Home – Home – Jornals – Combustion, Explosion and Shock Waves 2023 number 2

Specific features of the pyridine structure make it a convenient model system to describe coal combustion; however, the main attention of researchers has been paid to the formation of the ortho-pyridyl, whereas the formation of meta- and para-pyridyls has been yet poorly studied. The rate constants of the formation of three pyridine radicals by hydrogen atom abstraction by another hydrogen atom are compared. The geometry of the reactants is optimized within the framework of the density functional theory with subsequent refinement of single-point energies by the ab initio G3(MP2,CC) hybrid method. The calculations show that the formation of ortho-pyridyl is preferable, though the formation and further transformations of all three radicals should be taken into account for a detailed description of the coal combustion process.

This paper describes a numerical simulation of a laminar flame of a premixed mixture of ethanol and air at atmospheric pressure with the addition of a suspension of ethanol droplets. The initial fuel-oxidizer ratio in the gas phase is ϕ_gas = 0.844 and 1.125. With account for the fuel in the liquid phase, the total equivalence ratio is ϕ_tot = 1.195 and 1.476, respectively. The calculation is performed using the method of direct numerical simulation with a reduced chemical mechanism. Motion, heating, and evaporation of droplets are determined using the Lagrange approximation. The numerical simulation results are verified using experimental data (flame cone photographs and laser-induced fluorescence data). It is revealed that all the droplets evaporate in the flame front heating region and the presence of fuel in the liquid phase significant increases the CO concentration both in the calculation and in the experiment.

A numerical and experimental study of concentrations of combustion products and pollutant emissions in the case of combustion of premixed methane-hydrogen mixtures in a model combustion chamber of a gas-turbine power plant is performed. The mathematical model of combustion of methane--hydrogen mixtures used in the study ensures good qualitative and quantitative agreement between the numerical and experimental data on the main combustion products and also qualitative agreement on emissions of pollutants. In what follows, this mathematical model of combustion combined with the chosen kinetic mechanism of combustion can be used to analyze the emission characteristics of gas-turbine power plant combustion chambers designed for operation on hydrogen-containing mixtures.

The possibility of solving problems of chemical kinetics using artificial neural networks is investigated. The main laboriousness of solving problems of chemical kinetics lies in solving a rigid system of balance equations, whose right side contains the component mass production intensity. This problem can be singled out as a separate stage of solving a system of ordinary differential equations within a common time step of the global problem, and this stage is considered in this paper. A fairly simple model is developed that can solve this problem, which makes it possible to achieve a threefold acceleration of calculations as compared to numerical methods. The resulting neural network operates recursively and can predict the behavior of a chemical multicomponent dynamic system many steps ahead.

The geometric structures, vibration frequencies and relative energies of reactants, products, intermediates, and transients involved in the self-recombination of the indenyl radical were determined using G3(MP2,CC) // B3LYP/6-311G^** quantum chemical calculations. The barrierless association of a pair of indenyl radicals forms the C₁₈H₁₄ complex. The subsequent set of isomerizations of the complex is divided into five reaction channels, which in all cases end in H abstraction but with different four-ring isomers C₁₈H₁₄: in the form of condensed rings-tetraphene, tetracene, chrysene, dibenzoazulene; with an associated internal bond of the rings-dibenzofulvalene. The yield of chrysene prevails since the energy barriers encountered on the pathway of its formation are lower than the barriers on the formation pathways of other products.

Stability of a swirl flame of a premixed methane-air mixture under various gravity conditions is studied. Charts of stable combustion at normal and reverse gravity in the coordinates of the flow velocity and equivalence ratio. It is shown that the limits of stable combustion remain unchanged regardless of using a swirler with and without the central body, but the flame geometries are different. Swirlers are found to produce a minor effect on the flame blowout conditions, especially under the normal gravity condition. It is demonstrated that a swirler allows obtaining a rich lifted flame under the normal gravity condition and a lean lifted flame under the reverse gravity condition. It is found that dilution of the mixture with the fuel leads to expansion of the boundary of combustion stability under the reverse gravity condition as compared to the situation under the normal gravity condition.

The stationary diffusion combustion of a suspension of boron nanoparticles in isopropanol in cocurrent oxygen flow and the pulsed laser photolytic initiation of this combustion were studied. The experiments were carried out using a number of spectroscopic methods. Coherent anti-Stokes light scattering spectroscopy was used to determine the transverse distributions and concentrations of oxygen molecules diffusing into the fuel jet and the flame temperature change at different distances from the edge of the burner nozzle due to the addition of boron nanoparticles into the fuel. The dimensions zones of laser ignition initiation of the combustible mixture were determined by laser-induced fluorescence spectroscopy of electronically excited O₂^* molecules. Chemiluminescence spectroscopy of intermediate products of gas-phase reactions (OH* and BO₂^* radicals) from the ignition region made it possible to characterize the spatio-temporal dynamics of this process. The changes in the temperature field and ignition dynamics due to the addition of boron nanoparticles are explained based on an analysis of the obtained data. In particular, it is assumed that the characteristic rise in temperature in the region of the flame front is primarily due to an increase in the burning rate of the fuel with nanoparticles.

A method of calculating the characteristics of atomization of a liquid fuel by pressure swirl atomizer for setting the boundary conditions of injection into the primary combustion area is proposed. Results of simulating CO emission in a model combustion chamber are presented for two variants of the boundary conditions of liquid fuel injection: (1) with the use of the discrete phase model (DPM), where the parameters of fuel atomization are obtained by modeling a two-phase flow by the volume-of-fluid (VOF) method, and (2) for comparisons, with the use of the semi-empirical method of calculating pressure swirl atomizers developed by H. Lefebvre. The method of determining the boundary conditions of injection proposed in the paper makes it possible to increase the accuracy of predicting CO emissions by several times as compared to the classical semi-empirical method of calculating pressure swirl atomizers.

This paper presents the results of studies of the formation of polyaromatic hydrocarbons (PAHs) and carbon nanoparticles during pyrolysis of mixtures of ethylene with additives of linear ethers: dimethyl ether CH₃OCH₃ (DME), diethyl ether C₂H₅OC₂H₅ (DEE) and dimethoxymethane CH₃OCH₂OCH₃ (DMM). The studies were carried out behind reflected shock waves at temperatures of 1650-2550 K and pressures of 2.7-4.1 atm using optical diagnostic methods: laser-induced fluorescence (LIF) and laser extinction. These additives were found to accelerate the formation of PAHs and carbon nanoparticles. Kinetic modeling results show that this effect is due to the presence of methyl and ethyl groups in the molecules, which promote the formation of PAHs and soot.

Experiments on the filtration combustion of automobile tires mixed with a solid coolant are carried out. The mass content of tire particles in a mixture varies from 10 to 70%. Particles of chemically inert sapphire (Al₂O₃) and sulfur-absorbing marble (CaCO₃) are used as a heat carrier. Optimal conditions for the filtration combustion of automobile tires are determined (the tire content in a mixture is 50%, the combustion temperature is approximately 1 000 ºC, the mass burning rate is 0.40 kg/m³ of supplied air). It is established that the replacement of a solid inert coolant with marble has practically no effect on the combustion temperature. In this case, the composition of combustion products changes: the CO₂ content in gaseous products increases (their combustion heat decreases from approximately 2.5 to 2.2 MJ/m³), the yield of liquid pyrolysis products decreases approximately from 45 to 40%, and the sulfur content in solid combustion products increases from 28 to 40%.

The interaction of flow of burning and smoldering particles with some types of combustible building materials and wood-based structures was studied experimentally. The heat flux generated by glowing particles was determined, and the temperature fields of the most heat-stressed sections of the structures were analyzed. The sample heating rate was estimated based on the data of IR thermography. For the selected parameters of the experiment, the sample simulating a terrace was found to be the most resistant to ignition. Estimation of the temperature in the near-surface layer of the terrace element showed that after 15 min of continuous exposure to burning and smoldering particles, the temperature in the zone of maximum accumulation of particles did not exceed 130 ºC. A wooden guard model was found to the most prone to ignition (its ignition delay time was more than 15% lower than that of the other structures).

It is found that the problem of boundary layer stability with a diffusion flame under the conditions of a constant molecular weight over the boundary layer in the inviscid approximation and in the Dunn-Lin approximation with identical Schmidt numbers can be reduced to a similar problem for a single-component gas. Approximately, this conclusion is also valid for different Schmidt numbers. Calculations of the steady-state parameters of the boundary layer show that there are two generalized inflection points testifying to a necessary condition of the “inviscid” Rayleigh instability. Simulations show that the boundary layer with a diffusion flame is most unstable to two-dimensional disturbances. As the frequency is increased, the phase velocity of the growing wave tends to the value at the generalized inflection point. Despite sufficiently large growth rates, the degree of spatial enhancement of the wave is equal with high accuracy to the ratio of the time degree of enhancement to the group velocity.

This paper describes an experimental study of the operation parameters of a gas-dynamic pressure source with explosive initiation, in which black powder is used as a damping layer.

The enthalpy of formation, density, energy and detonation parameters of hypothetical zwitterionic nitrohydrazine H₃N+N-NO₂ were evaluated. The obtained probable values of the enthalpy of formation (-20 kJ/mol), density (1.90 g/cm³), and detonation velocity (9.4-9.8 km/s) of nitrohydrazine allow it to be considered as a promising energetic compound that justifies efforts to find ways to synthesize it.

Burning of a high-energy paste-like propellant aimed at creating engines with a burning end surface is studied. Specific features determining the burning rate, characteristics of the agglomeration process, and surface layer properties are found. It is demonstrated that these features are similar to those observed for solid propellants based on an active binder with a linear polymer. Possible aspects of improvement of propellants of this type are determined.

This paper describes the method and results of an experimental study of unsteady burning rate of high-energy materials containing metal powder additives under depressurization at a rate of 140-160 MPa/s. A method based on stating and solving the inverse problem of internal ballistics is used to determine the unsteady burning rate. The studies are carried out for high-energy materials, including energy additives in the form of metal powders (ASD-4, ASD-6, and Alex aluminum), aluminum diboride, and dodecaboride. It is shown by analyzing the results of the study that the unsteady burning rate of high-energy materials under sharp depressurization is oscillatory and depends on energy additive type.