Explosive Mode Research Articles

Synthesis of high purity Ti2AlC MAX phase by combustion method through thermal explosion mode: Optimization of process parameters & evaluation of microstructure

Obtaining high-purity MAX-phase powders is a challenging issue. Therefore, in this article, the effects of two key parameters, including mechanical activation time (1, 2, and 3 h), and preheating temperature (800 and 1000 °C) were investigated on the formation mechanism of Ti2AlC MAX phase using mechanically activated (assisted) self-propagating high-temperature synthesis (MA-SHS) combustion method through thermal explosion mode. For this aim, a powder mixture of titanium, aluminum, and carbon with a stoichiometry ratio of (2:1:1) was used. Differential thermal analysis (DTA) was carried out to evaluate the effect of mechanical activation and preheating temperature of the formation temperature of the target MAX phase. Subsequently, the microstructural, phase analysis, chemical composition, and determination of surface chemical states studies were carried out through scanning electron microscopy (SEM), X-ray energy distribution spectroscopy (EDS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectric spectroscopy (XPS), respectively. DTA results illustrated that applying mechanical activation alters the formation temperature, which leads to an increase in the purity of the MAX phase. The quantitative measurements were carried out using the Rietveld method to determine the purity of the achieved MAX phase. The results indicated that samples subjected to 2 h of mechanical activation at a preheat temperature of 1000 °C exhibited to contain 96.1 % of Ti2AlC MAX phase, which is the highest value among other specimens and the lowest amount of secondary and oxide phases (3.9 % of TiC) during the combustion synthesis process compared to other samples.

Spontaneous ignition and flame propagation in hydrogen/methane wrinkled laminar flames at reheat conditions: Effect of pressure and hydrogen fraction

Direct numerical simulations (DNS) with detailed chemical kinetics and chemical explosive mode analysis (CEMA) are performed to investigate the effect of operating pressure and hydrogen–methane blending on laminar wrinkled flames at reheat combustion conditions. Building upon previous three-dimensional DNS datasets of reheat hydrogen flames, the present work considers two-dimensional configurations that render computationally-feasible simulations of high-pressure combustion and significantly more complex hydrocarbon chemistry. A geometrically-simplified representation of the reheat combustor is adopted and the thermodynamic states considered in the simulations are carefully chosen to mimic gas turbine operation conditions, which are constrained to achieve a target flame position and flame temperature. The two-dimensional DNS results are first assessed against the available three-dimensional data and then analyzed to extract the main trends exhibited by the reheat combustion process with respect to the fraction of the fuel consumed by spontaneous ignition and flame propagation, for increasing pressures and hydrogen fractions. Due to significant differences in the characteristic features of the velocity and thermal boundary layers between the three-dimensional and the two-dimensional configurations, a different global flame shape is observed (V-shaped flame vs W-shape flame) together with a ∼10% bias in the fraction of fuel consumed by spontaneous ignition. Crucially, results from the scaling studies reveal very clear trends with a significant decrease in the fuel consumption by spontaneous ignition for increasing pressures and hydrogen fractions, at the conditions investigated. Finally, this study highlights the important role that first-principle direct numerical simulations, even when conducted in computationally affordable two-dimensional simplified geometrical configurations, can play in obtaining detailed insights and quantitative trends useful for the characterization of complex reactive flows.Novelty and significanceThe reheat burners of the two-stage sequential gas turbine combustors are designed to stabilize flames primarily due to spontaneous ignition. However, prior numerical simulations revealed the presence of an additional assisted-ignition mode aided by recirculation zones. In this study, we used practically feasible two-dimensional direct numerical simulations of premixed hydrogen–air mixtures under lean conditions to quantify the roles of the two flame stabilization modes at different operating pressures. Achieving fundamental understanding of the effect of pressure and hydrogen fraction on flame stabilization is crucial to the development of two-stage sequential combustion and the present two-dimensional calculations provide important new insights. We show that at high pressures, both modes consume fuel to a similar extent. We also investigated the effect of methane blending on flame stabilization. This study also discusses how two-dimensional direct numerical simulations can be leveraged in the design optimization of reheat burners at low technology readiness levels.

Experimental investigation on the dynamic response of vent plate under methane-air mixtures explosion load

The dynamic response study of explosion venting components is of great significance for the assessment of explosion disasters and the determination of damage. Based on the self-developed rectangular explosion venting device, a series of experimental investigations on the dynamic response and failure mode of calcium silicate vent plates under the methane explosion loads induced by a detonator were conducted. The results show that the vent plate mainly exhibits brittleness and presents a plastic hinge failure mode under the blasting loads. When the gas concentration is closer to the stoichiometric concentration, P2 (the peak overpressure generated by the vent plate rupture) and its pressure rise rate dP2/dt are higher. Conversely, when the methane concentration is closer to the upper or lower limits of the explosion, the explosion load tends to be static, the yield line of the vent plate is shorter, and there are fewer fragments generated by the failure of the plate. The pressure-displacement curve and the correlation diagram of failure modes proposed provide a reference for predicting the failure mode of light and fragile explosion venting components.

DNS on flame and flow characteristics of a H2-O2-H2O lifted flame with inclining impinging jets geometry

Hydrogen-fueled gas turbines play one of the key roles in future carbon-neutral energy structure. Due to hydrogen’s high flame speed and extreme flame temperature, design of burners applying hydrogen as fuel is of challenge. In this work, we conduct direct numerical simulations to investigate a non-premixed steam-diluted oxygen/hydrogen combustion, which is formed by inclined impinging fuel and oxidizer jets injected by sub-millimeter nozzles. This configuration inherently prevent flashback and has a higher mixing efficiency enhanced by jet impingement, thereby leveraging advantages of both conventional premixed and non-premixed configurations. The flame is lifted flame held at the jet impinging position far away from the wall boundary. The most intensive mixing process occurs at the outer sides of the two branches of hydrogen jet after impinging, forming the flame base and resulting in an edge-flame configuration. A larger jet inclination angle leads to more effective bulk turbulence mixing because of the increased mixing volume, thereby enhancing combustion completeness. Simultaneously, it results in lower wall heat flux due to gentler upstream recirculation of burnt products. Chemical explosive mode analysis is conducted to analyze the combustion procedure from ignition to burnt out. The flame is held by the recirculation of high-temperature burnt products upstream of the impingement position, and its structure is primarily formed by the simultaneous ignition of a widespread explosive mixture enhanced by intense turbulence.

Combustion of single micron-sized magnesium particles in carbon dioxide

An experimental system integrating micro-sized single particle generation, ignition, and observation was proposed and constructed for investigating the combustion characteristics of magnesium single particles in carbon dioxide. Defining the onset of combustion using the boiling point temperature allows for precise measurement of combustion time without artificial interference. Results revealed four modes of combustion for magnesium particles (Vapor-phase combustion, surface reaction, Micro explosion and flash-out mode) in carbon dioxide. Vapor-phase combustion is diffusion-controlled (with a D01.76 scaling, where D0 is the initial particle diameter). Additionally, the micro-explosion mode primarily occurs in particles with diameters exceeding 70 μm, and the combustion time is rather insensitive to the particle size (Typically 0.5 ∼ 2.2 ms in this study). The characteristic temperatures of the particles were determined using two-color pyrometry, indicating that the particle combustion temperature decreases with increasing particle size. Magnesium particles typically reach temperatures approximately 800 K higher than normal vapor-phase combustion temperatures before experiencing micro-explosions. Analysis of combustion products shows that the oxide shell formed by the combustion of magnesium particles has a three-layer structure. Both the outer and inner layers are mixed layers of magnesium oxide and solid carbon produced during combustion reactions, and the middle layer is the initial oxidation layer of the particles.

Investigation of hydrogen/air co-flow jet flame propagation mechanism in supersonic crossflow

The design of fuel injection schemes is crucial for improving the combustion performance of high-Mach number scramjet. To clarify the feasibility of the coaxial jet injection scheme, high fidelity Large Eddy Simulation of the supersonic coaxial jet flame is conducted. The simulations are in good agreement with the experimental results in terms of time-averaged velocity, temperature, and species distribution. Auto-ignition phenomenon and the characteristics of partially premixed flame are well captured. The introduction of co-flow air increases the vorticity magnitude close to the injection port and downstream near-wall region, which results in a 400 K rise in the time-averaged temperature on the downstream near-wall region and a 4% increase in the proportion of premixed combustion near the injection port. Moreover, the instantaneous distribution of hydroxy radical indicates that the spanwise width of the windward reaction shear layer is reduced utilizing the coaxial jet scheme. Chemical kinetic analysis is applied to reveal the propagation mechanism of partially premixed flames. Thermal explosion is the chemical explosion mode for all coaxial jet flame front, which are dominated by a high-temperature reaction path. The low-temperature reaction path mainly exists in the transverse jet injection port, downstream near-wall region of the single transverse jet and co-flow lifted flame base. These significant findings provide valuable insights for the potential engineering application of the coaxial jet injection scheme to a high Mach number scramjet.

The Structure Characteristics of Laminar Premixed Flames of Gasoline-like Fuel Under CI Engine-Relevant Conditions.

Gasoline compression ignition characterized by partially premixed and long ignition delays typically features complex flame structures such as deflagration or spontaneous ignition fronts. In this study, the flame structure and propagation characteristics of PRF90/air mixtures under compression ignition engine-relevant conditions are investigated numerically. Similar to other types of fuels, under such conditions, the propagation speed of PRF90 laminar premixed flames depends not only on the unburnt mixture properties but also on the residence time, and the transition of the flame regime depends only on the residence time. Nevertheless, due to the temperature-dependent autoignition chemistry of PRF90, flames with excessively high unburnt temperatures show different combustion behaviors after the transition from deflagration to autoignition-assisted flames. Sensitivity analysis showed that, the dominant chain branching reactions in the deflagration mode are H + O2 = OH + O and CO + OH = CO2 + H, and that in the autoignition-assisted flames with lower unburnt temperature are H2O2(+M) = 2OH(+M) and IC8H18 + HO2 = AC8H17 + H2O2, while for higher unburnt temperatures, the reactions C3H5 + HO2 = C2H3 + CH2O + OH and IC8H18 = IC4H9 + TC4H9 are more important than the fuel low-temperature oxidation reactions. In addition, a criterion based on chemical explosive mode analysis is used to analyze the local combustion mode. The results show that the difference in diffusion/chemical structure at the crossover progress variables C 0 and crossover temperature allows both C 0 and to be used as a flame location for distinguishing propagation modes in premixed flame. However, the effects of the equivalence ratio on C 0 are different from that on , which means that the selection of C 0 and may lead to different discriminant results for stratified mixtures. Comparing the applicability of C 0-based and -based locations in three-dimensional gasoline compression ignition flame, it is found that the flame location based on the value of C 0 at ϕ = 1.0 can more completely reflect the flame development characteristics in stratified premixed combustion.

Tuning Green Explosives through SNAr Chemistry.

Reactivity and regioselectivity of SNAr-type fluorine substitution with azide in polyfluorosubstituted nitrobenzenes was studied both theoretically and experimentally. The obtained polyazido-substituted nitrobenzene derivatives were extensively characterized by NMR, IR, HPLC, X-ray, and DFT methods. It was found that the substitution with the azide nucleophile occurs first at the para- and the ortho-positions to the NO2-group and that transazidation reactions also occur here. Thermal decomposition of prepared azidonitrobenzenes was studied both in controlled (kinetic decay) and uncontrolled (explosion) modes. In case of the controlled thermal decomposition of ortho-azidonitrobenzenes, benzofuroxans were found as major products of the reaction unless another azido group was adjacent to the furoxan moiety. The bursting power of azidonitrobenzenes was found to rise gradually with the number of the azide substituents in the aromatic ring.

Dialogue, Horizon and Chronotope: Using Bakhtin’s and Gadamer’s Ideas to Frame Online Teaching and Learning

The information explosion and digital modes of learning often combine to inform the quest for the best ways of transforming information in digital form for pedagogical purposes. This quest has become more urgent and pervasive with the ‘turn’ to online learning in the context of COVID-19. This can result in linear, asynchronous, transmission-based modes of teaching and learning which commodify, package and deliver knowledge for individual ‘customers’. The primary concerns in such models are often technical and economic – technology as a cost-effective ‘solution’ to educational challenges. In this paper I argue for the importance of dialogic learning space in teaching and learning by means of Information and Communication Technologies, whether in the form of fully online learning, blended learning or face-to-face encounters using ICT affordances. Although the 20th Century theorists Mikhail Bakhtin (1895–1975) and Hans-Georg Gadamer (1900–2002) produced their seminal works before the advent of ICTs, they were both concerned with the quality and authenticity of human engagement with texts and with other persons and contexts. Besides a shared interest in dialogue as an ontological feature of human life and being, they both used spatiotemporal concepts for understanding and interpreting texts. The article draws on Gadamer’s notions of dialogue and horizon, and Bakhtin’s notions of dialogue and chronotope, to conceptualize dialogic possibilities for online education. Its purpose is to provide a framework, grounded in Bakhtin’s and Gadamer’s ideas, for a dialogic approach to online teaching and learning in higher education.

Numerical Study of Ignition and Combustion of Hydrogen-Enriched Methane in a Sequential Combustor

Ignition and combustion behavior in the second stage of a sequential combustor are investigated numerically at atmospheric pressure for pure CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CH}}_{4}$$\\end{document} fueling and for two CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CH}}_{4}$$\\end{document}-H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} fuel blends in 24:1 and 49:1 mass ratios , respectively, using Large Eddy Simulation (LES). Pure CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CH}}_{4}$$\\end{document} fueling results in a turbulent propagating flame anchored by the hot gas recirculation zones developed near the inlet of the sequential combustion chamber. As the H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} content increases, the combustion process changes drastically, with multiple auto-ignition kernels produced upstream of the main flame brush. Analysis of the explosive modes indicates that, for the highest H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} amount investigated, flame stabilization in the combustion chamber is strongly supported by auto-ignition chemistry. The analysis of fuel decomposition pathways highlights that radicals advected from the first stage flame, in particular OH, induce a rapid fuel decomposition and cause the reactivity enhancement that leads to auto-ignition upstream of the sequential flame. This behavior is promoted by the relatively large mass fraction of OH radicals found in the flow reaching the second stage, which is approximately one order of magnitude greater than it would be at chemical equilibrium. The importance of the out-of-equilibrium vitiated air on the ignition behavior is proven via an additional LES that features weak auto-ignition kernel formation when equilibrium is artificially imposed. It is therefore concluded that parameters affecting the relaxation towards chemical equilibrium of the vitiated flow can have an important influence on the operability of sequential combustors fueled with varying fractions of H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} blending.

Phase Formation during the Synthesis of the MAB Phase from Mo-Al-B Mixtures in the Thermal Explosion Mode.

This work focused on the production of the MoAlB MAB phase through self-propagating, high-temperature synthesis in the thermal explosion mode. The influence of the method of a Mo-Al-B-powder reaction mixture preparation on the combustion temperature, mechanism, and stages of the MAB phase formation in the combustion process was investigated. The combustion temperatures of the mixtures obtained in the rotary ball mill and high-speed planetary ball mill were 1234 and 992 °C, respectively. The formation of intermediate compounds Mo3Al8 and α-MoB in the combustion front, along with MoAlB, was established using the time-resolved X-ray diffraction method. In the case of the mixture prepared in a ball mill, the primary interaction in the combustion front occurred through the Al melt, and in the case of using a planetary mill, solid-phase reactions played an important role. The mechanical activation of the mixture in a planetary mill also accelerated the processes of phase formation. The method of a reaction mixture preparation has virtually no effect on the MoAlB MAB phase content in combustion products (92-94%), but it does affect their structure. The synthesis products have a lamellar structure composed of MAB grains with a thickness of ~0.4 μm and a length of ~2-10 μm.

Dynamic buckling response of buried X70 steel pipe with bolted flange connection under two-charge explosion loads

It is of great significance to investigate the dynamic response of pipes under blasting loads for the operation, assessment, and repair of pipes. However, there are few studies available on the dynamic buckling response of pipes under multiple explosion loads. In the present study, pipe-soil coupling 3-D models are established to investigate the dynamic buckling response of X70 steel pipe with bolted flange connection (BFC) under two-charge explosion loads (Charge A lied on the ground surface and Charge B lied in the soil). The main influencing factors are also discussed, including explosion mode, internal pressure, interval time, mass ratio of charges, and diameter-to-thickness ratio (D/t ratio). When Charges A and B were exploded simultaneously, it is found that the non-pressurized X70 pipe produced more significant cross-sectional deformation than in one-point explosion (Charge A or B). Increasing D/t ratio is advantageous for the anti-explosion of the pipe with BFC. Suitable internal pressure can effectively prevent the buckling deformation of the pipe. Compared with the common straight pipe, BFC system can effectively decrease the local buckling deformation and improve the anti-explosion ability of the pipe due to its higher local stiffness and energy absorption.

A numerical study of ignition and flame development characteristics in GCI combustion using large eddy simulations and chemical explosive mode analysis

This work investigates the ignition and flame development processes of low reactivity fuel combustion under compression ignition conditions based on the large eddy simulation approach. The chemical explosive mode analysis (CEMA) is employed to characterize the local combustion features, including gas-liquid fuel zone, auto-ignition, diffusion-assisted, extinction, cool flame and post-ignition zone, among which auto-ignition and post-ignition are found to play a key role in the overall heat release process. The local flame propagation modes in gasoline compression ignition (GCI) are determined by quantifying the relative magnitude of diffusion/chemistry at a representative progress variable in the pre-ignition zone. The results show that autoignition fronts and deflagration waves exist simultaneously in the ignition and intense high temperature heat release (HTHR) stages, but autoignition fronts dominate. In addition, the chemical kinetic processes of four heat release periods are analyzed. The heat release during the ignition period is found to be dominated by the reactions CH3+ H (+M) <=> CH4 (+M) and CH3CHO + H <=> CH2CHO + H2. The reaction CH2OH + OH <=> CH2O + H2O always plays an important role in the heat releases during the other three combustion stages including intense HTHR, moderate HTHR and post-combustion.

OME[formula omitted]/air mixtures: The structure and propagation mechanism of their laminar premixed flames

Oxymethylene dimethyl ethers (CH3O(CH2O)xCH3 or OMEx) are synthetic substitutes of diesel and jet fuel. They can achieve soot-less combustion and have been shown to exhibit favourable ignition characteristics. With the aim to explore their combustion physics, the structure of their flames is analysed using the algorithmic tools of the Computational Singular Perturbation (CSP) method. It is demonstrated that the flame structure and the mechanism for its propagation is encapsulated in the fastest explosive mode, introduced by chemical dynamics in a narrow region of the flame front. This narrow region extends around the point where the maximum heat release rate (MHRR) is recorded. CSP diagnostics identify (i) reactions H + O2→ O + OH and CO + OH → CO2 + H beyond MHRR as initiating an upstream diffusion of heat and H radicals, both of which are generated by the exothermic reaction H2 + OH → H2O + H, (ii) a downstream convective motion that ensues and (iii) chemical activity that is initiated ahead of MHRR and sustained by the convective transport of fuel and oxygen. CSP also identifies differences in the action of the upstream diffusion of heat and H radicals and of the downstream transport of fuel and oxidiser. It is also shown that the fastest explosive mode far from the neighbourhood of MHRR has no influence on the structure and propagation of the flame front. Although OME2−4/air mixtures exhibit drastically different dynamics in the context of homogeneous autoignition, very small differences are recorded in terms of flame structure and propagation. The findings suggests that, since practically all major processes driving the flame front propagation are similar to those of hydrocarbons, OMEx fuels can be used as “drop-in” fuels in currently employed burners.

Electrothermal instability in different modes of underwater electrical wire explosion

Electrothermal instability and its effect on the uniformity of discharge channels during underwater electrical wire explosions at different energy deposition rates have been investigated. According to the liquid–vapor transition mechanism, we classified underwater electrical explosion into “phase explosion mode” and “supercritical mode.” Two sets of experiments corresponding to the two modes were conducted, and the exploding wires were observed by a shadow imaging system. Results showed that a bamboo-shaped discharge channel was formed in the phase explosion mode, whereas the discharge channel in the supercritical mode was a uniform cylinder. Self-consistent magnetohydrodynamic simulation results indicated that exploding wires transfer into liquid–vapor coexistence phase in the phase explosion mode, accompanied by a rapid increase in the density perturbation and the formation of bamboo-shaped structures. Moreover, a small perturbation model was derived to analyze the electrothermal instability in different thermodynamic states. It was indicated that the density perturbation is easier to grow in the liquid–vapor coexistence state than the supercritical state, which provides a theoretical explanation for the differences between the two electrical explosion modes.

Self-Propagating High-Temperature Synthesis of High-Entropy Carbides in the Gasless Thermal Explosion Mode

Self-Propagating High-Temperature Synthesis of High-Entropy Carbides in the Gasless Thermal Explosion Mode

Comparative study on damage effects of penetration and explosion modes on airport runway

As an important part of civil and military buildings, airport runway is an important research object in the field of protection. In this study, damage assessment of scaled-down target of airport runway was carried out through experiment and numerical simulation. Two experimental methods, static explosion of charge after penetration and explosion of prefabricated hole, were used to damage the target and crater size and surface acceleration of the target were measured and analyzed. The experiment proves that the damage effects of the two methods were obviously different. The crater size produced by static explosion of charge after penetration was obviously larger than that produced by explosion of prefabricated hole under the same explosion depth and explosive charge, of which the shapes were also different. The numerical calculation model was established, and static explosion of charge after penetration was realized and detonation products leakage in inward explosion were solved through restart and S-ALE numerical calculation methods. Calculation results were compared with the experimental results; state equation and parameters were verified; damage effect diagram was obtained by numerical calculation, and mechanism of damage difference was analyzed. The study noted that obvious difference in explosion pressure transmitting and structural failure modes in multi-layer medium and that in a single medium. It proved that the damage caused by penetration will affect cratering effect and the movement of detonation products. Based on the experimental and numerical results, two formulas were given for calculating the crater sizes of airport runway under static explosion of charge after penetration and under explosion of prefabricated hole. The effect of dimensionless penetration coefficient and dimensionless explosion coefficient on crater size was determined by analyzing the crater relation curve of airport runway. The study indicates that the size difference between static explosion of charge after penetration and explosion of prefabricated hole charge can reach 30%. To carry out more accurate study on the damage of the projectile to target, the experiment should adopt static explosion of charge after penetration.

Embedded direct numerical simulation of ignition kernel evolution and flame initiation in dual-fuel spray assisted combustion

The flame initiation process in dual-fuel spray assisted combustion is presently not fully understood. Here, diesel spray assisted combustion of premixed methane/oxidizer/EGR is explored in the post-ignition phase by scale-resolved simulations. The modified dual-fuel ECN Spray A forms the baseline configuration. An extensive local grid refinement (approaching DNS limit) around one of the first high-temperature ignition kernels is carried out in order to examine the validity of hypothesized flame initiation and deflagration. A high quality LES is used to solve the spray dynamics, while the embedded quasi-DNS (eq-DNS) region offers detailed information on the ignition kernel evolution. The finite-rate chemistry is directly integrated, utilizing 54 species and 269 reactions. Local combustion modes are investigated for the ignition kernel development toward spontaneous ignition and premixed flame propagation using various approaches, including the reaction front displacement speed, energy transport budget, and chemical explosive mode analysis. Furthermore, a new criterion based on reaction flux analysis is introduced, which is compatible with dual-fuel combustion. The spatial and temporal scales associated with the ambient methane consumption and consequent flame initiation are characterized. For the first time in dual-fuel spray assisted simulations, numerical evidence is provided on the initiation of premixed flames, and the corresponding timescale is reported. Particularly, there is a transient mixed-mode combustion phase of approximately 0.2 ms after the spray second stage ignition wherein extinction, ignition fronts, and quasi-deflagrative structures co-exist. After such a transient period, the combustion mode becomes essentially deflagrative. Finally, interactions between turbulence and premixed flame front are characterized mostly in the corrugated regime.

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OF HIGH-ENTROPY CARBIDES IN THE REGIME OF A GASLESS THERMAL EXPLOSION

High-entropy carbides are a new class of inorganic compounds promising for a wide range of applications. The paper presents a new concept for the synthesis of powders of high-entropy carbides by the method of self-propagating high-temperature synthesis (SHS) in the gasless thermal explosion mode from previously mechanically synthesized and structured reaction mixtures. For the first time, high-entropy carbides TaTiNbVWC5 and TaNbVMoWC5 were obtained by this method, their crystal structure was determined, which was compared with similar compositions obtained by sintering.

Simulation of the bulk synthesis of a composite from the mixture of Ni and Ti in a steel cylindrical reactor

A new mathematical model of high-temperature synthesis of intermetallic composite in the mode of dynamic thermal explosion is proposed. It is assumed that the heating of a powder compact placed in a steel cylindrical reactor is carried out by high frequency currents from an inductor. This model takes into account the reactions of formation of the main phases represented on the Ni-Ti diagram equilibrium state diagrams of the binary system Ti-Ni and known from experimental data. Composition changes (the fraction of pure components and synthesis products) are described using theory of formal chemical kinetic. It is assumed that the reaction rates depend on the temperature according to the Arrhenius law, and on the concentrations according to the law of the mass action. The formulated problem is solved numerically. The presented model makes it possible to investigate the regularities of intermetallic composite synthesis, taking into account the melting process. The gradual appearance of the liquid phase is described by a separate equation in the melting temperature interval, which is formally similar to the two-phase zone theory. The results of numerical studies of the composition evolution are described. Numerical results are compared with the experiment. It is shown that the material of complex composition is formed during the volume synthesis in all parameter area under study.