Home – Home – Jornals – Combustion, Explosion and Shock Waves 2025 number 3

The phenomenon of increased burning velocity of a laminar fuel-rich ethanol flame with droplet injection was investigated numerically, and the results were compared with calculations for ethanol combustion without injection with the same mass fuel consumption. The calculations show that the presence of a dispersed phase in the form of 14 μm droplets with a mass flow rate of 0.5 g/min and a gas flow rate of 1.6 g/min significantly increases the flame propagation velocity compared to the combustion of gaseous ethanol with a flow rate of 2.1 g/min. The laminar flame speed increases from 23 cm/s in the combustion of only the gaseous fuel to 42 cm/s in the combustion with droplet injection. This effect correlates with a more than threefold increase in atomic hydrogen concentration in the flame and with a twofold increase in HCO concentration.

The dynamics of gas temperature was studied using as an example a single cylindrical channel with a diameter of 2 mm - a Raschig ring - placed in a porous medium made of such rings. The gas and thermocouple wire temperatures on the channel axis and the temperature distribution in the channel were calculated for two processes: the first is the pressure rise in a closed vessel during flame propagation in the space free of the porous medium, and the second is the cooling of the gas after the flame passage through the channel. For both processes, the gas temperature and the equilibrium temperature of the gas and the porous medium were measured using a thermocouple with a wire diameter of 15 μm in a cylindrical pore with a diameter of 2 mm. It was shown that during gas compression at a constant low rate, the thermocouple provided adequate measurements of steady-state gas temperature. However, when reaching the steady-state value, the larger the wire diameter, the longer was the thermocouple lag. During cooling of the instantaneously heated gas, the thermocouple measurements of gas temperature were found to be significantly underestimated. This is due to the higher heat capacity of the thermocouple wire as compared to the heat capacity of the gas in the pore. During the heating of the thermocouple, the gas cools down due to heat transfer into the pore walls.

Based on the large-eddy-simulation (LES) turbulence model, the shock wave propagation process in the roadway with branch structure was studied, focusing on the changes of overpressure under different explosion intensities and a different number of branches. Four conditions of gas accumulation length of 5, 10, 15, and 20 m are used in four models to reveal the influence of the branch structure. The results show that the shock attenuation coefficient of the main roadway no longer changes linearly with the gas accumulation length when there are branch structures in the roadway. When the gas accumulation length is constant, the increase of the number of branches can effectively reduce the rise rate of the impact overpressure value within a certain propagation distance. The overpressure in the branch roadway away from the explosion site is less affected. Due to the influence of multi-branch structure of adjacent roadway, its fluctuation is more chaotic than that of main roadway.

A closed mathematical model of continuous spin detonation of a synthesis gas---air mixture is formulated in a three-dimensional unsteady gas-dynamic formulation, and an algorithm for numerically solving the problem is developed. The model is verified using experimental data on ignition delay at high temperatures and the results of one-dimensional numerical calculations of the Chapman---Jouguet detonation parameters. For three stoichiometric compositions in an annular cylindrical combustor 306 mm in diameter, single-wave continuous spin detonation modes are obtained and the three-dimensional structure and the main flow parameters are analyzed. The minimum possible flow rates for continuous detonation are obtained in the case of variable specific mixture flow rates in a range of 90 ÷ 260 kg/(s · m²). The resulting data are compared with existing experimental data.

The methodology of calculating the problem of detonation initiation in acetylene-oxygen mixtures by a small-diameter sphere flying with a velocity greater than the Chapman-Jouguet detonation velocity is presented. A reduced kinetic scheme of chemical reactions is tested against experimental data on the ignition delay time, detonation propagation velocity, and detonation cell size. Regimes of oblique detonation and combustion in an acetylene-oxygen mixture diluted by argon are obtained in experiments in the pressure range from 21.1 to 60.7 kPa. The energy of detonation initiation by a high-velocity projectile is estimated, which demonstrates good agreement between analytical, numerical, and experimental data. Based on this estimate, the initiation of oblique detonation by a high-velocity projectile in an acetylene-oxygen mixture is calculated. A correlation between the numerically predicted flow regimes and analytical estimates is obtained.

Flows with multiheaded rotating detonation in a combustor in the form of an annular gap between plates are numerically studied. It is assumed that a homogeneous propane-air mixture enters the combustor from a reservoir with specified stagnation parameters through elementary nozzles uniformly filling the outer ring that limits it. The gas-dynamic parameters of this mixture are determined as functions of the stagnation parameters and static pressure in the gap. The study of multiheaded rotating detonation is carried out under the following conditions: the number of waves is 1, 2, 4, and 8, while the stagnation pressure slowly decreases over time according to a linear law. It is revealed that shock-wave structures can be qualitatively different, depending on the stagnation pressure, and that detonation ceases at a stagnation pressure lower than the critical pressure. The dependences of the power characteristics of the traction equipment on time are presented. Calculations are performed on the Lomonosov supercomputer at the Moscow State University using an original software package implementing a modified Godunov method and a one-step reaction kinetic model.

This paper presents generalized results of numerical analysis of the effect of mesoscopic thermal dissipation and heat transfer processes on the temperature field formed in a shock-compressed viscoplastic porous material containing spherical pores with a thin layer of plasticizer on the surface of pores in plastic flow. Based on the results, a theoretical estimate is made of the effect of the mechanical properties of the phases on the critical conditions of shock-wave initiation of chemical reaction in the two-phase porous energetic material.

The investigation of the energy output resulting from alterations in the aluminum powder content in emulsion explosives permits the expeditious transformation of civilian explosives into military explosives during wartime, while simultaneously enhancing the energy capacity of the equipment. One can choose the appropriate scenario based on the form and energy yield of the explosives. The experiments were conducted using emulsion explosives with 0%, 5%, 10%, 20%, 30% and 40% mass percentage of aluminum powder. The study investigates the effects of varying aluminum powder contents on detonation velocity, brisance, underwater explosions, and aerial explosions. The experimental outcomes show that the detonation speed decreases with increasing aluminum powder content. The brisance of the emulsion explosive initially ascends and subsequently descends, reaching its pinnacle value of 22.71 mm at an aluminum powder content of 20%, reflecting a surge of 19.97%. As the aluminum powder content increases, all underwater explosion parameters of the emulsion explosive increase linearly, with the total energy reaching its maximum at 40%, showing increases of 120% compared to the aluminum-free emulsion explosive. The highest pressure increase in aerial explosions is achieved at an aluminum powder content of 30%, reaching 113.28 kPa and signifying a 78% rise. The experimental findings demonstrate that in the context of underwater munitions employing high-energy emulsified explosives, including 40% aluminum powder results in the optimal level of destructive capability. Conversely, when considering applications for aerial weaponry, the maximum explosive potential is attained with an aluminum powder content of 30%.

A wide-range semiempirical equation of state of liquid and gaseous neon is constructed with account for evaporation and thermal ionization based on a modified van der Waals model for mixed substances. The model and the simplifications used in this study are described. The values of the key parameters are given. The results of model calculations are compared with experimental data up to a pressure of ≈1 000 GPa and with the results of calculations based on other models, including those at a pressure of >1 000 GPa. In the low-density limit, the model transforms into an equation of state of a mixture of ideal gases of atoms, ions of all multiplicities, and electrons with a concentration determined by the Saha equations.

Experiments on measuring the electrical resistance of copper foil under shock compression are analyzed for determining the basic parameters responsible for the concentration of shock-induced defects in the metal. Based on the excessive electrical conductivity of the metal, the concentration of point defects of the crystal structure in copper samples placed in various cartridges (Plexiglas, micarta, and fluoroplastic) is estimated. The cartridge material is found to affect the number of defects arising due to shock compression of the metal. The cartridge with a higher shock impedance corresponds to a smaller concentration of defects in the sample (at identical pressures of the shock wave in the cartridge). A physical model of generation of crystal structure defects due to shock compression is formulated to explain the experimental results obtained. According to this model, defects are formed during matter compression in the shock wave front and remain “frozen” after unloading. A new portion of defects is formed after secondary compression of matter, resulting in accumulation of defects. It is assumed that the parameter determining the number of defects arising under dynamic loading is the algebraic sum of metal deformations at each stage of shock compression. The data presented in the variables concentration of defects - deformation yield a dependence that mitigates the difference in the cartridge material. The analysis performed shows that the sum of deformations can be considered as a parameter determining the concentration of defects generated by shock compression of copper.

The expansion and rupture of metal casing under internal explosion loads may form a large number of fragments. An understanding of how the relevant parameters of metal casing influence the fragment mass distribution, is essential for the prediction of the power of metal casing explosive devices and the effective design of protection systems. In this paper, the important influence factors of metal casing (mechanical properties of casing material, geometric structure of casing, performance of explosive) were determined by a dimensional analysis. Several complete recycle tests of fragment were carried out to analyze the influence of these relevant parameters on the natural fragment mass distribution. Based on the test results, it is found that these relevant parameters have a linear relationship with the distribution modulus of the fractal model of natural fragment mass distribution in double-logarithmic coordinates. A formula was developed to predict the distribution modulus, whose influence parameters were considered in a dimensionless way. The applicability of the estimating method was verified with the test data of a casing with irregular axial geometry. The error between the calculation result and test result was only 6.9%. In addition, the test data compared with the prediction results of two theories, and the fractal model of natural fragment mass distribution showed better accuracy. This work can provide a reference for the hazard assessment and protection system design of metal casing explosive devices.