Propellant performance of organic explosives and their energy output and detonation velocity limits

Methods for determining the propellant performance of high explosives (HEs) are considered. The common and distinguishing features of the techniques of end acceleration of plates and shell expansion are shown. Experimental data on the propellant performance of individual explosives are given. The influence of metal additives on the brisance (propellant performance) and blast effect of explosive compositions is considered. A theoretical method for estimating the propellant performance is proposed, and the propellant performance of hydrogen-free HEs is calculated using experimental data on the enthalpies of formation and densities of single crystals. The energy output and detonation velocity limits of organic HEs are considered and estimated. Promising directions in the investigation of the properties of HEs are considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 99–111, January–February, 2007.     

Continuous spin detonation of fuel-air mixtures

Results of an experimental study of controlled continuous spin detonation of acetylene-air and hydrogen-air mixtures, as well as propane-air-oxygen and kerosene-air-oxygen mixtures in a flow-type cylindrical combustor 30.6 cm in diameter are described. The flow structure and the conditions, properties, and areas of existence of continuous detonation are considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 107–115, July–August, 2006.     

Bubble detonation conditions

Initiation of bubble detonation in the system “inert liquid-explosive gas bubbles” by a detonation wave in a gas was studied experimentally. Compression-wave pressure profiles were determined as functions of the length of the initiation section and the initial pressure of the explosive gas mixture in it. It was shown that because of the effect of the explosive-gas volume between the diaphragm and the upper boundary of the bubble medium, the pressure in front of the initiating wave increased much more slowly than the initial pressure. The optimal length of the initiation section was found, and the critical (minimum) initiation pressure in it and at the shock-wave front were determined. It was found that for a fixed gas volume concentration in the bubble medium, the pressure in the initiation section increased insignificantly as the length of the section decreased. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 84–90, March–April, 2007.     

Density dependence of detonation velocity for some explosives

The nonmonotonic dependence of the detonation velocity of a cylindrical charge on density for explosives of the 2nd type is due to the effect of the finite charge diameter and is related to an increase in the width of the reaction zone with a reduction in the porosity of the explosive. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 116–124, July–August, 2006.     

Dependence of the Time‐Space Structure of the Chemical‐Reaction Zone on the Initial Density of the Explosive

The results of a study of the chemicalreaction zone structure for a number of high explosives (HEs) are discussed. It is found that an increase in the initial density of the HEs leads to a structural change in the chemicalreaction zone involving elimination of the Von Neumann spike at the critical density point. Conversely, as the initial density of the explosive decreases, the ratios of the gasdynamic parameters (in particular, mass velocities) at the Von Neumann point to the same parameters at the Jouguet point increase. It is shown that to explain the indicated regularities, one does not need to invoke the assumption of an increasing contribution of the exothermic decomposition of the HE the shock. The results can be explained within the framework of classical Zeldovich–Von Neumann–Döring theory with an ordinary shock at the detonationwave front and, hence, with a nearly zero contribution to the total energy release in the chemical reaction zone.     

Theory of solid-state detonation

The Jouguet theory allows one to estimate the detonation velocity from the known shock adiabat of the product of a solid-state chemical reaction initiated by a shock wave. Using manganese and zinc chalcogenides as an example, it is shown that such estimates are close to experimental detonation velocities in these systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 108–110, March–April, 2007.     

Some numerical issues on simulation of detonation cell structures

The present study examines several numerical issues on simulation of detonation cell structures. Various stability regimes ranging from weakly to highly unstable detonations are considered. The analysis treats two-dimensional inviscid fluid-dynamics equations and a one-step reaction model. A series of investigations is carried out to identify numerical requirements for high-fidelity simulations of detonation cell structures. Emphasis is placed on the wave-front dynamics and evolution of cellular patterns. The effects of the preexponential factor, grid size, time step, domain length, and exit boundary condition on the cellular structure and cell size are examined systematically. The required numerical grid size is determined and compared with various length scales associated with a steady Zel’dovich-von Neumann-Döring detonation wave. A general rule for the grid-resolution requirement is proposed for the first time: a minimum of 5 grid points should be included in the heat-release zone of the corresponding steady Zel’dovich-von Neumann-Döring detonation wave, in order to achieve an accurate simulation of detonation cell structures.     

Conditions of detonation initiation by focusing shock waves in a combustible gas mixture

Based on experiments on focusing shock waves in hydrogen-air mixtures and available publications, the critical shock-wave Mach number at which detonation is initiated near the apex of a concave reflector is analyzed as a function of the reflector size and reactivity of the mixture. The effect of the reflector shape and size on the value of this Mach number is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 84–89, November–December, 2007.     

Influence of the initial gas pressure on the detonation limits and parameters of low-density secondary explosives in an inert porous medium

This paper reports the results of an experimental study of the detonation of low-density (3–40 mg/cm³) secondary high explosives (HEs) in evacuated and gas-filled inert porous media. A convective-jet mechanism of detonation propagation was found to occur under all conditions studied. The effects of the type of HE and initial gas pressure on the critical density of the HE and detonation parameters were elucidated. It is shown that, in the presence of air, detonation can occur at a lower volume-averaged density of the HE than in the case of the evacuated media and there are two limits (minimal and maximal) for the initial gas pressure. As the volume-averaged density HE decreases, the limits approach each other and, for a certain critical density of the HE, detonation exists only at one value of the initial pressure. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 106–117, May–June, 2009.     

Mathematical model of continuous detonation in an annular combustor with a supersonic flow velocity

A two-dimensional unsteady mathematical model of a continuous spinning detonation wave in a supersonic incoming flow in an annular combustor is formulated. The wave dynamics in a combustor filled by a gaseous hydrogen-oxygen mixture is studied. The possibility of continuous spin detonation with a supersonic flow velocity at the diffuser entrance is demonstrated numerically for the first time; the structure of transverse detonation waves and the range of their existence depending on the Mach number are studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 83–91, November–December, 2008.     

Experimental investigation of gasless detonation in metal-sulfur compositions

Samples of zinc-sulfur and manganese-sulfur mixtures are shocked using an explosive pentolite charge to investigate if a shock-initiated reaction is able to support continued shock wave propagation. Samples of two different nominal densities (62 and 86% of theoretical maximum density) are prepared as weakly confined cylinders 50 mm in diameter and are instrumented along their length (⩽280 mm) with sensitive piezoelectric pins. Experimental results showed that the shock wave transmitted into the sample by the explosive rapidly decays to an acoustic wave in all four sample types. Furthermore, in denser samples, the part of the sample farthest from the explosive is recovered intact and unreacted, which clearly indicates that the wave is unable to trigger reactions after 100 mm of travel along the sample. Thus, it is concluded that insufficient reaction energy is transmitted forward to the shock wave to prevent its decay as it travels along the sample. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 116–123, March–April, 2009.     

Heat fluxes to combustor walls during continuous spin detonation of fuel-air mixtures

Pioneering measurements of heat fluxes to the walls of flow-type combustors of different geometries were performed in regimes of continuous spin detonation of fuel-air mixtures under unsteady heating. These heat fluxes are compared with those observed in the regime of conventional turbulent combustion in the same combustor. Air is used as an oxidizer, and acetylene or hydrogen is used as a fuel. For identical flow rates of the fuel, the heat fluxes to the combustor walls in regimes of continuous spin detonation and conventional combustion are close to each other; their mean steady values are ≈1 MW/m² (≈0.5% of the enthalpy flux of the products over the channel cross section). In both detonation and combustion regimes, the maximum heat fluxes penetrate into the walls in the mixing region (where the heat release occurs). In the case of detonation, regenerative cooling of the combustor walls by the flow of the fresh mixture occurs in the heat-release region (region of propagation of the detonation-wave front). The regeneration becomes less effective in the downstream direction because of the shorter time of contact between the walls and the cold mixture and a longer time of contact between the walls and the hot products. More intense heating persists downstream of the front, where the regeneration ceases, but the temperature of the products is high. The character of heating of the wall in the region of rotation of the front of spin detonation waves depends on the number of these waves: the zone of the maximum heat release becomes narrower with increasing number of waves. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 80–88, January–February, 2009.     

Gas detonation in a channel with transverse ribs

Results of experiments on detonation propagation in a rectangular horizontal channel with high ribs on the lower wall are presented. The experiments were performed with acetylene-oxygen mixtures. An interval of initial pressures is found, in which low-velocity detonation with a steady velocity of 0.38–0.55 of the Chapman-Jouguet velocity without losses exists. This detonation wave is a system consisting of a shock wave and a flame. Owing to gas outflow to the layer occupied by the ribs, the flame is maintained at a constant distance from the shock wave, which is approximately equal to the free transverse size of the channel. This distance weakly decreases with increasing initial pressure and is almost independent of the burning rate of the gas at standard temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 82–86, September–October, 2007.     

Studies in comparative detonation sensitivities

Detonation testing has been conducted by the National Fertilizer Development Center of the Tennessee Valley Authority to determine the relative detonation sensitivity for solid fertilizer materials which contain ammonium nitrate. Selected data are given that describe the application of the procedure to various types of mixtures. The test sample is placed in a cardboard cylinder with a kraft paper bottom. These containers vary in diameter from 3-3/8 to 6 inches; the smaller diameter containers are used for relatively sensitive materials and the larger diameter containers are used for less sensitive items. To provide a quantitative measure of the relative sensitivity to detonation, an index of sensitivity (I_s) is given, defined as 100/mean weight of booster in grams. The mean weight is that at which one-half of the tests would be expected to detonate. The booster used was pentaerythritol tetranitrate (PETN).A test procedure is described for predicting the behavior of fertilizer materials containing ammonium nitrate when exposed to flame or heat. Illustrative data from such testing of materials, both with and without potassium chloride, are given.It is recommended that additives be used to reduce detonation sensitivities.     

Radiographic study of interaction of shock and detonation waves in a high explosive

Collisions of shock and detonation waves in an HMX-based high explosive are experimentally studied with the use of flash radiography. Based on X-ray patterns, specific features of the wave-interaction process are identified, and qualitative differences are found in detonation formation and evolution in an explosive precompressed by a weak shock wave and in an undisturbed explosive. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 132–138, May–June, 2007.     

Effect of chemically active additives on the detonation wave velocity and the detonation limits in lean mixtures

On the basis of the formalism of the one-dimensional theory of detonation with heat losses and the theory of branched-chain processes by the example of the oxidation of hydrogen-air mixtures in the presence of a hydrocarbon additive, it is shown that taking into account the reactions of termination of reaction chains on molecules of the additive, trimolecular termination, and also chain oxidation of the hydrocarbon additive allows one to qualitatively describe both the passage of the detonation velocity through a maximum with an increase in the additive content of a lean mixture and the existence of two concentration limits of detonation.     

Limits of gaseous detonation spraying

The maximum possible values of adhesion and cohesion are calculated for a number of powder materials, substrate materials, sizes of installation barrels, and compositions of explosive gas mixtures. These data give a clear idea about the areas of applicability of gaseous detonation spraying. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 113–116, September–October, 2006.     

正交法分析PBX浇注炸药爆速的影响因素

研究以奥克托今(HMX)为主体、与其他各组分混合而成的PBX炸药。通过改变炸药中主炸药与其他成分的配比、粒度和抽真空时间3个影响爆速的因素,采用3因素3水平的正交实验分析各个因素的最佳水平。结果表明,粒度对爆速的影响是最主要的;其次是配比;最后是抽真空时间。得到最佳爆速的工艺条件为:HMX质量分数90%,粗细比2∶1,抽真空时间10 min。     

Calculation of detonation gas spraying

A model of processes in the barrel of a detonation facility for application of powder coatings, which takes into account the variable composition of the working gases in the barrel, is presented. It is demonstrated that varying the volume of the gas mixer is an effective tool for stabilizing particle parameters and coating properties if powders with wide fractions are used. The code proposed is a convenient instrument for predicting coating properties. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 112–120, November–December, 2007.     

Reliability of kinetic data used for estimating multifront detonation parameters

A faster increase in the cell size and other important parameters of multifront detonation than that predicted by kinetic calculations is obtained for fuel-oxygen mixtures of hydrogen and typical hydrocarbons diluted by nitrogen. In a stoichiometric hydrogen-oxygen mixture diluted by an additional amount of oxygen or hydrogen, experimental and calculated data are also found to diverge with increasing concentration of the added species. This effect, however, is not observed if these mixtures are diluted by helium or argon. An assumption about the reason for this difference in data is put forward. A conclusion is made that kinetic data should be corrected as applied to detonation conditions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 89–94, May–June, 2009.