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Results of investigations of flame acceleration and deflagration-to-detonation transition in circular smooth tubes performed for several last years at the ITMO University (Minsk, Belarus) are briefly reviewed and systematized. All stages of the flame acceleration process from initiation with a weak source to detonation are demonstrated and described.

Results of simulations of a high-velocity reacting flow of a non-premixed hydrogen-air mixture in a channel with sudden expansion in the form of backward-facing steps with transverse injection of hydrogen jets are reported. The computations are performed with the Ansys Fluent software package based on solving three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with the κ-ω SST turbulence model and equations of detailed chemical kinetics of hydrogen combustion in air. The simulations predict self-ignition of the hydrogen-air mixture subsequently transforming to intense combustion with upstream motion of the flame from the ignition region. It is demonstrated that combustion occurs in thick subsonic regions, which merge at the channel axis in areas of elevated heat release, thus, forming a thermal throat. As a result, a system of normal shock waves is formed, which separate the boundary layer from the channel wall. The reverse flow transfers hot reaction products toward the step wall; thus, the thermal throat and shock waves are shifted upstream. As a result, the combustion wave and the shock wave enter the injector area, the “knocked-out” shock wave merge with the bow shock ahead of the jets, and thermal choking of the channel occurs.

Results of numerical simulations of flame acceleration in a semi-open channel filled by acetylene-based mixtures are reported. The computations are performed by the advanced dissipationless method CABARET. The effects of the channel width and the roughness of the inner wall of the channel on the flame evolution dynamics at various stages of the flame acceleration process are demonstrated based on comparisons of results obtained in different formulations. In particular, it is shown that the flame velocity and the amplitude of velocity fluctuations at the quasi-steady stage of flame propagation increase with an increase in the channel width. It is also demonstrated that flow deceleration at the channel walls produces the most pronounced effect at the stage of quasi-steady propagation of the flame owing to faster development of the boundary layer and vortex generation in the near-wall region and vortex interaction with the flame extended along the channel walls.

This paper presents experimental data on the ignition induction period of synthetic hydrocarbons at various temperatures and pressures obtained using a shock tube. The influence of the ignition induction period on the combustion completeness of hydrocarbons in high-enthalpy flows for diffusion-kinetic regimes was determined based on the experimental results. An integral mathematical model is presented that takes into account the influence of the kinetic factors of ignition and combustion on the completeness of physicochemical processes in the air flow. The results of calculations of the combustion completeness of synthetic hydrocarbons in flows with different parameters.

The gasification of a two-layer solid porous fuel in a combined low-temperature charge of a gas generator has been studied using the developed mathematical model and computational algorithm implemented in the OpenFOAM software. The influence of the two-layer nature of the solid porous fuel on its gasification has been studied in computational experiments using as an example gasifiers containing a fuel based on polymethylmethacrylate and polyethylene with different mutual arrangement of their layers. It has been shown that in a two-layer fuel, two waves of gasification propagate simultaneously, due to which the relative mass flow rate of gasification products can have two local maxima. The operating time of a gas generator using a two-layer porous fuel ambiguously depends on the mutual arrangement of the layers and can go beyond the range between the times of operation of the gasifier using each of the fuels.

Dispersed metallic fuels are energy-intensive components of various gel-like and mixed solid fuels, which significantly increase the performance of propulsion systems. This article presents the combustion characteristics of a high-energy material (HEM) containing an oxidizer, a polymeric combustible and a dispersed metallic fuel - aluminum Al, aluminum borides AlB₂ and AlB₁₂, amorphous boron. In a constant-pressure bomb, the combustion rates of HEM were measured in the pressure range of 0.7-4.0 MPa, the effect of aluminum dispersion and the nature of the metallic fuel on the combustion rate and temperature, the fuel sensitivity to pressure changes in the chamber, and the composition of condensed combustion products was established. An increase in the fineness of Al particles in the HEM significantly increases the burning rate and the sensitivity of the fuel composition to pressure changes. Replacing microsized Al powder with amorphous boron, AlB₂ or AlB₁₂ in HEM increases the combustion rate by 2.1-2.2 times at a pressure of 4.0 MPa, while the power exponent in the combustion rate law u(p) = Bp^ν increases from 0.22 to 0.45.

The processes occurring during the induction of a thermal explosion in mixtures of titanium and aluminum powders are analyzed. The role of the oxide film on aluminum particles and the heating rate of samples during the interaction of titanium with aluminum is considered, and various mechanisms of destruction of the oxide film at temperatures near the melting point are proposed. It is shown that, depending on the heating rate of the samples, three mechanisms for the formation of direct contact between titanium and aluminum are possible: mechanical destruction of the oxide film on aluminum, the reaction of aluminum oxide with titanium, and the reaction of aluminum oxide with aluminum. Mechanical activation of the powder mixture lowers the ignition temperature by 20-30 °C. Reducing the average particle size of titanium from 90 to 10 microns lowers the ignition temperature by 100 °C. It is shown that in a number of cases a two-stage ignition mechanism is observed. After the isothermal section of aluminum melting, the stage of a slow temperature rise to 700-800 °C begins, after which the temperature rise rate increases by an order of magnitude.

The formation of a complex of magnesium and 4-ethylterpiridyl-(N-tert-butyl-N-(1-diethylphosphone-2,2-dimethylpropyl))-nitroxide alkoxyamine (SG1-tpy) was investigated by means of NMR spectroscopy. The stoichiometry of the complex was determined by constructing the Job’s plot. The homolysis rate constant of the alkoxyamine used was determined by means of EPR spectroscopy, and the activation energy was estimated. Polystyrene was obtained by radical controlled polymerization, and its molecular weight characteristics were studied by gel-permeation chromatography. When magnesium trifluoroacetate is added to the polymer solution, the molecular weight of the polymer increases, which indicates the formation of the complex. Polystyrene was also synthesized using the complex form of the initiator. It is shown that all the obtained polymers are narrowly dispersed, polydispersity is less than 1.5.

Mass spectrometric characteristics of N-alkyl-4-nitro-1,2,3-triazoles were investigated using a gas chromatograph with a quadrupole mass spectrometric detector in the mode of electron ionization (70 eV). The stability of the molecular ion was studied depending on the position, structure and nature of the alkyl substituent at the endocyclic nitrogen atoms of nitrotriazole heterocycle. N2-alkyl-4-nitro-1,2,3-triazoles were found to have the highest stability and molecular ion intensity, independently of the alkyl substituent in the structure of the compound. The pathways of molecular ion fragmentation are proposed for the compounds under consideration, and characteristic ions are identified. Molecular ion fragmentation in N-alkyl-4-nitro-1,2,3-triazoles was discovered to start with the elimination of the exocyclic NO₂ group, followed by detachment of the respective alkyl substituent and generation of the cation radical of 1,2,3-triazole. Fragmentation of non-substituted cation radical of 1,2,3-triazole proceeds through characteristic detachment of N atom or neutral molecules N₂ and HCN. In turn, the ionic decay of bulky alkyl substituents (cyclohexyl and benzyl radicals) leads to a group of characteristic ions with high relative intensity. In general, the findings demonstrate that mass spectrometry can be efficiently used for robust identification of structural isomerism ( N1-, N2- and N3-isomers) of alkyl-4-nitro-1,2,3-triazoles and the products of their decomposition.

Vitrinite concentrates of coal at different stages of metamorphism are studied by means of scanning electron microscopy and X-ray diffraction analysis. The results show that the cleaves and fractures on the surface of maceral particles have a structure characteristic of vitreous amorphous bodies for the whole metamosphism series. An increase in metamorphism degree is accompanied by an increase in the electrical conductivity of vitrinite particles and a decrease in the reflectivity with respect to electrons due to a decrease in the content of oxygen atoms. It is shown by means of X-ray diffraction that vitrinites have a turbostratic carbon structure, formed by polyarene layers with the interlayer spacing (d₀₀₂) decreasing from 3.64 to 3.50 Å with an increase in metamorphism stage, at the same time an increase in the dimensions of structured vitrinite fragments - height (L_c) andd width (L_a) of arene layer packets - is observed. A linear dependence is revealed between d₀₀₂ and vitrinite reflectance.