Modeling the shock initiation of detonation of heterogeneous explosives

Conclusions The present review shows that accurate experiments on determining the evolution of predetonation-wave parameters and the high time resolution achieved in recording the interaction of steady DW with barriers form the basis of modern numerical modeling. The Zel'dovich-Neumann-Dering physical model used in most calculations has received sufficient experimental confirmation in modern investigations. One basic reason for the formation of hot spots as centers of chemical reaction is heating of the material as a result of SW interaction with the pores.The review has illustrated the diversity of existing approaches to modeling and forms of macrokinetic equations obtained and shown that they now allow the initiation to be described in a one-dimensional formulation and, in a number of cases, in two-dimensional geometry, including the action of rarefaction waves, as well as permitting the estimation of critical conditions of excitation and propagation of detonation. The use of numerical models offers the possibility of obtaining new qualitative information on the processes accompanying the initiation of detonation and correctly interpreting the experimental results.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 23, No. 5, pp. 132–147, September–October, 1987.     

Structure of detonation waves in nitromethane and a nitromethane/methanol mixture

The results of experimental studies of the structure of the reaction zone for steady-state detonation of nitromethane and its mixtures with methanol. For pure nitromethane, the characteristic reaction time and detonation parameters were determined. For a nitromethane/methanol mixture, a dependence of the detonation parameters of the mixtures on methanol concentration is presented. It is shown that in pure nitromethane and with small additions of methanol, the detonation front is stable, or the size of the inhomogeneities of the front is less than 1 m. At a methanol concentration of 10% or higher, instability of the front is observed.     

Sensitivity of nitromethane for low velocity detonation

Recently the occurrence of a low velocity detonation (LVD) in nitromethane has been demonstrated. In the present study this phenomenon has been further investigated by mapping the shock loading regime in which a stable LVD can develop. A confinement geometry has been chosen that earlier appeared to be able to sustain the LVD. A calibrated shock donor system has been used, so that loading shock strengths were known. The critical shock strengths for the occurrence of both high and low velocity detonation could thus be determined. Including LVDs, nitromethane appears to have a sensitivity comparable to that of relatively sensitive high explosives. The results also indicate that the geometries of some standard shock sensitivity tests are not fully adequate to detect an LVD in nitromethane.     

Investigation of shock detonation of TATB using proton radiography

The initiation of detonation of plasticized TATB by shock loading using an initiator pressure charge of an HMX based explosive was studied by radiography. In the experiments, the size of the initiator and the initial density of the TATB charge were varied. During initiation of TATB detonation, part of the material did not react, forming so-called dark zones. As the process goes on, the detonation wave bends around the dark zones, without initiating the material within them. The evolution of the area of dark zones was compared for samples of different initial density and initiators of different sizes. The characteristic boundaries and X−t diagrams of detonation front propagation under different loading conditions were constructed from images of the explosive process. Density distributions behind a divergent detonation wave front at different times were obtained and analyzed.     

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.     

Investigation of shock initiation of desensitized RDX

The process of initiation of detonation of pressed desensitized RDX is considered. Pressure profiles were recorded by manganin gauges in different cross sections of a charge and processed by the Lagrange analysis for a reacting flow. The analysis has shown that the decomposition rate immediately behind the initiating wave front is low and increases with increase of pressure in it. A maximum in the dependence of the decomposition rate on the reaction coordinate can be observed when the values of the reaction coordinate are 0.4–0.6.Institute of Hydrodynamics, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 3, pp. 110–117, May–June, 1995.     

Numerical study of shock initiation threshold of detonation burning in a monofuel gas suspension

Some results of numerical simulation of shock initiation of plane heterogeneous detonation waves in homogeneous monodisperse gas suspensions of a monofuel are reported. The influence of the initial size of monofuel particles on the critical (minimum) Mach number of the initiating shock wave is studied. The dependence of the critical (maximum) size of fuel particles on the initial relative mass content of the reacting dispersed phase is analyzed.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 4, pp. 110–112, July–August, 1996.     

Effect of diethylenetriamine on the structure of detonation waves in nitromethane

This paper presents the results of experimental studies of the reaction zone structure in steady-state detonation of nitromethane sensitized by diethylenetriamine (DETA). The concentration of DETA was varied within 0.0125–15%. It is shown that small additions of DETA lead to a qualitative change in the flow pattern in the reaction zone. After the shock, the mass flow rate continues to increase for about 10 ns, reaches a maximum, and only then decreases. The amplitude of the chemical spike decreases by an order of magnitude. These features are explained by the decomposition of nitromethane sensitized by DETA in front of the shock wave, which is due to a sharp increase in the initial reaction rate.     

Plane initiation of a detonation

The conditions for exciting a plane detonation wave were experimentally observed to be independent of the initial [gas] pressure. The explanation is based on the concept that impacts of transverse waves play a leading role in initiating and propagating the detonation. The dimension of the effective zone which is responsible for initiating the detonation is close to the dimension of the chemical [energy] peak. Formulas are presented for estimating the energy equivalent of the initiator, based on the concept of transforming the plane detonation wave into a spherical, cylindrical, or plane detonation by diffracting the initial wave by convex angle. The basic analytical conclusions of the concept are confirmed by experiment.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 164–170, May–June, 1993.     

Stabilization of unstable detonation waves in mixtures of nitromethane with inert diluents

Mass velocity profiles of detonation waves in mixtures of nitromethane with acetone and methanol with added diethylenetriamine sensitizer were measured using a VISAR laser interferometer. It was found that even small, about 1%, concentrations of acetone and methanol, inert diluents, led to instability of the one-dimensional detonation front in nitromethane. The results of the experiment show that the use of the sensitizer is an effective method of flow stabilization and if the concentration of the inert diluent does not exceed 10%, the detonation front becomes stable with the addition of 1% diethylenetriamine. At a higher diluent concentration, the sensitizer does not suppress the instability but decreases the oscillation amplitude by several times. The addition of diethylenetriamine to the mixture has been found to increase the detonation velocity.