Detonation Behavior Research Articles

METHOD OF IMPROVING THE CHARACTERISTICS OF A GAS ENGINE, DEVELOPED ON THE BASE OF A DIESEL ENGINE

Methane, as an alternative to traditional motor fuels, is the most perspective for the incoming decades of the current century. The most widely spread method of the modification of diesel engines for operating with methane is a conversion of a basic model by changing both the way of ignition - compulsory spark ignition instead of self-ignition by compression, and the method of power control - quantitative, with the help of a throttle in case of a gas version, instead of qualitative in a diesel version. The main task of such conversion is to achieve the best possible energy and economic performance of the engine. Moreover, the peculiarity of the operation procedure of the gas engine, the necessity to avoid detonation combustion, should be taken into account. Consequently, in the process of converting a diesel engine into a gas one manufacturers have to decrease both the compression ratio and boost pressure, which leads to decline in engine efficiency. The authors found out, that there is a potential possibility to achieve much better eco-nomic and power characteristics of gas engines by applying Miller cycle to the operation procedure. In this case it becomes possible having very high geometric compression ratio and corresponding high val-ues of gas expansion to obtain relatively low values of actual compression ratio. This is the value that can lead to detonation combustion. The program of calculating the characteristics of operation procedure of Miller-cycle gas engines was worked out. The authors suggested a system of calculation, according to which detonation behavior is estimated on the basis of actual data of a particular model of the engine. Due to such analyses of the particular model of the engine we found out actual maximum values of compression pressure and compression temperature, which do not lead to the onset of detonation. So it may be stated that the parameter value that significantly increases the overall efficiency of the Miller-cycle gas engine, created on the base of Kamaz engines, is found.

Thermal decomposition pathways of nitro-functionalized metal-organic frameworks.

The decomposition behavior of high energy metal-organic frameworks (MOFs) with extensive nitration is disclosed. In contrast to the detonation behavior observed in molecular energetic compounds, deflagration transforms cubic MOFs into anisotropic carbon structures with highly dispersed metal. Both the structural metal and intimate mixing are found to be critical.

The Escape of High Explosive Products: An Exact-Solution Problem for Verification of Hydrodynamics Codes

This paper documents the escape of high explosive (HE) products problem and demonstrates the use of the problem for code verification assessment. The problem, first presented by Fickett and Rivard (1974, “Test Problems for Hydrocodes,” LASL Report, Los Alamos Scientific Laboratory, Los Alamos, NM, Report No. LA-5479), tests the implementation and numerical behavior of a high explosive detonation and energy release model and its interaction with an associated compressible hydrodynamics simulation code. The problem simulates the detonation of a finite-length, one-dimensional piece of HE that is driven by a piston from one end and adjacent to a void at the other end. The HE equation of state is modeled as a polytropic ideal gas. The HE detonation is assumed to be instantaneous with an infinitesimal reaction zone. Via judicious selection of the material specific heat ratio, the problem has an exact solution with linear characteristics, enabling a straightforward calculation of the physical variables as a function of time and space. Implementation of the exact solution in the Python code ExactPack is discussed, as are verification cases for the exact solution code. The problem is used to conduct code verification assessment on a Lagrangian hydrodynamics code.

Experimental investigation of detonation quenching in non-uniform compositions

This paper presents an experimental investigation into the dynamical behavior of detonation in non-uniform mixtures of propane and oxygen at initial pressure and temperature of 200 mbar and 290 K, respectively, with gradients of initial composition parallel to the direction of detonation propagation. The experiments were carried out in a 50 × 50-mm2-square section, 665-mm-long, vertical chamber. Filling was made from the chamber top-end by means of a planar, separate injection of the mixture components. The non-uniform distributions in the chamber were then controlled by molecular diffusion with diffusion time defining the composition gradient. A Chapman–Jouguet detonation was smoothly transmitted at the chamber bottom-end from a 3.6-m-long driver tube connected to the chamber. Injection and diffusion were monitored in such a way that the mixture composition at the chamber bottom-end was the same as the uniform composition in the driver tube at ignition time. Fast pressure transducers, sooted plates, Schlieren and CH* chemiluminescence visualizations were used to characterize the longitudinal velocities and cell widths, the front structure, the propagation modes and the quenching mechanisms of detonation. Detonation dynamics was found to depend on the steepness of the composition distribution and on the local and initial values of the equivalence ratio. In particular, a sudden one-dimensional detonation quenching of the multicellular detonation was observed in a lean to leaner distribution with a large gradient, whereas a progressive quenching through marginal propagation was obtained with a small gradient and a lower local equivalence ratio. The quenching mechanisms appear to be controlled by the rates of variation of composition and of detonation characteristic lengths: the faster the rate of change, the more sudden the quenching.

Effect of Coating Deposition Methods on the Properties of Titanium Aluminide Materials

The behavior of detonation and plasma coatings in conditions of dry friction against titanium alloy OT-4 and stainless steel 07Kh16N6 has been studied. The detonation coatings show significantly better tribological properties than the plasma coatings. This is probably due to the presence of aluminum and titanium nitrides possessing high wear resistance in the detonation coatings. Oxidation of the plasma and detonation coatings at a temperature of 900°C in air has been examined. The detonation and plasma coatings exhibit greater oxidation resistance than uncoated titanium alloy VT-16.

A Study of the Detonation Behavior of an Annular Booster Pellet

ABSTRACTAn annular-shaped booster pellet has been developed in order to study the capability of such a design to initiate the detonation of insensitive high explosives (IHE). The detonation characteristics of an annular booster design were studied theoretically by numerical simulation and experimentally. Results showed that if the annular booster pellet were detonated simultaneously at four symmetrical points, the detonation wave collision could be achieved within the pellet. The pairs of impacts of the four detonation wavefronts generated enhanced shock pressures in four radially symmetric directions. The tangential energy flow from the collision of detonation plays a major part in improving the initiation capability of an annular booster pellet. The numerical simulation is qualitatively consistent with the experimental results.

Methane–oxygen detonation characteristics near their propagation limits in ducts

In this study, the near-limit behavior of gaseous detonations in three methane–oxygen mixtures (CH4–2O2, CH4–1.5O2 and CH4–4O2) is investigated experimentally. A 36-mm diameter circular tube and three annular channel gaps (w=2mm, 4.5mm and 7mm) were used to look at the effect of different geometries on the detonation limits phenomenon. Photodiodes and smoked foils were employed to measure the time-of-arrival of the detonation wave and record the cellular detonation structure, respectively. As the detonation propagates within the limits, the velocity is steady with only a few percent deficit. By decreasing the initial pressure and, hence, reducing the sensitivity of the mixture, the detonation velocity deficit increases gradually. When the initial pressure is approaching the detonation limits, no steady detonation velocity can be realized, and failure occurs. With decreasing initial pressure, the smoked foil records indicate clearly that the cellular detonation evolves from a multi-headed to double-headed and eventually to a single-head spin as the limits approaches. The single-headed spinning detonations for CH4–2O2, CH4–1.5O2 and CH4–4O2 mixtures in the 36-mm round tube occurs from p0=3–7kPa, 4–10kPa and 7–16kPa, respectively. Using different annular channel widths, it is observed that the detonation velocity decreases as the channel gap is reduced.

A multi-phase theory for the detonation of granular explosives containing an arbitrary number of solid components

Multiphase continuum models are commonly used to predict the shock, combustion and detonation behavior of granular energetic mixtures containing solid reactants and gaseous products. These models often include phase interaction terms that formally satisfy the strong form of the Second Law of Thermodynamics and provide flexibility in distributing dissipation between phases arising from non-equilibrium phenomena. This work presents a thermodynamically compatible constitutive theory for reactive systems containing an arbitrary number of solid components. The theory represents a rigorous extension of the two-phase theory formulated by Bdzil et al., based on the well-studied Baer–Nunziato model. Forms of the gas–solid and solid–solid interphase sources suggested by general reactions of type A → B are considered, where the combustion processes discussed in Bdzil et al. are treated as a special case. The model energetics are augmented by supplemental evolutionary equations that track local changes in phase temperatures due to dissipative and transport processes allowing for the identification of dominant energetic processes. This capability provides a mean to identify system parameters (e.g., metal particle size and mass fraction in metalized energetic mixtures) which optimize performance metrics. Detonation predictions are given for mixtures of granular HMX and aluminum to demonstrate model features and to highlight the effect of aluminum particle self-heating by oxidation on detonation. Predicted spatial profiles for mechanical fields, and the heating contributions from individual dissipative processes, illustrate how aluminum particle size can affect the coupling of oxidative heating to the explosive reaction zone.

Numerical modelling of underwater detonation of non-ideal condensed-phase explosives

The interest in underwater detonation tests originated from the military, since the expansion and subsequent collapse of the explosive bubble can cause considerable damage to surrounding structures or vessels. In military applications, the explosive is typically represented as a pre-burned material under high pressure, a reasonable assumption due to the short reaction zone lengths, and complete detonation of the unreacted explosive. Hence, numerical simulations of underwater detonation tests have been primarily concerned with the prediction of target loading and the damage incurred rather than the accurate modelling of the underwater detonation process. The mining industry in contrast has adopted the underwater detonation test as a means to experimentally characterise the energy output of their highly non-ideal explosives depending on explosive type and charge configuration. This characterisation requires a good understanding of how the charge shape, pond topography, charge depth, and additional charge confinement affect the energy release, some of which can be successfully quantified with the support of accurate numerical simulations. In this work, we propose a numerical framework which is able to capture the non-ideal explosive behaviour and in addition is capable of capturing both length scales: the reaction zone and the pond domain. The length scale problem is overcome with adaptive mesh refinement, which, along with the explosive model, is validated against experimental data of various TNT underwater detonations. The variety of detonation and bubble behaviour observed in non-ideal detonations is demonstrated in a parameter study over the reactivity of TNT. A representative underwater mining test containing an ammonium-nitrate fuel-oil ratestick charge is carried out to demonstrate that the presented method can be readily applied alongside experimental underwater detonation tests.

Research progress on the dynamic characteristics of gaseous detonation

We review the recent research progress on dynamic characteristics of gaseous detonation,i.e., cellular structure of detonation, detonability limit, critical tube diameter and critical energy for direct detonation initiation, those characteristics are the fundamental knowledge of gaseous detonation physics research, as well as on the basis of which the dynamic behavior of detonation is determined. The investigations on the gaseous detonation physics have important academic significance and application background, for example, the understanding of the characteristics of gaseous detonation can supplement gaseous detonation theory and further promote the development of detonation study from macroscopic into microscopic. From the application aspect consideration, better comprehension of the dynamics of gaseous detonation and the critical conditions delineating initiation and failure of a detonation is of great significance to safety protection research in gas explosion accident of coal mine and combustible gas leaking of the chemical plant. In this review, we focus on the recent research progress on the dynamic characteristics of gaseous detonation, we also point out areas where our understanding is still far from being complete and contains some suggestions of ways in which progress might be made in the future.

Acceleration of plates using non-conventional explosives heavily-loaded with inert materials

The detonation behavior of high explosives containing quantities of dense additives has been previously investigated with the observation that such systems depart dramatically from the approximately "gamma law" behavior typical of conventional explosives due to momentum transfer and thermalization between particles and detonation products. However, the influence of this non-ideal detonation behavior on the divergence speed of plates has been less thoroughly studied and existing literature suggests that the effect of dense additives cannot be explained solely through the straightforward application of the Gurney method with energy and density averaging of the explosive. In the current study, the acceleration history and terminal velocity of aluminum flyers launched by packed beds of granular material saturated by amine-sensitized nitromethane is reported. It was observed that terminal flyer velocity scales primarily with the ratio of flyer mass to mass of the explosive component; a fundamental feature of the Gurney method. Velocity decrement from the addition of particles was only 20%-30% compared to the resulting velocity if propelled by an equivalent quantity of neat explosive.

Differences between the detonation behavior of emulsion explosives sensitized with glass or with polymeric micro-balloons

The differences between the detonation behaviour of ammonium nitrate based emulsion explosives sensitized with polymeric and those sensitized with glass micro-balloons is presented and discussed. Expancel® are hollow polymeric micro-balloons that contain a hydrocarbon gas. The mean particle size of these particles is 30 μm with a wall thickness of about 0.1 μm. The detonation velocity and the failure diameter of the emulsion explosive sensitized with different amounts of these particles have been measured in cylindrical charges by optical fibers. The detonation velocity demonstrates non-linear behaviour in relation to density and reaches the maximum value for a density lower than that of the matrix. The detonation fails when the density approaches that of the matrix. The detonation in the emulsion explosives extinguishes itself at a porosity value that seems to be independent from the nature of the sensitizing agent. For low densities, the detonation velocity is almost independent of the charge diameter, and is close to the values predicted by BKW equation of state.

Features of the incorporation of single and double based powders within emulsion explosives

In this work, features of the thermal and detonation behaviour of compositions resulting from the mixture of single and double based powders within ammonium nitrate based emulsion explosives are shown. Those features are portrayed through results of thermodynamic-equilibrium calculations of the detonation velocity, the chemical compatibility assessment through differential thermal analysis [DTA] and thermo gravimetric analysis [TGA], the experimental determination of the detonation velocity and a comparative evaluation of the shock sensitivity using a modified version of the "gap-test". DTA/TGA results for the compositions and for the individual components overlap until the beginning of the thermal decomposition which is an indication of the absence of formation of any new chemical species and so of the compatibility of the components of the compositions. After the beginning of the thermal decomposition it can be seen that the rate of mass loss is much higher for the compositions with powder than for the one with sole emulsion explosive. Both, theoretical and experimental, values of the detonation velocity have been shown to be higher for the powdered compositions than for the sole emulsion explosive. Shock sensitivity assessments have ended-up with a slightly bigger sensitivity for the compositions with double based powder when compared to the single based compositions or to the sole emulsion.

Dependence on the sectional shape of tube for propagation behavior of three-dimensional detonation

This paper is concerned with numerical simulation on propagation behavior of three-dimensional detonations in square tubes. Influence on motion trajectories of high pressure region (shock triple points) due to the change of aspect ratio of tube is solved by a finite difference method which consists of the semi-implicit MacCormack method and Non-MUSCLE type TVD scheme in order to prevent numerical stiffness and Gibb's phenomena. Reaction mechanism utilized in this study is the Nagoya model constructed for the stoichiometric hydrogen and oxygen gas mixture. It was found from numerical results that distinction in propagation mode could be explained from the relation between the geometric form of the tube section and the behavior of triple points. Moreover, it was shown that the transition of the configuration and the mode of propagation might not be settled causing the aspect ratio of the section.

A continuum constitutive model and computational method of explosive detonation

Some basic thermodynamic relationships are used to develop a theroretical framework for modeling the detonation in explosives, on the assumption that explosive and detonation product are in a local thermodynamic equilibrium state, i.e., their pressures and temperatures are identical. Using this framework, a continuum constitutive model for explosive detonation is composed of a group of ordinary differential equations including the state equations of explosive and its product, simple mixing law, reaction rate equation and energy conservation equation, which are easily solved by a mature computational method such as trapezoidal rule. A group of nonlinear constitutive equations in a generalized Maxwellian form describe the relationship among the time evolution rates of pressure and temperature, the strain rate, and the chemical reaction rate. Coefficients appearing in the constitutive equations are determined only by parameters of the explosive and the product through using simple mixing rule. The continuum constitutive model and the corresponding computational method are verified by simulating the detonation behaviour of PBX9404 impacted by high velocity Cu flyer, and in the simulation the JWL equation of state for unreacted explosive and detonation product and the two-term Lee-Tarver reaction rate equation are adopted.

Numerical study of acoustic coupling in spinning detonation propagating in a circular tube

Spinning detonations propagating in a circular tube were numerically investigated with a two-step reaction model by Korobeinikov et al. The time evolutions of the simulation results were utilized to reveal the propagation behavior of single-headed spinning detonation. Three distinct propagation modes, steady, unstable, and pulsating modes, are observed in a circular tube. The track angles on a wall were numerically reproduced with various initial pressures and diameters, and the simulated track angles of steady and unstable modes showed good agreement with those of the previous reports. In the case of steady mode, transverse detonation always couples with an acoustic wave at the contact surface of burned and unburned gas and maintains stable rotation without changing the detonation front structure. The detonation velocity maintains almost a CJ value. We analyze the effect of acoustic coupling in the radial direction using the acoustic theory and the extent of Mach leg. Acoustic theory states that in the radial direction transverse wave and Mach leg can rotate in the circumferential direction when Mach number of unburned gas behind the incident shock wave in the transverse detonation attached coordinate is larger than 1.841. Unstable mode shows periodical change in the shock front structure and repeats decoupling and coupling with transverse detonation and acoustic wave. Spinning detonation maintains its propagation with periodic generation of sub-transverse detonation (new reaction front at transverse wave). Corresponding to its cycle, whisker is periodically generated, and complex Mach interaction periodically appears at shock front. Its velocity history shows the fluctuation whose behavior agrees well with that of rapid fluctuation mode by Lee et al. In the case of pulsating mode, as acoustic coupling between transverse detonation and acoustic wave is not satisfied, shock structure of spinning detonation is disturbed, which causes failure of spinning detonation.

Stability of viscous detonations for Majda’s model

Using analytical and numerical Evans-function techniques, we examine the spectral stability of strong-detonation-wave solutions of a version of Majda’s scalar model for a reacting gas mixture with an Arrhenius-type ignition function. We introduce an energy estimate to limit possible unstable eigenvalues to a compact region in the unstable complex half plane, and we use a numerical approximation of the Evans function to search for possible unstable eigenvalues in this region. Our results show, for the parameter values tested, that these waves are spectrally stable. Combining these numerical results with the pointwise Green function analysis of Lyng, Raoofi, Texier, & Zumbrun [G. Lyng, M. Raoofi, B. Texier, K. Zumbrun, Pointwise Green function bounds and stability of combustion waves, J. Differential Equations 233 (2) (2007) 654–698.], we conclude that these waves are nonlinearly stable. This represents the first demonstration of nonlinear stability for detonation-wave solutions of a Majda-type model without a smallness assumption. Notably, our results indicate that, for this simplified, scalar model, there does not occur, either in a normal parameter range or in the limit of high activation energy, Hopf bifurcation to “galloping” or “pulsating” solutions as is observed in the full reactive Navier–Stokes equations. This answers in the negative, for this model, a question posed by Majda as to whether such scalar detonation models capture this aspect of detonation behavior.

Multi-phase simulation of ammonium nitrate emulsion detonations

Ammonium-nitrate-based explosives used by the mining industry exhibit strong non-ideal detonation behaviour. Detonation velocities in rate-sticks with radii close to the failure radius, can be as low as one third of the ideal detonation velocity, which poses a significant challenge for their accurate predictive computational modelling. Given that these emulsions are highly heterogeneous, multi-phase formulations are well suited for their representation in numerical hydrocodes. To this end, a single-pressure, single-velocity multi-phase model is employed for the simulation of an explosive emulsion widely used by the mining industry. The model is modified to rectify a problem related to the calculation of a unique detonation state, and is evaluated using a high-resolution, shock-capturing Riemann problem-based scheme. In order to perform high-resolution numerical simulations at a reduced cost, a shock-following method is implemented and validated against the full-domain solutions. An improved iterative fitting procedure for steady-state detonation kinetics is also presented. Validation against experimental evidence shows that the model can reproduce confined VOD experimental data, solely by adjusting the reaction kinetics to match unconfined experimental VOD data. Furthermore, the model can match experimental front curvature measurement without further adjustments.

A hybrid two-phase mixture model of detonation diffraction with compliant confinement

A multi-material two-phase hybrid model of heterogeneous explosives, with a reaction rate that is proportional to the gas-phase pressure excess above an ignition threshold, is examined computationally. The explosive is confined within a compliant inert, and the focus is on the behavior of an established detonation as it rounds a 90° corner and undergoes diffraction. The numerical approach, a variant of Godunovʼs method, is designed to capture interfaces between materials that can undergo phase change, and extends previous work of the authors on rigidly-confined two-phase detonations. The dependence of the post-diffraction conduct on the strength of the confinement is explored by holding the reaction-rate prefactor and the ignition threshold fixed, and considering confiners of two different strengths. The aim is to determine whether a detonation that turns the corner successfully when rigidly confined can experience failure when the confinement is compliant.

The influence of erodent hardness on the erosion behavior of detonation sprayed WC-12Co coatings

Abstract The solid particle erosion behavior of detonation sprayed WC-12Co coatings obtained at three oxygen to fuel ratios has been characterized using SiC, Al2O3 and SiO2 as erodents at two impact velocities (25 m/s, 45 m/s) and two impact angles (30°, 90°). The results indicate that the erosion rate increases with increasing hardness of the erodent and more importantly, the erosion mechanism changes depending upon the erodent type. The ranking of the materials in terms of erosion resistance also depends on the type of erodent used. The extent of decarburization of WC-12Co coatings, varied by using three levels of oxygen to fuel ratio during the coating process has a marginal influence on erosion behavior. The results have been understood in terms of ploughing and sub-surface cracking mechanisms and also on the basis of insufficient transfer of energy from the erodent to the coating especially in the case of SiO2 erodent.