This work presents, for the first time, both experimental and numerical investigations of the thermal and chemical structure of laminar premixed flames of aviation kerosene TS-1 and its four-component surrogate fuel, SU4 (n-decane, isocetane, methylcyclohexane, and tetralin). Experiments were conducted for lean ((p = 0.8) and stoichiometric ((p = 1.0) mixtures at atmospheric pressure. Species mole fraction profiles for more than 20 compounds, including key intermediates and radicals, were measured using soft-ionization molecular-beam mass spectrometry. The flame structures of TS-1 and SU4 show good agreement for most species, confirming the suitability of the surrogate for modeling high-temperature combustion behavior of the real fuel, with the exception of soot formation processes. Based on the experimental data, the detailed kinetic mechanism CRECK_2003_TOT_HT was validated. The main discrepancies were associated with the tetralin sub-mechanism. A reduced skeletal mechanism, KCPsur, consisting of 85 species and 183 reactions, was developed using the Directed Relation Graph (DRG) and Computational Singular Perturbation (CSP) methods. The KCPsur mechanism demonstrates predictive performance comparable to the detailed CRECK mechanism, while reducing computational cost by more than a factor of 32. This makes it suitable for CFD simulations of gas turbine combustion systems, particularly in cases where soot formation is not the primary focus.

Featured Application This study aims to address the scarcity of experimental data on the combustion of ammonia/ethane mixtures. It presents measurements of flame structure, ignition delay times, and speciation in JSR for various ammonia/ethane blends under a wide range of conditions. The flame structure of these mixtures is investigated for the first time at both atmospheric and elevated pressures, simulating conditions relevant to engine combustion chambers. These new data, combined with ignition delay times obtained in a shock tube and oxidation data from the JSR, enable a comprehensive evaluation of published mechanisms for ammonia-ethane combustion. The experimental data are used to assess the predictive capability of 11 detailed published kinetic models. Overall, this significantly extends the experimental database for the oxidation of ammonia/hydrocarbon mixtures, contributing to the refinement of chemical kinetic models. This, in turn, offers the prospects for the large-scale use of ammonia-based mixtures as alternative fuels.Abstract Ammonia is considered as a promising hydrogen carrier and a carbon-free fuel. Methods for improving ammonia combustion characteristics often involve its co-firing with more reactive fuels (natural gas, biofuels, etc.). Among the natural gas components, ethane is second most abundant. Therefore, the development of detailed chemical-kinetic mechanisms that accurately consider the interactions between ammonia and each component of natural gas is very important. Such mechanisms must be based on experimental data obtained under a wide range of conditions. In this work, NH3/C2H6/O2/Ar blends were studied in JSR (phi = 0.5-2.0, p = 1 atm, tau = 1 s, T = 800-1300 K) and in a shock tube (p = 7.3-8.6 atm, T = 1260-1590 K). Additionally, the structure of premixed flames was investigated (phi = 0.8-1.2, p = 1-5 atm). Eleven recently published detailed chemical-kinetic mechanisms were tested. The model Shrestha-2025 was updated to achieve better agreement with the entire set of experimental data. The effect of p and phi on intermediate species concentration was analyzed. Ammonia and ethane consumption pathways were also examined.

Ammonia-methane mixtures are considered promising low-carbon fuels for future power generation, yet the understanding of ion chemistry in such flames remains limited. This work presents the first comprehensive study of positive ion chemistry in laminar premixed NH3/CH4 flames at 1 atm by combining molecular beam mass spectrometry (MBMS), saturation current measurements, and detailed kinetic modeling supported by quantum chemistry calculations. Mass spectra recorded in the flame reaction zone identified a number of key flame cations, including H3O*, NH4*, NO*, HCNH*, CH2NH2*, CH3NH3*, C2H3NH3+, H2NCO*, CHN2H4* and C2H5NH3+, as well as their ammonia and water clusters formed during sampling. Saturation current measurements confirmed the CH + O pathway as the primary route of chemiionization, leading to the selection of the Zhang et al. mechanism (Fuel 341 (2023) 127676) as the optimal neutral chemistry basis. Based on the experimental findings, a comprehensive ion-chemistry mechanism was constructed by merging previously developed models for hydrocarbon flames and for the carbon-free NH3/H2 system, and extending them with reactions for the identified nitrogen-carbon cations. The proposed mechanism reproduces the spatial profiles of the major cations and captures key experimental trends. Notably, the inclusion of HONO-mediated pathways proved essential for correctly predicting NO+ formation in the post-flame zone, a significant improvement over previous mechanisms that substantially underestimated NO+ abundance. These results provide detailed insight into the coupled N-C-H-O ion chemistry in ammonia-methane flames and establish a foundation for simulation of ion currents and behavior of electrified flames, and the development of ion-based diagnostics and control strategies for ammonia-fueled combustion systems. Novelty and significance statement This study presents the first comprehensive investigation of positive ion chemistry in NH3/CH4 flames. Multiple cations specific to ammonia-methane combustion are identified by molecular beam mass spectrometry, and their structural and thermochemical characterization is provided using high-accuracy quantum chemical calculations. An ion chemistry mechanism, validated against measured spatial distributions of ions and saturation currents, offers novel insights into ion formation pathways during the combustion of ammonia-methane blends. The significance of this work lies in enabling ion-based technologies for ammonia-methane combustion, a promising low-carbon energy solution. By identifying key ions and providing the first validated ion chemistry mechanism for an H-C-O-N system, we establish a direct path for developing advanced combustion diagnostics and control strategies. The mechanism enables reasonable prediction of ion currents, which is crucial for designing sensors to monitor flame stability and optimize combustion in real time, thereby facilitating the practical implementation and reliability of ammonia-fueled systems.

In the originally published paper [...]

We present a combined experimental and modeling study of premixed atmospheric-pressure tetralin flames. Chemical speciation in near-stoichiometric (φ = 0.8–1.0) tetralin/O2/Ar flames was characterized by probe-sampling molecular-beam mass spectrometry (MBMS) with soft ionization (12.3–18 eV). Total ionization cross-sections (TICSs) for heavy intermediates were computed ab initio to enable quantitative MBMS processing. Laminar burning velocities (LBVs) of tetralin/air flames were measured in a range of equivalence ratios (φ = 0.75–1.5) on a nozzle burner via the stretch-corrected total area method. This is the first reported LBV data for tetralin/air flames (maximum LBV was 47.3 ± 2 cm/s at φ = 1.1). The experimental mole fraction profiles and LBVs were interpreted using three detailed mechanisms. None of the mechanisms were able to correctly describe the LBV profile, and a number of discrepancies were observed in the mole fraction profiles. Reaction network and sensitivity analyses were performed to identify specific sub-mechanisms requiring refinement. In particular, the subchemistry of naphthalene and indene strongly affects the accuracy of model predictions, whereas the flame speciation data indicate large uncertainties in the simulated concentrations of these species.

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.

Ammonia is a prospective hydrogen carrier and a carbon-free fuel. Its reactivity can be improved by co-burning with hydrogen. The use of ion-sensitive technologies shows great potential for controlling the combustion of ammonia-hydrogen blends. In this regard, there is a demand for the models reliably predicting ion currents and the behavior of electrified ammonia flames. Understanding the ion chemistry in relevant flames is crucial for developing these models. A flame sampling molecular beam mass spectrometry is used in this work to measure the spatial distributions of positively charged species naturally occurring in the atmospheric-pressure burnerstabilized premixed flames of ammonia/hydrogen/oxygen/argon mixtures with equivalence ratios phi = 0.8, 1.0, and 1.2. NH4+, NO+ and H3O+ are detected in the fuel-lean and stoichiometric flames, whereas NH4+ is found to be a dominant cation under the fuel-rich conditions. An ion chemistry mechanism for this carbon-free system, that includes the reactions involving the three cations, three anions and electron, is proposed and validated against the experimental data. The highly accurate W2-F12 quantum chemical calculations are used to obtain the thermodynamic parameters for NH4+ and NO+. The mechanism reproduces properly the measured relative abundance of NH4+ and H3O+ in stoichiometric and fuel-rich flames, however, it underestimates the NO+ relative abundance under fuel-lean and stoichiometric conditions. The major reaction pathways responsible for the production and consumption of the cations are considered to explain the observed tendencies, and the directions for the further mechanism improvement are discussed.

The influence of the forced convection rate on the chemical structure of a polymethyl methacrylate (PMMA) flame in an oxidizer flow under microgravity conditions was studied using numerical modeling. Gas flow around a solid sphere was simulated using the full Navier–Stokes equations for a multicomponent mixture. A multistep chemical kinetic mechanism was considered in the gas phase. The heat transfer and radiation in both the condensed and gas phases were considered in the modeling. On the PMMA surface, the pyrolysis reaction leading to the transformation of fuel from the condensed phase to the gas phase is specified. The forced convection speed varied in the range from 3 to 20 cm/s. Analysis of CO2 concentration fields near the burning surface under microgravity conditions showed that the maximum CO2 concentration is observed in the downstream zone. The width of the flame zone and its chemical structure depend on the intensity of forced convection. The width of the flame against the flow decreases, and the maximum CO concentration increases as the forced convection rate increases. Analysis of the rates of fuel consumption reactions showed that at a low convection speed (vst=3 cm/s), the reaction with the H radical, which has the highest diffusion coefficient, plays a crucial role in MMA oxidation.

Improvement of firefighting means and methods for measuring their effectiveness are important tasks in the field of fire safety. The paper presents the results of experimental measurements of the minimum extinguishing concentration of powder mixtures that can be applied as effective explosion-suppressing barriers. Measurements of the minimum extinguishing concentration of the investigated powders were carried out using a laboratory method with their pulsed delivery to a microfire of class B using compressed air. In order to justify and assess possible errors of the mentioned laboratory method for measuring extinguishing efficiency, numerical 3D modeling of the interaction of a multiphase flow with a model combustion focus was performed. The analysis of the numerical modeling results has shown that, for the applied laboratory method, almost the entire portion of the investigated powder enters the combustion zone. Additionally, the numerical calculations indicate that under the specified experimental conditions, the particle size of the powder has no noticeable effect on their loss into the surrounding flame space. Thus, these results justified the use of the mentioned laboratory method for he comparative evaluation of fire-extinguishing powders with a wide range of dispersity. The application of this laboratory method for assessing the effectiveness of the fire-extinguishing powder allowed for the development of an optimal powder composition for explosion suppression, incorporating inert mineral particles as the main component and an additive of a chemically active potassium-containing combustion inhibitor.

Results of studying interaction of two colliding axisymmetric laminar microjets of hydrogen in the course of their diffusion combustion are reported. Gas exhaustion occurs with identical velocities through pairs of micronozzles, which are thin-walled cylindrical tubes with an inner diameter of 200 μ m. The transverse positions of the tubes with respect to each other are changed during the experiment. Specific features of flame formation from two interacting microjets are found for different transverse positions of the tubes, and the results are compared with flames of single microjets with the same exhaustion velocity.

A possible method for a flammability reduction of the polymeric materials is the introduction of flame retardants into their composition. An effective search for optimal flame retardants and an understanding of their inhibition mechanisms requires the extensive information on the chemistry of their transformation in flames. A new data on chemical flame structure of a premixed H2/O2/Ar flame doped with 1000 ppm of triphenyl phosphate (TPP) at a pressure of 1 atm was obtained with a molecular-beam mass-spectrometry technique. Among intermediate products of the TPP decomposition were identified: several large phosphorus containing compounds, small phosphorus containing species (PO, PO2, HOPO, HOPO2), cyclic hydrocarbons (benzene, toluene, phenol), phenyl and phenoxy radicals. The detailed kinetic mechanism proposed earlier for the thermal degradation of TPP was updated with several new reactions including reactions with common flame radicals H/OH/CH3. Reaction rate constants were calculated using the Rice-Ramsberger-Kassel-Marcus theory and potential energy surfaces obtained by the DLPNO-CCSD(T)/cc-pVQZ//omega b97xd/6-31G(d) method. A comparison between experimental data and simulation results with the new model has shown a satisfactory qualitative and quantitative agreement, which confirmed that, the TPP decomposition occurs in flame according to the proposed scheme.

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.

In the article, the normative extinguishing capacity of substances is compared with the results of experiments on extinguishing class B fires. It is shown that the normative, real and laboratory effectiveness of powder extinguishing compositions are in good agreement. The presented studies confirm that the effectiveness of class B flame suppression can be improved by a factor of two by adding a small amount of inhibitor to the inert substance. The issue of equipping the object of protection with powder fire extinguishers is discussed from the point of view of taking into account their effectiveness. It is shown that due to the low requirements for the quantity and quality of fire extinguishers, a fire safety specialist must carefully pay attention to the weight, installation location and actual effectiveness of the fire extinguisher to improve the quality of the fire prevention system at the protection facility.

The microjet flame structure of a hydrogen-oxygen mixture exhausting into air is studied experimentally. A cylindrical metallic micronozzle with a diameter of 0.5 mm and a parabolic velocity profile at its cross-section is used to form a microjet of the hydrogen-oxygen mixture. It is found that adding oxygen to the hydrogen flow leads to a significant change in the dimensions of the laminar combustion zone and the structure of the flame jet. As the microjet exhaustion velocity increases, it is necessary to decrease the oxygen content in the mixture to ensure flame stability. It is shown that adding oxygen to the hydrogen flow transforms the spherical shape of the laminar combustion zone into a narrow and elongated cylinder-shaped flame region. As the microjet exhaustion velocity increases, the longitudinal size of the laminar combustion zone grows.

In this work, a comparative analysis of the properties of glass fiber-reinforced epoxy resin (ED-20) composites and composites based on glass fiber-reinforced phosphorus-containing ester methacrylate oligomers (PEAO) was carried out. Reinforced fiberglass plastics made on the basis of PEAO have demonstrated promising fireproof characteristics, especially in limited oxygen index and smoke emission tests. It is also worth noting that the mechanical properties of materials based on phosphorus-containing ester-acrylate resins are outstanding. The samples of a widely used glass fiber reinforced epoxy resin ED-20 with 9,10-dihydro-9-hydroxy-10-phosphaphenanthrene-10-oxide-4,4`-diaminodiphenylmethane (DDM-DOPO) additive demonstrated lower flammability compared to the samples without fire retardant additives. A mixture of DDM-DOPO and graphene added to the samples led to a low smoke generation rate of the samples; however, the rate was 1.5-2 times higher than that of the samples based on phosphorus-containing ester methacrylate resins. The addition of fire retardants has reduced the mechanical properties of fiberglass plastics based on epoxy resin, which can be a problem for the use of these materials in the aviation industry. These results clearly show better prospects of using fiberglass-reinforced plastics based on phosphorus-containing ester methacrylate oligomers in comparison with modified plastics based on the widely used epoxy resin.

In this paper, a methodology for experimental investigation of chemical and thermal structure of weakly stretched counterflow flames under terrestrial conditions is proposed. The non-premixed counterflow flames are stabilized in a narrow channel between quartz plates, and the flame gases are sampled by a microprobe inserted via a thin slit in one of the quartz plates. The gas samples are then analyzed by mass spectrometry. The results of the measurements of mole fraction profiles of the main components of methane-air non-premixed flames, namely, CH4, O2, H2O, CO2, and CO, are presented. The temperature profiles are also reconstructed using the measurement data for the gas composition. The experimental profiles are compared to the results of the 3D numerical simulations undertaken within the global reaction mechanisms (one- and four-step) and a detailed reaction mechanism (San-Diego). The results of this work clearly show that the thermal and chemical structures of the counterflow flame in the planar channel are essentially non-one-dimensional, and 3D-calculations are necessary to correctly predict the flame behavior in this configuration. The methodology demonstrated in the current work can be successfully employed for the investigation of the low stretched counterflow flames of various hydrocarbon fuels and fuel blends. This will allow verifying and developing the reaction kinetic models capable of quantitative prediction of weakly stretched flame behavior in confined conditions.

In this paper, we examine the combustion of a hydrogen microjet outflowing from a curved channel with a round micronozzle. Jet flows that are generated using rectilinear and curved channels differ in that, in the second case, Dean vortices make a noticeable contribution to the formation of the jet and its combustion. The interaction of the latter with Kelvin–Helmholtz vortices, the formation of which is typical for flows with a velocity shift, causes changes in the combustion characteristics. They include spatial distortions of the laminar flame zone near the nozzle exit, the area of turbulent combustion downstream, as well as the turbulent flame under the conditions of its separation from the nozzle exit and the cessation of laminar combustion in the initial section of the flow. The results of these studies provide the possibility to understand better the combustion features of hydrogen microjets under conditions of their hydrodynamic instability.

PMMA burning in counterflow has been studied experimentally and numerically. Thermal and chemical structure including concentrations of main species, i.e. ММА, O2, N2, CO2, CO and H2O, as well as an integral parameter (mass loss rate of a sample) were measured. The mathematical model is set in a coupled gas–solid formulation to resolve heat and mass transfer between gas-phase flame and thermally degrading solid combustible. Gas-phase combustion was modeled in the open-source Cantera software in a one-dimensional counterflow flame configuration. Governing equations of solid fuel was solved in an in-house code in two-dimensional formulation. Two chemical mechanisms of MMA oxidation (skeletal and detailed) were employed to resolve gas-phase combustion. Two sets of parameters of PMMA pyrolysis reaction were investigated. Gas phase temperature distribution was experimentally shown to be almost uniform in the direction parallel to the sample's burning surface in the area up to 4 mm from the sample's axis. The best agreement for macroscopic parameter, mass loss rate, was obtained by employing Lengelle pyrolysis kinetics, which is within 10 %. Total heat flux from gas-phase flame to the solid sample is about 23 kW/m2. Both gas-phase combustion mechanisms overpredict maximal temperature in flame by about 200 °C.

This paper presents the results of an experimental investigation of the diffusion combustion scenario of a round hydrogen microjet flowing from a cylindrical thin-walled micronozzle with a diameter of 200 μm when ignited near and at any distance from the nozzle exit. A review of the literature on the research topic is presented and a comparison is performed in dimensionless parameters based on the Reynolds number. It has been established that stabilization of the torch during the expiration of a round microjet of hydrogen is associated with heating of the nozzle by the laminar region of the flame. A hysteresis of the process of diffusion combustion of round hydrogen microjets was discovered depending on the region of ignition of the microjet (laminar or turbulent region of the torch) and on changes in the jet velocity.

The objective of the present study is an experimental investigation of diffusion combustion of round microjets, i.e., mixtures of hydrogen with methane, helium, and nitrogen. It is found that the evolution of burning microjets is associated with generation of a “bottleneck flame region” close to the nozzle exit, as it was observed earlier during hydrogen combustion. Combustion of a mixture of hydrogen and methane with increasing flow velocity occurs with the transformation of the torch. At first, a torch stabilized on the nozzle is observed, then it is divided into a stabilized part in contact with the nozzle and into a raised part of the torch. The combustion process occurs in two areas. A further increase in velocity promotes the breakdown of the raised torch, but maintains combustion in the nozzle area. The results on hydrogen/methane combustion are obtained in a smaller range of the microjet velocity than those of a hydrogen microjet. Somewhat similar data are derived for other gas additives. To make combustion of gas mixtures more stable with increasing microjet velocity, one has to increase the portion of hydrogen in the gas mixture or reduce the fractions of other gas additives.