Expansion Of Detonation Products Research Articles

DETERMINATION OF DETONATION FRONT CURVATURE RADIUS OF ANFO EXPLOSIVES AND ITS IMPORTANCE IN NUMERICAL MODELLING OF DETONATION WITH THE WOOD-KIRKWOOD MODEL

Nitratebased commercial explosives, such as ANFO (ammonium nitrate/fuel oil mixture) and emulsion explosives, are characterized by a curved detonation front. The curvature is directly related to the rate of radial expansion of detonation products in the detonation driving zone and the rate of chemical reactions, and it is one of the characteristics of nonideal explosives. The detonation theories used to model the nonideal behaviour of explosives require both reaction rate and rate of radial expansion to be known/specified as input data. Unfortunately, neither can be measured and what is mostly used is a link between these rates and parameters which can be more easily measured. In this paper, the Wood-Kirkwood approach of determination of radial expansion through the radius of detonation front curvature and the electro-optical technique for experimental determination of detonation front curvature of ANFO explosives is applied. It was shown that an experimentally determined radius of detonation front curvature vs charge diameter, incorporated in the Wood-Kirkwood detonation theory, can satisfactorily reproduce experimental detonation velocity-charge diameter data for ANFO explosives, especially when the pressure-based reaction rate law is also calibrated (D=1.3 and k=0.06 1/(μs/GPaD)).

A nonlinear characteristic line model of the detonation process of aluminized explosives

Aiming at the non-ideal properties of aluminized explosive, a local isentropic hypothesis of the expansion of aluminized explosive detonation product was proposed, and a nonlinear characteristic line model for aluminized explosive detonation was established, which provides a new theoretical analysis method for studying the non-isentropic flow and the expansion of detonation products. A lot of studies have shown that for micron aluminum powder, the reaction mainly occurs in the expansion zone of detonation products. The aluminum powder was treated as inert in the detonation reaction zone in the model. Considering the reaction rate of the aluminum powder is relatively slow, the expansion process of the detonation products of aluminized explosive was divided into finite time regions. The energy released from the reaction of aluminum powder has a relaxation effect on the state of the products. Based on the relaxation effect, it was assumed that the detonation products flow was approximately isentropic in each time region. Due to the reaction of aluminum powder, the entropy in each time region was different. Based on the theory of isentropic flow of ideal explosive and local isentropic hypothesis, the non-isentropic expansion process of the detonation products of aluminized explosives can be analyzed theoretically. To verify the correctness of the model, metal plate experiments were conducted. Experiments on aluminized explosives and LiF explosives with a particle diameter of 5μm and 50μm to drive 0.5 mm and 1 mm metal plates were designed. The velocity history of the metal plate was measured by a laser displacement interferometer, and then the reaction degree of aluminum powder in the detonation products was calculated from the experimental results. Combined with the nonlinear characteristic line model of the detonation products of aluminized explosives, the velocity of the metal plate driven by aluminized explosives was calculated theoretically. Compared with the experimental results, the non-isentropic model can well describe the contribution of the secondary reaction of aluminum powder to the work ability of explosives, which verifies the correctness of the model for aluminized explosives (micron aluminum powder).

Definition of scaled distance of close-in explosion and blast load calculation model

How to accurately define “close-in explosion” has always been a hotspot in the field of protection engineering research. In this paper, based on the fully validated 2D axisymmetric fine finite element model, the characteristics and laws of the propagation of air shock waves and high-speed expansion of detonation products generated by TNT spherical charge were studied. It is found that there is a significant influence of the detonation products on the blast load on rigid wall when the range of the scaled distance less than 0.8 m/kg1/3. It is recommended to use the scaled distance range from 0.30 m/kg1/3 to 0.80 m/kg1/3 as the definition criterion of close-in explosion for spherical TNT charge explosion. It was found that: due to the inhomogeneity and randomness of the detonation product rapid expansion, the peak value of the rigid-wall reflected overpressure experienced a sharp drop within a range of incident angle of 0°～5° in the case of close-in explosion defined in the paper. In addition, there were two peaks on the reflected overpressure curve in close-in explosion cases, and the first peak overpressure was caused by the interaction between the shock wave and rigid wall while the second peak overpressure was generated by the interaction between the detonation products and rigid wall. Based on curve fitting, the formulas for calculating the two peak values were proposed, respectively, and a simplified load model suitable for calculation of engineering structure response was put forward; The distribution law of the reflected overpressure on the rigid wall under close-in explosion was revealed.

The growth of agglomerates in the conditions of detonation synthesis of diamond

The conditions of detonation synthesis of nanodiamonds do not affect the size of diamond microcrystallites too much, as was shown in numerous experimental studies. This is because microcrystallites are formed almost instantly at the moment of explosive detonation, when conditions are created for crystallization of the diamond carbon phase. Further expansion of detonation products only leads to the creation and enlargement of particle agglomerates. The product of detonation synthesis is always a powder consisting of agglomerates of carbon particles of diamond and non-diamond phases with impurities. The size, density and specific surface area of the agglomerates can be different depending on the synthesis conditions. These product characteristics are of great importance for further technological applications. Meanwhile, the processes of agglomerate formation under conditions of expansion of detonation products have not yet been considered. In this paper, we theoretically consider this process. The dependences of the size and specific surface of carbon agglomerates on the conditions of detonation synthesis were obtained, and comparison with experimental data was made.

A non-isentropic model of aluminized explosives involved with the reaction degree of aluminum powder for post-detonation burning behavior

The post-detonation burning effect of aluminum (Al) powder plays an important role during the expansion of detonation products (DPs) of aluminized explosives (AEs). Lithium fluoride (LiF) is an inert substitute for Al, and hence, a comparison of the performance of composite explosives based on cyclotrimethylenetrinitramine (RDX), such as RDX/Al and RDX/LiF, clearly illustrates its contribution to accelerating ability due to Al oxidation. A series of metal plate tests is conducted to measure the velocity history of a metal plate driven by RDX/Al and RDX/LiF through a photonic Doppler velocimetry system with 5%, 15%, and 25% Al or LiF contents. The detonation and expansion process of the AEs is generally divided into two stages: the detonation zone (DZ) and the post-detonation zone (PDZ). In the DZ, the Al powder remains inert, while it absorbs the detonation energy from pure explosives. Therefore, the equivalent inert dilution model is established and the equivalent inert dilution coefficient of the Al powder is introduced. In the PDZ, the Al powder reacts with DPs, and the Al oxidation reaction results with a change in entropy related to the reaction degree of the Al powder. Based on the local isentropic assumption, as well as the function of the reaction degree of the Al powder, a non-isentropic model is established. The method of the non-linear characteristic line is applied to theoretically calculate the metal plate velocity based on the non-isentropic model. In addition, the theoretical results show good agreement with the metal plate test results with an acceptable error (less than 10%), indicating that the non-isentropic model can be effectively applied to analyze the accelerating ability of the AEs.

Estimation of Jones-Wilkins-Lee parameters of emulsion explosives using cylinder tests and their numerical validation

A microspheres-sensitized emulsion explosive, to be used in rock blasting tests, is characterized by means of the cylinder test. This test measures the expansion of a copper tube upon detonation of an explosive charge inside. Eight cylinder tests have been made with two different diameters (50 mm and 100 mm) and two different densities (1180 kg/m3 and 1030 kg/m3) in a 2 × 2 × 2 test matrix. The expansion energy is affected by the density but not by the test diameter, which suggests that this explosive, at the densities studied, behaves close to ideal already at 50 mm. The explosive velocity of detonation had been also measured within the trials. In addition, velocities of detonation were measured in six production blasts and reported here. The Jones–Wilkins–Lee (JWL) equation of state parameters have been obtained for this emulsion at the densities and diameters tested. The calculation method includes a radial expansion function, with a non-zero initial velocity at the onset of the expansion. The equations reflecting the CJ state conditions and the measured expansion energy were solved for the JWL parameters by a non-linear least squares scheme. These parameters have been validated with three different LS-DYNA models (Lagrangian-Lagrangian, Smooth Particle Hydrodynamic-Lagrangian, Arbitrary Lagrangian Eulerian-Lagrangian). All models show a good correlation with the test results when comparing them against the detonation pressure, the cylinder wall expansion, the Gurney limit velocities and the radial wall velocities. The Smooth Particle Hydrodynamic is the best numerical model for replicating the detonation pressure, the Lagrangian for the cylinder wall expansion radius and velocity history, and Arbitrary Lagrangian Eulerian on the overall performance. Arbitrary Lagrangian Eulerian and Smooth Particle Hydrodynamic techniques are widely used to describe the materials subjected to large deformations, such as explosives, on full-scale simulations for civil and mining applications. The good agreement between numerical and experimental results justifies the use of these methods to model the expansion of detonation products.

Multi-stage nozzle-shape optimization for pulsed hydrogen–air detonation combustor

Thermal engines based on pressure gain combustion offer new opportunities to generate thrust with enhanced efficiency and relatively simple machinery. The sudden expansion of detonation products from a single-opening tube yields thrust, although this is suboptimal. In this article, we present the complete design optimization strategy for nozzles exposed to detonation pulses, combining unsteady Reynolds-averaged Navier–Stokes solvers with the accurate modeling of the combustion process. The parameterized shape of the nozzle is optimized using a differential evolution algorithm to maximize the force at the nozzle exhaust. The design of experiments begins with a first optimization considering steady-flow conditions, subsequently followed by a refined optimization for transient supersonic flow pulse. Finally, the optimized nozzle performance is assessed in three dimensions with unsteady Reynolds-averaged Navier–Stokes capturing the deflagration-to-detonation transition of a stoichiometric, premixed hydrogen–air mixture. The optimized nozzle can deliver 80% more thrust than a standard detonation tube and about 2% more than the optimized results assuming steady-flow operation. This study proposes a new multi-fidelity approach to optimize the design of nozzles exposed to transient operation, instead of the traditional methods proposed for steady-flow operation.

The Effect of Nano-Aluminumpowder on the Characteristic of RDX based Aluminized Explosives Underwater Close-Filed Explosion

In order to investigate the effect of nano-aluminum powder on the characteristic of RDX based aluminized explosives underwater closed-filed explosions, the scanning photographs along the radial of the charges were gained by a high speed scanning camera. The photographs of two different aluminized explosives underwater explosion have been analyzed, the shock wave curves and expand curves of detonation products were obtained, furthermore the change rules of shock waves propagation velocity, shock front pressure and expansion of detonation products of two aluminized explosives were investigated, and also the parameters of two aluminized explosives were contrasted. The results show that the aluminized explosive which with nano-aluminum whose initial shock waves pressure propagation velocity, shock front pressure are smaller than the aluminized explosive without nano-aluminum and has lower decrease rate attenuation of energy.

Numerical Investigation on Detonation Control Using a Pulse Hot Jet in Supersonic Combustible Mixture

ABSTRACTTo investigate the mechanism of detonation control using a pulse hot jet in the supersonic hydrogen-oxygen mixture, high-resolution simulations with a detailed reaction model were conducted using an adaptive mesh refinement method. After the successful detonation initiation, a contractive passway is generated between the hot jet and the main flow field behind the detonation front. Due to the contractive passway, the expansion of detonation products is prevented, hence, resulting in overdriven detonation. By setting up various contractive passways through adjusting the width of the hot jet, the overdrive degree of overdriven detonation also changes. It is suggested that the width of the hot jet has an approximately linear relation with the relative and absolute propagation velocities. When the contractive passway gradually disappears after the shutdown of the hot jet, overdriven detonation attenuates to the dynamically stable Chapman–Jouguet (CJ) detonation. When the contractive passway is re-established once again after the reinjection of the hot jet, the CJ detonation develops to the same overdriven detonation, indicating that the contractive passway controlled by the pulse hot jet can indeed control detonation propagation in the supersonic combustible mixture to some extent.

Effects of Initial Perturbations in the Early Moments of an Explosive Dispersal of Particles

Recent experiments have shown that when a dense layer of solid particles surrounding a high-energy reactive material is explosively dispersed, the particles cluster locally leading to jetlike patterns. The formation of these coherent structures has yet to be fully understood and is believed to have its origin in the early moments of the explosive dispersal. This paper focuses on the early moments of an explosive dispersal of particles. In particular, the effect of initial perturbations on both the gas and particulate phase is investigated, considering heavy particles with a low initial particle volume fraction. Two-dimensional simulations are carried out, and results suggest that a distinctive heterogeneity in the form of a single wavelength perturbation in the rapidly expanding detonation products does not have a significant impact on the early evolution of neither the gas phase nor the cloud of particles. In contrast, the equivalent distinctive heterogeneity in the initial particle volume fraction distribution lingers for the duration of our simulations. Developing instabilities in the gas phase and at the inner- and outer-most front of the particle bed display a dominant wavelength equal to the wavelength of the initial perturbation in the particle volume fraction.

On the reaction of detonation products of condensed explosives with the ambient air

The propellant performance and the velocity of expansion of detonation products of explosives based on RDX and HMX and their mixtures with particulate Al were investigated. Measurements were performed in air at atmospheric pressure and in rarefied air. Comparison of the results shows that the detonation products of explosives, including those containing no Al additives, react with the surrounding air. The completeness of the reaction increases with increasing velocity of detonation products in air.

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.

Expansion of detonation products of phlegmatized RDX and its mixtures with dispersed aluminum

Videorecording was used to measure the velocities of expansion of detonation products (DPs) in the axial and radial directions during the detonation of phlegmatized RDX (PRDX) and its mixtures with ASD-4 aluminum powder (PRDXA). It was demonstrated that the initial particle velocities of the DPs in the axial and radial direction for PRDXA are 1–2 km/s higher than those for PRDX for expansion into an atmospheric-pressure air medium and 0.5–2.0 km/s lower for expansion into a low-pressure (10 kPa) air medium. The result of this can be explained by the rapid reaction of aluminum particles during the turbulent mixing of DPs with air due to the formation of cumulative microjets at the surface of the charge.

Kinetics and Mechanism of Explosive Decomposition of Heavy Metal Azides

The explosive decomposition of heavy metal azides initiated by a laser pulse was studied experimentally over a broad range of action levels (from the threshold values to those exceeding the threshold ignition energy by a factor of 100) and in the time interval including the induction period, and rapid explosive decomposition, and the expansion of detonation products. The explosive glow and expansion dynamics of the decomposition products in air and vacuum were investigated, and the velocities of the explosive decomposition front, the compression pulse, and the expansion of the explosion products were measured. Based on the results obtained, the possibility of the occurrence of preexplosion phenomena is discussed and the mechanism of laser initiation of heavy metal azides is analyzed.

Specific Features of Synthesis of Detonation Nanodiamonds

It is demonstrated that the Chapman-Jouguet parameters for high explosives used in nanodiamond synthesis are located in the region of liquid nanocarbon; therefore, the chemical reaction zone of the detonation wave involves formation of carbon nanodroplets, which are later crystallized into nanodiamonds on the segment of the isentrope of expansion of detonation products, passing through the region of stability of nanodiamonds in the pressure range of 16.5–10 GPa and the temperature range of 3400–2900 K. Soot in the resultant mixture is the product of amorphization of nanodroplets rather than graphitization of ultrafine diamonds. The influence of detonation conditions of high-explosive charges in an explosive chamber on nanodiamond synthesis is analyzed.

A Further Study on the Mechanism of Airdecking

Airdecking is used in mining for two quite different applications. One is to enhance the fragmentation by amplifying the induced fracturing and the second is for pre-split blasting in which the borehole fracturing is reduced. This paper deals with the first of these effects. A forth coming paper will describe pre-splitting by airdecking. The use of air decks to enhance rock fragmentation and so to reduce explosive costs has been the practice for quite long time. Although a number of studies has been conducted to verify the advantages of blasting with air decks and to investigate the mechanisms involved, the proposed mechanisms still cannot explain clearly the phenomena observed in practice and the design approach adopted for this kind of blasting is still primary based on rules-of-thumb. In this paper, the theory of shock tubes is adopted to (a) investigate the processes of the expanding detonation products, (b) study the interactions between the explosion products and the stemming or bottom of blasthole, and (c) to decide the distribution of the changing pressure of explosion products along blasthole. Numerical simulation and theoretical analyses are then performed to study the physical process of blasting with air decks. Finally, a reasonable value for the airdecking ratio is decided theoretically. It is shown that the pressure-unloading process caused by the propagation of the rarefaction wave and the reflected rarefaction waves in the detonation products plays an important role in the enhanced fragmentation of rock when blasting with air decks. The unloading process can induce tensile stresses of rather high magnitude in the rock mass surrounding blasthole. This favors fracturing of the rock. The reflected shock wave with a magnitude of gas pressure higher than that of the average detonation pressure in a fully charged blasthole acts as the main energy source to break the rock in the air deck and stemming portions. The second and succeeding strain waves induced by the unloading or reloading of the pressurewithin the blasthole also contribute to form the initial fracture network in the rock around the blasthole. It is also revealed that there exists a reasonable range of values for the airdecking ratio. For ANFO, this value varies from 0.13-0.40.

Detonation Properties and Electrical Conductivity of Explosive–Metal Additive Mixtures

Detonation properties of mixtures of condensed high explosives with metal additives are studied. A scheme of measurement of high electrical conductivity of detonation products (σ > 10 Ω−1 · cm−1) with a time resolution of ∼ 10 nsec is developed. It is shown that the properties of detonation products depend significantly on the content of the additive in the HE and on dispersion and density of the mixture. The electrical conductivity of detonation products of the compositions examined reaches ∼ 5 · 103 Ω−1 · cm−1, which is more than three orders higher than the electrical conductivity of the HE without the additive. Significant variation of electrical conductivity of detonation products over the conducting region thickness has been found. The main conductivity corresponds to a sector ∼ 1 mm long near the detonation front. The overdriven state of the detonation wave has a strong effect on electrical conductivity and conducting region thickness. It is assumed that the behavior of electrical conductivity with time is caused by successive processes of shock compression of the HE, excitation of the chemical reaction (including the reaction of the additive with detonation products), and expansion of detonation products. The measurement technique used is highly informative due to the possibility of studying detonation in various regimes.

Diffraction estimate of the critical energy for initiation of gaseous detonation

A criterion for the excitation of detonation is proposed: the critical initiation energy equals the work performed by the expanding detonation products along a path length equal to the longitudinal dimension of a cell. The initial radius of the layer is chosen to be equal to the radius of the detonation wave diffracted at 90° edge at the time the axial rarefaction wave converges on the axis of the gaseous charge. Formulas are obtained for estimating the critical energy for initiation of plane, cylindrical, and spherical detonation waves. The calculated values are in good agreement with experiment.

Real-time measurement and control of particle-number density and size of the detonation products of lead azide

Time-resolved measurement and modeling of the number density and size of lead particles produced following the detonation of Lead Azide (LA) are presented. Particles expanding freely into vacuum through a supersonic nozzle or interacting with a barrier placed above the LA sample are monitored via attenuation of laser beams at 0.67, 1.3 and 10.6 µm. The attenuation depends on the conditions of expansion, but is always much more pronounced at 0.67 µm and 1.3 µm. From the ratio between the attenuations at 0.67 µm and 10.6 µm, the radius and number density of the particles are calculated applying Beer's law and Mie's theory. It is found that 20–90 µs following the detonation the attenuation at 32–36 mm above the LA sample is due to particles with radii of ≈0.9, ≈0.7 and ≈0.1 µm for free expansion into vacuum through the nozzle or near the barrier, respectively. Also, the expansion through the nozzle results in a transparent medium above the nozzle exit for the first few µs following the detonation. The effect of the nozzle is attributed to the fact that the velocity of the expanding detonation products is supersonic, which leads to compression and heating in the throat region, in contrast to the more familiar phenomenon of cooling at subsonic velocities. The dynamics of particles expanding under the different conditions and the mechanism of size reduction and elimination of particles is discussed.

Universal thermodynamic criterion for the effectiveness of an explosive

A criterion is presented for the effectiveness of an explosive, based upon a thermodynamic model of the work done by the expanding detonation products. The criterion enables evaluation of the explosive effectiveness at various stages of expansion of the explosion products or conversion of the energy output from the products into mechanical work at various times during their expansion.