Home – Home – Jornals – Combustion, Explosion and Shock Waves 2002 number 3

The formation of ions in the volumetric reaction of methane and hydrogen with air is analyzed. In methane

Results of numerical simulation of the influence of intensity of hydrogen injection through a porous surface in the case of hydrogen burning in the boundary layer are presented. Turbulent characteristics of the flow were simulated using the k-ε turbulence model with Chien's modification for low Reynolds numbers. The diffusion model (infinitely large burning rate) was used to describe the chemical reaction process, but the difference in diffusion coefficients of different substances was taken into account. A comparison of injection with and without combustion shows that the presence of a heat-release front delays the laminar

The problem of spark ignition of a gas suspension including a fuel, an oxidizer, and reactive particles is considered using a two-temperature thermodiffusion model of combustion. Dependences of the minimum ignition energy on disperse-phase parameters are obtained. It is shown that the presence of  exothermically reacting disperse-phase particles has an ambiguous effect on the minimum spark energy leading to ignition of the gas suspension. The values of the lower and upper concentration limits for ignition of a methane

The thermal decomposition of ammonium dinitramide (ADN) was studied using a two-temperature flow reactor. The vapor pressure at temperatures of 80

To study spontaneous combustion and explosion of brown-coal dust, an experimental setup was designed and a method for analysis of these processes was proposed. Kinetic parameters (activation energy and preexponent) of the brown coal from the Irsha--Borodino deposit were determined. It was shown in experiments that, for certain coal/oxidizer ratios, the explosion has a two-stage character. The repeated explosion of dust is caused by thermal activation of coal at the first stage of the explosion. Mathematical models for a qualitative description of spontaneous combustion of brown-coal dust are considered.
Key words: brown coal, spontaneous combustion of dust, kinetic parameters, numerical modeling.

Results of experiments performed in a constant-volume bomb are presented. The conditions in the bomb were typical of starting regimes of diesel engines. Cooled (down to 286 K) or noncooled inserts were placed in the bomb volume on the way of the fuel

In order to determine the heat release in an irradiated particle, it is necessary to know the intensity distributions of internal optical fields in nitromethane. In the droplet volume, the optical field becomes inhomogeneous with increase in the radius of the droplet or with decrease in incident-radiation wavelength. In the present paper, internal optical fields in nitromethane droplets for the CO₂ laser wavelength are calculated using the Mie theory. It is shown that for the wavelengths of a chemical laser (2.9 μm) and a CO₂ laser (10.6 μm), the optical fields in the volume of nitromethane droplets are identical if the droplet sizes do not exceed 10 μm.
Key words: droplets, explosion, optics, fuel, Mie theory, CO₂ laser.

A nonstationary mathematical model of thermal propagation of flame in a layered heterogeneous system is proposed. The structure and dynamics of the frontal exothermal transformation in quasihomogeneous, transitional, and relay-race regimes are studied. Averaged characteristics of the front and dynamics of transformation of individual elements of a "discrete" combustion wave are analyzed using the model proposed. A correlation is established between the combustion of a model medium and real heterogeneous compositions. It is shown that the maximum combustion velocity is reached at an intermediate level of medium dispersion in a transitional parametric region.
Key words: combustion waves, heterogeneous systems, multilayered nonstationary regimes, modeling.

A mathematical model of lifting of dust particles under the action of transient shock waves is proposed, which takes into account a simultaneous action of the Saffman force and aerodynamic interference on the particle. This model provides an adequate description of the initial stage of lifting of single particles of a dusty layer under the action of shock waves of weak and moderate strength. Satisfactory agreement of numerical and experimental data is reached. It is shown that particle lifting is caused by the action of the Saffman force in the case of weak shock waves (the shock-wave Mach number is less than 1.5) and medium-sized particles (the particle diameter is less than 100 μm) and aerodynamic interference between the particle and the surface in the case of shock waves of moderate strength (the shock-wave Mach number is 2.1

It is shown that the Iordanskii

A microscopic model of detonations in condensed substances is proposed. It is used to derive a nonempirical equation for detonation velocity, which contains three parameters characterizing the model and three parameters characterizing an individual explosive. The agreement between experimental and calculation data is not worse than that for the well-known models of Becker

The problem of explosion in a hole surrounded by a porous medium is considered. Integral equations describing pressure relaxation in the hole due to gas filtration into the surrounding porous space are obtained within the framework of plane one-dimensional, radial, and spherical formulations. An analysis of numerical solutions of these equations shows that the characteristic time of pressure relaxation in the hole depends weakly on its initial value.
Key words: pressure relaxation, explosion in a hole, porous medium, filtration of explosion products, bottom-hole cleaning.

Simple estimates of the coefficient of dynamic viscosity of some metals are considered. Experimental results on shock loading of aluminum, copper, and steel plane specimens are given. It is shown that the coefficient of dynamic viscosity depends on the characteristic size of the structural level of plastic strain at which loading-energy dissipation is considered. It was found that the main level that determines the viscosity of materials under high-velocity loading is the mesoscopic level with a characteristic size of ≈10 μm.
Key words: viscosity, high-velocity loading, mesoscopic level, interferogram.

A three-dimensional phase diagram of carbon has been built in the coordinates "pressure

The paper considers a physical model for the explosive synthesis of ultrafine aluminum oxide, which assumes that in a compression wave the starting material is divided into layers with different states of aggregation and grain-size compositions. The relationship between the synthesis conditions and the properties of the product is studied. It is shown that the yield of the ultrafine fraction in the synthesized powder depends on the conditions of metal oxidation during dispersion, shock-wave parameters, and the velocity of dispersion of the starting material into the gas medium of the explosion chamber. Experimental data are used to determine the layer sizes and the constants characterizing the possibility of vapor-phase oxidation of aluminum during explosive synthesis. In the coordinates corresponding to the process parameters (yield of the ultrafine fraction and the masses of the explosive and the starting metal), a synthesis surface is constructed and optimum parameters for production of ultrfine material are determined.
Key words: ultrafine aluminum oxide, explosive synthesis, layer-by-layer separation of material in a compression wave, conditions of synthesis, properties of material.

Despite all safety measures in handling objects containing explosives, the probability of their accidental explosion is not completely eliminated. Effective environmental protection against explosions is achieved by localization of an explosion in the closed volume of an explosion-proof container. The use of such containers can considerably improve safety in operation of ammunition and other explosive devices.
Key words: container, charge, high explosive, fiberglass plastic, composite material, shell, fracture, strain, strength.

An analysis is made of the main kinematic parameters that determine the beginning of weld formation near the lower boundary of the region of explosion welding. The welding of aluminum with steel is considered. The paper reports experimental results for the flow of material in the gap under oblique collision of metal plates.
Key words: oblique collision, particle flow, explosion welding.

Experimental data on the kinetics of preexplosion conduction of silver azide in the early stage of explosive decomposition initiated by a pulse action were obtained for the first time. It is found that the kinetics of conduction in the early stage is more complex than that at later stages. In the early stages, the difference between kinetic curves for various samples is greater than that for the steady process.
Key words: silver azide, explosion, chain reactions, conduction, kinetics, pulse photolysis.