Home – Home – Jornals – Combustion, Explosion and Shock Waves 2019 number 4

Within the framework of the classical one-dimensional theory of detonation based on conservation laws, the lower branch of the adiabat of energy release of the combustible mixture as a geometric place of the points of the final state of the system admits a solution; for combustion waves whose propagation velocity is D_fl, this solution stays in the range from zero to the deflagration velocity: 0 ≤ D_fl ≤ D_def . The normal combustion wave propagation velocity S_u is located in this interval (0 ≤ S_u ≤ D_def), but it is traditionally calculated with the use of the thermal theory of combustion rather than detonation theory. Various approaches to choosing the final state point on the lower branch of the energy release adiabat for the normal flame are analyzed in the present paper. An analysis is performed and estimates are provided both for the degree of correspondence of the predicted and experimental velocities of flame propagation and for the degree of correspondence of the qualitative behavior of these dependences on the basis parameters of the mixture. For most hydrocarbon fuels considered in the study, the best agreement with the experimental data on S_u is provided by the formula defining the flame velocity D_fl as the mean geometric value between the diffusion velocity S_diff and deflagration velocity D_def .

A two-stage reduced model of chemical kinetics of detonation combustion of a mixture of two fuels, i.e., hydrogen and carbon oxide (syngas), with an oxidizer is proposed. Based on this model, a two-dimensional numerical calculation of the parameters of an irregular cellular structure of the detonation wave in the considered binary mixture of two fuels with an oxidizer is performed.

Initiating explosive charges in a cylindrical tube with one end face being plugged, vortex rings with diameters of the order of 1 m and initial velocity of motion greater than 100 m/s are obtained. Such rings emit a clearly heard acoustic signal, which is of interest for studying generation of acoustic waves by vortices and scaling mechanisms of noise generation. Vortex rings are generated due to exhaustion of a high-velocity gas jet formed after shock wave propagation over the tube. The measured vortex velocities are found to be weakly dependent on the explosive mass, i.e., as the mass increases, the fraction of energy transformed to the vortex ring energy becomes smaller.

This paper presents a physicomathematical model and the results of numerical solution of the spark ignition problem of a suspension of a bidisperse aluminum powder in air. The critical ignition conditions of the aluminum powder suspension in air are determined numerically as a function of on the particle size and mass concentration and the content of large and small particles in the suspension. The study has shown the effect of the fine fraction of particles in the bidisperse aluminum powder on the critical spark ignition conditions of the aluminum powder suspension in air with the subsequent establishment of a steady regime of combustion front propagation.

The differential thermal analysis is applied to study the influence of activated charcoal with multilayer graphenes (three and more layers) on the thermal decomposition of a substance based on hydroxyl ammonium nitrate and carboxyl methyl cellulose. It is demonstrated that addition of activated charcoal with multilayer graphenes lead to an increase in the burning rate of hydroxyl ammonium nitrate up to four times. Addition of activated charcoal at the stage of thermal decomposition leads to a decrease in temperature and time of the chemical reaction until complete decomposition of ammonium nitrate.

Comparative results of experiments aimed at studying the evolution of dust-laden jets induced by the presence of structural elements and grooves on the surface of loaded specimens are reported. The results are obtained with the use of pulsed X-ray radiography and synchrotron radiation. Information on dust density changes in synchrotron diagnostics is obtained by using multiframe filming. In the case of single-frame recording by means of pulsed X-ray radiography, a glancing detonation wave was used for studying the dust behavior instead of the normal wave.

An analytical model of the equation of state is developed based on theoretical ideas about the structure of TATB. The model is validated against experimental data obtained in static and dynamic experiments. The theoretically sound equation of state was used to match different experimental data in order to maximize the use of empirical information. It is expected that the application of the obtained equation of state will increase the accuracy of description thermodynamic parameters of unreacted TATB in numerical simulations of shock-wave and detonation processes.

The detonation pressure of an emulsion explosive sensitized by polymer microballoons was determined for normal and oblique incidence of a detonation wave on the target. The initial density of the explosive ranged from 0.2 to 1.2 g/cm³. The obtained pressure values are in good agreement with the calculated values known from the literature and are compared with the detonation pressure values of an emulsion explosive sensitized by glass microballoons. The reaction time and isentropic exponent of the emulsion explosive used were calculated.

Instability of a conical liner during shaped-charge jet formation has been studied. To establish the metal flow pattern during shaped-charge jet formation, we fabricated three-layer copper-copper-constantan liners consisting of a solid copper conical funnel with an cone angle of 45^oC, a wall thickness 1.5 mm, and a funnel pressed into it and rolled from a copper sheet 1.0 mm thick clad by explosion welding with constantan 0.2 mm thick. Liner implosion was carried out by an RDX charge 20 mm thick. The jet formation process was recorded by flash radiography, and the metal flow pattern was determined by micro sections of recovered slugs. Since the boundary of explosion welded metals is clearly distinguishable on the sections, the residual deformation in different sections of the slug shows the occurrence of instability of the liner during the implosion, which manifests itself in the form of folds oriented along the generatrix of the cone. However, the general flow pattern described in terms of the theory of an ideal incompressible fluid is not disturbed, which follows from radiographs of the shaped-charge jet formation process.

Experiments on the explosive welding of low-plasticity steels through thin plastic layers show that, aside from the geometric features of collision (thickness and angle of collision of plates and contact point velocity), the dimensions of waves arising in the junction region are also highly affected by the mechanical properties of welded materials (hardness, density, and sound velocity). It is determined that waves of different dimensions can be formed under the same conditions, but their length lies in a certain range of values. On the basis of the resulting experimental data and with involvement of the Landau model, which describes the instability of a steady flow of viscous fluid, expressions for estimating the top and bottom boundaries of wavelengths are constructed with allowance for geometric parameters of collision and mechanical properties of colliding metal plates.

This paper describes the structural studies of hollow cylindrical shells made of D16 and AMts aluminum alloys, loaded by sliding detonation. Explosive loading conditions for the complete convergence and closure of shells are established. Light optics scanning electron microscopy, and transmission electron microscopy are applied to study the structural and phase transformations in shells under shock-wave loading. The relation of composition, structure, and mechanical characteristics of alloys with their behavior under the action of shock loading is shown. There are several scenarios of convergence of shells, depending on their composition and loading conditions - from complete and steady convergence to multiple spalling.

The structural mechanisms of buckling and the deformation behavior of copper and steel cylindrical shells (pipes) during convergence under the action of an explosion are studied. The dependence of deformation behavior on the transverse dimensions of the shell and properties of the loaded material is described. It is established that the stability of radial convergence depends on absolute dimensions of the shell rather than relative dimensions, with the convergence of large-diameter shells occurring more stably. It is demonstrated that the convergence stability is violated due to the formation of a characteristic pattern of localized deformation in the sample, consisting of homogeneous, orderly arranged structural elements whose dimension depends little on the material properties and experimental conditions. A criterion for stable radial convergence that relates the characteristic dimensions of the structural element of localized deformation and the shell radius is proposed.

Numerical simulation studies of shaped charges with hemispherical liners of degressive thickness (decreasing from the top to the bottom) have been continued. The possibility of increasing not only the velocity but also the mass of the head sections of the formed shaped-charge jets to the level provided by conical liners of progressive thickness has been analyzed. For this purpose, liners of degressive thickness in the form of a truncated sphere and a semi-ellipsoid slightly elongated along the charge axis have been additionally studied.

The results of numerical simulation of the blast impulse of explosive charges on structural elements are presented. The numerical method was validated against available experimental data describing the blast effect in the near zone of explosion. Additional experiments on explosive acceleration of steel discs were performed. The effect of explosion conditions (the presence or absence of air, additional reflecting surfaces) on the blast impulse was studied.

An X-ray pulse video recording method is used to study the projecting ability of coaxial combined explosive charges containing dispersed aluminum in a thin peripheral layer as compared with charges containing a uniformly distributed aluminum additive and charges with no additives. The significant influence of the burnout of detonation products on the projecting ability of explosive charges containing dispersed aluminum is confirmed. It is shown that aluminum in a composition with explosive charges burns out because of reacting both with detonation products and ambient air, including in a rarefied environment.

Experiments on detonation spraying of ceramic coatings are carried out by feeding a powder as part of a suspension into a barrel for the first time. Spraying of Al₂O₃ and TiO₂ nanopowders and hydroxyapatite shows that the new method for obtaining coatings (suspension detonation spraying) can be implemented on a CCDS2000 detonation device. Unlike conventional detonation spraying technologies using micron-sized powders, suspension spraying makes it possible to work with powders whose particle size is smaller than 1  m, serving as a basis for a suspension fed into the projector barrel during spraying.

Fundamental features of explosive packing of powder mixtures containing refractory metal carbides and metal bonds are under consideration. The effect of acoustic rigidity of metal bonds on the residual porosity of samples after explosive treatment is revealed. It is shown that the degree of packing of mixtures of carbide powders with metals under explosive pressing is determined by the possibility of arrival of shock waves in the metal bond particles at their surfaces free of contacts with other particles and with a mass velocity acquired by the metal bond at these surfaces due to unloading.

A number of modern scientific and practical problems in design of multifunctional safety systems for coal mines and requirements to such systems are discussed. The reasons and the dynamics of accidents in mines are analyzed; examples of approaches to preventing such accidents are given. Available and promising directions of the development of engineering tools and systems for ensuring miners' safety are considered. The efficiency of using the scanning gas monitoring technology is demonstrated. Combining this technology with the automatic system of fire quenching allows the fire to be suppressed at the initial stage of ignition of the methane-air mixture.

One method of pulse pressure loading of material or plasma is axisymmetric compression using a convergent cylindrical detonation wave. Such a wave is often formed by multipoint initiation and has a number of specific features that may affect the properties of the objects under study. To solve specific problems, it is proposed to use an explosive laboratory setup based on a converging cylindrical detonation wave with 12-48 initiation points. The TNT equivalent of the charge is less than 1 kg. The main method of research is process visualization using a domestic high-speed Nanogeit camera with a nanosecond time resolution. The structure and velocity of the converging detonation wave along the radius were determined. It is shown that for a charge of limited thickness, the curvature of the detonation wave front for various explosives depends only on the distance to the initiation point.