction path and sensitivity analyses. Initiation and combustion were identified as distinct kinetic regimes and burning velocities were found to be controlled by two primary reactions: unimolecular decomposition of CH2F2 → CHF + HF and the subsequent reaction, CHF + O2 → CHFO + O, the latter reaction initiating the radical chain propagating and branching by producing O atoms. Sensitive rate constants in the kinetic model were critically adjusted within their uncertainties and current knowledge bounds to best fit the experimental burning velocities. We found that rate constants in the model could be adjusted to match a given experimental Su for specific conditions (O2 loading, P, T, ϕ). This, however, then fixes predicted burning velocities for other all conditions within (3 to 4)% if physically realistic rate parameters are maintained. Thus, the entire set of experimental data is fit, not just to particular conditions. Relative random uncertainties in the experimental Su measurements were (4 to 6)%, but assumptions made for thermal radiation lost by the burned gas in the spherical-flame experiments add an additional systematic uncertainty. Systematic differences between the limiting cases of adiabatic (no thermal radiation lost) and optically-thin (all thermal radiation lost) varied significantly with conditions and ranged from (4 to 30)% at high to low velocities, respectively, translating into uncertainties of (2 to 15)% considering the average of two limiting cases. Comparison of experimental and kinetically modeled Su values suggests that the burned gas tends towards the optically-thin limit at the lowest pressures and fuel loadings and toward the adiabatic limit at the highest pressures and loadings. We tested and found support for this conclusion with a detailed analysis as a function of all the conditions (T, P, % O2, ϕ). This behavior appears to transition from optically-thin to adiabatic as the density of the initial fuel increases, which results in increased CO2 in the burned gas and thus increased absorption of the thermal radiation (consistent with the Beer-Lambert Law). The validated detailed model based on evaluated kinetics is shown to accurately predict burning velocities for R-32 O2/N2 mixtures over a wide range of conditions and provides a reliable basis for extrapolation to other conditions.

In this work, we introduce a global kinetic model that includes fuel, oxygen, products and two radical species involved in the reversible chain-branching, chain-propagation and chain-termination re...

Powders of Sm0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950 °C.

The combustion of premixed gas mixtures containing micro droplets of water was studied using one-dimensional approximation. The dependencies of the burning velocity and flammability limits on the i...

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 C 1 -C 2 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 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.

A kinetic model of inhibition by the potassium-containing compound potassium bicarbonate is suggested. The model is based on the previous work concerning kinetic studies of suppression of secondary flashes, inhibition by alkali metals, and the emission of sulfates and chlorides during biomass combustion. The kinetic model includes reactions with the following gas-phase potassium-containing species: K, KO, KO2, KO3, KH, KOH, K2O, K2O2, (KOH)2, K2CO3, KHCO3, and KCO3. Flame equilibrium calculations demonstrate that the main potassium-containing species in the combustion products are K and KOH. The main inhibition reactions, which comprise the radical termination inhibition cycle are KOH + H=K + H2O and K + OH + M=KOH + M with the overall termination effect: H + OH=H2O. Numerically predicted burning velocities for stoichiometric methane/air flames with added KHCO3 demonstrate reasonable agreement with available experimental data. A strong saturation effect is observed for potassium compounds: approxi...

A simple kinetic model has been suggested to describe the inhibition and extinction of flame propagation in reaction systems with chain-branching reactions typical for hydrocarbon systems. The model is based on the generalised model of the combustion process with chain-branching reaction combined with the one-stage reaction describing the thermal mode of flame propagation with the addition of inhibition reaction steps. Inhibitor addition suppresses the radical overshoot in flame and leads to the change of reaction mode from the chain-branching reaction to a thermal mode of flame propagation. With the increase of inhibitor the transition of chain-branching mode of reaction to the reaction with straight-chains (non-branching chain reaction) is observed. The inhibition part of the model includes a block of three reactions to describe the influence of the inhibitor. The heat losses are incorporated into the model via Newton cooling. The flame extinction is the result of the decreased heat release of inhibited...

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 CF(3)Br (halon 1301) and potential alternative fire-extinguishing agents (C(2)HF(5), C(2)HF(3)Cl(2), and C(3)H(2)F(3)Br). 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 H(2)O formed in the inner zone is converted further, primarily in the outer zone, to HF and CF(2)O through exothermic reactions most significantly with the C(2)HF(5) addition. The total heat release of the entire flame decreases (inhibiting) for CF(3)Br but increases (enhancing) for the halon alternative agents, particularly C(2)HF(5) and C(2)HF(3)Cl(2). Addition of C(2)HF(5) results in unusual (non-chain branching) reactions.

Phosphorus-containing compounds (PCCs) have been found to be significantly more effective than CF(3)Br for reducing burning velocity when added to stoichiometric hydrocarbon-air flames. However, when added to lean flames, DMMP (dimethylmethylphosphonate) is predicted to increase the burning velocity. The addition of DMMP to lean mixtures apparently increases the equivalence ratio (fuel/oxidizer) and the combustion temperature, as a result of hydrocarbon content of DMMP molecule. Premixed flames studies with added DMMP, OP(OH)(3), and CF(3)Br are used to understand the different behavior with varying equivalence ratio and agent loading. Decrease of the equivalence ratio leads to the decrease of inhibition effectiveness of PCCs relative to bromine-containing compounds. For very lean mixtures CF(3)Br becomes more effective inhibitor than PCCs. Calculations of laminar burning velocities for pure DMMP/air mixtures predict the maximum burning velocity of 10.5 cm/s at 4.04 % of DMMP in air and at an initial temperature of 400 K. Adiabatic combustion temperature is 2155 K at these conditions.

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.

This study is the first to examine the inhibition effectiveness of C2HF3Cl2 (HFC-123) on premixed hydrocarbon–air flames and is motivated by the eventual phase-out of CF3Br (Halon 1301) used in civilian aircraft cargo compartments. To study the inhibition effectiveness, we measured the laminar burning velocity of CH4–air flames with added C2HF3Cl2 in a spherical, constant-volume combustion vessel, over a range of inhibitor concentration and fuel–air equivalence ratio. Burning velocities at ambient (T = 298 K; P = 1.01 bar) and elevated (T = 400 K; P = 3 bar) conditions were compared to numerical predictions obtained using a newly-developed kinetic mechanism describing the decomposition of hydrochlorofluorocarbons (HCFCs) in hydrocarbon–air systems. The agreement was very good, considering the model parameters were not adjusted, and the present study was the first to test the mechanism against experimental data of a two-carbon HCFC. In addition to providing model validation, the effectiveness of C2HF3Cl2 was compared to the analogous HFC compound C2HF5 to explore the advantages of Cl substitution for F. Experimental measurements of agent influence on burning velocity, as well as numerical modeling of premixed flame structures, demonstrated that C2F3Cl2H is a more effective flame inhibitor than C2F5H, particularly for very lean CH4–air mixtures. The reaction pathways and sensitivities were analyzed to interpret the differences in the inhibition mechanisms of C2F5H and C2HF3Cl2 and to prioritize elementary reactions for further study.

Due to their high global warming potentials, many existing working fluids are being phased out. Their replacements will often be slightly flammable, and the burning velocity of refrigerant-air mixtures is a metric for ranking their flammability. To allow estimates of the flammability of new blends of agents, predictive tools for the burning velocity are being developed and require a kinetic mechanism. A hydrofluorocarbon (HFC) mechanism was developed 20 years ago to describe hydrocarbon-air flames with added trace amounts of hydrofluorocarbon fire retardants. In the present work, the mechanism has been updated slightly to include new HFC compounds, new rate data. The modified mechanism is used to predict steady, planar, 1D, unstretched burning velocities for mixtures of air with one- and two-carbon saturated HFC compounds R41 (CH3F), R32 (CH2F2), R161 (C2F5H), R152 (CH2F-CH2F), R152a (CH3-CHF2), R143 (CH2F-CHF2), R143a (CH3-CF3), R134 (CHF2-CHF2), and R134a (CH2F-CF3), for which existing experimental data were available.

Summary The effectiveness of phosphorus-containing compounds as gas-phase combustion inhibitors varies widely with flame type. To understand this behavior, experiments are performed with dimethyl methylphosphonate (DMMP) added to the oxidizer stream of methane–air co-flow diffusion flames (cup-burner configuration). At low volume fraction, phosphorus (via DMMP addition) is shown to be about four times as effective as bromine (via Br2 addition) at reducing the amount of CO2 required for extinguishment; however, above about 3000 μL/L to 6000 μL/L, the marginal effectiveness of DMMP is approximately zero. In contrast, the diminished effectiveness does not occur for Br2 addition. To explore the role of condensation of active phosphorus-containing compounds to the particles, laser-scattering measurements are performed. Finally, to examine the behavior of the flame stabilization region (which is responsible for extinguishment), premixed burning velocity simulations with detailed kinetics are performed for DMMP addition to methane–air flames. Analyses of the numerical results are performed to understand the variation in the inhibition mechanism with temperature, agent loading, and stoichiometry, to interpret the loss of effectiveness for DMMP in the present experiments. Copyright © 2015 John Wiley & Sons, Ltd.

In this work, we report a detailed chemical kinetic mechanism to describe the flame inhibition chemistry of the fire-suppressant 2-bromo-3,3,3-trifluoropropene (2-BTP), under consideration as a replacement for CF3Br. Under some conditions, the effectiveness of 2-BTP is similar to that of CF3Br; however, like other potential halon replacements, it failed an U.S. Federal Aviation Authority (FAA) qualifying test for its use in cargo bays. Large overpressures are observed in that test and indicate an exothermic reaction of the agent under those conditions. The kinetic model reported herein lays the groundwork to understand the seemingly conflicting behavior on a fundamental basis. The present mechanism and parameters are based on an extensive literature review supplemented with new quantum chemical calculations. The first part of the present article documents the information considered and provides traceability with respect to the reaction set, species thermochemistry, and kinetic parameters. In additional work, presented more fully elsewhere, we have combined the 2-BTP chemical kinetic mechanism developed here with several other submodels from the literature and then used the combined mechanism to simulate premixed flames over a range of fuel/air stoichiometries and agent loadings. Overall, the modeling results qualitatively predicted observations found in cup-burner tests and FAA Aerosol Can Tests, including the extinguishing concentrations required and the lean-to-rich dependence of mixtures. With these data in hand, in a second phase of the present work, we perform a reaction path analysis of major species under several modeled conditions. This analysis leads to a qualitative understanding of the ability of 2-BTP to act as both an inhibitor and a fuel, depending on the conditions and suggests areas of the kinetic model that should be further investigated and refined.

The effect of water vapor on hydrocarbon combustion (CH 4 , C 2 H 4 , C 3 H 8 ) was studied in the presence of an HFC agent (HFC-125). The effect depends on the F/H ratio of the initial mixture. A promotion effect was observed in mixtures with the F/H ratios ranging approximately from 0.9 to 2. The calculated maximum increase in peak flame temperature was in the range of 100–150 K, and in burning velocity, in the range of 1–2 cm/s. The change of the ratio from F/H ratio 1 corresponds to the disappearance of H 2 O and a substantial increase of CF 2 O in the combustion products. Thermodynamic and laminar premix flame calculations demonstrate that “extra” fluorine, which is in excess of hydrogen (F/H > 1), reacts with added H 2 O forming HF molecules. Calculations demonstrate that the equilibrium volume fractions of the fluorine atom can be as large as 0.5–3% for mixtures with an F/H > 1. The main reaction of H 2 O conversion to HF is the F + H 2 O = HF + OH reaction. Dependencies of the F/H ratio as a function of HFC-125 (C 2 F 5 H) concentration and showing the possible range of mixture compositions for a promotion effect, were generated for methane, ethylene and heptane at different equivalence ratios.

A kinetic mechanism for hydrocarbon flame inhibition by the potential halon replacement 2-BTP (2-Bromo-3,3,3-trifluoropropene) has been assembled, and is used to study its effects on premixed methane–air flames. Simulations with varying CH4–air stoichiometry and agent loading have been used to understand its flame inhibition mechanism. In particular, the response of lean methane–air flames is examined with addition of 2-BTP, CF3Br, C2HF5, and N2 to illustrate the effect of agent heat release on these flames. The results predict that addition of 2-BTP or C2HF5 can increase the burning velocity of very lean flames, and 2-BTP is less effective for lean flames than for rich. The flame inhibition mechanism of 2-BTP involves the same bromine-species gas-phase catalytic cycle as CF3Br, which drives the flame radicals to equilibrium levels, which can be raised, however, by higher temperatures with added agent (for initially lean flames). Simulations for pure 2-BTP–O2–N2 mixtures predict burning velocities on the order of 1 cm/s at 300 K initial temperature.

Numerical simulations of cup-burner flames in normal Earth gravity have been performed to study the combustion inhibition and unwanted enhancement by fire-extinguishing agents CF 3 Br (Halon 1301) and some potential replacements (C 2 HF 5 , C 2 HF 3 Cl 2 , and C 3 H 2 F 3 Br). A propane–ethanol–water mixture, prescribed for a Federal Aviation Administration (FAA) aerosol can explosion simulator test, was used as the fuel. The time-dependent, two-dimensional numerical code, which includes a detailed kinetic model (up to 241 species and 3918 reactions), diffusive transport, and a gray-gas radiation model, revealed unique two-zone flame structure and predicted the minimum extinguishing concentration of agent when added to the air stream. Despite striking differences in the flame shape, the agent effects were similar to, but stronger than, those in microgravity flames studied previously (for two of the agents). The peak reactivity spot (i.e., reaction kernel) at the flame base stabilized a trailing flame, which was inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of agent in the coflow ( X a ) increased gradually: (1) the premixed-like reaction kernel weakened; (2) the flame base detached from the burner rim, oscillated (particularly for CF 3 Br), until finally, blowoff-type extinguishment occurred; (3) the calculated maximum flame temperature remained nearly constant (≈1800 K) or mildly increased; and (4) the total heat release of the entire flame decreased (inhibited) for CF 3 Br but increased (enhanced) for the halon replacements. In the trailing flame with C 2 HF 5 , a two-zone flame structure (with two heat-release-rate peaks) developed: in the inner zone, H 2 O (a product of hydrocarbon–O 2 combustion and a fuel component) was converted further to HF and CF 2 O through exothermic reactions occurring in the outer zone, where exothermic reactions of the inhibitor also released heat; CO 2 was formed in-between. Thus, addition of C 2 HF 5 resulted in unusual (non-chain branching) reactions and increased total heat release (combustion enhancement) primarily in the trailing diffusion flame.

A kinetic model is suggested for hydrocarbon/air flame propagation with addition of hydrochloroflurocarbon (HCFC) fire suppressant, encompassing the combined chemistry of fluorine- and chlorine-containing species. Calculated burning velocities using the kinetic model are in good agreement with available experimental burning velocity data for CF3Cl, CF2Cl2, or CFCl3 added to CO/H2/O2/Ar flames. The agent CF3CHCl2 is more effective than C2HF5, and reaction pathway analysis shows that the inhibition effect of chlorine reactions is greater than that of fluorine. The main reactions of the chlorine inhibition cycle are H+HCl=H2+Cl, OH+HCl=H2O+Cl, Cl+CH4=HCl+CH3, Cl+HCO=HCl+CO, and Cl+CH2O=HCl+HCO. The inhibition effect of CF3CHCl2 is largely the result of competing reactions of chlorine-containing species with hydrogen (and other radical pool) species, decreasing the rate of the chain-branching reaction H+O2, with additional effects from substitution of the reactive chain-branching radicals for less reactive fl...

Computation has been performed for a methane-air co-flow diffusion flame, in the cup-burner configuration, with a phosphorus-containing compound (PCC), dimethyl methylphosphonate (DMMP) or phosphoric acid, added to the oxidizer stream. The effectiveness of compounds in gaseous flame inhibition depends upon the additive and flame types, which lead to different reaction environments. The time-dependent axisymmetric numerical code, which includes a detailed kinetics model (77 species and 886 reactions), diffusive transport, and a gray-gas radiation model (for CH4, CO, CO2, H2O, and soot), has revealed the interaction of the gas-phase mechanisms of PCCs with the flame structure. The PCCs behave similarly with regard to flame inhibition: both raise the maximum temperature in the trailing flame, lower radical concentrations, and lower the heat-release rate at the peak reactivity spot (i.e., reaction kernel) at the flame base where the flame is stabilized. The mechanism of lowered radical concentrations is primarily due to catalytic cycles involving phosphorus species in both regions of the flame. For DMMP, which contains three methyl groups, the flame exhibited higher temperature and combustion enhancement in the trailing flame, with unique two-zone flame structure.

A kinetic model for flame inhibition by antimony-halogen compounds in hydrocarbon flames is developed. Thermodynamic data for the relevant species are assembled from the literature, and calculations are performed for a large set of additional species of Sb-Br-C-H-O system. The main Sb- and Br-containing species in the combustion products and reaction zone are determined using flame equilibrium calculations with a set of possible Sb-Br-C-H-O species, and these are used to develop the species and reactions in a detailed kinetic model for antimony flame inhibition. The complete thermodynamic data set and kinetic mechanism are presented. Laminar burning velocity simulations are used to validate the mechanism against available data in the literature, as well as to explore the relative performance of the antimony-halogen compounds. Further analysis of the premixed flame simulations has unraveled the catalytic radical recombination cycle of antimony. It includes (primarily) the species Sb, SbO, SbO2, and HOSbO, and the reactions: Sb + O + M=SbO + M; Sb + O2 + M=SbO2 + M; SbO + H=Sb + OH; SbO + O=Sb + O2; SbO + OH + M=HOSbO + M; SbO2 + H2O=HOSbO + OH; HOSbO + H=SbO + H2O; SbO + O + M=SbO2 + M. The inhibition cycles of antimony are shown to be more effective than those of bromine, and intermediate between the highly effective agents CF3Br and trimethylphosphate. Preliminary examination of a Sb/Br gas-phase system did not show synergism in the gas-phase catalytic cycles (i.e., they acted essentially independently).

The use of the large retention index database for identification and filtering of false positive hits in GC–MS analysis of the ylang-ylang essential oil is illustrated. Differences between experimental retention indices and database values of retention indices of candidate compounds provide additional constraints on the list of candidates for a target compound. Over 100 components of ylang-ylang essential oil (total grade) were identified. The main components, with concentrations more than 4 %, are β-caryophyllene, germacrene D, benzyl benzoate, linalool, geranyl acetate, α-(E,E)-farnesene and isobornyl acetate.

A review of recent results of the use of chromatographic retention data in peptide identification and in the development of procedures for peptide retention prediction is presented. In recent years, reversed phase LC (RP-LC) has become an important tool in the separation of peptides in MS analysis. A challenging problem in a further expansion of RP-LC applications is the use of already available retention information for the identification purposes simultaneously with MS–MS identification. This overview focuses on the retention characteristics suggested in LC. We will discuss the application of the retention index concept in LC, which is widely used in GC to characterize retention of organic compounds. The use of retention indices as retention characteristics of analytes in LC was first suggested at the end of 1970s, however the application of retention indices is still somewhat rare today. There are several reasons for this. One is the relatively high sensitivity and variability of retention indices to the change of parameters of chromatographic systems. Another is the chemical restrictions in the search of the universal set of reference compounds suitable for retention scaling. Several methods were suggested for the prediction of the retention times of peptides. A frequently used approach is based on the additivity scheme and calculation of the elution time through the summation of retention coefficients of amino acids constituting the peptide. Such an approach allows fairly accurate predictions of the retention time of peptides made up of not more then 15–20 amino acid residues. Additional correction factors were suggested to improve predictions including corrections for the peptide length, peptide hydrophobicity, sequence of amino acids, etc. Suggested procedures are discussed in detail. Application of predicted retention times in the identification of peptides is considered. Current status of LC retention data collections is presented.

The optimization procedure was developed to derive the global kinetic parameters using experimental dependence of burning velocity on the equivalence ratio. The simple model of laminar premixed flame propagation with assumed constant parameters was used to demonstrate the features of the suggested procedure. The suggested method allows finding optimal parameters for the defined functional dependence of the reaction rate on the temperature and reactant concentrations. The dependence of combustion adiabatic temperature on equivalence ratio is assumed to be known from the flame equilibrium calculations. The global kinetic parameters of combustion reaction were determined for methane, ethylene and propane mixtures with air on the basis of experimental data on burning velocity as function of the equivalence ratio. The calculated overall kinetic parameters are compared with parameters obtained by other methods within similar global model.

The ignition of stoichiometric and fuel-lean hydrogen–air mixtures near 1000 K was studied, for varying amounts of iron additives. Depending on the initial conditions, the addition of iron pentacarbonyl promotes or inhibits the ignition of hydrogen/air mixtures. The simulations show that iron compounds at 1 μL/L 1 reduce the ignition delay by about 30%, and that 50 μL/L can reduce the ignition delay by a factor or two or three for lean and stoichiometric conditions; at slightly higher volume fraction (>150 μL/L), the ignition is retarded. The effectiveness of the iron compounds is influenced by the form of the added iron, stoichiometry, and initial temperature of the mixture. At low additive volume fraction, the promotion is the result of relatively fast decomposition of iron pentacarbonyl, which provides a source of radicals at the initial reaction stage during radical pool build-up; the ignition promotion is proportional to the amount of iron-containing additive, and mostly does not involve cycling reactions. In contrast, at higher additive volume fraction, the ignition is retarded by the iron compounds, through catalytic radical recombination cycles similar to those acting in flame inhibition. The reduction in chain-carrying radical concentrations occurs at later times in the ignition process when the radicals have reached high concentrations.

Retention indices were evaluated for one hundred most commonly reported essential oil compounds in gas chromatography (GC) using a large retention index database. Retention data are presented for three types of stationary phases: dimethyl silicone, dimethyl silicone with 5% phenyl groups, and polyethylene glycol stationary phases. The data evaluations are based on the treatment of multiple measurements with the number of data records ranging between 30 and 470 per compound. Data distribution analysis was limited to temperature programming conditions. Data reported include the most probable value of retention index, average and median values, standard deviation, and confidence intervals. The values of most probable retention indices correspond to frequently used GC conditions of measurements (temperature program, column parameters, gas flow conditions). The results are compared with data from several available retention index collections.

Some of the most effective flame inhibitors ever found are metallic compounds. Their effectiveness, however, drops off rapidly with an increase of agent concentration, and varies widely with flame type. Iron pentacarbonyl, for example, can be up to two orders of magnitude more efficient than CF 3 Br for reducing the burning velocity of premixed laminar flames when added at low volume fraction; nevertheless, it is nearly ineffective for extinction of co-flow diffusion flames. This article outlines previous research into flame inhibition by metal-containing compounds, and for more recent work, focuses on experimental and modeling studies of inhibited premixed, counterflow diffusion, and co-flow diffusion flames by the present authors. The strong flame inhibition by metal compounds when added at low volume fraction is found to occur through the gas-phase catalytic cycles leading to a highly effective radical recombination in the reaction zone. While the reactions of these cycles proceed in some cases at close to collisional rates, the agent effectiveness requires that the inhibiting species and the radicals in the flame overlap, and this can sometimes be limited by gas-phase transport rates. The metal species often lose their effectiveness above a certain volume fraction due to condensation processes. The influence of particle formation on inhibitor effectiveness depends upon the metal species concentration, particle size, residence time for particle formation, local flame temperature, and the drag and thermophoretic forces in the flame.

A kinetic model of a laser-induced breakdown spectroscopy (LIBS) plume of cyclotrimethylenetrinitramine (RDX) was developed for the analysis of processes responsible for the LIBS signature of explosives. Air and argon were considered as buffer gases. The model includes a set of processes involving ion chemistry, as well as excitation, ionization, and other processes affecting neutral and ion species. Modeling results show that the overall reaction process can be considered a two-stage process. The first stage corresponds to a fast approach to a quasi-stationary state, while the second stage corresponds to the change of quasi-stationary species concentrations due to the change in temperature. As a result of the two-stage process, the initial mechanism of explosive decomposition is not important in determining its signature in the LIBS measurement time window (1–30 μs). The main processes responsible for generation of excited states for the LIBS emission are electron-excitation impact processes. A mechanism for the appearance of a double peak of the C2 species concentration in the RDX plasma plume was suggested. Double-peak behavior of the C2 species was previously experimentally observed during laser ablation of graphite. Published by Elsevier B.V.

We have constructed a group contribution method for estimating Kováts retention indices by using observed data from a set of diverse organic compounds. Our database contains observed retention indices for over 35,000 different molecules. These were measured on capillary or packed columns with polar and nonpolar (or slightly polar) stationary phases under isothermal or nonisothermal conditions. We neglected any dependence of index values on these factors by averaging observations. Using 84 groups, we determined two sets of increment values, one for nonpolar and the other for polar column data. For nonpolar column data, the median absolute prediction error was 46 (3.2%). For data on polar columns, the median absolute error was 65 (3.9%). While accuracy is insufficient for identification based solely on retention, it is suitable for the rejection of certain classes of false identifications made by gas chromatography/mass spectrometry.

A review of recent results of the studies of double laser pulse plasma and ablation for laser induced breakdown spectroscopy applications is presented. The double pulse laser induced breakdown spectroscopy configuration was suggested with the aim of overcoming the sensitivity shortcomings of the conventional single pulse laser induced breakdown spectroscopy technique. Several configurations have been suggested for the realization of the double pulse laser induced breakdown spectroscopy technique: collinear, orthogonal pre-spark, orthogonal pre-heating and dual pulse crossed beam modes. In addition, combinations of laser pulses with different wavelengths, different energies and durations were studied, thus providing flexibility in the choice of wavelength, pulse width, energy and pulse sequence. The double pulse laser induced breakdown spectroscopy approach provides a significant enhancement in the intensity of laser induced breakdown spectroscopy emission lines up to two orders of magnitude greater than a conventional single pulse laser induced breakdown spectroscopy. The double pulse technique leads to a better coupling of the laser beam with the plasma plume and target material, thus providing a more temporally effective energy delivery to the plasma and target. The experimental results demonstrate that the maximum effect is obtained at some optimum separation delay time between pulses. The optimum value of the interpulse delay depends on several factors, such as the target material, the energy level of excited states responsible for the emission, and the type of enhancement process considered. Depending on the specified parameter, the enhancement effects were observed on different time scales ranging from the picosecond time level (e.g., ion yield, ablation mass) up to the hundred microsecond level (e.g., increased emission intensity for laser induced breakdown spectroscopy of submerged metal target in water). Several suggestions have been proposed to explain the mechanism of double pulse enhancement.

A kinetic model of the laser-induced breakdown spectroscopy (LIBS) plume of lead in argon has been developed to gain an understanding of the physical and chemical factors controlling the LIBS signature. This model includes processes involving ion chemistry, excitation, ionization, and other processes affecting the concentrations of argon and lead atoms (in 9 different electronic states) and their ions. A total of 15 chemical species and 90 reactions are included in the model. Experimental measurements of the temporal dependence of a number of lead emission lines in the LIBS plume of metallic lead have been made in argon and air. The modeling results are compared with these observations and with previous modeling of LIBS of lead in air.

A relationship between the Kovats and Lee retention indices was obtained for dimethylsilicone stationary phase and isothermal conditions. The temperature dependence of the retention indices was taken into account. Based on numerous experimental data for dimethylsilicone stationary phase, parameters of the linear temperature dependence of the Kovats indices were determined for the reference compounds of the Lee scale.

Acetylene decomposition flame propagation was numerically analyzed and was found to be the result of the condensation reaction. Condensation processes provide reaction heat and act as a driving force for C 2 H 2 flame propagation. The kinetic model reasonably predicts the level of burning velocity of the acetylene decomposition flame. The model does not demonstrate the relatively strong positive pressure dependence of burning velocity as was observed experimentally in the work of Cummings et al. [Proc. Combust. Inst. 8 (1962) 503–510]. Heat-release kinetics demonstrates a two-stage process. The first stage corresponds to heat release due to benzene formation, and the second stage of heat release corresponds to soot inception and carbonization processes. It was demonstrated that the burning velocity is sensitive to the surface growing rate constant. The use of a simplified form of presentation of the surface growing process [P.R. Lindstedt, in: Soot Formation in Combustion: Mechanisms and Models, Springer-Verlag, Berlin/New York, 1994, pp. 417–441] represents positive thermal feedback in the heat generation in a flame reaction zone.

A cosolvent-assisted spray pyrolysis process was developed for the formation of phase-pure metal particles from metal salt precursors without the direct addition of hydrogen or other reducing gas. Generation of phase-pure copper and nickel particles from aqueous solutions of copper acetate, copper nitrate, and nickel nitrate over the temperature range of 450 to 1000 °C was demonstrated. Addition of ethanol as a cosolvent plays a crucial role in producing phase-pure metal powders. Results of a modeling study of ethanol decomposition kinetics suggest that cosolvent decomposition creates a strong reducing atmosphere during spray pyrolysis via in situ production of hydrogen and carbon monoxide.

The first experimental measurements of the influence of manganese- and tin-containing compounds (MMT, TMT) on the burning velocity of methane/air flames are presented. Comparisons with Fe(CO) 5 and CF 3 Br demonstrate that manganese and tin-containing compounds are effective inhibitors. The inhibition efficiency of MMT is about a factor of two less than that of iron pentacarbonyl, and that of TMT is about 26 times less effective, although TMT is still about twice as effective as CF 3 Br. There exist conditions for which both MMT and TMT show a loss of effectiveness beyond that expected because of radical depletion, and the cause is believed to be particle formation. Kinetic models describing the inhibition mechanisms of manganese- and tin-containing compounds are suggested. Simulations of MMT- and TMT-inhibited flames show reasonable agreement with experimental data. The decomposition of the parent molecule for the tin and manganese species is found to have a small effect on the inhibition properties for the concentrations in this work. The inhibition effect of TMT is determined mostly by the rate of the association reaction H + SnO + M ↔ SnOH + M, and the catalytic recombination cycle is completed by the reactions SnOH + H ↔ SnO + H 2 and SnOH + OH ↔ SnO + H 2 O. The inhibition mechanism by manganese-containing compounds includes the reactions: MnO + H 2 O ↔ Mn(OH) 2 ; Mn(OH) 2 + H ↔ MnOH + H 2 O, and MnOH + OH (or H) ↔ MnO + H 2 O (or H 2 ), and the burning velocity is most sensitive to the rate of the reaction Mn(OH) 2 + H ↔ MnOH + H 2 O.

Chemically active fire suppressants may, due to their properties or the means by which they are added to flames, have strong inhibition effects in particular locations in a flame. To study the spatial effects of chemically active inhibitors, numerical experiments are conducted in which the rates of reactions of model inhibitors are varied in spatial regions defined by temperature. The influence of three types of spatial regions are investigated, those with the inhibitor (1) active only within a narrow temperature band (offon-off), (2) active below a cutoff temperature (on-off), and (3) active above a cutoff temperature (off-on). The effect of several localized chemical perturbations on the burning velocity are studied, including the

The effect of hydrocarbon fuel type on the ranking of inhibitor effectiveness has been investigated through computer simulations. The approach involves carrying out sensitivity analysis on the detailed kinetics of the combustion of C1-C4 hydrocarbons. It is demonstrated that the main reactions determining burning velocities are the same. Similar suppressant rankings from the combustion of different hydrocarbon fuels are largely due to the reactions of a number of small radicals that are common to all of these systems. Inhibitor addition reduces the concentration of these radicals with the active agents being recycled by the common breakdown products of the fuel. Inhibitor effectiveness of additives in a variety of fuels was analyzed using experimental data on the effects of additives on burning velocity in small additive concentration ranges. An universal ranking of additive efficiency is presented. The results demonstrate that the active agents in practically all cases are the small inorganic compounds created from decomposition processes. Inhibition effectiveness of agents is at a maximum at low concentrations. At higher concentrations, saturation effects, brought about by the approach of active radicals to their equilibrium concentrations, lead to substantial decreases in the effectiveness of high efficiency suppressants in comparison with their effects at small concentrations. The results show that the probable maximum increase in total flame suppression effectiveness of high efficiency agents will not exceed one order of magnitude in molar fractions in comparison with the effect of halon 1301 (CF3Br).

The burning velocity of premixed carbon monoxide–nitrous oxide flames (background water levels of 5 to 15 ppm) has been determined experimentally for a range of fuel–oxidizer equivalence ratio φ from 0.6 to 3.0, with added nitrogen up to a mole fraction of X N 2 = 0.25, and with hydrogen added up to X H 2 = 0.005. Numerical modeling of the flames based on a recently developed kinetic mechanism predicts the burning velocity reasonably well, and indicates that the direct reaction of CO with N 2 O is the most important reaction for CO and N 2 O consumption for values of X H 2 ≤ 0.0014. The calculations show that a background H 2 level of 10 ppm increases the burning velocity by only about 1% compared to the bone-dry case. Addition of iron pentacarbonyl, Fe(CO) 5 , a powerful flame inhibitor in hydrocarbon–air flames, increases the burning velocity of the CO–N 2 O flames significantly. The promotion is believed to be due to the iron-catalyzed gas-phase reaction of N 2 O with CO, via N 2 O + M = N 2 + MO and CO + MO = CO 2 + M, where M is Fe, FeO, or FeOH.

The production of the fire suppressant CF3Br has been banned, and finding a replacement with all of its desirable properties is proving difficult. Iron pentacarbonyl has been found to be up to several orders of magnitude more effective than CF3Br, but it is flammable and highly toxic. Ferrocene [Fe(C5H5)2], which is much less toxic and flammable than Fe(CO)5, can also be used to introduce iron into a flame. We present the first experimental data and numerical modeling for flame inhibition by ferrocene and find it to behave similarly to Fe(CO)5. A ferrocene mole fraction of 200 ppm reduced the burning velocity of slightly preheated premixed methane/air flames by a factor of two, and the effectiveness dropped off sharply at higher mole fractions. For air with a higher oxygen mole fraction, the burning velocity reduction was less. We also present experimental data and modeling for flames with ferrocene blended with CO2 or CF3H. The combination of the thermally acting agent CO2 with ferrocene mitigated the loss of effectiveness experienced by ferrocene alone at higher mole fractions. An agent consisting of 1.5% ferrocene in 98.5% CO2 performed as effectively as CF3Br in achieving a 50% reduction in burning velocity. Likewise, four times less CO2 was required to achieve the 50% reduction if 0.35% ferrocene was added to the CO2. In contrast, addition of 0.35% ferrocene to the hydrofluorocarbon CF3H reduced the CF3H required to achieve the 50% reduction in burning velocity by only about 25%. Thermodynamic equilibrium calculations predict that the formation of iron/fluoride compounds can reduce the concentrations of the iron-species oxide and hydroxide intermediates which are believed to be responsible for the catalytic radical recombination cycles.

A gas-phase mechanism for the formation of polychlorinated benzene, in systems where chlorine concentration need not be high, is presented. The key features are the quenching and mixing of lean and rich mixtures and the involvement of propargyl radicals as a key intermediate. It is dependent on the resistance of this radical to oxidation and the formation of chlorine in lean mixtures as a result of the oxidation of HCl. Results are derived on the basis of simulation studies using data on the combustion and chlorination of small hydrocarbons. Carbon monoxide and hydrogen in the effluent stream catalyze the release of chlorine from HCl. These results may have implications on dioxin formation mechanisms since they suggest that even in the absence of surface processes there may be a residual contribution purely from gas-phase reactions.

Iron pentacarbonyl (Fe(CO){sub 5}) is an extremely efficient flame inhibitor, yet its inhibition mechanism has not been described. The flame-inhibition mechanism at Fe(CO){sub 5} in premixed and counterflow diffusion flames of methane, oxygen, and nitrogen is investigated. A gas-phase inhibition mechanism involving catalytic removal of H atoms by iron-containing species is presented. For premixed flames, numerical predictions of burning velocity are compared with experimental measurements at three equivalence ratios (0.9, 1.0, and 1.1) and three oxidizer compositions (0.20, 0.21, and 0.24 oxygen mole fraction in nitrogen). For counterflow diffusion flames, numerical predictions of extinction strain rate are compared with experimental results for addition of inhibitor to the air and fuel stream. The numerical predictions agree reasonably well with experimental measurements at low inhibitor mole fraction, but at higher Fe(CO){sub 5} mole fractions the simulations overpredict inhibition. The overprediction is suggested to be due to condensation of iron-containing compounds since calculated supersaturation is suggested to be due to condensation of iron-containing compounds since calculated supersaturation ratios for Fe and FeO are significantly higher than unity in some regions of the flames. The results lead to the conclusion that inhibition occurs primarily by homogeneous gas-phase chemistry.

This paper deals with the ultimate limits of chemical contributions to flame inhibition. Particular attention is focussed on the inhibition cycles which regenerate the inhibitor. This leads to the definition of an idealized “perfect” inhibition cycle. It is demonstrated that for such an inhibitor in a stoichiometric methane/air flame, additive levels in the 0.001–0.01 mole percent range will lead to a decrease in flame velocity of approximately 30%. This efficiency corresponds roughly to the observed behavior of metallic inhibitors such as iron pentacarbonyl which is known to be as much as 2 orders of magnitude more effective than currently used suppressants. This correspondence between the behavior of a “perfect inhibitor” and iron carbonyl leads to the conclusion that only gas-phase processes can account for its inhibitive power.

The special problems associated with the destruction of highly fluorinated one and two carbon organics under combustion conditions are discussed in terms of their fundamental chemical kinetic prope...

This paper presents experimental and modeling results for laminar premixed methane-air flames inhibited by the fluoroethanes C{sub 2}F{sub 6}, C{sub 2}HF{sub 5}, and C{sub 2}H{sub 2}F{sub 4}, and experimental results for the fluoropropanes C{sub 3}F{sub 8} and C{sub 3}HF{sub 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{sub 2}HF{sub 5}, C{sub 2}H{sub 2}F{sub 4}, and C{sub 3}HF{sub 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.