Home – Home – Jornals – Combustion, Explosion and Shock Waves 2020 number 5

Insensitive munitions are munitions that are chemically stable enough to withstand thermal, mechanical, or electrical stimuli during storage and transportation, and can still explode as intended to defeat their targets. Extensive programmes have evolved worldwide for the development and introduction of insensitive munitions (IMs). The use of insensitive energetic materials significantly improves the protection of modern nuclear warheads and increases the survivability of conventional munitions in hustle environment. The most basic level to obtain insensitive munitions is the use of intrinsic insensitive energetic materials, either by synthesizing new, less sensitive crystalline materials or by improving the physical properties of existing sensitive materials. In light of the growing importance of insensitive munitions, this review paper brings out some potential insensitive energetic materials and plasticizers emphasizing their significant role in the development of futuristic IM formulations. This review also concisely brings out the recent work carried out globally, including India, on the development of advanced energetic materials and their insensitive energetic formulations

This study describes the effect of preliminary mechanical activation and SiO₂ quartz content on combustion rate, maximum combustion temperature, sample elongation during combustion, compressibility of mixtures, composite particle size, phase composition, and the structural features of combustion products in a Ni-Al-SiO₂ system. In Ni + Al + SiO₂ initial mixtures, not subjected to mechanical activation, it is not possible to initiate combustion at room temperature if the mass content of SiO₂ quartz exceeds 10 %. Preliminary mechanical activation of the Ni + Al+ x SiO₂ reaction mixture expands the limit of quartz content in the mixture, at which it is possible to realize the combustion of pressed samples at room temperature, up to 40 %. The burning rate and sample elongation during combustion increase significantly after the reaction mixtures are mechanically treated, and the relative density of the samples, obtained at a fixed pressing pressure, decreases. The increasing quartz content in the Ni + Al + x SiO₂ reduces the combustion rate, the maximum combustion temperature, and the sample elongation during the combustion of both the initial and mechanically activated mixtures. Moreover, as the quartz content increases, so does the sample density reached at a fixed pressing pressure in the case of initial mixtures, while the density in the case of mechanically activated mixtures is virtually not affected. The increasing quartz content also reduces the composite particle size after mechanical activation and increases the number of phases formed in the reaction products. An explanation for most of the observed relationships is proposed.

Using conservation laws, formulas for evaluating conditions for suppressing combustion and detonation waves using dust or water curtains are proposed that allow the determination of the minimum concentration of dust or atomized water in a curtain and the minimum length of the curtain. Specific data on the conditions for quenching a methane-air mixture typical of coal mines are given. These data indicate that the dust concentration and curtain dimensions recommended by RF regulations allow, at best, to suppress only low-velocity combustion waves.

This study experimentally confirms the intensification of kerosene combustion in the case where a mixture simulating steam reformation products in a model combustion chamber with a supersonic velocity of the flow at the inlet. It is shown that the used mixture has a higher chemical activity than ethylene. The use of steam reformation products of hydrocarbon or synthetic propellants in schemes with pulse-periodic combustion control increases combustion efficiency without the use of special design solutions for organizing initiation and stable combustion.

Regimes of continuous detonation of CH₄/H₂-air mixtures with mass fractions of H₂ in the fuel equal to 0 ÷ 1/5 are obtained in an annular combustor 503 mm in diameter with variation of the combustor geometry. The influence of the combustor geometry on the velocity and number of transverse detonation waves, pressure in the combustor, and specific impulse is considered. It is found that three-fold constriction of the combustor exit cross area allows obtaining two-wave regimes of continuous spin detonation in the pure methane-air mixture. Based on stagnation pressures measured at the combustor exit, the specific impulses in the case of continuous detonation are determined for different compositions of the fuel.

An improved reactive flow model with thermodynamic consistency is proposed to deal with the detonation hydrodynamics of solid explosives. Based on the assumption that the chemical mixture composed of solid-phase reactants and gas-phase products can arrive at mechanical equilibrium, but cannot arrive at thermal equilibrium, the solid-phase reactants and gas-phase products may possess one pressure and one velocity, but two temperatures or internal energies. With the help of the energy conservation of the mixture and pressure equivalence between the constituents, the conservation equation of internal energy and the evolution equations of the volume fraction for the solid-phase reactants and of pressure for the chemical mixture are derived. Thus, the full governing equations of the proposed detonation model include the conservation equations of mass, momentum, and total energy, and the evolution equation of pressure for the chemical mixture, and the conservation equations of mass and internal energy, and the evolution equation of the volume fraction for the solid-phase reactants. The theoretical analysis shows that there exists a distinct discrepancy between the proposed model and the Zel'dovich-Neumann-Doring detonation model for the steady structure of the detonation wave. The numerical simulation results of typical detonation problems show that the important characteristics of detonation flows can be well captured and also demonstrate that the proposed detonation model of solid explosives is reasonable.

Experimental studies of the structure of detonation waves in mixtures of tetranitromethane with methanol and nitrobenzene have been performed. Mass velocity profiles at the arrival of detonation waves at the boundary with a water window were recorded by a laser interferometer. It has been shown that the flow pattern in the reaction zone changes sharply at a concentration of diluents in the vicinity of stoichiometry, resulting in a decrease in the amplitude of the Von Neumann spike up to its complete disappearance. The detonation waves are resistant to the formation of a cellular structure of the front over almost the entire concentration range, except in the range near the limit values. At the same time, the amplitude values of mass velocity are poorly reproduced from experiment to experiment performed under the same conditions. The obtained experimental dependences of the detonation velocity on the concentrations of methanol and nitrobenzene are in good agreement with the thermodynamic calculations performed.

The dispersion of oxidized Al nanoparticles into clusters by rapid heating in a shock wave has been studied. Clusters distribution characteristics were calculated as a function of the parameters of the initial nanoparticle distributions and the nature of the interaction of deformation waves with the nanoparticle shell and core. The studies were carried out using the author's proposed resonant mechanism for dispersion of the liquid core of a nanoparticle by a shock pulse upon destruction of the solid oxide shell. The ignition of Al nanoparticles after dispersion in air was analyzed using the previously described kinetic oxidation mechanism with the evaporation of clusters taken into account. Initial distributions of nanoparticles and their ignition times are validated against published experimental data.

Several aluminum-based explosives are prepared and their underwater explosion performances, including the specific bubble energy and specific shock wave energy, are measured in underwater explosion experiments. The formulation characteristics of the explosives involve the aluminum/oxygen (Al/O) ratio, aluminum particle size, and the total content of all solid components, including ammonium perchlorate (AP), aluminum (Al), and cyclotrimethylenetrinitramine (RDX). The results indicate that the Al/O ratio of the explosives produces a great effect on the specific shock wave energy and specific bubble energy of the explosives. The total specific energy of the explosive reaches the maximum value at Al/O = 0.44. It is notable that an increase in the total solid content (AP, Al, and RDX) in the explosive formulation can effectively increase the specific total energy of the explosives. When the total solid content is increased by 2 wt. % in the explosive formulation, the total energy of the explosive can be increased by about 0.1 times the TNT equivalent. Moreover, the particle size of the aluminum powder can also significantly affect the energy of the explosives. The smaller particle size of the aluminum powder is beneficial to the energy release of aluminum and can increase the total explosion energy.

The effect of friction on the critical temperature of ignition is considered by establishing the friction ignition model based on the principle of the heterogeneous reaction of Semenov. The effects of the oxygen concentration, flow velocity, friction force, and contact area on the critical temperatures of two fireproof titanium alloys (TB12 and TF550) are studied. The results show that the critical temperature decreases with an increase in the oxygen concentration and increases with the flow velocity. The critical temperature increases approximately linearly with an increase in the friction force and decreases exponentially with an increase in the contact radius. As the contact radius increases to 0.007 m, the critical temperatures of TF550 and TB12 are 1029 and 1016 K, respectively. As the contact radius reaches 0.014 m, the critical temperatures of TF550 and TB12 are 962 and 960 K, respectively

This paper introduces a simple and new correlation between the impact sensitivity and activation energy for pyrotechnic compositions where both the fuel and oxidizer are inorganic in nature. The database consists of various drop height (impact sensitivity) and activation energy values obtained from in-house experimentation and various literature studies. This paper also proposes a method to calculate the activation energy from the thermal properties obtained using only single-heating-rate differential scanning calorimetry experimental data. The correlation coefficient between the impact sensitivity and activation energy is found to be 0.84.

Operation of shaped charges with copper hemispherical facings of degressive (decreasing from top to bottom) thickness is experimentally studied. The velocity of the head of generated shaped-charge jets is determined along with how deep they penetrate a type-setting barrier made of steel disks and the sizes of holes made in the disks. The experimental data on an increase in the velocity and a decrease in the mass of the heads of shaped-charge jets, which occur with an increase in the difference in the thicknesses of the hemispherical liner at the apex and at the base are in good agreement with the results of numerical modeling carried out within the framework of a two-dimensional axisymmetric problem of continuous mechanics. According to the experimental results, the effect of technological manufacturing errors on the operation of these charges becomes stronger, which eliminates or significantly limits the increase in the penetrating action. In one of the versions of facings of degressive thickness, the depth of penetration of a barrier, which is average in two tests, increases by 7.5% as compared to the facing of constant thickness.

This paper presents the results of an experimental study of the influence of the strength of the thin-walled casing of a PETN charge on the performance of small-sized pulsating explosive devices for various applications.