This paper presents a study of flammability and downward flame spread rate in an opposed oxidizer flow over glass fiber-reinforced epoxy resin (GFRER) with the added flame retardants 6,6 '-((methylenebis(4,1-phenylene))bis(azanediyl)) bis(6 H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (DDM-DOPO) and graphene and with a binder content (BC) of similar to 35 wt% and similar to 52 wt%; the mass ratio of the glass fiber to the binder in the composite was 2:1 and 1:1, respectively. To evaluate the flammability and thermal stability of the obtained materials, the LOI test, the UL-94HB test, and thermogravimetric analysis were conducted. The effective DDM-DOPO concentration for decreasing the flammability of GFRER was found based on the LOI results. During the flame spread experiment with an opposed oxidizer flow, the addition of flame retardants resulted in an increase in the limiting oxygen concentration (LOC). Oxygen concentration increase in the oxidizer flow led to a decrease in the flame retardant effect on the rate of flame spread (ROS) for samples with a BC of similar to 35 wt%. The flame retardant effectiveness for samples with a BC of similar to 52 wt% remained almost the same at 40-60 vol% O-2 concentrations. The relationship among the LOI, LOC, and ROS was experimentally established. A numerical simulation of flame spread over reinforced material was performed using a coupled gas-solid heat and mass transfer model to predict the ROS over GFRER with and without flame retardants. The model correctly predicted the ROS for GFRER with similar to 35 wt% BC, while for samples with similar to 52 wt% BC, the model gave lower ROS compared to experiment.

Organometallic complexes of transition metals with inorganic anions are considered as promising precursors for the synthesis of nanoscale materials used in various applications including chemical catalysis. In this work, organometallic complexes of nickel, iron, and copper with imidazole as an organic ligand and the nitrate anion as an inorganic ligand were synthesized and characterized. The kinetic parameters of thermal decomposition of the synthesized organometallic complexes were determined by low heating-rate thermogravimetric analysis and high-speed dynamic mass spectrometric thermal analysis. The main gaseous products of thermal decomposition of the complexes under high-speed heating were identified. The chemical and phase compositions of condensed combustion products of the organometallic complexes in air were studied.

Systematic experiments and complementing numerical simulations have been reported for the first time to understand the spread of a ground fire over pine needle bed of the Siberian boreal forests (Pinus silvestris) in still air. Using equipment and instrumentations specifically developed for the purpose, careful experiments have been conducted to reveal the effects of the bed width, fuel moisture content, fuel load, and the packing ratio on flame spread rate, temperature distributions in both gas and condensed phases. Temperatures are measured using fine thermocouples fixed at various locations from the bed surface. The surface temperature of the bed during flame propagation has been measured using a micro-thermocouple inserted in a single pine needle in the bed as well as using an infrared (IR) camera. Further, for the first time, the total and radiant heat fluxes from the flame to the bed surface have been measured using compact cooled sensors placed inside the needle bed, over which the flame propagates. In order to understand more about the flow field and flame spread process, a 3D numerical model based on the Fire Dynamics Simulator (FDS) has been used to simulate few of the experiments. The processes governing pine needle pyrolysis, char oxidation, gas phase combustion and radiation have been modeled using simplified approaches reported in literature. The model is capable of predicting experimentally measured flame propagation velocities for most of the cases quite well.

For the first time, on the basis of a systematic experimental study of the propagation of a model ground fire over pine needles bed at a low wind speed (in the range of 0.1 m/s-0.4 m/s), in which there have been no measurements reported so far, a nonlinear dependence of flame spread rate on the wind speed has been established. Further, the total heat flux and its radiation counterpart have been measured using compact cooled sensors placed in the needles bed. Furthermore, the influences of the bed width and its moisture content on the flame propagation rate are studied. A three-dimensional numerical model based on Fire Dynamics Simulator (FDS) is used to investigate the processes governing the pyrolysis of pine needles, oxidation of char, gas phase combustion and radiation, using parameters from literature. The model, with simplified moisture release and pyrolysis sub-model, is able to predict the experimentally measured flame spread rates for most of the cases well within the measurement uncertainties. A sensitivity analysis is done to demonstrate the importance of pyrolysis chemistry over char oxidation rate. The predicted flow, temperature and species fields are presented to bring out the physics involved in the flame propagation. The validated model, coupled with detailed turbulence and radiation models, can be used as a first-hand predictive tool for scaled up ground fire scenarios.

The effect of triphenyl phosphate (TPP) retardant inhibition on flame propagation over the horizontal surface of polymethyl methacrylate (PMMA) has been studied experimentally and numerically. Regarding the flame spread behavior over the surface of PMMA (pure and inhibited by TPP), the following parameters were measured: thermal decomposition with TG / DTG analyzer, the flame spread rate, the pyrolysis zone length, the mass loss rate and spatial distribution of temperature by thermocouples and species concentration in the gas-phase flame by probing mass spectrometry. The previously developed coupled heat and mass transfer mathematical model describing the feedback interaction between flame and solid fuel, as well as volatilization of pyrolysis products, was modified to resolve the effect of TPP on flame spread by introducing the correcting factor of the gas-phase combustion reaction rate relating to the inhibitor concentration in the solid material. Good agreement between the measured and calculated flame spread parameters (flame spread velocity, mass burn-out rate, pyrolysis zone length), as well as a detailed flame structure (gas phase temperature and species concentration), has been obtained for pure PMMA and PMMA+10%TPP. It has been shown that the proposed approach describes a satisfactory retardant effect of TPP on the flame spread over PMMA surface by inhibiting the gas-phase combustion reaction.

Experimental and numerical studies of downward flame spread over polymethyl methacrylate (PMMA) with and without addition of triphenyl phosphate (TPP) are reported. Using the micro-thermocouple technique and molecular beam spectrometry, detailed flame structures of PMMA and PMMA+10%TPP were measured. From the experiments and quantum chemistry calculations, the retardancy capability of TPP on gas-phase reaction is proposed. Addition of flame retardant (10%, 20% TPP) results in reduction of the flame spread rate, the mass burning rate and conductive heat flux from the flame to the polymer surface. Numerical calculation was carried out to simulate the downward flame spread over PMMA and PMMA-TPP slabs. Based on the assumption of the TPP gas phase retardancy performance, a modified one-step reaction rate constant with pre-exponent dependent on the TPP mass content in the polymer and TPP retardancy effectivity is proposed. The predicted results have been compared with the data from sophisticated experimental measurement on thermal and chemical structures of both PMMA and PMMA+TPP flames.

Spatial distributions of positively charged species naturally occurring in the stoichiometric and fuel-rich premixed H2/CO/O2/Ar flames are measured with molecular beam mass spectrometry. The hydronium (H3O+) ion and its clusters are found to be most abundant cations in the flames. The ion chemistry model proposed earlier by Belhi et al. (2018) for lean methane flames is validated against the measurement data. The model was found to adequately predict the observed tendencies in the flames, once the exact mixture composition, including hydrocarbon impurities (∼5 ppm), is considered.

In our work, we studied the effect of the triphenyl phosphate flame retardant (TPP) on the flammability of polymethyl methacrylate (PMMA) using probe (microthermocouples) and non-disturbing planar laser-induced fluorescence (PLIF) diagnostic methods. Addition of TPP results in a decrease of the burning rate, reduction of the size of the pyrolysis zone, abatement of the heat flux from the flame to the polymer surface, and also decrease in the concentration of OH radicals in the flame, leading to quenching. Thus, the gas-phase effect of the TPP flame retardant on the flammability of the PMMA polymer was demonstrated.

Introduction. Polymer materials are widely used, however the actual object is to provide polymers combustion ­model to predict their behavior under fire, and reducing flammability. The work is devoted to the experimental ­study and numerical simulation of flame propagation over the surface of horizontally and vertically placed slabs of polymer in still air. Methods. The object of the investigation was cast polymethylmethacrylate (PMMA). The experiment was focused on measurement of the spatial distributions of the temperature and species concentrations of the PMMA pyrolysis and combustion products in the gas-phase over the surface of PMMA. Temperature was measured by micro­thermocouple with diameter of 50 microns. Probe mass-spectrometry was used for the measurement of the spa­tial distribution of species concentrations in the flame. Results and discussion. The main species (mehylmethacrylate (MMA), O2, CO2, H2O, N2, C2H4 (ethylene), C3H6 (propylene)) were identified and their concentration profiles were measured on the different distance from the flame front. The chemical structure of the flame was established to be in good agreement with the thermal one. The size of the “dark zone” of the flame, in which the temperature near the surface of the polymer is minimal, correlated well with the size of the oxygen-free zone. The mass burning rate, the velocity of flame propagation, the width of the pyrolysis zone and the temperature distribution in the condensed phase were also measured. Based on the experimental results, densities of conductive and radiation heat fluxes from the flame to the fuel surface were deter­mined. Calcula­tion of the radiation heat flux density was carried out under the assumption of an optically thin ­model. Modeling of the horizontal flame propagation over the PMMA surface was carried out using a two-dimen­sional conjugated laminar combustion model that takes into account one-step reactions — the decomposition reaction of PMMA in the condensed phase and the oxidation of decomposition products in the gas phase. Modeling of the vertical flame propagation over the PMMA surface was carried out using economical model of FDS. Conclusion. The model was shown to describe satisfactorily the experimental data such as the mass burning rate, flame propagation velocity, as well as the temperature distribution and concentration of species near the flame front.

Using the methods of differential mass-spectrometric thermal analysis (DMSTA), thermogravimetric analysis (TGA), microscale combustion calorimetry (MCC), and fast pyrolysis (FP), thermal decomposition of high-molecular-weight polymethylmetacrylate (PMMA) has been investigated in the temperature range of 315 + 500 degrees C. Based on these data, the kinetic parameters (the activation energy, the pre-exponential factor) were obtained of a one-step pyrolysis reaction in supposition of a first-order reaction using simple mathematical fitting and an iso-conversion method. Validity of the obtained kinetic parameters was verified by comparing the experimental data on dependence of the decomposition rate on temperature in the broad range of the heating rates with the results of simulating the above dependence, using these kinetic parameters. These parameters, obtained in the broad temperature range, may be further used in numerical simulation of PMMA combustion under fire conditions and for assessing the polymer's flammability.

This study presents the results of a comprehensive experimental investigation and numerical simulation of the downward flame spread over PMMA slabs. For the first time, in the case of downward flame spread over PMMA slab 9.6mm thick, temperature and species concentration fields in the gas-phase flame, temperature profiles in the condensed phase and dependence of the heat flux to the burning surface on the distance from the flame front were obtained. A coupled model of heat and mass transfer involving two-dimensional elliptic conservation equations both for gas phase and solid fuel has been used with the fuel surface approximation of the samples burnout. This allowed us to state, for the indefinite intermediate mode (in terms of the sample thickness, which are not neither thermally thin nor thermally thick), a mathematical model ensuring good agreement between the experimental and calculated macro parameters of combustion. The results of comparing the experimental and calculated data allowed us to determine a number of facts, which, despite the satisfactory agreement between the simulation and the experimental data in the main macro parameters, indicate the necessity of further improvement of the model derived. Such facts are: the increasing disagreement between the calculation and the experiment in the position of the maxima of the temperature in the gas phase as the distance from the flame front grows; essential difference in the width of the MMA and O-2 consumption zone between the calculation and the experiment; identification in the experiment of CO as an intermediate product. Further improvement of the model should be aimed m more detailed development of the combustion reaction mechanism, which should consider at least two steps. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

SummaryThe burning behavior of polyethylene in the counterflow of oxidizing air has been studied numerically with a coupled model describing feedback heat and mass transfer between gas‐phase flame and polymeric solid fuel. A 2‐dimensional elliptic equation in axisymmetric formulation (revealing the cylindrical shape of the polymer sample used in the experiment) has been employed to simulate heat transfer in solid fuel, and a set of 1‐dimensional hyperbolic equations has been used to determine the solid‐to‐gas conversion degree of the pyrolysis reaction. Four sets of products compositions and two modifications for the kinetic parameters of solid fuel pyrolysis reaction have been taken into account. Gas‐phase formulation is presented by set of 1‐dimensional conservation equations for multi‐component flow with detailed kinetic mechanism of combustion. The profiles of temperature and species concentrations in the flame zone have been calculated and compared with the results of experimental study of combustion of ultrahigh molecular weight polyethylene. Higher hydrocarbon composition (dodecane) has been found to show the best agreement between the temperature and species concentration profiles with the measurements, especially for the low‐level mass fractions of the by‐product components—propylene, butadiene, and benzene.

The combustion of ultrahigh molecular weight polyethylene (UHMWPE) in airflow perpendicular to the polyethylene surface (counterflow flame) was studied in detail. The burning rate of pressed samples of UHMWPE was measured. The structure of the UHMWPE–air counterflow flame was first determined by mass spectrometric sampling taking into account heavy products. The composition of the main pyrolysis products was investigated by mass spectrometry, and the composition of heavy hydrocarbons (C7—C25) in products sampled from the flame at a distance of 0.8 mm from the UHMWPE surface was analyzed by gas-liquid chromatography mass-spectrometry. The temperature and concentration profiles of eight species (N2, O2, CO2, CO, H2O, C3H6, C4H6, and C6H6) and a hypothetical species with an average molecular weight of 258.7 g/mol, which simulates more than 50 C7—C25 hydrocarbons were measured. The structure of the diffusion flame of the model mixture of decomposition products of UHMWPE in air counterflow was simulated using the OPPDIF code from the CHEMKIN II software package. The simulation results are in good agreement with experimental data on combustion of UHMWPE.

Experimental data are reported on the structure of laminar premixed methane/oxygen/argon flames stabilized over a flat burner at 1, 3, and 5 atm with different equivalence ratios phi (0.8-1.2). Mole fraction profiles of the reactants (CH4, O-2), major stable products (CO2, H2O, H-2, CO) and intermediates such as H, OH, CH3 radicals, as well as ethylene and acetylene, were measured by molecular-beam mass spectrometry. The temperature profiles in the flames were measured by thermocouples in the presence of a sampling probe to take into account the flame cooling effect due to the probe. The structures of stoichiometric flames at 1, 3 and 5 atm were compared to elucidate the effect of pressure on the mole fractions of the flame species. Fuel-lean (phi = 0.8) and fuel-rich (phi = 1.2) flames at 5 atm were also investigated in this work. All the experimental data were compared with the numerical simulations using the Premix code and three detailed chemical kinetic mechanisms for methane combustion available in the literature: the GRI-Mech 3.0, AramcoMech 1.3 and USC Mech II. The absolute mole fractions of CH4, O-2, H2O, CO, CO2, H-2, H, OH, CH3 in the flames and their dependences on pressure were captured by both mechanisms reasonably well. An analysis of the reaction mechanisms was performed to gain insights into the kinetics of methane combustion in stoichiometric conditions in the range of pressures from 1 to 5 atm and to explain the observed pressure effects on peak mole fractions of flame radicals. The decrease of peak mole fractions of acetylene and ethylene with pressure increase, which was observed in the experiments, was not reproduced by the mechanisms. Both mechanisms predicted the increase in their peak mole fractions with pressure (in the range from 1 to 3 atm). The kinetic analysis indicated the need to revise the pressure-dependent chemistry of acetylene and ethylene formation in the mechanisms. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A kinetic mechanism for combustion of hydrogen azide (HN 3 ) comprising 61 reactions and 14 flame species (H 2 , H, N, NH, NH 2 , NNH, NH 3 , HN 3 , N 3 , N 2 H 2 , N 2 H 3 , N 2 H 4 , N 2 , and Ar) was developed and tested. The CHEMKIN software was used to calculate the flame speed at a pressure of 50 torr in mixtures of HN 3 with various diluents (N 2 and Ar), as well as the self-ignition parameters of HN 3 (temperature and pressure) at a fixed ignition delay. The modeling results of the flame structure of HN 3 /N 2 mixtures show that at a 25–100% concentration of HN 3 in the mixture, the maximum temperature in the flame front is 25–940 K higher than the adiabatic temperature of the combustible mixture. Analysis of the mechanism shows that burning velocity of a HN 3 /N 2 mixture at a pressure of 50 torr is described by the Zel’dovich-Frank-Kamenetskii theory under the assumption that the burn rate controlling reaction is HN 3 + M = N 2 + NH + M (M = HN 3 ) provided that its rate constant is determined at a superadiabatic flame temperature. The developed mechanism can be used to describe the combustion and thermal decomposition of systems containing HN 3 .

The flame structure of the premixed H2/O2/Ar mixture (13%/14.5%/72.5% vol.) with and without 0.12 vol.% of titanium tetraisopropoxide (Ti(OC3H7)4) has been studied experimentally using the flame-sampling molecular beam mass-spectrometry and the microthermocouple techniques. The flame was stabilized on a flat burner at 1 atm. The temperature and concentration profiles for Н2, О2, H2O, and Ti(OC3H7)4 have been measured. The mass peak intensity profiles of the titanium-containing species TiO2, HTiO2, TiO, HTiO, Ti, TiH, Ti2O3, TiO3 have been measured as well. The experimental results were analyzed using kinetic modeling and quantum chemical calculations. It was established that hydrolysis of Ti(OC3H7)4 is the dominating primary reaction of its decomposition in the flame. The rate constant of hydrolysis was estimated to be k = 2 × 1012 exp(−6160/T) mol−1 cm3 s−1. The results of quantum chemical computations support this conclusion. On the basis of concentration profiles of the Ti-containing intermediates, the schematic mechanism of the Ti(OC3H7)4 conversion in the flame has been proposed.

The thermal degradation and combustion of ultra-high-molecular-weight polyethylene (UHMWPE) doped with triphenyl phosphate (TPP) at atmospheric pressure was studied by molecular beam mass spectrometry, dynamic mass spectrometric thermal analysis, microthermocouples, thermogravimetry, gas chromatography/mass spectrometry. The kinetics of thermal degradation of pure UHMWPE and that mixed with TPP at high (≈150 K/s) and low (0.17 K/s) heating rates was investigated. The effective values of the rate constant and activation energy of the thermal degradation reaction were determined. Burning velocity and temperature profiles in UHMWPE and UHMWPE + TPP flames were measured. The composition of the combustion products in a flame zone adjacent to the burning surface of the sample was determined. TPP vapor in the flame was detected. The addition of TPP to UHMWPE was found to reduce the flammability of the polymer. It is shown that TPP acts as a fire retardant in both the condensed and gas phases.

The mechanism of reducing the flammability of ultrahigh-molecular-weight polyethylene (UHMWPE) with triphenyl phosphate (TPP) additives was investigated, using the methods of molecular-beam mass spectrometry (MBMS), differential mass spectrometric thermal analysis (DMSTA), thermocouple, thermogravimetry (TGA), and gas chromatography mass spectrometry (GC/MS). Kinetics of thermal degradation of pure UHMWPE and of that mixed with TPP was studied at high (∼150K/s) and low (0.17K/s) heating rates at atmospheric pressure. Effective values of the rate constants of the thermal degradation reaction were determined. Times of ignition delay, the limiting oxygen index, the burning rates of UHMWPE and UHMWPE+TPP and their temperature profiles in the flames were measured. The flame structure was investigated and the composition of the combustion products in the flame zone adjacent to the specimen’s combustion surface. TPP vapors in flame were found. Addition of TPP to UHMWPE was found to result in reduction of polymer flammability. TPP was shown to act as flame retardant both in the condensed and gas phases.

In thermocouple measurements in flames of gaseous or condensed systems, it is usually assumed that due to the small sizes of thermocouples, the flame perturbations caused by thermocouples are negligible. It is shown, however, that these perturbations can be significant. Temperature measurements in a laminar methane flame at atmospheric pressure revealed a systematic overestimation of measured temperatures compared with the temperature of the unperturbed flame in the temperature gradient region and in the region of the maximum concentration of radicals. This overestimation was measured, and its causes were analyzed. Previously, such effects have not been studied in the literature.

Flame perturbations caused by the presence of a thermocouple have been studied by modeling the external flow of a reactive gas mixture around a thermocouple using the complete system of unsteady Navier-Stokes equations modified to approximately account for the effect of heat release due to chemical reactions. The modeling was performed for a methane gas flame and for the flame of a condensed system exemplified by RDX under the experimental conditions described in the literature. It is found that the deceleration of the flow in the vicinity of the thermocouple leads to a local increase of heat due to chemical reactions and the corresponding increase in temperature relative to the thermocouple unperturbed value. This effect has not been previously discussed in the literature.