Detonation Conditions Research Articles

Effect of charge structure on the stability of charge penetration

Abstract When the penetrating warhead penetrates the target, the internal charge is subjected to extremely high overload and impact loads. If the load intensity and duration meet the detonation conditions, the warhead may experience early detonation, compromising both the penetration effect and safety. To study the influence of charge structure on penetration stability, a specific warhead was used as a model reference, and finite element simulation software was employed to numerically simulate the penetration of concrete targets by the warhead. The results showed that stress concentration occurred at the warhead head during the penetration process, with the maximum stress exceeding the critical detonation stress of the charge, indicating a possibility of early detonation. To improve penetration stability while maintaining the original damage performance, different models of penetration warheads with various charge structures were constructed to analyze the influence of baffle position and number on charge stress. The results show that the loading structure with added partitions can effectively reduce the stress on the charge during penetration. The optimal effect is achieved when the partition is located at 1/2 of the interior of the projectile, with a maximum pressure of 3.75 GPa, which is 44.36% lower than that of the structure without partitions, thereby improving the penetration stability of the projectile.

Analytical study of rotating detonation and engine operating conditions

In this paper, the mechanism of rotating detonation is analytically discussed using a two-dimensional sheet model. Two ratios are employed in this discussion: the ratio of the sonic point width to the detonation front width, and the ratio of the effective mixture injection area to the injection area. In the rotating detonation, the unconfined boundary can increase the width at the sonic point and decrease the detonation wave speed. Although the high detonation pressure hinders mixture injection, effectively preventing some injectors from functioning, the high pressure acting on the injection end wall produces thrust. Mass, momentum, energy, and angular momentum conservations are used to determine these ratios. The calculated results are in reasonable agreement with past experimental and numerical findings. The present model succeeds to clarify the features, parameter relationships, and overall mechanism of the rotating detonation analytically and to specify flow field of the rotating detonation under given boundary conditions, e.g., the velocity deficit and the effective injection area ratio. The specific impulse of a rotating detonation engine was lower than that of an ordinary rocket engine due to the lower combustion gas pressure when the combustion gas expanded to 1 atm. The thrust coefficient and the specific impulse of an air-breathing rotating detonation engine were shown to be lower than those of a ramjet engine, respectively, primarily because of the smaller airflow rate into the engine.

On the interaction between a detonation wave and an inert gas plug: A numerical investigation

Employing inert gases to attenuate and obstruct the propagation of detonation waves has proven to be an effective strategy for mitigating potential damage in the realm of industrial safety, which involves complex physical and chemical mechanisms. This study utilizes an in-house solver built on the OpenFOAM platform to examine the interaction between a detonation wave and an inert gas plug of various lengths. The results reveal that as the length of the inert gas plug increases, various detonation states emerge downstream of the gas plug, and an exponential relationship is observed between the detonation re-initiation distance and the gas plug's length. In the process of detonation re-initiation, the non-isentropic process within the viscous boundary layer plays a crucial role in initiating the flames at the upper and lower channel walls. Later, the collision between flames initiates the detonation wave. Additionally, a localized detonation can also be triggered through the interaction between the compression wave and the wall. Notably, the impingements of the detonation wave and the transmitted shock wave induce the mixing and downstream motion of the gas plug. In the presence of the detonation re-initiation, the motion patterns of the left and right interfaces of the gas plug can be categorized into two distinct stages, which are mainly because of the impingement of backpropagation expansion waves and the hindrance of the high pressure generated by the detonation re-initiation, respectively. Also, as the length of the inert gas plug increases, the velocity difference between the two stages gradually decreases.

Effect of oxygen rich environment on detonation characteristics of pulse detonation engine

The detonation tests of propane/air pulse detonation engine at normal temperature were carried out in this paper. The effects of chemical ratios on the detonation performance of propane/air pulse detonation engine in oxygen-rich environment were studied. The propagation modes and characteristics of detonation waves and the detonation characteristics of the engine under different conditions were analyzed. Detonation tests were conducted on propane/air mixtures with oxygen mass fraction of 20%, 25%, 30% and 35% respectively. The results showed that: In the detonation experiment of the propane/air mixture with oxygen content of 20%, 25% and 30%, the flame wave propagation velocity in the detonation tube is low, which fails to form a stable detonation wave. The detonation effect of the fuel mixture with oxygen content of 20% is the worst, and the propagation velocity of flame wave is 384.00 m/s. In the experiment of propane/air mixture with oxygen content of 35%, the detonation velocity and pressure obtained by pressure signal analysis are both greater than the theoretical CJ detonation velocity, and the detonation state is successfully reached.

Influence of overdriven detonation on the energy release of aluminized explosives in underwater explosion

An underwater explosion experiment was designed for the cyclotrimethylenetrinitramine-based aluminized explosives to study the influence of detonation conditions on the explosion performance and the afterburn reaction of aluminum (Al) particles. The research results showed that the performance of shock wave and bubble pulsation grew stronger under the influence of overdriven detonation (ODD), and the contribution of ODD to the bubble energy was associated with the proportion of the inner core and the outer coat. Considering the propagation characteristics of the detonation wave in the ordinary charge and the inner/outer charge, the attenuation of ODD and its role in the initial pressure of the bubble were investigated, and this relationship was used to establish a numerical model for the bubble dynamic behaviors of aluminized explosives. According to the experimental results, the correctness of the established model for the bubble dynamics under ODD was verified, and the variation laws of the afterburn reaction during the bubble pulsation were investigated. It was found that the initial pressure of the bubble under ODD was higher than that under steady detonation. The improvement on the initial pressure promoted the afterburn reaction during the accelerating expansion and enhanced the bubble expansion capacity to support the formation and propagation of shock waves. In the subsequent bubble pulsation, the duration of the decelerating expansion was significantly longer than that of the accelerating expansion, and the ODD had little effect on the afterburn reaction in this stage.

Entropy and nitrogen oxides production in steady detonation wave propagating in hydrogen-air mixtures

Detonation engine, relying on the Fickett-Jacob cycle, may offer higher thermodynamic efficiency than engine relying on the Brayton (constant pressure) or Humphrey (constant volume) cycles. The present work quantitatively investigates the entropy production in steady detonation wave propagating in hydrogen-air mixtures. In particular, the contribution of each elementary chemical reaction to the total entropy production was investigated. The change of entropy during chemical processes was divided into the sensible and the reaction contributions. The study of the influence of several parameters including equivalence ratio, reactor model, initial pressure and temperature was embedded in a parametric study. It is shown that detonation conditions favor higher entropy production than constant volume and pressure combustion processes when considering the von Neumann state as the reference thermodynamic state. In general, the largest modifications in the entropy production pathways are induced by a change of equivalence ratio. In most cases, the largest contributions to total entropy production comes from the reactions H2 + OHH2O + H and H + OH + M = H2O + M, which are also the largest contributors to the energy release. The contributions of the sensible and reaction parts to the total entropy production demonstrate complex variations whose details depend on which specific reaction is considered. Besides, we studied the evolution of the main radicals and nitrogen oxides within the Taylor-Zeldovich expansion wave which brings the flow to rest. Significant change of the nitrogen oxides mole fraction occurs in this region, which indicates that this process should be accounted for when estimating pollutant formation in detonation.

Multi-peak phenomenon of large-scale hull structural damage under near-field underwater explosion

The underwater explosion (UNDEX) may cause more serious damage to the hull structure under certain detonation conditions. In this study, through a near-filed UNDEX test with a full-scale barge in a natural environment, a detailed simulation of the entire UNDEX process applying the S-ALE method is conducted and validated. Several near-field UNDEX simulations of the barge with different detonation distances are then conducted to study the response characteristics and damage results. The double-peak phenomenon of ship bottom deformation and the single-peak phenomenon of residual strength under different detonation distances, which is referred to as the multi-peak phenomenon, are identified based on the results of local deformation and residual strength, and their mechanisms are further analyzed and clarified.

Rotating detonation combustion of liquid kerosene under near-ramjet limit conditions

The feasibility of using preheated kerosene and pre-evaporation to assist in liquid kerosene detonation ignition and self-sustaining combustion under near-ramjet limit conditions was investigated. Additionally, the detonation decoupling and self-sustaining mechanisms were analyzed in depth. Owing to the forced heat transfer effect of supersonic flow on kerosene droplets, self-sustaining detonation combustion could not be achieved using preheated kerosene alone. The detonation wave was still decoupled due to the forced heat exchange effect of the cold kerosene droplets on the detonation wave, even if the distribution of C12H23 reached the detonation conditions through the pre-evaporation of fuel.

Detonation Wave Propagation of Double-Layer Shaped Charge and Its Driving Characteristics to the Liner

The double-layer charge can effectively improve the axial driving ability of explosives, which shows a considerable engineering application prospect in highly efficient damage warheads. Due to the complex wave structure produced by the overpressure detonation of a double-layer charge, a series of dynamic behaviors inside the shaped charge liner will be affected. By comparing the detonation wave shapes of single-layer charge and double-layer shaped charge structure and the jet shaping parameters of a double-layer shaped charge with different structural parameters, the evolution of detonation wave and the state parameters in the wave system are analyzed in this research. The research found that the double-layer charge with high detonation velocity in the outer layer and low detonation velocity in the inner layer can produce continuous overpressure detonation, which makes the overpressure detonation state be applied efficiently. Meanwhile, this study found that the overpressure detonation field formed by the double-layer charge changes the action law of the traditional single charge on the shaped charge liner. The detonation waveform of the entire charge is controlled by different detonation velocities and detonation energies, and a detonation waveform that matched well with the shaped charge liner is obtained. This study solves the matching relationship between the structure of the overpressure detonation wave system and the properties of a double-layer charge, which is of great value for improving the detonation-driving effect of condensed explosives on surrounding media. The double-layer charge can effectively enhance the potential of explosive charge. It is not only widely used in military fields such as improving the armor-breaking power of shaped charge penetrators and improving the muzzle velocity and concentration of fragments of directional warheads, but also can promote the development of industrial fields such as explosive processing.

Detonation simulations in supersonic flow under circumstances of injection and mixing

The unsteady, reactive Navier-Stokes equations with a detailed chemical mechanism of 11 species and 27 steps were employed to simulate the mixing, flame acceleration and deflagration-to-detonation transition (DDT) triggered by transverse jet obstacles. Results show that multiple transverse jet obstacles ejecting into the chamber can be used to activate DDT. But the occurrence of DDT is tremendously difficult in a non-uniform supersonic mixture so that it required several groups of transverse jets with increasing stagnation pressure. The jets introduce flow turbulence and produce oblique and bow shock waves even in an inhomogeneous supersonic mixture. The DDT is enhanced by multiple explosion points that are generated by the intense shock wave focusing of the leading flame front. It is found that the partial detonation front decouples into shock and flame, which is mainly caused by the fuel deficiency, nevertheless the decoupled shock wave is strong enough to reignite the mixture to detonation conditions. The resulting transverse wave leads to further mixing and burning of the downstream non-equilibrium chemical reaction, resulting in a high combustion temperature and intense flow instabilities. Additionally, the longitudinal and transverse gradients of the non-uniform supersonic mixture induce highly dynamic behaviors with sudden propagation speed increase and detonation front instabilities.

Investigating the electronic structure of high explosives with X-ray Raman spectroscopy

We investigate the sensitivity and potential of a synergistic experiment-theory X-ray Raman spectroscopy (XRS) methodology on revealing and following the static and dynamic electronic structure of high explosive molecular materials. We show that advanced ab-initio theoretical calculations accounting for the core-hole effect based on the Bethe-Salpeter Equation (BSE) approximation are critical for accurately predicting the shape and the energy position of the spectral features of C and N core-level spectra. Moreover, the incident X-ray dose typical XRS experiments require can induce, in certain unstable structures, a prominent radiation damage at room temperature. Upon developing a compatible cryostat module for enabling cryogenic temperatures (approx 10 K) we suppress the radiation damage and enable the acquisition of reliable experimental spectra in excellent agreement with the theory. Overall, we demonstrate the high sensitivity of the recently available state-of-the-art X-ray Raman spectroscopy capabilities in characterizing the electronic structure of high explosives. At the same time, the high accuracy of the theoretical approach may enable reliable identification of intermediate structures upon rapid chemical decomposition during detonation. Considering the increasing availability of X-ray free-electron lasers, such a combined experiment-theory approach paves the way for time-resolved dynamic studies of high explosives under detonation conditions.

Insight on the growth mechanism of TiO2 nanoparticles via gaseous detonation intercepting collection

In a closed tube, TiO2 nanoparticles can be prepared by hydrolyzing TiCl4 under extreme conditions of hydrogen-oxygen explosion. In this process, the chemical reaction is complex and violent, and TiO2 nanoparticles can achieve particle growth and phase transition in a very short time. The photocatalytic activity of TiO2 is closely related to its particle size and phase composition, however, it is difficult to observe the growth process of TiO2 in the explosion process. An intercepting collection scheme was proposed to explore the growth mechanism of TiO2 nanoparticles during gaseous detonation. The characterization results illustrated that the TiO2 nanoparticles were successfully collected by the intercepting device. The particle size of intercepted powders is smaller than that of the powders precipitated on the tube wall, and as the distance between the intercept position and the initiation point increases, the particle size decreases. The growth of TiO2 nanoparticles closely depends on the propagation and attenuation of detonation wave. After detonation nucleation and combustion sintering, TiO2 nanoparticles with anatase phase and rutile phase are fabricated. The proposed intercepting collection method is helpful to reveal the dynamic growth mechanism of nanomaterials under the extreme conditions of gaseous detonation.

Experimental study on the explosion characteristics of methane-air mixtures initiated by RDX in a rectangular venting chamber

Methane-air mixtures initiated by Hexogen (RDX) were experimentally investigated in a custom-designed rectangular venting device. By changing the methane concentration, the overpressure characteristics and flame propagation were studied under the conditions of RDX detonation and electric spark ignition, respectively. The results indicate that, compared with spark ignition, the RDX explosion shock wave leads to the structural vibration and interacts with the flame, shortening the methane reaction time and substantially increasing the explosion overpressure. When the methane concentration is close to the equivalence ratio of unity, only one pressure peak occurs after the vent plate opening. The pressure peak caused by the interaction between acoustic waves and flames, P3, appears only at methane concentrations of 8 vol% and 13 vol% under RDX detonation. The acoustic vibration of the structure induced by different masses of RDX has a nonlinear impact on the increase of P3. The long reaction duration and the weakening of the shock wave result in a relatively small frequency of high-frequency oscillations at high concentrations.

Detonation cell size of liquid hypergolic propellants: Estimation from a non-premixed combustor

An experimental approach for estimating the detonation cell size for liquid hypergolic propellants is presented and applied for monomethylhydrazine (MMH) and a MON-3 variant of nitrogen tetroxide (NTO) in a non-premixed combustor. The method utilizes a correlation between cell size and reactant fill height in an annular combustor geometry. Reactant fill height is inferred using a control-volume analysis to relate the geometry of the reactant fill zone to the propellant flow rate, detonation wave-speeds and number, and annular gap size. High-speed videography is used to measure the number of waves and their speed over a range of quasi-steady continuous detonation conditions. The detonation criteria is also proven valid in the transient conditions as the decrease of the fill height below a critical value identified in this work matches modal transitions with decreasing number of waves. A power law relating the cell width with induction length further supports the validity of the present technique down to cell sizes of 1–10 µm, a scale not practically resolvable with conventional methods.

Predicted Melt Curve and Liquid Shear Viscosity of RDX up to 30 GPa

AbstractRecent grain‐scale simulations of HMX and TATB have shown that predictions for hot spot formation in high explosives are particularly sensitive to accurate determinations of the pressure‐dependent melt curve and the shear viscosity of the liquid phase. These physics terms are poorly constrained beyond ambient pressure for the explosive RDX. We adopt an all‐atom modeling approach using molecular dynamics (MD) simulations to predict the melt curve of RDX near to detonation conditions (30 GPa) and determine the shear viscosity of the liquid as a function of temperature and pressure above the melt curve. Phase‐coexistence simulations were used to determine the melt curve, which is predicted to vary by almost 1100 K as the pressure increases from 0 GPa to 30 GPa. Equilibrium MD simulations and the Green‐Kubo formalism were used to obtain the pressure‐temperature‐dependent shear viscosity. The shear viscosity of RDX is predicted to be of similar magnitude to the viscosity of TATB at low GPa‐range pressures, and to be roughly an order of magnitude lower than the viscosity of HMX. The temperature dependence of the shear viscosity is Arrhenius at a given pressure, and the exponential pre‐factor and activation term exhibit a strong, yet complicated, pressure dependence. An empirical pressure‐temperature dependent function for RDX shear viscosity is developed that simultaneously captures a wide range of MD predictions while taking an analytic form that extrapolates smoothly beyond the fitted regime. The relative strength of the pressure and temperature dependencies of these two physics terms is found to be of similar magnitude for RDX, HMX, and TATB, which motivates incorporating these results in future RDX grain‐scale modeling.

A new simplified virial equation of state for high temperature and high pressure gas

In this paper, in order to accurately describe the high temperature and high pressure state of gas under detonation conditions, a new simplified form of the virial equation of state (EOS)—the Virial–Peng–Long (VPL) EOS—is proposed based on the theoretical calculation results of dimensionless virial coefficients based on the Lennard-Jones 6-12 (LJ 6-12) molecular potential. In this EOS, the virial coefficients of the third to the fifth order are expressed in the form of an empirical fitting formula. In order to more accurately describe the PVT state of gas at higher temperature than the Virial–Han–Long (VHL) EOS, we theoretically calculate the fourth-order dimensionless virial coefficient in a higher temperature range and apply it to the fourth-order term of the equation, and the fifth-order term of the equation is based on the theoretical calculation results by Kofke in the higher temperature range. Then, in order to verify and evaluate the accuracy of the VPL EOS in describing the PVT state of high temperature and high pressure gas, we refer to relevant molecular dynamics PVT data and NIST database PVT data of methane in the range of P = 0.028 19–187.2648 GPa and T = 623.7–4369.3 K, oxygen in the range of P = 0.01–111.4876 GPa and T = 519.9–4066.8 K, and nitrogen in the range of P = 0.1–2.2 GPa and T = 700–2000 K. The PVT data were calculated by the VPL EOS and compared with the reference values and the calculated values of the Virial Wu (VLW) EOS and VHL EOS. The mean absolute percentage deviation of the calculated values of the VPL EOS is less than 2.0%, which is better than that of the VLW EOS and VHL EOS.

Modelling non-ideal detonations in commercial explosives

Highly non-ideal explosives usually react expressively below their ideal velocities of detonation. In these cases, dimensional effects and product heterogeneities become important to proper model their respective detonation state. Although Direct Numerical Simulation (DNS) techniques can provide a complete and exact solution for this problem, their actual computation cost are still not practical for industrial applications. In order to minimize these constrains, a simplified two-dimensional steady non-ideal detonation model for cylindrical stick explosives is presented. Based on an ellipsoidal shock shape approach (ESSA), the proposed model combines the quasione-dimensional theory for the axial flow solution with the unconfined sonic post-flow conditions at the edge of the explosive. Once calibrated, the model offers the possibility to predict the non-ideal detonation state for any charge diameter, resulting in a full mapping of the diameter-effect curve of the explosive. In addition, the effect of the inert confiner on the detonation flow is calculated by coupling a mechanistic confinement approach with the ESSA model. Thus, the proposed engineering approach is used to model the main properties of one of the most common ammonium nitrate-based explosive used in mining and quarrying industries, including the complete axial flow solution.

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.

Refraction of Oblique Shock Wave on a Tangential Discontinuity

The refraction of an oblique shock wave on a tangential discontinuity dividing two gas flows with different properties is considered. It is shown that its partial reflection occurs with the exception of the geometrical diffraction of an oblique shock. Another oblique shock, expansion wave or weak discontinuity that coincides with the Mach line can act as a reflected disturbance. This study focuses on the relationships that define the type of reflected discontinuity and its parameters. The domains of shock wave configurations with various types of reflected discontinuities, including characteristic refraction and refraction patterns with a reflected shock and a reflected rarefaction wave, are analyzed. The domains of existence of various shock wave structures with two types of reflected disturbance, and the boundaries between them, are defined. The domains of parameters with one or two solutions exist for the characteristic refraction. Each domain is mapped by the type of refraction with regard to the Mach number, the ratio of the specific heat capacities of the two flows and the intensity of a refracted oblique shock wave. The conditions of the regular refraction and the Mach refraction are formulated, and the boundaries between the two refraction types are defined for various types of gases. Refraction phenomena in various engineering problems (hydrocarbon gaseous fuel and its combustion products, diatomic gas, fuel mixture of oxygen and hydrogen, etc.) are discussed. The result can be applied to the modeling of the shock wave processes that occur in supersonic intakes and in rotating and stationary detonation engines. The solutions derived can be used by other researchers to check the quality of numerical methods and the correctness of experimental results.

Investigation of Shock Initiation in Covered Charges under Shock Wave and Fragment Impacts

In the current work, a series of step-by-step research methods have been applied to address the damaging effects of near-field strong shock waves and high-speed fragments on covered charge. In the first step, the defects of covered plates due to high-speed fragments were simplified to penetrated notches, and then, these notches were used to evaluate the impact of shock wave loads on charges covered with metal plates. In the next step, we developed a theoretical model to take into account the shock initiation of charges covered with defected metal plates. Explosive initiation standards coupled with shock wave evolution characteristics were applied to specify the crucial conditions of explosive detonation. Finite element program, for instance, was applied for the simulation of shock initiation processes in pressed charges (when TNT was covered with a steel plate containing a penetrated notch), and then, numerical simulations were validated by experimental findings. Finally, the results obtained from the numerical simulations and theoretical model were applied to evaluate the impacts of shock wave intensity, the thickness of covered metal plate, and the geometrical features of penetrated notch on pressed charge shock initiation. The least squares method was applied to determine critical initiation criteria (n and K). Theoretical calculation results were found to be highly consistent with those obtained from numerical simulations, indicating that covered metal plates significantly contributed to charge protection. The results also revealed that notches could undermine the protective function of covered plates and the size and shape of notch significantly affected charge critical detonation distance. Critical detonation distances of noncontact explosions were found to be 25 and 81 mm for a 3 mm thick pressed TNT in the presence and absence of 45# steel-covered plate, respectively. According to the results, increase in the diameter of covered plates containing a cylindrical notch increased pressed TNT critical detonation distance. When dealing with a covered plate containing a normally reflected frustum notch, however, we figured out that any increase in normal reflection slope could decrease pressed TNT critical detonation distance.