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Combustion, Explosion and Shock Waves

2013 year, number 3

1.
CONDUCTIVE–RADIATIVE MODEL OF A LAMINAR FLAME IN DUST SUSPENSIONS

A. E. Sidorov, V. G. Shevchuk, E. N. Kondrat'ev
Keywords: gas suspension, flame velocity, conductive and radiative heat transfer, magnesium
Pages: 257-263

Abstract >>
A mathematical model is proposed to describe a laminar flame in gas suspensions with particles burning in the diffusion mode. Conductive and radiative heat transfer in the combustion wave and also the differences in temperatures and velocities of the solid and gas phases are taken into account. An analytical expression for the normal flame velocity as a function of the fuel and oxidizer concentrations and the particle size is derived. Theoretical predictions are demonstrated to agree well with experimental data on the flame velocity dependence on the particle size in suspensions of magnesium particles in air. The relative role of radiative heat transfer and sedimentation of particles in the suspension is analyzed.
																								



2.
VALIDITY OF EXPERIMENTAL AND THEORETICAL MODELING OF COMBUSTION OF HIGH-ENERGY MATERIALS

I. G. Assovskii, A. G. Merzhanov
Keywords: high-energy materials, combustion models
Pages: 264-272

Abstract >>
Problems of theoretical and experimental modeling of combustion of high-energy materials in technological devices are considered. Requirements for modeling, validation criteria of modeling, and similarity criteria of combustion conditions are formulated. Classification of the validity of theoretical and experimental modeling is considered taking into account the features of intrachamber combustion of high-energy materials in technological devices.
																								



3.
MECHANISM OF THE NEGATIVE EROSION EFFECT

K. O. Sabdenov, Erzada Maira
Keywords: negative erosion effect, critical Vilyunov number, Bulgakov–Lipanov number
Pages: 273-282

Abstract >>
A mechanism of the negative erosive burning (effect) in the channel of a rocket motor propellant charge is proposed. Reduction in the burning rate results from a decrease in the flame temperature due to conversion of the chemical reaction heat to the kinetic energy of the gas. There is a critical value of the Vilyunov number above which steady-state propellant combustion is impossible. Steady-state combustion is possible up to a factor of 1/e1/2 decrease in the burning rate compared to the original value. An explanation is given for the weak manifestation of the negative erosion effect with a decrease in the initial propellant temperature: reducing the threshold rate of positive erosive burning narrows the region of negative erosive burning.
																								



4.
SOLID-PROPELLANT BURNING RATE AS A FUNCTION OF PRESSURE

A. M. Lipanov
Keywords: combustion, burning rate, pressure, approximation
Pages: 283-287

Abstract >>
Dependences of the burning rate of powders, solid propellants, and explosives on pressure are analyzed. For this purpose, the coordinates are rotated by an angle whose tangent is equal to the burning rate coefficient in its one-term dependence on pressure. Different versions of approximation are considered, and an expression that best approximates the dependence of burning rate on pressure in the pressure range from zero to infinity is proposed.
																								



5.
COMBUSTION OF DOUBLE-BASE PROPELLANTS OF VARIOUS COMPOSITIONS CONTAINING AMMONIUM NITRATE

Zaw Htwe Ye, A. P. Denysiuk
Keywords: ammonium nitrate, double-base propellant, combustion, catalysis
Pages: 288-298

Abstract >>
The combustion of various propellants containing ammonium nitrate (AN) is studied. It is shown that the effect of AN on the burning rate depends on the heat of combustion of the starting propellant, the amount of AN, and the pressure at which combustion occurs. Thus, AN slightly increases the burning rate of low-calorific value propellants and significantly reduces that of high calorific value formulations. It is shown that combined catalysts can considerably increase (by a factor of up to ≈ 6 at a pressure of 2–4 MPa) the burning rate of propellants containing 50–70% of AN, and reduce the pressure dependence of the burning rate.
																								



6.
COMBUSTION OF SPHERICAL AGGLOMERATES OF TITANIUM IN AIR. I. EXPERIMENTAL APPROACH

O. G. Glotov
Keywords: титановый агломерат, горение, фрагментация, время горения, метод гашения и отбора, конденсированные продукты горения, распределение по размерам, titanium agglomerate, combustion, fragmentation, burning time, quenching and sampling technique, condensed combustion products, size distribution
Pages: 299-306

Abstract >>
This paper describes a method for studying the combustion of titanium particles with a diameter of 300–500 μm obtained by agglomeration of many small particles. Burning monodisperse particles of titanium were produced by ignition of miniature pieces of a pyrotechnic composition containing 69% titanium powder placed in the burning sample. The resultant agglomerated particles burned in free fall in air. Their motion and evolution, including fragmentation, were video-recorded. Condensed combustion products were quenched, sampled, and studied.
																								



7.
COMBUSTION OF SPHERICAL AGGLOMERATES OF TITANIUM IN AIR. II. RESULTS OF EXPERIMENTS

O. G. Glotov
Keywords: titanium agglomerate, titanium particle, combustion, glow intensity, drag coefficient, fragmentation, size distribution, combustion time
Pages: 307-319

Abstract >>
Combustion of titanium particles in free fall in air were investigated. Burning monodisperse particles with a diameter of 300, 390, and 480 μm were obtained by merging of many small particles during ignition of miniature pieces of a pyrotechnic composition comprising 69% powdered titanium. Motion parameters and the drag of the burning particles were determined. The fragmentation phenomenon (the onset time and duration of the phenomenon, dispersion dynamics of fragments, fragment size distribution functions) were described qualitatively. For the investigated particles, the dispersion of fragments has the form of a spruce branch: the mother particle is retained and ejects small fragments. The distance and velocity of a particle at the moment of fragmentation and at the end of combustion were determined. Data are given on the structure and morphology of the combustion product particles represented by the reside of the mother particle and the set of small fragmented particles and data on changes in the size and glow intensity of the burning particle. At the end of combustion, the mother particle is transformed to a sphere consisting of a mixture of oxides of the averaged composition TiO2.76.
																								



8.
PHASE FORMATION SEQUENCE IN COMBUSTION OF PRESSED ALUMINUM NANOPOWDER IN AIR STUDIED BY SYNCHROTRON RADIATION

A. P. Il'in, A. V. Mostovshchikov, N. A. Timchenko
Keywords: nanopowder, aluminum, synchrotron radiation, combustion, combustion products, stages, filtration combustion
Pages: 320-324

Abstract >>
The intermediate and final combustion products of pressed aluminum nanopowder are studied. It is found that the main combustion product is aluminum nitride. In the intermediate stages of combustion, aluminum oxide (γ-Al2O3) and oxynitride (Al5O6N) are the first to form on the sample surface, and aluminum nitride is formed next. The use of sliding (incident at a small angle to the surface) synchrotron radiation made it possible to determine with high accuracy (in time) the sequence of stages of formation of crystalline products during combustion of the aluminum nanopowder.
																								



9.
REGIMES OF DETONATION OF SOLID EXPLOSIVES WITH NONCLASSICAL FAST KINETICS

A. P. Ershov
Keywords: macrokinetics, high explosives, reaction zone structure, nonideal detonation, weak detonation
Pages: 325-334

Abstract >>
Detonation development in a system whose exothermal reaction kinetics depends on the rate of change of the specific volume is studied numerically. In the case of sudden compression, e.g., in a shock front, this kinetics leads to a finite degree of conversion. If the contribution of such fast processes is significant, detonation regimes that differ from the standard Zel'dovich–Neumann–Döring regime are obtained. The wave profiles qualitatively coincide with those obtained for some explosives by Utkin et al. The modeling confirms the importance of fast processes in the wave front.
																								



10.
CALCULATION OF DETONATION WAVE PROPAGATION IN A GAS SUSPENSION OF ALUMINUM AND INERT PARTICLES

A. V. Fedorov, Yu. V. Kratova
Keywords: gas suspension, heterogeneous detonation, detonation suppression by inert particles, numerical simulation
Pages: 335-347

Abstract >>
Propagation of a detonation wave in a plane channel filled by a gas suspension of fine aluminum particles and inert particles in oxygen is studied. Heterogeneous detonation of aluminum particles in oxygen propagates in the Chapman–Jouguet regime. Two types of the flow resulting from detonation interaction with a cloud of particles are found: continuous propagation with a smaller detonation velocity and flow with detonation failure. The influence of physical and spatial parameters of the inert component of the cloud on these regimes is found, including the mechanism of suppression of heterogeneous detonation, which means separation of the ignition and combustion wave from the leading shock front. Dependences of the velocity deficit on the mass fraction and size of inert particles are determined.
																								



11.
EFFECT OF THE SHEAR AREA ON THE PROBABILITY OF AN EXPLOSION OF HIGH EXPLOSIVES UNDER SHOCK-INDUCED SHEAR

N. A. Bilyk, A. L. Mikhailov, V. P. Khanin, A. S. Mikhailov
Keywords: high explosive, sensitivity to friction, probability of the explosion, distribution law, HE explosion under shock-induced shear
Pages: 348-352

Abstract >>
The applied pressure resulting in an explosion in the case of shock-induced shear is demonstrated to depend on the shear area [area of the contact of the high explosive (HE) with the metal surface]. The dependence of the probability of an explosion of the HE (phlegmatized HMX and PETN) compressed between two steel plates (end faces of two rollers) on the applied pressure and the contact area of the HE with the upper roller is confirmed in experiments on sensitivity to friction under shock-induced shear. The upper roller is shifted by 1.5 mm. It is demonstrated that an increase in the area of the shock-pressed HE contact with the roller increases the probability of the HE explosion under shock-induced shear of the upper roller at identical pressures applied to the HE. A scale factor of the influence of the HE/roller surface contact area on the pressure at which the HE explosion occurs under shock-induced shear of the surface contacting the HE is found. It is shown by statistical methods that the pressure leading to the HE explosion under shock-induced shear of the adjacent steel surface with respect to the HE is distributed in accordance with Weibull's two-parameter law.
																								



12.
NUMERICAL METHOD TO DISCUSS THE MECHANISM OF NANO-MN FERRITE POWDER PREPARATION BY DETONATION OF EMULSION EXPLOSIVES

X. H. Wang, X. J. Li, H. H. Yan, Yo. Yin, Zh. Yu. Liu
Keywords: numerical method, detonation synthesis, phase diagram, MnFe2O4
Pages: 353-358

Abstract >>
In the present research, the phase distribution of the detonation products of emulsion explosives used to prepare nano-MnFe2O4 powders by detonation is simulated by a numerical method. The mechanism of nano-MnFe2O4 powder synthesis via detonation of emulsion explosives is discussed and explained. The results obtained indicate that FeO and MnO form in the reaction zone before the Chapman–Jouguet detonation state is reached; these oxides react with surplus oxygen in air during the decrease in temperature and pressure, resulting in MnFe2O4 generation.
																								



13.
Electrical Conductivity of Copper Powders under Shock Compression

S. D. Gilev
Keywords: shock compression, metal powder, electrical conductivity, copper, compressibility
Pages: 359-366

Abstract >>
The electrical conductivity of some compositions based on the copper powder under shock compression is measured. The commercial copper powder, mixtures of copper with glass microspheres, and copper–aluminum mixtures are studied. The electrical conductivity is measured by the author's electrocontact technique, which allows the insulator–metal transition to be measured. Dependences of the electrical conductivity of powders on the shock wave pressure are obtained. As for aluminum powders examined previously, this dependence for the copper powder has a nonmonotonic character. The maximum electrical conductivity is ≈ 9 · 104 W–1 · cm–1. With a further increase in the shock pressure, the electrical conductivity decreases approximately by an order of magnitude, which is explained by intense temperature heating. The results for the electrical conductivity at high shock pressures is qualitatively consistent with known broad-range models of conductivity proposed by Garanin and Bakulin.
																								



14.
PHASE TRANSITION IN PYROXENITE UNDER SHOCK LOADING

S. A. Bordzilovskii, S. M. Karakhanov, A. I. Turkin, A. S. Yunoshev, V. M. Titov
Keywords: shock waves, pyroxenite, pyroxene, phase transition, VISAR, laser interferometry
Pages: 367-373

Abstract >>
Shock loading of natural pyroxenite samples and synthetic pyroxene samples sintered from a mixture of oxides with stoichiometry Mg0.9Fe0.1SiO3 was investigated. X-ray analysis of the recovered material was performed. Particle velocity profiles recorded by laser interferometry indicate the existence of a phase transition at a pressure of ≈ 60 GPa. At this pressure, the Lagrangian sound velocity in the shock-loaded samples of natural pyroxenite is 13.9 km/s. From an evaluation of the compression, the Eulerian sound velocity is 9.4 km/s.
																								



15.
STUDY ON THE ANTI-PENETRATION PERFORMANCE OF TWO-LAYER EXPLOSIVELY WELDED PLATES IMPACTED BY A SPHERICAL PROJECTILE

Zhou Nan, Wang Jin-Xiang, Yang Rui
Keywords: steel/aluminum plates, anti-penetration performance, ballistic limit, damage mechanism, SPH method
Pages: 374-381

Abstract >>
The anti-penetration performance of two-layer explosively welded steel/aluminum plates 5 mm thick impacted by a spherical steel projectile 6 mm in diameter with a velocity of 260–900 m/s is studied in this paper. The effects of the thickness distribution and the incident angle on the anti-penetration performance and damage mechanism are analyzed. At incidence angles of 0–60 oC, the minimum projectile velocity is needed for penetration at the steel/aluminum thickness ratio equal to 2/3. The good coherence of numerical and experimental results indicates that the finite-element method coupled with the smoothed particle hydrodynamics method can predict the anti-penetration performance of two-layer explosively welded plates well.