Steady-state Detonation Research Articles

Shock Initiation and Propagation of Detonation in ANFO

The ammonium nitrate (AN) and fuel oil (FO) mixture known as ANFO is a typical representative of non-ideal explosives. In contrast to ideal explosives, the detonation behavior of ANFO exhibits a strong dependence on charge diameter, existence, and properties of confinement, with a large failure diameter and long distance required to establish steady-state detonation. In this study shock initiation and propagation of detonation in ANFO were studied experimentally by determining the detonation velocity at different distances from the initiation point, as well as by numerical modeling using AUTODYN hydrodynamics code and a Wood–Kirkwood detonation model incorporated into EXPLO5 thermochemical code. The run-to-steady-state detonation velocity distance was determined as a function of charge diameter, booster charge mass, and confinement. It was demonstrated that a Lee–Tarver ignition and growth reactive flow model with properly calibrated rate constants was capable of correctly ascertaining experimentally observed shock initiation behavior and propagation of detonation in ANFO, as well as the effects of charge diameter, booster mass, and confinement.

Numerical modeling of charge diameter effect on detonation properties of emulsion explosives using Wood-Kirkwood detonation model

ABSTRACT Emulsion explosives exhibit strong nonideal detonation behavior, which provides a challenge for accurate numerical modeling. We present a nonideal detonation model based on the Wood–Kirkwood detonation theory and EXPLO5, capable of modeling the effect of the charge diameter on steady-state detonation velocity. The elements of the model are calibrated based on experimental data for four different emulsion explosives. It was demonstrated that both simple pressure-dependent and Kirby and Chan’s two-step reaction rate models can satisfactorily reproduce the detonation velocity–charge diameter data of unconfined charges. In addition, the reaction rate parameters are found to be a function of the density of explosives.

Numerička analiza inicijacije glavnog eksplozivnog punjenja artiljerijskog projektila

The importance of investigation of main explosive charge initiation using booster charge stems directly from the objective to optimize the mass of booster charge needed to ensure steady state detonation of main explosive charge in order to achieve maximum projectile efficiency. Considered configuration consists of two explosives and three metal parts which represent elements of fuze and projectile. The main objective of this paper is to develop a numerical model of initiation of main explosive charge of an insensitive artillery ammunition. Through this research two variants of detonation point location were analyzed, ideal and stochastic one. The effects of the detonation transfer are analyzed using the Jones-Wilkins-Lee and Ignition and Growth equation of state models for explosives, applying the Coupled Eulerian-Lagrangian approach in the Abaqus/Explicit software. Analytical computation is introduced in this paper with a purpose to present P-u interaction between configuration elements and for comparison with results obtained by numerical method. The results of analytical and numerical approach are presented and discussed in detail. It is shown that suggested numerical model enables simulation and optimization of explosive train in fuzes of HE projectiles.

Preliminary experimental study on the mechanisms of explosion-electric coupling

Electric energy is one of the most widely used forms of energy. It is valuable to couple electric energy with an explosion to boost detonation performance. The phenomenon of electric energy enhancing an explosion is referred to herein as explosion-electric coupling (EEC) by the author. An experimental device was designed to explore this phenomenon, and the device was equipped with measuring devices to collect data related to the electric and detonation characteristics of explosives. Trinitrotoluene and aluminized explosives were selected as test explosives and pressed into flat and cylindrical charges. Thus, different kinds of explosives with different shapes were able to be studied. The change of the current-voltage curve of the EEC was analyzed, and the process of the EEC was divided into three stages: explosion initiation, detonation growth, and steady-state detonation propagation. The results showed that the enhanced pressure of the von Neumann spike varied with the explosive type, the same as for the increase of the detonation velocity. However, the increased pressure of the Chapman-Jouguet point mattered for the shape of the explosive charges. According to the features of the electrical characteristics and the increases of the detonation properties, a hypothesis was proposed to explain how the electric energy affected the explosion. The external electric field and the large pulse current were two forms of electric energy that influenced the explosion, and these forms of electric energy had different effects on different detonation properties.

Energy efficiency of detonation combustion in supersonic ramjet engines

The energy efficiency of a supersonic ramjet engine with detonation combustion of a hydrogen-air mixture in an axisymmetric Laval nozzle is considered. First of all, within the framework of the one-dimensional (1D) theory, it is shown that extreme combustion corresponding to the Chapman-Jouguet (C.-J.) deflagration, like constant pressure combustion, surpasses detonation in energy efficiency. However, this advantage becomes insignificant with an increasing the free-flow Mach number. Based on the results of the 1D theory, an axisymmetric Laval nozzle is constructed, which provides steady-state detonation combustion of a stoichiometric hydrogen-air mixture at an altitude of about 40 km and with freestream Mach numbers 9 and 12. The efficiency of detonation combustion in this case is about 35% instead of the maximum 65% according to the 1D theory.

Transients following the loss of detonation confinement

We present a theory for the evolution of a one-dimensional, steady-state detonation reaction zone to a two-dimensional reaction zone, when the explosive experiences a sudden loss of side-on confinement as a boundary of the explosive is impulsively withdrawn. Our focus is on condensed-phase explosives, which we describe as having a constant adiabatic gamma equation of state and an irreversible, state-independent reaction rate. We consider two detonation models: (i) the instantaneous reaction heat release Chapman–Jouguet (CJ)-limit and (ii) the spatially resolved reaction heat-release Zel’dovich–von Neumann–Doring (ZND) model, in the limit where only a small fraction of the energy release is resolved (the SRHR-limit). Two competing rarefaction waves are generated by this loss of confinement: (i) a smooth wave coming off the full length of the withdrawn boundary and (ii) a singular fan spreading out from the point where the detonation shock and the withdrawn boundary meet. For the CJ-limit, in all cases the singular rarefaction fan eventually dominates the competition to control the steady-state behaviour. For the SRHR-limit, the spatially resolved heat release moderates this competition. When the withdrawal speed is fast, the rarefaction fan dominates; when the withdrawal speed is slower, the smooth rarefaction eventually dominates, although the flow features a fan at early times. By examining the mathematical properties of the steady two-dimensional fan-based solution, we set down a mechanism for this transition in behaviours.

Multiplicity of detonation regimes in systems with a multi-peaked thermicity

The study investigates detonations with multiple quasi-steady velocities that have been observed in the past in systems with multi-peaked thermicity, using Fickett's detonation analogue. A steady-state analysis of the travelling wave predicts multiple states, however, all but the one with the highest velocity develop a singularity after the sonic point. Simulations show singularities are associated with a shock wave which overtakes all sonic points, establishing a detonation travelling at the highest of the predicted velocities. Under a certain parameter range, the steady-state detonation can have multiple sonic points and solutions. Embedded shocks can exist behind sonic points, where they link the weak and strong solutions. Sonic points whose characteristics do not diverge are found to be unstable, and to be the source of the embedded shocks. Numerical simulations show that these shocks are only quasi-stable. This is believed to be due in part to a feature of the model which permits shocks anywhere behind a sonic point.

A novel method for prediction of the critical diameter of solid pure and composite high explosives to assess their explosion safety in an industrial setting

ABSTRACTFor the explosion safety assessment in an industrial setting, the knowledge of critical diameter of high explosives provides important information on the sensitivity and conditions whereby detonations are likely to occur. The critical diameter or failure diameter is the minimum diameter of a cylindrical charge of high explosive which sustains a high order steady-state detonation. Available predictive methods require complex models, which are based on complicated variables such as the shock adiabat, and the generalized kinetic characteristic of decomposition of a high-explosive charge under shock-wave compression. For the first time, this paper describes a novel simple method for assessment of the critical diameter of pure and composite CHNO high explosives. The new model is based on the contribution of the number of nitrogen and oxygen atoms as well as some conditions, which are based on shock sensitivity, impact sensitivity and the negative values for core critical diameter of the desired explosives under certain situations. Experimental data of 42 high explosives have been used to derive and test the new model. The predicted critical diameters for building the model (29 explosives) and the test set (13 explosives), under the unconfined condition of these explosives, have the values of root-mean-square deviation (RMSD) of 5.14 and 3.96 mm, respectively.

Quantifying How Density Gradients and Front Curvature Affect Carbon Detonation Strength during SNe Ia

Abstract Accurately reproducing the physics behind the detonations of SNe Ia and the resultant nucleosynthetic yields is important for interpreting observations of spectra and remnants. The scales of the processes involved span orders of magnitudes, making the problem computationally impossible to ever fully resolve in full-star simulations in the present and near future. In the lower density regions of the star, the curvature of the detonation front will slow the detonation, affecting the production of intermediate mass elements. We find that shock strengthening due to the density gradient present in the outer layers of the progenitor is essential for understanding the nucleosynthesis there, with burning extending well below the density at which a steady-state detonation is extinct. We show that a complete reaction network is not sufficient to obtain physical detonations at high densities and modest resolution due to numerical mixing at the unresolved reaction front. At low densities, below 6 × 105 g cm−3, it is possible to achieve high enough resolution to separate the shock and the reaction region, and the abundance structure predicted by fully resolved quasi-steady-state calculations is obtained. For our best current benchmark yields, we utilize a method in which the unresolved portion of Lagrangian histories are reconstructed based on fully resolved quasi-steady-state detonation calculations. These computations demonstrate that under-resolved simulations agree approximately, ∼10% in post-shock values of temperature, pressure, density, and abundances, with expected detonation structures sufficiently far from the under-resolved region, but that there is still room for some improvement in the treatment of subgrid reactions in the hydrodynamics to before better than 1% can be achieved at all densities.

Estimating Chemical Conversion Rates for Composite Explosives on the Basis of Experimental Data on Pseudo-Ideal Detonation

The conditions for the appearance of a plateau-like region called pseudo-ideal detonation in the dependence of the velocity of detonation (VOD) of composite explosives on the diameter of a charge were considered. A theoretical model of steady-state non-ideal detonation with a slightly curved front and a two-stage mechanism of chemical reaction was used for analysis. The calculations were performed for a trinitrotoluene-50% ammonium nitrate mixture and a mechanically activated ammonium perchlorate-20% aluminum mixture. The coefficients of the equations describing the global chemical conversion rates of components were fitted in the calculations. In both cases, the dependence of the VOD on the diameter of the reciprocal charge with a plateau-like region was obtained for an increasing conversion rate of the major explosive (trinitrotoluene and ammonium perchlorate, respectively).

МОДЕЛИРОВАНИЕ УПРУГОПЛАСТИЧЕСКОГО ДЕФОРМИРОВАНИЯ ЭЛЕМЕНТОВ ПРОСТРАНСТВЕННЫХ КОНСТРУКЦИЙ ПРИ ИМПУЛЬСНОМ ВЗАИМОДЕЙСТВИИ С ЖИДКОСТЬЮ НА ОСНОВЕ МЕТОДА ГОДУНОВА ПОВЫШЕННОЙ ТОЧНОСТИ

The spatial problem of internal explosive loading of an elastoplastic cylindrical container filled with water in Eulerian - Lagrangian variables using multigrid algorithms is considered. A defining system of three-dimensional equations of the dynamics of gas, fluid, and elastoplastic medium is presented. For numerical modeling, a modification of S.K. Godunov scheme of the increased accuracy for both detonation products and liquids, and elastoplastic container is used. At the moving contact boundaries “detonation products - liquid”, “liquid - deformable body”, the exact solution of the Riemann's problem is used. A time dependent model is used to describe the propagation of steady-state detonation wave through an explosive from an initiation region. In both cases, the initiation of detonation occurs at the center of the charge. Two problems have been solved: the first task for the aisymmetric position of the charge, the second for the charge shifted relative to the axis of symmetry. In the first task, the processes are two-dimensional axisymmetric in nature, in the second task, the processes are essentially three-dimensional. A comparison is made of the results of calculations of the first problem using a three-dimensional method with a solution using a previously developed two-dimensional axisymmetric method and experimental data. Good agreement is observed between the numerical results for the maximum velocities and circumferential strains obtained by various methods and experimental data. There is good agreement between the numerical results obtained by various methods and the known experimental data. Comparison of the results of solving the first and second problems shows a significant effect of the position of the charge on the wave processes in the liquid, the processes of loading the container and its elastoplastic deformation. The dynamic behavior of a gas bubble with detonation products is analyzed. A significant deviation of the bubble shape from the spherical one, caused by the action of shock waves reflected from the structure, is shown. Comparison of the results of solving the first and second problems showed a significant effect of the charge position on wave processes in a liquid, the processes of loading a container and its elastoplastic deformation. In particular, in the second problem, shock waves of higher amplitude are observed in the liquid when reflected from the walls of the container.

МОДЕЛИРОВАНИЕ УПРУГОПЛАСТИЧЕСКОГО ДЕФОРМИРОВАНИЯ ЭЛЕМЕНТОВ ПРОСТРАНСТВЕННЫХ КОНСТРУКЦИЙ ПРИ ИМПУЛЬСНОМ ВЗАИМОДЕЙСТВИИ С ЖИДКОСТЬЮ НА ОСНОВЕ МЕТОДА ГОДУНОВА ПОВЫШЕННОЙ ТОЧНОСТИ

The spatial problem of internal explosive loading of an elastoplastic cylindrical container filled with water in Eulerian - Lagrangian variables using multigrid algorithms is considered. A defining system of three-dimensional equations of the dynamics of gas, fluid, and elastoplastic medium is presented. For numerical modeling, a modification of S.K. Godunov scheme of the increased accuracy for both detonation products and liquids, and elastoplastic container is used. At the moving contact boundaries “detonation products - liquid”, “liquid - deformable body”, the exact solution of the Riemann's problem is used. A time dependent model is used to describe the propagation of steady-state detonation wave through an explosive from an initiation region. In both cases, the initiation of detonation occurs at the center of the charge. Two problems have been solved: the first task for the aisymmetric position of the charge, the second for the charge shifted relative to the axis of symmetry. In the first task, the processes are two-dimensional axisymmetric in nature, in the second task, the processes are essentially three-dimensional. A comparison is made of the results of calculations of the first problem using a three-dimensional method with a solution using a previously developed two-dimensional axisymmetric method and experimental data. Good agreement is observed between the numerical results for the maximum velocities and circumferential strains obtained by various methods and experimental data. There is good agreement between the numerical results obtained by various methods and the known experimental data. Comparison of the results of solving the first and second problems shows a significant effect of the position of the charge on the wave processes in the liquid, the processes of loading the container and its elastoplastic deformation. The dynamic behavior of a gas bubble with detonation products is analyzed. A significant deviation of the bubble shape from the spherical one, caused by the action of shock waves reflected from the structure, is shown. Comparison of the results of solving the first and second problems showed a significant effect of the charge position on wave processes in a liquid, the processes of loading a container and its elastoplastic deformation. In particular, in the second problem, shock waves of higher amplitude are observed in the liquid when reflected from the walls of the container.

Detonation properties of hydrazine nitrate

The results of investigation of the detonation waves structure, the critical diameter, detonation parameters and the dependence of detonation velocity on the charge diameter for pressed hydrazine nitrate (HN) charges in the density range of 1.40–1.68 g/cm3 are presented. It was found that the critical diameter drops with the initial density decrease. Under steady-state detonation conditions at an initial density of 1.68 g/cm3, a high detonation velocity of 8.92 km/s is observed in HN charges. The change of the detonation velocity with variation of the initial density is not monotonous, but has a characteristic s-shape.

Non-classical detonation regimes of liquid high explosives

This paper presents experimental data of studies of the liquid explosives characteristics, in the reaction zone of which the distribution of parameters does not correspond to the classical detonation theory. An increase of the pressure and particle velocity behind a shock jump in liquid explosives and the possibility of the existence of a steady-state detonation wave without a von Neumann spike are interpreted within the framework of models that take into account the possibility of chemical reactions directly in the shock wave front.

Simulating the blast wave from detonation of a charge using a balloon of compressed air

This paper investigates a simple numerical method, based on the release of a pressurized spherical air volume, to predict or reproduce the main characteristics of the blast environment from the detonation of solid or gaseous charges. This approach aims to give an alternative to the use of a steady-state detonation model and a Jones–Wilkins–Lee equation of state to describe the expansion of the detonation products, especially when the explosive parameters are unknown and a TNT equivalent is used. The validity of the proposed approach is assessed through the comparison of predicted overpressure and impulse at different distances from the explosion with that of TNT and stoichiometric propane–oxygen explosions. It is also shown that, for gaseous detonations, a better agreement is obtained with the rationally optimized compressed balloon than with the use of a Jones–Wilkins–Lee model and a TNT equivalent mass.

Deflagration to detonation transition in mechanoactivated mixtures of ammonium perchlorate with aluminum

Deflagration-to-detonation transition (DDT) in aluminum-ammonium perchlorate (Al/AP) loose-packed charges (80% porosity) has been studied. The charges were manufactured from preliminary mechanoactivated mixtures. The mixtures placed in steel tubes 10 mm in diameter were ignited by Nichrome wire. It was found that it is possible to distinguish three parts corresponding to different stages of DDT process development. Steady-state detonation velocity reached the level of 2500 m/s at the distance of 90 mm from the ignition point.

Detonation of a gas fuel based on methyl acetylene and allene

A special facility for investigating gaseous detonation was designed using a CCDS2000 computerized detonation-spraying complex to implement flow-through supply of the components of an explosive mixture and activation of deflagration-to-detonation transition in a long cylindrical channel. The detonation velocity and the cell size of the detonation front in mixtures of a composite fuel based on methyl acetylene and allene with oxygen were experimentally determined, and the concentration limits of steady-state detonation in a tube of 26 mm diameter were obtained. Detonation parameters were calculated and compared with experimental values. For comparison, the detonation of mixtures of acetylene and propane-butane with oxygen under similar conditions was studied.

Application of heterodyne velocimetry and pyrometry as diagnostics for explosive characterisation

The results of four cylinder tests performed on two batches of the HMX based explosive EDC37 using a new suite of diagnostics are described. Heterodyne laser velocimetry (het-v) and pyrometry were fielded for the first time on cylinder tests within AWE. Pyrometry gave a measurement of the temperature of the detonating HE of 2600-3485 K. Sixteen channels of het-v were fielded and provided high fidelity expansion data at distances of up to 30 mm. High speed framing camera images were obtained and show no signs of cylinder break up or spallation until distances greater then 35 mm. The het-v expansion data made it possible to resolve up to 8 shock reverberations in the wall as it expands. The expansion of the cylinder wall was recorded both before and after steady state detonation was reached and the results compared. Het-v probes were fielded at different angles to the expanding cylinder wall allowing both the vertical and horizontal expansion velocity to be determined. The extra information that these cylinder tests yielded will allow for more accurate code validation and determination of the equation of state of the explosive products.

Feasibility analysis of SPH method in the simulation of condensed explosives detonation with ignition and growth model

The smoothed particle hydrodynamics (SPH) method has the advantage in modeling detonation process. But in most previous applications of SPH method in the simulation of explosives, the detonation process of explosives is usually regarded as steady-state detonation in which the reaction rate of explosive is ignored and propagation of detonation wave is at the Chapman–Jouguet (C–J) state. The simulation of steady-state detonation process cannot predict the von Neumann spike state of explosives which is another important feature in studying condensed explosives. The simulation of condensed explosives response under impact load also cannot base on the steady-state detonation assumption. In this paper, the SPH method is applied to simulate the detonation process of condensed explosives with reaction rate. The ignition and growth model is incorporated into the SPH method to represent the reaction model of condensed explosives. One-dimension detonation process of condensed explosives PBX-9404 and TATB are taken as numerical examples to analyze the feasibility of SPH method in the simulation of detonation with ignition and growth model. Numerical results show that the SPH method combined with ignition and growth model can give good prediction for the von Neumann spike state of detonation in condensed explosives. Propagation and interaction of cylindrically divergent detonation wave in PBX-9404 have also been successfully simulated by SPH method combined with ignition and growth model.

Breakup of steady-state detonation in hydrogen-air mixtures under the action of propane admixtures

Minor amounts of propane effectively inhibit the detonation of hydrogen-air mixtures at atmospheric pressure. Controlled variation of the amount of the admixture provides means to break up the steady-state detonation wave at a preset distance from the place of its origination and to regulate its velocity in a certain range. This is possible due to the branched chain character of the combustion reaction in the detonation mode. Propane is not inferior to propylene in the effectiveness of action on detonation and, owing to its low cost and higher availability, is preferable as a means of preventing the explosion and detonation of hydrogen-air mixtures.