The present paper reports experimental and modeling results on the laminar burning velocity and structure of stoichiometric and fuel-rich premixed laminar flames of DME with and without TMP additives. The spatial variations of the mole fractions of H, OH, PO, PO2, HOPO, HOPO2 and some intermediate hydrocarbons in the one-dimensional burner-stabilized flames with various equivalence ratios are measured by the flame-sampling molecular beam mass spectrometry. The novel measurement data for the DME flames are used to validate a kinetic mechanism available in the literature for flame inhibition by organophosphorus compounds. The TMP inhibition effectiveness of DME flames has been determined and revealed to be lower than that of CH4/air flame. The speeds of CH4/air and DME/air flames were found to be sensitive to the same reactions involving phosphorus compounds, while the sensitivity of the methane flame speed to inhibition reactions is higher than that of DME/air flame. The observed differences were explained by the higher concentration of the chain carriers H, OH, and O in the DME flame. Based on the results obtained, we conclude that the phosphorus-containing inhibitors are promising candidates for reducing the flammability and ensuring the fire safety of DME mixtures with air.

Numerical simulation has shown that replacing a part of methane by carbon monoxide in a rich mixture while maintaining the equivalence ratio leads to a decrease in the superadiabatic temperature effect due to the competition of chemical reactions. This is explained by a decrease in the H content in the combustible mixture and a decrease in the superequilibrium concentration of water in combustion products. Using numerical tracer simulation and a comparative analysis of the rates of consumption of CH4 and CO, it has been found that the consumption of both fuels in the CH4/CO/air flame is a competitive reaction path and CO monoxide does not act as an inert component in the low-temperature region of the front (contrary to the statements of a number of authors). Furthermore, the rate of consumption of CH4 is much higher than that of CO due to the larger number of consumption reactions of CH4 and their higher rates. The main contribution to the increase in the concentration of H atoms in the flame in passing from a methane–air mixture to a CH4/CO/air mixture is due to the same reactions that increase the heat release rate: O + CH3 = H + CH2O and CO + OH = CO2 + H. The results obtained and their comparison with literature data lead to the conclusion that the increase in the heat release rate and, hence, the flame propagation rate should be greater in rich mixtures since there the thermophysical effect is higher.

This paper presents a method for determining the optimal (in terms of fire-suppression effectiveness) composition of synergistic binary fire suppressants consisting of a chemically active inhibitor (e.g., trimethylphosphate) and an inert diluent (CO2). The method is based on the numerical simulation of the speed and structure of onedimensional premixed CH4/air and methyl methacrylate/air flames with the addition of a binary fire suppressant using reduced multistep chemical kinetic mechanisms. A decrease in the normal flame speed to 4.7-5.5 cm/s by the addition of a binary fire suppressant was used as a flame extinguishment criterion, and the minimum index of interaction of the components of the binary fire suppressant as a criterion for the maximum fire-suppression effectiveness. The proposed simulation method can help reduce the need for laborious experiments to determine effective mixtures of fire suppressants, thereby saving time and resources. The kinetic analysis performed in this study provides an insight into the mechanism of the synergism between trimethylphosphate and carbon dioxide in flame extinguishment. The results show that at the optimal ratio of fire-suppressant agents (for a specific flame and initial conditions), the rate of H atom production in methane combustion reactions is minimal and, at the same time, the H consumption rate in inhibition reactions is maximal.

In the present paper, the laminar burning velocity and structure of near-stoichiometric premixed laminar flames of methyl methacrylate (MMA) with and without trimethylphosphate (TMP) additives have been studied experimentally and by numerical modeling. The MMA+TMP combustion system is considered as a model system, which simulates gas-phase combustion of polymethyl methacrylate (PMMA) with additive of phosphorus-containing fire retardants (PFRs). The motivation of the present research is to provide a basis for development of a predictive gas-phase chemical kinetic model for inhibition of PMMA by PFRs. The flame sampling molecular beam mass spectrometry was used to determine the spatial variation of the mole fractions of H, OH, PO, PO2, HOPO, HOPO2 and some intermediate hydrocarbons in the one-dimensional burner-stabilized flames. The effect of TMP on the hydrocarbon intermediates in the flames is investigated. The reaction mechanism for combustion of MMA+TMP system has been validated against the novel laminar burning velocity and chemical speciation data. Performances and deficiencies of the kinetic mechanism for MMA flame inhibition are discussed. The sensitivity analysis showed that the insufficiently accurate prediction of mole fraction of H, O and OH results in disagreement for mole fraction profiles of hydrocarbon intermediates in the inhibited flame. Inhibition effectiveness of MMA flame by TMP is compared with that derived from experimental data for other fuels and the observed tendencies are discussed.

This paper deals with the nature of the synergistic effect in flames of methane and formaldehyde mixtures with air. Combustion of mixtures of different fuels is of great practical and fundamental interest. It has been found that the addition of formaldehyde to a rich methane/air flame at a constant concentration of methane first reduces the flame speed and then begins to increase it. The synergism mechanism in this case is due to the predominant and complete consumption of formaldehyde due to its higher reactivity and its negative impact on the rate of methane consumption. The predominant combustion of one of the fuels leads to the existence of two spatially separated heat release zones in the flame. In the first zone, heat release is mainly due to the oxidation of formaldehyde and formyl radical, and in the second zone, it is due to the recombination of methyl radicals. An analysis of the flame speed sensitivity has shown that the key reactions affecting the flame speed are the stages of formation of radicals (mainly hydroxyl) or products that lead to their formation. Reactions that make the main contribution to the heat release generally do not affect the flame speed. It has been found that the interaction of two fuels CH 4 and CH 2 O in a mixture with air leads to a marked increase in the superadiabatic temperature effect.

The combustion chemistry of formaldehyde in fuel-rich flames has been studied by numerical modeling and sensitivity analysis. It has been shown that the wide flammability limits of CH 2 O/air mixtures are due to features of the combustion chemistry of formaldehyde at high equivalence ratios rather than to the superadiabatic temperature effect. In this case, the thermal decomposition reaction of hydrogen peroxide H 2 O 2 plays a key role in the conventional branching reactions.

As dimethyl ether is being extensively used as an environmentally friendly motor fuel, the issue of its fire and explosion safety is becoming increasingly urgent. In this work, the action of trimethylphosphate, bromotrifluoromethane (CF3Br), trifluoroiodomethane (CF3I) and iron pentacarbonyl (Fe(CO)5) on the upper and lower concentration flammability limits (CFLs) of dimethyl ether/air mixture was studied using the counterflow burner technique and chemical kinetic modeling. Iron pentacarbonyl was shown to extend the lower limit and to have a small inhibition effect on the upper limit. The other additives, even in small concentrations, were shown experimentally to narrow the flammability limits with the effect on the rich limit being greater than that on the lean one. The kinetic mechanisms for flame inhibition by the abovementioned compounds used in the numerical simulations unsatisfactorily predicted the effect of inhibitors on the lower CFL. In addition, modeling greatly overpredicted the inhibiting effect of Fe(CO)5 on the upper limit compared to experimental data. As for the rich limit, the modeling predicted the effect of CF3I and TMP well and underpredicted the inhibition effect of CF3Br. As compared to other inhibitors, CF3I was found to narrow the upper CFL most effectively, whereas TMP is known to have the greatest effect on the speed of freely propagating flames. A possible explanation of the different inhibiting effects of chemically active inhibitors on freely propagating and counterflow flames has been proposed. As, in counterflow flames, the residence time can be less than the characteristic time of chemical reactions, the influence of some reactions on the flame parameters can be different in stretched (counterflow) flames and non-stretched (laminar freely propagating) flames. For TMP, this suggestion has been validated by analysis of the contributions of reactions involving phosphorus species to the rates of production and consumption of H atoms.

The distribution of air oxygen atoms in the oxidation products of rich mixtures of syngas with air in flame and the under autoignition conditions at constant volume has been investigated by numerical simulation using the tracer method. It has been found that in rich mixtures, the oxidation of hydrogen and carbon oxide has a stepwise nature, which is clearly visible in the profiles of the rates of production of H 2 O and CO 2 . The observed stepwise nature inevitably results in the heat-release rate occurring in steps. The reaction pathways and the role of the oxygen atom of the CO molecule in the heat release in these flames has been investigated.

The paper presents an experimental and modeling study of the chemical structure of laminar premixed stoichiometric H-2/CH4/C3H8/O-2/Ar flames stabilized on a flat burner at 1, 3, and 5 atm. The flame structure was simulated using four different detailed chemical kinetic mechanisms proposed in the literature for oxidation of small hydrocarbons. The width of the zone of consumption of the fuel components was shown to differ appreciably at the three pressures. Hydrogen was shown to have the largest consumption zone, while propane has the smallest one. The kinetic analysis provided an explanation for the observed phenomenon, which assumes the formation of additional pathways for hydrogen and methane production in the flames of ternary fuel mixtures. Comparison of the measured and simulated flame structures shows that all the mechanisms satisfactorily predict the mole fraction profiles of the reactants, products, and some intermediates at atmospheric and elevated pressures. It is noteworthy that the mechanisms adequately predict the spatial variations in the mole fractions of free radicals, including the H, OH, and CH3, within the pressure range. However, some drawbacks of the mechanisms used have been identified. The mechanisms were shown to overpredict the mole fractions of some unsaturated hydrocarbons, including ethylene and acetylene, at elevated pressures. Therefore, the rate constants of the crucial reactions responsible for production/consumption of these species, as well as their pressure dependences, should be specified, and the mechanisms should be refined. To provide a deeper insight into the combustion chemistry of ternary fuel mixtures, one should focus on the structure of rich flames.

A lack of available experimental data for spatial distributions of the species mole fractions in the flames of hydrogen at the pressures higher than atmospheric, which are required for developing and validating reliable kinetic models for hydrogen combustion, motivated this study. Stoichiometric laminar premixed H2/O2/Ar flames stabilized on flat burners at pressures 1, 3 and 5atm were examined in this work by molecular beam mass spectrometry. Mole fraction profiles of all flame species (H2, O2, H2O, H2O2, H, O, OH, HO2) were measured. A decrease in the peak mole fractions of H, O, OH radicals and an increase in the peak mole fractions of HO2 and H2O2 with pressure was observed. Two detailed kinetic mechanisms proposed recently by Konnov (2008) and Burke et al. (2012) for hydrogen combustion were validated against new experimental data reported in this work. Both mechanisms reproduced well the mole fraction profiles of H2, O2, H2O and H, O, OH radicals in the flames. However, the mechanism of Burke et al. was found to be more adequate in predicting the mole fraction profiles of peroxy species in the flames. The observed changes in the flame structure with pressure were explained on the basis of a kinetic analysis of the model developed by Burke et al. The experimental data reported in this work can help in further development and improvement of the future kinetic models of hydrogen combustion at elevated pressures.

The search for reactive additives capable of reducing the combustibility of dimethyl ether is an important problem due to the widening use of ether as an alternative environmentally friendly motor fuel. This paper presents a numerical study of the autoignition chemistry of mixtures of dimethyl ether with air in the presence of atomic iron. Atomic iron, which is an effective inhibitor of premixed laminar hydrocarbon flames, was found to shorten the induction period. However, the additive affects only the first stage of the induction period. The mechanism of promotion of the low-temperature oxidation of dimethyl ether–air mixtures by atomic iron is the formation of hydroxyls in reactions involving iron compounds. Since the additive hardly changes the duration of the second stage of the induction period, it can be suggested that OH radicals play an insignificant role in the low-temperature oxidation of dimethyl ether at this stage.

Fuel-rich laminar adiabatic flames of premixed dimethyl ether/air mixtures at a high initial temperature and atmospheric pressure have been studied by numerical simulation and sensitivity analysis. These flames, having two heat release zones, are of great interest as an unusual and little-studied subject. We have investigated the chemical processes occurring in the two zones and analysed themechanism of heat release in the flame. It has been found that the key reactions that have a significant influence on the flame speed are those involving dimethyl ether and the products of its incomplete oxidation. Calculation of the heat release rate confirms the presence of two heat release zones in the flame. A comparison of the reactions making a major contribution to the heat release with those significantly affecting the flame speed indicates that the main factor determining the flame speed is the formation of hydroxyls, rather than heat release. Analysis of the flame speed sensitivity shows that in the case of a two-zone structure of the flame, its speed is mainly determined by the reactions taking place in the low-temperature zone. That is, the cool zone with a higher temperature gradient is the leading one.

Interest in the combustion chemistry of multifuel blends is motivated by the need to study the combustion of natural gas, which is known to be a mixture of alkanes. The present study performed using molecular beam mass spectrometry and numerical modeling has shown that the width of the zones of hydrogen and methane consumption in the H2/CH4/C3H8/O2/Ar flame and the width of the zones of methane and propane consumption in the CH4/C3H8/C4H10/O2/Ar flame differ significantly from each other. The causes of this phenomenon were determined by analyzing the modeling results. It has been found that in the presence of heavier compounds, lighter fuels, such as H2 and CH4, are formed, which reduces the total rate of their consumption and, hence expands the zone of their consumption in the flame. The influence of the presence of hydrogen in the fuel mixture on the concentration of C2 hydrocarbons has also been studied. It has been established that the addition of hydrogen reduces the maximum concentration of ethane, ethylene, and acetylene in the flame, and the fraction of unsaturated C2 hydrocarbons with respect to saturated ones also decreases.

This paper presents a numerical and experimental study of the effect of flame-retardant additives on the autoignition of methane behind shock waves. It is shown that at a temperature of 1300–1900 K, the compounds CCl4, CF3H, and (CH3O)3PO not only do not suppress ignition but significantly reduce the induction time of methane–oxygen mixtures. A kinetic mechanism is proposed which relates the promoting effect to the reactivity of the pyrolysis products of the additives.

The enthalpy distribution at the front of one-dimensional flames of homogeneous mixtures of hydrogen, propane, formaldehyde, and methanol with air was numerically investigated. It is shown that the enthalpy distribution is more complex than the classical concepts: the enthalpy can both increase and decrease relative to the initial value. The specific form of the distribution is determined, in particular, by intermediate components formed at the flame front as they are also carriers of chemical energy and transfer it due to diffusion.

Normal burning velocities in methanol–air mixtures and in the same mixtures with added 4.5 and 7.2% hydrogen as a second fuel were measured over a wide range of equivalence ratio and for initial conditions of 0.16 MPa and 354 K. It has been shown that the mechanism previously proposed for the combustion of mixtures of CO, CH 2 O and CH 3 OH with air is applicable to multicomponent mixtures containing hydrogen and methanol.

A skeletal mechanism of inhibition and suppression of H2/O2/N2 by addition of trimethylphosphate was developed. It includes a mechanism of hydrogen oxidation (13 elementary steps involving 7 species) and two elementary reactions involving trimethylphosphate and its conversion products. This skeletal mechanism adequately predicts the burning velocity of flames with added inhibitor in the range of equivalence ratios studied, and can be used to model fire suppression.