Home – Home – Jornals – Combustion, Explosion and Shock Waves 2025 number 1

Data on the parameters of combustion and detonation of single-fuel systems methane-oxygen (air) and hydrogen-oxygen (air), as well as double-fuel systems methane-hydrogen-oxygen (air) with variation of the ratio between the initial species are presented. The influence of combustible system preheating on the parameters of detonation and combustion products is analyzed for fuel-lean, stoichiometric, and fuel-rich mixtures. It is found that preheating has a strong effect in fuel-lean combustible systems, which is manifested as reduction of the critical energy of initiation by several orders of magnitude.

The effect of different obstacle positions on the explosion flame dynamics of hydrogen-air mixtures with concentration gradients is investigated by numerical simulations. The numerical simulations predict explosion characteristic parameters matching correctly with the experimental results. The calculation results show that the influence of the obstacle position on the explosion flame of an inhomogeneous mixture is more significant compared to that of a homogeneous mixture. The analysis of the flame morphology and flow field reveals that, as the obstacle position increases, the premixed flame undergoes more complex deformation after passing through the obstacle and generates eddies near the obstacle under the action of vortices. By comparing the flame front position and peak overpressure after the explosion, it is found that, as the obstacle position increases, the concentration gradient has a stronger inhibitory effect on flame propagation. The influence of the concentration gradient on the peak overpressure is more pronounced when the obstacle is 200 mm from the ignition point. This research can provide theoretical guidance for industrial explosion protection and safety management.

This paper presents experimental and calculated results of studying the development of turbulent mixing at the air--water interface after the passage of an oblique shock wave. The shock-wave Mach number in the experiments varied in the range 2-2.3. The angle of inclination of the shock wave front to the interface was 0,15 °C, and 30 °C. When the shock wave was incident on the water surface, Kelvin-Helmholtz instability developed, which over time led to turbulent mixing of the substances in contact. In the experiments, the flow field structure was recorded by high-speed video cameras. It was found experimentally that with increasing angle of incidence of the shock wave on the interface, turbulent mixing increased and the droplet size of the dispersed liquid decreased due to more intense droplet fragmentation. Numerical modeling of the experiments using a two-dimensional technique shows that the technique satisfactorily predicts the dynamics of the turbulent mixing zone in the vicinity of the interface.

This paper is devoted to the preparation of Al-Mn-Si-based compounds with different Si contents (0, 5, 10, and 15 at.%) using self-propagating high-temperature synthesis (SHS). This method is used for the first time to obtain the Al₉Mn₃Si γ-phase with a hexagonal crystal lattice (P6₃/mmc space group) as part of a synthesized alloy with a content of 15 at.% of Si in the initial mixture. The X-ray diffraction analysis of the synthesized alloys from mixtures with a silicon content of 5-10 at.% also shows the presence of γ₂-Al₈Mn₅ (trigonal, R3m space group) and MnSi (cubic, Pm-3m space group) phases. The phase formation of intermediate compounds at silicon content in a mixture below 15 at. % may be associated with combustion temperature, which is insufficient for complete interaction of the system components. Synthesized alloys are characterized by a porous structure with pore size up to 20 μm and a grain size in the pore space of 10-90 μm.

A method for obtaining burning aluminum agglomerate particles with a diameter of 215-840 μm is described, and their combustion in free fall in air at atmospheric pressure has been studied. The combustion time as a function of particle diameter was determined by processing video recordings of the combustion process. The morphological and granulometric characteristics of condensed products (large residues of combustion of agglomerates) - final oxide particles were investigated. The ratios of the diameters and masses of the oxide residue and initial agglomerate particles were determined. An empirical formula for estimating the density of the final oxide particles is proposed.

The effects of the content of Ti + 2B and Ti + C mixtures and mechanical activation (MA) on the burning rate, the yield of the mixture after MA, and the morphology and phase composition of combustion products of the (Ti + 2B) + (Ti + C) composition has been investigated. During Mechanical activation of the Ti + 2B mixture for 5 min leads to mechanochemical synthesis of TiB₂ product. Mechanochemical synthesis does not occur when adding Ti + C powder to the activated Ti + 2B mixture. Increasing the content of Ti + C in the (Ti + 2B) + (Ti + C) mixture leads to deterioration of the compressibility of samples after MA. The burning rate of the initial (Ti + 2B) + Ti + C) mixtures decreases with increasing content of Ti + C. Samples of the combustion products of the initial mixtures retain integrity after the synthesis. Mechanical activation doubles the burning rate of samples from the Ti + C mixture. The burning rate of the activated Ti + 2B) + (Ti + C) mixture increases with increasing content of Ti + C, and samples of the products are dispersed during combustion. For a mixture of equal mass fractions of the initial Ti + 2B powder and the activated Ti +C powder, the dependence of the burning rate of the mixture on the content of Ti + C in it has a minimum; if the investigated composition is dominated by the Ti + 2B mixture, the product samples retain integrity.

The influence of the method and duration of mixing of the refractory metals Ta, Mo (Ti), Nb, V, and W with carbon (soot) on the formation of high-entropy carbides in the thermal explosion mode was investigated. The ignition temperature of the mixtures and the composition of the resulting products were determined depending on the method of preparing mixtures of metals with soot. Among the investigated methods of obtaining TaTiNbVWC₅ and TaNbVMoWC₅ high-entropy carbides, the multistep method of mixture preparation has been shown to be the most efficient. In the first step, a high-entropy solid solution of metals is prepared by high-energy mechanical treatment, after which soot is added to it and additional high-energy mechanical treatment is carried out. Thermal explosion of this mixture results in high-entropy carbides.

The structure of hybrid detonation waves in gas suspensions of boron particles in hydrogen-air mixtures of different compositions is calculated using the detailed kinetics of hydrogen combustion and the PSU-model of boron particle combustion. The effect of particle diameter and concentration on detonation wave velocity in a stoichiometric hydrogen-air mixture is revealed. It is shown that particles with a diameter of less than 5 μm enhance detonation waves in stoichiometric and rich mixtures, and those with a diameter of more than 10 μm only weaken detonation. The effect of the gas mixture composition on detonation processes is studied. It is revealed that, as the amount of oxidizer in the mixture decreases, the maximum detonation velocity decreases and shifts toward lower volume concentrations of particles.

Data are presented on the adaptation of photonic doppler velocimetry (PDV) for gas-dynamic studies using barrel loaders. Measuring channels are time-matched via direct measurements of relative time corrections of PDV with an accuracy of up to 0.1 ns using the correlation analysis of the transit time of femtosecond pulses with different repetition periods through the measured fiber lines. The angle of impact of the projectile with the sample studied is determined using a linear regression method, which allows for the most complete use of the entire volume of experimental data and statistical determination of confidence intervals of the estimates obtained. Reliable recording of elastic wave parameters is carried out using a method of active-passive diagnostics of the PDV, which allows one to completely eliminate the interfering reference line and, accordingly, to increase the time and velocity resolution of the PDV.

In this paper, the effect of oxidizers on the near-ground explosion performance of HMX-based thermobaric explosives (charges' mass of 500 g) are studied by means of experiments and numerical calculations. The trajectory of the Mach triple point motion shows that its height dramatically increases above the incidence angle of 70 °C. The Mach stem exceeds the height of the explosion centre at a distance greater than 3.6 m. The experimental results show that the temperature distribution on the fireball surface is asymmetrical, and the temperature of the upper fireball is higher than that of the lower fireball. The peak temperature of the thermobaric explosive is higher than 2400 K, and the fireball temperature is above 400 K for nearly 1000 ms. The oxidizers, i.e., potassium perchlorate and Fe₂O₃ slightly enhance the overpressure of the incident wave and significantly prolong the barotropic duration. In addition, potassium perchlorate can quickly participate in the afterburning reaction, while polytetrafluoroethylene is less efficient. The energy released by the thermite reaction of Fe₂O₃ contributes to the maintenance of temperature, especially the late fireball temperature.

A method for studying the propelling effect of explosion products of condensed explosives is proposed and substantiated by calculations. This effect allows for a wide range of states on the isentrope of explosion products: from pressures and densities in the range of the Chapman-Jouguet state to a pressure of ≈0.1 GPa and a density of ≈0.2 g/cm³. This method is applied to perform experimental studies of the propelling effect of TG 25/75 explosion products, in which information on the movement of thin aluminum liners is recorded by a PDV multichannel heterodyne-interferometer.

To study the effect of the height and thickness of a steel shell on the velocity of an explosively formed projectile (EFP), an EFP forming test is carried out, the EFP velocity is tested, and the EFP is soft recovered. The results show that the influence of the shell on the EFP velocity is mainly concentrated in the upper part of the liner. If the shell height is 0.5 times the charge height, the EFP velocity can reach more than 90% of its velocity in a situation where the shell height is equal to the charge height. By removing the lower half shell of the EFP warhead, the overall mass of the warhead can be effectively reduced without significantly affecting the EFP velocity.

The present study is focused on joining Al 5052 (aluminium alloy) and AZ31B (magnesium alloy) with and without silicon carbide particles (SiC(p)) through explosive welding. The scanning electron microscopy image of the weld interface reveals the formation of a molten zone and pores in the AZ31B and Al 5052 weld (without SiC(p) particles), whereas they are absent if SiC(p) is introduced between the alloys. The X-ray diffraction analysis reveals Al₁₂Mg₁₇ and AlMg intermetallic compounds in the conventional weld (without SiC(p)), whereas no intermetallic compounds are detected in the silicon carbide reinforced weld. The maximum microhardness is witnessed close to the interface due to significant plastic strains of colliding plates. The shear (124.5 MPa) and tensile (201 MPa) strengths of the silicon carbide reinforced weld are higher than those of the conventional weld without SiC(p) particles (104~MPa and 135~MPa, respectively). Concerning the corrosion behavior, after 120 days of immersion of samples in the marine broth solution, the weight reduction is negligible (0.01692 g/cm²).

To study the damage effect of cylindrical charges on steel plates at different impact velocities and angles, a numerical simulation study on the damage effect of cylindrical charges on a steel target plate is carried out at impact velocities of 0-800 m/s and impact angles of 0-90 °C without changing the vertical distance between the center of the cylindrical charge and target plate. It is demonstrated that four main damage modes of the steel plate exist in this case: plastic deformation, boundary tearing, tear at the center of the steel plate, and petal-shaped break. At a zero impact velocity, the damage pattern of the target plate is not affected by the impact angle, and it is plastic deformed. With an increase in the impact angle, the maximum deflection of the steel plate decreases first and then increases; with an increase in the impact velocity of the charge, at the impact velocities of 200 and 400m/s and the impact angles greater than 75oC, the damage mode of the steel plate is no longer plastic deformation, but boundary tear or central petal damage. With an increase in the impact velocity, the energy acting on the plate increases; hence, the energy density affecting the plate also increases. As a result, the breaking effect of the charge on the plate always increases with increasing impact velocity.

Regimes of continuous spin detonation of carbonless ammonia-air mixtures in a flow-type annular cylindrical combustor 503 mm in diameter have been obtained for the first time.