Calculation of the detonation velocity of porous water-containing RDX-based charges

A nomographic method for predicting the detonation velocity of a porous explosive mixture prepared from RDX powder and water is proposed. It is shown that, in contrast to the existing calculation methods for predicting the detonation velocity, the use of the proposed nomogram greatly simplifies the procedure and requires knowledge of only two parameters: the mass fraction of RDX and the density of the mixture in the charge. At the same time, the nomogram is a coordinate system that enables to place and to compare on one field experimental data obtained at different parameters of the charge. It is shown that RDX powder-water hand-prepared charges can have a detonation velocity of 6–8 km/s. The detonation velocity of cylindrical water-containing charges 10–36 mm in diameter and 120–1000 mm in length with RDX mass fractions of 0.6–1.0 is measured.     

Propagation of detonation in fuel–air mixtures in flat channels

The wide scatter of the values of the measured detonation cell size in fuel + air mixtures restricts the applicability of this parameter in the estimation of the geometric limits of detonation propagation, including in rectangular channels whose height is much larger than their width. The critical channel height for the propagation of detonation has been experimentally determined for hydrogen + air, propane + air, and ethylene + air mixtures. In order to reveal the specific features of the propagation and decay of detonation in a narrow channel, numerical simulation has been carried out for a hydrogen + air mixture with account taken of the cellular structure of the detonation wave.     

Dynamics of detonation waves in a channel with variable cross section and filled with bubbly fluid

The flow of bubbly fluid comprising a mixture of bubbles filled with explosive and inert gases, which is driven through a converging channel, was studied. Depending on the velocity of the hummer hitting the bubbly fluid boundary, the flow may be accompanied by the development of detonation waves which compress the bubbles with inert gas.     

矩形管内临界爆轰动力学数值分析

 对矩形管内临界爆轰动力学特征进行了数值分析。采用基元反应描述爆轰化学反应过程,采用二阶附加半隐的龙格-库塔法和5阶WENO格式求解二维反应欧拉方程。对于25%氩稀释化学计量比的氢氧预混气体,当管道宽度为30 mm、初温为300 K时,产生临界爆轰的预混气体初压为3.5 kPa。在此临界条件下,获得了临界爆轰胞格结构、沿壁面的速度和峰值压力曲线及流场波系演变特征。着重对比分析了矩形管内临界爆轰与普通爆轰在爆轰波速度、平均速度、胞格宽长比、横波结构、未反应气囊及旋涡结构之间的差异,深入认识了临界爆轰的不稳定性和化学反应动力学特征。     

爆炸磁压缩发生器爆炸管运动研究

 报导了对爆炸磁压缩发生器(MFCG)的爆炸管进行的爆轰试验结果。用电子学方法测试了爆炸管采用的粉状RDX炸药的爆轰速度;采用高速分幅摄影方法,观测了爆炸管在管内RDX炸药爆轰产物驱动下的膨胀运动过程,测试了膨胀角、对称性和膨胀速度。试验表明,爆炸管在膨胀至 3倍初始半径内未发现破裂现象,其性能满足MFCG的设计要求。     

Embedded particle size distribution and its effect on detonation in composite explosives

This paper discusses the effects of stochastically varying inert particle parameters on the long-term behaviour of detonation front propagation. The simulation model involves a series of cylindrical high explosive unit cells, each embedded with an inert spherical particle. Detonation shock dynamics theory postulates that the velocity of the shock front in the explosive fluid is related to its curvature. In our previous work, we derived a series of partial differential equations that govern the propagation of the shock front passing over the inert particles and developed a computationally efficient simulation environment to study the model over extremely long timescales. We expand upon that project by randomising several properties of the inert particles to represent experimental designs better. First, we randomise the particle diameters according to the Weibull distribution. Then we discuss stochastic particle spacing methods and their effects on the predictability of the shock wave speed. Finally, we discuss mixtures of plastic and metal particles and material inconsistency among the particles.     

Detonation propagation with velocity deficits in narrow channels

Propagation limits of detonations in narrow channels have been studied with a focus on velocity deficits and variation in cell widths. A channel was formed by a pair of metal plates of 1500 mm length which were inserted in a detonation tube of 50.5 mm inner diameter. Test gases were hydrogen–oxygen mixtures diluted with argon or nitrogen, which were selected as representatives of regular and irregular mixture systems. The velocity deficits predicted using the concept of negative boundary layer displacement thickness were compared to those obtained experimentally. From good agreement between the predicted and the experimental velocity deficits, the cell width enlarged in the channel was calculated using the induction zone length behind the decelerated leading shock front. Although this calculation underestimates the cell widths, the calculated cell widths were found to be well predicted when they were multiplied by an appropriate proportionality factor. It is found that for given mixtures, a combination of the calculated velocity deficit and the number of cells in a channel contributes to the prediction of propagation limits of detonations.     

Formation and characteristics of composite reaction – Shock clusters in narrow channels

High-speed schlieren visualizations show that a composite reaction-shock cluster structure is formed in the last flame acceleration stage prior to detonation transition for ethylene/oxygen mixture in a narrow channel. The composite structure is bounded by a normal shock at the leading edge of the structure, and series of parallel oblique shocks interweave with reaction front on the other end in the cluster. Propagating velocity of the reaction front at the inception of the cluster is ～ 45–50% of Chapman-Jouguet detonation velocity of the mixture. Reaction front accelerates rapidly after the formation of the reaction-shock cluster, and run into detonation in tens of microseconds except for very lean mixtures. The angle between the parallel oblique shocks in the cluster and the side wall, defined as ω-angle, is found to be constant for a specific mixture as the reaction wave propagates. Dependence of ω-angle on mixture equivalence ratio and channel size are investigated in the study. Analysis shows that DDT distance is linearly proportional to ω-angle, and an empirical correlation is derived.     

Nano-MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder synthesis by detonation of emulsion explosive

Nano-MnFe₂O₄ powders were synthesized by detonation of specially prepared emulsion explosives. X-ray diffraction and transmission electron microscopy were carried out to characterize the as-prepared powders. The results indicated that relatively finely dispersed spherical powders were obtained when the content of RDX in the emulsion explosives was 9.18 wt. %. A certain content of internal-phase ammonium nitrate was not only favorable to control the ingredients of the detonation products, but also advantageous to stabilize the detonation structure of the emulsion explosive according to differential thermogravimetry experimental results. PACS 81.07.Bc; 81.20.-n     

Detonation propagation across a stratified layer with a diffuse interface

A study was conducted to examine detonation propagation in a stratified layer of hydrogen-oxygen-nitrogen above an inert gas in a horizontal narrow channel. The stratified layer was produced by a gravity current, generated by retracting a door initially separating a hydrogen-oxygen-nitrogen mixture in the predetonator and a heavier inert gas in the test-section. A steady detonation wave generated in the predetonator was transmitted into the stratified layer. The reactivity of the predetonator mixture was varied via the hydrogen-oxygen equivalence ratio and the amount of nitrogen dilution. Schlieren photography was used to visualize the detonation front in the test-section, and soot foils were used to obtain the cellular structure. Schlieren imaging showed a curved detonation front that decoupled at about mid channel height, into a shock wave and trailing contact surface. Both the hydrogen-oxygen-nitrogen reactivity and the type of inert gas initially in the test-section affected the distance travelled by the detonation wave in the stratified layer. The mixture composition distribution within the test-section before ignition was obtained via a three-dimensional CFD simulation. The lateral extent of the cellular structure captured on the soot foil, coincided with the calculated inert gas mole fraction contour that corresponds to a sharp increase in the ZND induction zone length, e.g., 70% argon dilution for a stoichiometric hydrogen-oxygen predetonator mixture.     

A flame technique to isolate the detonation/product interface relevant to rotating detonation engines

A novel experimental technique is proposed to study the detonation propagation in a layer of non-reacted gas weakly confined by combustion products. This problem is relevant to rotating detonation engines, where transverse detonations are confined by products of a previous rotation cycle, and other applications such as industrial safety. The experimental technique utilizes a flame ignited along the top wall in a long channel. The preferential growth of the flame along the long direction of the channel creates a finger flame and permits to create a narrow layer of unburned gas. A detonation ignited outside of this layer then propagates through the layer. This permits to conduct accurate observations of the detonation interaction with the inert gas and determine the boundary condition of the interaction. The present paper provides a proof-of-concept demonstration of the technique in a 3.4 m by 0.2 m channel, in which long finger flames were observed in ethylene-oxygen mixtures. The flame is visualized by high-speed direct luminosity over its entire travel, coupled with pressure measurements. A direct simulation of the flame growth served to supplement the experiments and evaluate the role of the induced flow by the flame growth, which gives rise to a non-uniform velocity distribution along the channel length. Detonation experiments were also performed at various layer heights in order to establish the details of the interaction. The structure was visualized using high speed Schlieren video. It was found that an inert shock always runs ahead of the detonation wave, which gives rise to a unique double shock reflection interaction.     

Propagation of shock and detonation waves in channels with U-shaped bends of limiting curvature

Systematic experimental and theoretical studies of the propagation of shock and detonation waves in cylindrical tubes and planar channels with two U-shaped bends of limiting curvature were performed. It was demonstrated that U-shaped bends substantially facilitate detonation initiation in gases. The minimum shock wave velocity required to initiate the detonation of a stoichiometric propane-air mixture under normal conditions in a near-critical diameter tube with two U-shaped bends of limiting curvature was found to be ～800 m/s.     

Generation of blast waves in a channel by nonideal detonation of aluminum-enriched high-density compositions

The results of experimental studies of the nonideal detonation of high-density, high-energy aluminum-ammonium perchlorate-organic fuel-HE compositions and of the blast waves it generates in a channel filled with air are presented. Aluminum-enriched compositions have high densities (up to 2 g/cm³) and high heats of explosion, nearly twice that for TNT. The studies were performed to work out scientific fundamentals of controlling nonideal detonation and to explore the possibility of creating new high-energy high-density formulations with an enhanced fugacity effect. The factors that enable controlling the nonideal detonation of such charges were determined. It was demonstrated that, at RDX contents above 15%, the detonation velocity increases linearly with the charge density while the critical detonation diameter decreases. Adjusting the density, HE content, ratio of the components makes it possible to vary the detonation velocity in high-density charges over a wide range, from 4 to 7 km/s. The experimental data were compared to the thermodynamically calculated velocity of ideal detonation. For the compositions under study, the pressure- time histories of the blast wave generated in a cylindrical tube by the expanding detonation products at different distances from the charge were measured. The results were compared to analogous data obtained under the same conditions for the detonation of the same mass of TNT (100 g). The parameters of blast waves generated by the test compositions are markedly superior to those characteristic of TNT: the pressure at the leading front of the wave and pressure impulse at a given distance from the charge were found to be 1.5–2.0 (or even more) times those observed for TNT. The TNT equivalency at pressures 30–60 atm has similar values. The TNT equivalencies in pressure and pressure impulse depend nonmonotonically on the distance from the charge, so far unclear why. It was established that the interaction between excess fuel and air oxygen during the expansion of detonation products contributes little to supporting the blast wave.     

Initiation of detonation by a high-voltage discharge in powdered explosives with nanosize inert admixtures

It is shown that admixtures of a copper nanopowder in a high-disperse low-sensitivity explosive of the FOX-7 type sharply increase the sensitivity of the mixture to the action of a high-voltage electric discharge and facilitate detonation. The percolation model of propagation of the electric breakdown over a powdered mixture with nanosize admixtures and the model of initiation of detonation by a high-voltage discharge in the mixture of a brisant explosive with an inert admixture are developed. These models are in qualitative and quantitative agreement with experimental data.     

固体炸药爆轰的一种考虑热学非平衡的反应流动模型

基于固体炸药爆轰过程中化学反应混合区内的固相反应物与气相生成物处于力学平衡状态及热学非平衡状态的事实,提出一种考虑热学非平衡效应的反应流动模型来描述固体炸药的爆轰流动现象.该爆轰流动模型的主要特点是,在反应混合物Euler方程和固相反应物质量守恒方程的基础上,通过附加一套关于固相反应物的组分物理量的流动控制方程来表达固相反应物与气相生成物之间的热学非平衡效应.根据反应混合区内固相反应物与气相生成物这两种化学组分保持各自内能守恒的混合规则,并借助它们具有压力相等的性质以及满足体积分数总和为1的条件,推导获得的附加方程有：固相反应物的内能演化方程、体积分数演化方程及反应混合物的压力演化方程.这样,建立的爆轰模型包括：反应混合物的质量守恒方程、动量守恒方程、总能量守恒方程、压力演化方程,以及固相反应物的质量守恒方程、内能演化方程、体积分数演化方程.对所获得的爆轰模型方程组采用一个时空二阶精度的有限体积法进行数值求解,典型爆轰问题算例结果表明本文提出的固体炸药爆轰模型是合理的.     

爆炸磁通量压缩发生器金属管爆炸试验研究

 描述了对爆炸磁通量压缩发生器（MFCG）的爆炸金属管进行的爆轰测试试验。利用电探针方法,测试得到了金属管中的粉状RDX炸药的爆轰速度。采用高速分幅相机测试技术,得到了金属管膨胀运动过程的分幅照片,掌握了金属管的膨胀及破裂情况,并由此测得了膨胀角。本试验结果为MFCG的设计和改进提供了依据。     

Detonation of explosives containing heavy inert particles

The physical and mathematical aspects of the theory of a detonation wave containing heavy inert particles are considered. The detonation wave intensity and structure are determined by the relaxation of velocities of both the reactive explosive and the inert admixture. The generalized Jouguet condition is formulated for the velocity of a self-sustained detonation wave. The results of analytical treatment and the model numerical solutions of the problem of the detonation wave velocity selection and the wave structure determination are presented as a function of the ratio of the characteristic times of the heat evolution and the two-component flow velocity relaxation. A limiting case of the fast particle drag is represented by the shock wave structure determined by relaxation of the two-component flow velocity.     

Propagation of gaseous detonation across inert layers

In rotating detonation engines and explosion accidents, detonation may propagate in an inhomogeneous mixture with inert layers. This study focuses on detonation propagation in a stoichiometric H₂/O₂/N₂ mixture with multiple inert layers normal to the detonation propagation direction. One- and two-dimensional simulations considering detailed chemistry are conducted. The emphasis is placed on assessing the effects of inert layer on detonation reinitiation/failure, detonation propagation speed, detonation cell structure and cell size. Specifically, the inert layer thickness and the spacing between two consecutive inert layers are varied. Either detonation reinitiation or failure across the inert layers is observed. It is found that successful detonation reinitiation occurs only at relatively small values of the inert layer thickness and spacing. For each given value of the inert layer spacing, there is a critical inert layer thickness above which detonation fails after crossing the inert layers. This critical inert layer thickness is found to decrease as the inert layer spacing increases. The detailed process of detonation reinitiation across the inert layers is analyzed. The interaction between the transverse shock waves is shown to induce local autoignition/explosion and eventually over-driven detonation development in the reactive layer. The averaged detonation propagation speed in the inhomogeneous mixture is compared to the CJ speed and very good agreement is achieved. This indicates that the inert layer does not affect the detonation propagation speed once successful detonation reinitiation happens. Unlike the detonation speed, the detonation cell structure and cell size are greatly affected by the inert layer results. For the first time, large cellular structure with size linearly proportional to the inert layer spacing is observed for detonation propagation across inert layers. Besides, a double cellular structure is observed for relatively large spacing between inert layers. The formation of double cellular structure is interpreted.     

Calculation of the equilibrium and transport characteristics of gaseous and liquid mixtures of noble gases in complex narrow-pore systems

The molecular-kinetic theory of transfer of the components of the gaseous and liquid mixtures of inert gases is generalized to the case of narrow pores of complex structure. The theory is based on the latticegas model, which provides a self-consistent method for calculating the equilibrium and transport characteristics of noble gases and liquids. This model is used to describe the supramolecular structure of finely dispersed bodies and to calculate the distributions of the mixture components within the pore space. The supramolecular structure is composed of slitlike, cylindrical, spherical, and globular model elements and their joints. An analysis of the effect of the molecular properties of the mixture components, physicochemical properties of the pore walls and the width of the cylindrical and complex sections of variable diameter of spherocylindrical pores on the concentration dependences of the local label transfer coefficients and viscosity coefficients for mixtures of spherical molecules at supercritical temperatures range is performed. Correlations between the partial degrees of filling of pores with mixture components and the local dynamic characteristics of the mixture in the spherocylindrical systems are considered. It is shown that an increase in the binding energy increases the local flow viscosity and reduces the diffusion coefficients of the labeled mixture components.     

Blast waves in a cylindrical channel generated by the nonideal detonation of aluminum-Teflon-RDX high-density formulations

The pressure at the front and the pressure impulse of blast waves generated in a cylindrical tube by the expanding products of the nonideal detonation of low-porosity charges prepared by pressing of fine-grained powders of aluminum, Teflon, and RDX were measured. The measured parameters are compared to the same parameters of blast waves produced by the detonation of TNT charges of identical mass. The relative quantities were used to evaluate the effectiveness of blast waves with respect to those generated by TNT. Mixed compositions differing in the shape (brand) of the aluminum powder particles and the ratio between the components at 30% RDX are studied. It is shown that, for the investigated compositions, the pressure at the leading front of the wave exceeds the pressure achieved during TNT explosion on average by 10–30%, almost independently of the distance traveled along the tube in the range from 0.8 to 3.8 m. The dependence of the wave amplitude on the particle shape and aluminum content was weak. In the same range of distances, the relative pulse pressure increases strongly, from 0.5 to 2.1 and higher, mainly due to an increase in the width of the wave. This result is of interest from the point of view of achieving a high pressure impulse of the blast wave in an area remote from the charge. The obtained data suggest that RDX mainly reacts in the detonation wave, with the chemical transformation of Teflon and aluminum in the detonation wave and near-to-charge zone occurring, if at all, to a small extent. On the contrary, as the blast wave front moves through the channel, the burning of aluminum in the fluoride formed during the decomposition of Teflon provides an appreciable support to the blast wave, causing a significant increase in the pressure impulse.