Home – Home – Jornals – Combustion, Explosion and Shock Waves 2025 number 2

The control of combustion by throttling jets in a two-section channel with high-velocity flow has been studied numerically. Pulses of the first throttling jet are used to produce intense transonic combustion of hydrocarbon fuel in the first section. Side fuel supply is applied after the switching-off of the first jet to maintain the combustion mode before the channel expansion. The completeness of fuel combustion in the second section is increased using a second throttling jet. The Reynolds-averaged Navier-Stokes equations closed by the eturbulence model are solved. Combustion was modeled by the overall reaction. A pulsating mode of hydrogen combustion in the second section when exposed to the cold throttling jet was established. The influence of this jet on the completeness of hydrogen combustion was studied.

We investigated the possibility of the existence of combustion waves in CH₄/air mixtures with a methane content α = 5-8 vol.% and in CH₄/air/coal dust mixtures in a closed vertical channel 6.75 m long and 0.07 m in diameter when ignited at the top. The experiments were carried out at an initial pressure of 0.1 MPa using dust with an average volume concentration of 100-530 g/m³ and a particle size 0-200 mm. It was found that combustion was not initiated in gas and gas/coal dust mixtures with α ≤5-5.5 vol.%. The results of the study indicate that the direction of gravity influences the ignition and combustion of the mixtures and that the energy contribution of coal particles is low compared to that of methane.

This paper presents new data on the detonation parameters of lean, stoichiometric, and rich methane-oxygen (air) and hydrogen-oxygen (air) mixtures inhibited by nitrogen and carbon dioxide. By varying the ratio between the initial components, carbon dioxide was found to have a stronger inhibiting effect on the parameters of combustion and detonation products.

An experimental study was performed to investigate thermal processes during gas detonation coating. Before impact on the target, particles of the sprayed material were accelerated to velocities of 300-500 m/s by the flow of detonation products of a gas mixture whose temperature reached 4200 °C. Due to intense heat transfer, the temperature of the particles increased. The highest quality coating was obtained at a heating temperature close to the melting point. Therefore, to estimate the heating temperature of the particles, we measured the heat fluxes from the detonation products of the gas mixture to their frontal and lateral surfaces using a method based on the Seebeck effect.

An X-ray radiography method for contactless diagnostics of solid rocket motors (SRM) is presented. An experimental study was performed to visualize intrachamber processes and determine the solid propellant burning rate in a model E-5-0 SRM using an X-ray system consisting of an X-ray source and a dynamic X-ray detector located at a given distance from the object of study. The possibility of contactless determination of the propellant burning rate based on an analysis of gray level changes near the burning surface was confirmed experimentally. Radiographic results are in satisfactory agreement with the results of other methods for determining the solid propellant burning rate.

Effect of carbon additives on burning rate of model composite propellants is studied. Paste-like propellant compositions are used, which are an analog of composite solid fuel with an uncured binder. The role of nanocarbon additives is played by different substances: detonation nanodiamond (DND), which is sometimes heat-treated or crushed to a size of 4 nm, multilayer carbon nanotubes, soot, activated carbon, graphite, adamantane, and graphene. Among all the allotropic forms of carbon, the maximum increment of the burning rate (23%) is ensured by an additive of 2% DND with 2% plasticizer (by weight). At the same time, the combustion product temperature decreases by ≈200 °C, thereby reducing the probability of rocket engine burnout.

The growth of particles behind the detonation wave front in condensed explosives has been investigated based on physical estimates and experimental results obtained in recent years. The focus is on the large difference in particle size due to the presence or absence of hydrogen in the explosive composition.

A computational method has been developed to model the shock-wave mechanism of detonation wave initiation during the interaction of a fast flying body (FFB) with a combustible hydrogen-oxygen mixture diluted with 50% argon under normal conditions. The FFB velocities at Mach numbers M = 3-4 are considered, which are lower than the Chapman-Jouguet detonation velocity in the mixture under study at normal pressure and temperature. It is shown that the detonation wave is initiated at a FFB velocity exceeding M = 3.9. In this case, the shock-wave mechanism of detonation initiation occurs where a detonation wave is formed at the shock wave separated from the combustion wave by an induction zone. The modeling identified a new regime of reaction gas flow around the FFB. In the range of FFB velocities M = 3.4-3.85, a quasi-stationary mode of shock-initiated combustion occurs. The flow parameters required for direct initiation of multifront detonation of the FFB are consistent with analytical estimates of the initiation energy.

Optical methods for recording fast processes are applied to study a flow behind a detonation wave front in a nitromethane/polymethyl methacrylate (NM/PMMA) mixture. It is shown that, an increase in the PMMA concentration leads to an increase in the critical detonation diameter, which, as in pure NM, is determined by the occurrence of reaction failure waves at the charge-shell boundary. A NANOGATE-22/16 high-speed eight-channel sixteen-frame electron-optical camera is used not only to properly study the spatial occurrence and propagation of reaction failure waves, but also to determine their characteristic size. It is shown that unstable flow at the edge of the charge in the NM/PMMA mixture can be stabilized by adding amines or glass microspheres.

Based on model experiments, approaches to numerical modeling of detonation wave propagation in small-section channels filled with PETN-based explosive (pentaerythritol tetranitrate) are investigated with account for macroscopic detonation kinetics.

This paper describes the process of obtaining homogeneous mixtures of RDX, HMX, PETN, TNT, Fox-7, and benzotrifuroxane of various dispersions with polysiloxane (SKT) as an inert soft polymer. The specific surface area of crystalline explosives (HE) varies from 440 to 4750 cm²/g, and the explosive content in the mixtures ranges from 65 to 82% (wt.). Each binary mixture (explosives/polysiloxane) yields solid, practically nonporous, flat (round ones with a diameter of 40 mm and square ones with a size of 40 × 40 mm) charges of various thicknesses and elongated cylindrical (cord) charges of various diameters. Flat and cord charges are characterized by the same composition, dispersion, density, and defectiveness of explosive crystals. Critical thicknesses and critical diameters of detonation of all mixtures are determined experimentally with an accuracy of 0.05 mm. Test conditions: flat and cord charges without shells located on a metal base. It is revealed that the ratio of the critical diameter to the critical thickness of detonation is practically constant and equal to 1.83 ± 0.1. The previously obtained dependence of the critical detonation diameter of explosives and explosive mixtures on the change porosity is also taken into account. An equation for the correct recalculation of the experimental critical detonation thickness of pressed charges of crystalline explosives with real porosity into the critical detonation diameter of high-density charges is obtained. This equation is additionally confirmed by testing many individual explosives of different dispersion and known literature data conducted in this work.

This paper presents thermodynamic calculations of characteristics of explosive mixtures based on tetramethylammonium perchlorate. Their sensitivity, explosion heat, and volume are determined. The composition of gaseous explosion products is analyzed. This paper also demonstrates the possibility of creating promising explosive mixtures with detonation ability and mechanical sensitivity in the TNT-RDX range, with an explosion heat of higher than 6 MJ/kg and a hydrogen content of gaseous explosion products of more than 50% by volume.

This paper presents the results of a study of explosive compositions with the replacement of the combustible filler-aluminum powder-by an aluminum- and boron-containing composite mixture prepared by mechanical activation. Thermodynamic calculations of the characteristics of fillers and explosive compositions were made using the TERRA software and the NIST database. The compatibility of fillers with active binders and the influence of fillers on the detonation characteristics, blast and propulsive effects, and brisance of model explosive compositions were studied.

Response of materials to pulse loading by cylindrical specimens is determined via two interrelated processes: shock wave motion toward the sample axis and perturbation motion in the form of triple shock configurations along the shock wave front. The surface area of the perturbed shock wave front increases due to protrusions strengthened as a result of merging with shock-wave-generated smaller perturbations. Because the front area sharply increases as the shock wave approaches the axis, several large triple shock configurations are formed and the shock wave front is divided into separate sectors in which they oscillate. The collision of powerful shock structures ensures the shock wave front motion toward the axis by removing a portion of the compressed material from the collision zone forward ahead the shock wave front and the additional compaction of the shock-compressed material by longitudinal shock structures under the wave front. The cumulation process is completed when the height of the protrusions becomes equal to the distance from the shock wave front to the axis. The near-axis space is occupied by the front protrusions, and the resulting reflected shock wave slows down the oncoming flow.

The convergence of cylindrical copper shells subjected to explosion has been investigated. The shell surface was covered with an explosive layer. Explosion was initiated at eight points evenly spaced on a cylindrical surface. During the convergence, eight ejections were formed on the inner surface the shells; i.e., buckling of the smooth deformation front occurred. The formation of ejections is attributed to the occurrence of plastic (cumulative) jets during the interaction of adjacent shock and deformation waves. The structural mechanism of convergence of thick-walled copper shell consists of the formation, expansion, and closure of ejections. It has been found that the formation of ejections is preceded by another buckling mechanism of the deformation front-corrugation.

This paper presents the results of a study of hydrodynamic instability during the collapse of shells, in particular, shaped charge liners. Initially, this instability was initiated by harmonic surface perturbations or perturbations of the load parameters. The instability manifested itself in the form of the development of these perturbations over time. The absence or limited growth of surface perturbations was considered as a manifestation of the stability of the liner deformation process. In this study, we take into account the results of both numerical simulation and available experimental data. Based on the results of the study, conclusions are formulated about the causes and possible forms of manifestation of instability during the deformation of collapsing metal liners, the governing parameters of this process, and its features and mechanism.

The present paper describes an X-ray experiment on explosive compression of spherical shells made of boron carbide and lead with single-point initiation of detonation on the surface of a spherical explosive layer. Experimental data are compared with numerical modeling results using the LEGAK technique. There is satisfactory agreement in the type of failure of boron carbide shells in the calculation and experiment.

The brightness and color temperatures of shock-heated fused silica were determined at thermal radiation wavelengths of ~390 to 630 nm using a four-channel pyrometer. The measurements were carried at shock compression pressures of 27.6-50.5 GPa. It is shown that the emission spectrum of shock-heated fused silica is a superposition of the thermal emission spectrum and the line spectrum. Baric dependences of the emissivity and absorption coefficient of shock-compressed fused silica were determined.

A heuristic model has been formulated to calculate the pressure behind the shock wave front in condensed matter. The model is based on the empirical relationship between the total pressure and the product of the potential pressure component by the degree of shock compression. The model is supported by molecular dynamics calculations of the thermodynamic state of shock-compressed condensed matter and by comparison with experimental data on the isothermal and isentropic compression of iron.

The possibilities of increasing the performance of shaped charges by using lens assemblies made of high-modulus ceramics are considered. In this case, an increase in the loading parameters of a shaped-charge liner can be achieved if the detonation wave enveloping the lens propagates in a pre-compressed but unreacted explosive. Pre-compression of an explosive charge without detonation initiation can be achieved by its shock desensitization with the advanced wave transmitted through the ceramic lens. Numerical simulation of detonation wave propagation in a shaped charge with different lens assemblies have shown the potential for using composite lenses in which the inner part adjacent to the axis of symmetry is made of high-modulus ceramics and the outer part is made of an ordinary inert material.