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 Combustion, Explosion, and Shock WavesJournal Prestige (SJR): 0.294 Citation Impact (citeScore): 1Number of Followers: 20      Hybrid journal (It can contain Open Access articles) ISSN (Print) 0010-5082 - ISSN (Online) 1573-8345 Published by Springer-Verlag  [2658 journals]
• Analysis of the Penetration of Shaped Charges with Hemispherical and
Semi-Ellipsoidal Liners of Degressive Thickness

Abstract: This paper presents a comparative computational analysis of the penetration of shaped charges with copper liners in the form of a cone of progressive thickness with a cone angle of 60°, a hemisphere of constant thickness, and a hemisphere and a semi-ellipsoid of degressive (decreasing from apex to base) thickness. The polar semi-axis of the semi-ellipsoidal liner slightly exceeded the equatorial semi-axis. The parameters of the generated shaped-charge jets were determined by numerical simulation within the framework of a two-dimensional axisymmetric problem of continuum mechanics, and the depth of their penetration into a steel target was determined using an engineering technique that takes into account the influence of the manufacturing precision of the charges. The parameters of the liners of degressive thickness were selected so that the tip velocity of the jets formed from them was close to the velocity provided by the conical liner. In this case, the penetration of the shaped charge with a hemispherical liner of degressive thickness was significantly lower than that of the charge with a conical liner, and the latter, in turn, was slightly inferior in the maximum depth of penetration to the charge with a semi-ellipsoidal liner. The physical reasons of the results are discussed.
PubDate: 2021-09-01

• Acceleration of Dispersed Particles by Gas Detonation Productions in an
Expanding Channel

Abstract: This paper describes an experimental study and a quasi-one-dimensional calculation of acceleration of dispersed particles by gas detonation products in an expanding channel. The calculations show the possibility of a significant increase in the velocity of powder particles due to the conical expansion of a detonation channel. For particles with sizes of 30–40  $$\mu$$ m at cone angles of 2–4°, the maximum velocity increase reaches 35–60%. A method is developed for fixing the radiation of a packet of dispersed particles accelerated in a detonation channel by a photosensor, which makes it possible to measure the particle velocity with an accuracy of  $$\pm$$ 5%. The calculation results are in good agreement with the experimental data.
PubDate: 2021-09-01

• Multiple Venting Behavior of Inner Dust Explosions

Abstract: Explosion venting experiments of corn starch are carried out in a small-scale container. With the help of a high-speed camera and a pressure sensor, an interesting multiple venting behavior and its physical mechanism are comprehensively analyzed. The results suggest that the failure of the venting structure could cause three times intermittent explosion venting at most, which is negatively correlated with the opening pressure. Only the first venting significantly changes the internal explosion pressure. The flame behavior changes substantially from one venting to the other, even under the same operating conditions. The first venting flame occurs in an underexpanded jet form (with point sparks at the front), the second one is bright and spherical (without sparks), and the third one is dim and exhibits a striped pattern. In addition, the earlier the venting, the larger the average velocity of the external flame. With the opening pressure increasing, a decrease in the maximum propagation distance and time of the first venting flame is observed; simultaneously, the average flame velocity and the maximum instantaneous flame velocity increase. There is no such a phenomenon in secondary venting, although the flame brightness gradually decreases. Overall, the results may provide a theoretical basis for the safety design of explosion venting and further exploration of the explosion mechanism.
PubDate: 2021-09-01

• Modeling of an Electrothermal Explosion with Account for Changes in the
Thermoelectric Characteristics of a Gasless System

Abstract: This study describes the mathematical modeling of an electrothermal explosion (ETE) of a gasless system placed in the annular layer of a conductive product. The influence of a change in the thermoelectric characteristics of a sample on the implementation, thermal conditions, and heat patterns of an ETE are considered. Based on the results obtained, the previously established experimental result about the anomalous effect of the electric heating power on the parameters of an ETE of a mixture of titanium and soot powders is explained.
PubDate: 2021-09-01

• Synergistic Effects in Flames of Mixtures of Methane and Carbon Monoxide
with Air

Abstract: Numerical simulation has shown that replacing a part of methane by carbon monoxide in a rich mixture while maintaining the equivalence ratio leads to a decrease in the superadiabatic temperature effect due to the competition of chemical reactions. This is explained by a decrease in the H content in the combustible mixture and a decrease in the superequilibrium concentration of water in combustion products. Using numerical tracer simulation and a comparative analysis of the rates of consumption of CH4 and CO, it has been found that the consumption of both fuels in the CH4/CO/air flame is a competitive reaction path and CO monoxide does not act as an inert component in the low-temperature region of the front (contrary to the statements of a number of authors). Furthermore, the rate of consumption of CH4 is much higher than that of CO due to the larger number of consumption reactions of CH4 and their higher rates. The main contribution to the increase in the concentration of H atoms in the flame in passing from a methane–air mixture to a CH4/CO/air mixture is due to the same reactions that increase the heat release rate: O + CH3 = H + CH2O and CO + OH = CO2 + H. The results obtained and their comparison with literature data lead to the conclusion that the increase in the heat release rate and, hence, the flame propagation rate should be greater in rich mixtures since there the thermophysical effect is higher.
PubDate: 2021-09-01

• Combustion Modes of Mixtures of Copper (II) Oxide with Aluminum and
Titanium

Abstract: The influence of the ratio of the initial components on the combustion parameters and modes of mixtures of aluminum with copper oxide has been studied. It has been shown that under normal conditions, such mixtures can burn stably when they contain not less than 30% copper oxide. Moreover, with an increase in the content of copper oxide to the stoichiometric ratio, there is a regular change in combustion mode: self-oscillatory, spin, combined convective and multi-hotspot, flame, and fireball combustion modes. In addition, the effect of the ratio of the components on the combustion of copper oxide–aluminum–titanium ternary mixtures was studied, and concentration regions were determined for four main modes of their combustion: the self-oscillatory, hotspot, flame, and fireball modes. It has been shown that the hotspot combustion of such mixtures can proceed in five different modes: a spin mode, a multi-hotspot mode, a combined convective and multi-hotspot mode, a multi-hotspot mode with the formation of a counter front, and a multi-hotspot mode with periodic ejection of combustion products. Depending on the ratio of the initial components, the condensed combustion products of mixtures of copper oxide with aluminum and titanium were found to contain copper, Al3Ti, Ti3Al, and CuAl5Ti2 intermetallic compounds, and Al2O3, TiO2, TiO, Cu2O, Al2TiO5, and Cu3Ti3O oxides.
PubDate: 2021-09-01

• Reduced Kinetic Model for Complex Turbulent n-Heptane Flame Simulations

Abstract: In large-scale turbulent flame simulations, the exploitation of detailed chemistry and transport models often necessitates expensive memory and CPU requirements. To maintain the practicality and flexibility of such simulations, the combustion chemistry is commonly represented by reduced reaction mechanisms. The present paper describes the development of such a reduced short kinetic scheme for high-temperature oxidation of n-heptane suitable for application in complex turbulent flame simulations. Through a combination of the directed relation graph and quasi-steady state approximation methodologies, a skeletal 65-species kinetic model is formally reduced down to a 25-species derivative suitable for atmospheric lean to stoichiometric conditions. Further removal of appropriate reactions and species is facilitated by using the reaction path flux analysis, yielding a short chemical scheme of 25 species and 69 reactions. Particular attention is given to avoid addition of lumped reactions (for all isomer compounds) and artificial kinetic rates expressed as nonlinear algebraic combinations of excluded elementary steps. In addition, most of the original radical reaction pathways are duly preserved, and an adequate number of intermediate lighter-chain hydrocarbon species is represented in the reduced scheme to ensure a proper breakdown and oxidation of the main hydrocarbon. A series of 0D and 1D propagating and counterflowing premixed flames and axisymmetric coflowing laminar jet flames are computed throughout an iterative validation procedure. Complementary computations with the 65-species base scheme, as well as available experimental data are exploited for the assessment of the optimization effort. The comparisons demonstrate that the derived scheme ensures satisfactory agreement with these data over the investigated parameter space.
PubDate: 2021-09-01

• Prospects of Using Boron Powders As Fuel. III. Influence of Polymer
Binders on the Composition of Condensed Gasification Products of Model
Boron-Containing Compositions

Abstract: The effect of polymer binders on the thermal behavior, combustion, and composition of condensed gasification products of model boron-containing compositions was studied to determine the optimal fuel composition for the gas generator of a ducted rocket engine. The physicochemical transformations of boron particles during combustion wave propagation in a solid propellant and during the interaction with the decomposition products of oxidizer and binder were investigated. The binder components were oligodiene urethane and polyether urethane rubbers plasticized with various substances: phthalic acid dimethyl ester, transformer oil, and dioctyl sebacate. Samples of successively complicated composition with the same rubber-to-plasticizer ratio were studied. After thermal analysis of plasticizers and rubbers, plasticized binders and compositions of these binders with boron were investigated and the combustion parameters of model compositions obtained by adding a third component—ammonium perchlorate—were determined. It was found that the thermal decomposition of the more heat-resistant binder and the melt formation of boron oxide largely overlapped and proceeded simultaneously. Features of the combustion of compositions with various binders were identified by high-speed video recording. The composition and microstructure of condensed gasification products collected from the gas phase directly from the burning surface and those remaining in the form of a porous framework after combustion were studied in detail by electron microscopy and thermogravimetry. Based on a comparative analysis of experimental data, it is concluded that it is preferable to use plasticizers and rubbers with reduced thermal stability in inert binders for compositions with amorphous boron designed for gas generators of ducted rocket engines. The possibility of the formation of boron suboxide (B6O) crystals during combustion of boron-containing compositions is shown for the first time.
PubDate: 2021-09-01

• Sympathetic Detonation Reaction Behavior of a Fuze Explosive Train

Abstract: Insensitive munition assessments are required to carry out sympathetic detonation experiments, in which detonation of an explosive charge triggers detonation of another, and a chain reaction subsequency starts. In this paper, a numerical simulation method is developed to predict the sympathetic detonation behavior of fuze explosive trains, which includes the ignition and growth model, the Jones–Wilkins–Lee equations of state, and the constitutive relationship. The sympathetic detonation behaviors of a fuze is studied for a single donor and a single acceptor. The causes of sympathetic detonation of the fuze explosive trains are analyzed for different fragment and shock wave loading conditions. A sympathetic detonation criterion in different modes of loading is established, which provides a theoretical model for predicting the relationship between the detonation sequence and the placement distance of the fuze. The conclusions obtained in this paper can provide a reference for studying sympathetic detonation of fuze conditions.
PubDate: 2021-09-01

• Equation of State of Gas Detonation Products. Allowance for the Formation
of the Condensed Phase of Carbon

Abstract: A model of thermodynamics of a reacting mixture of rarefied gases and a suspension of condensed species is developed by using statistical physics methods. An NVT ensemble is considered for determining the detailed equilibrium chemical composition, and the minimum of the free energy of the mixture of possible species is found numerically. Tabular data for the species are used for determining the enthalpy and free energy of chemical compounds. An algorithm that allows the Chapman–Jouguet detonation parameters to be determined for a wide range of combustible mixtures is developed. The model is tested through comparisons of the predicted and experimental detonation velocities. Good agreement for mixtures with oxygen excess is demonstrated. For compositions with the formation of a significant amount of condensed carbon, the predicted and experimental detonation velocities agree reasonably well.
PubDate: 2021-09-01

• Gasification of Pulverized Fuel in a Filtration Combustion Reactor with a
Coolant Counterflow

Abstract: A stationary mathematical model is used to estimate the characteristics of gasification of pulverized fuel in a filtration combustion reactor with a coolant counterflow are estimated. The high efficiency of the gasification method under study is established. The movement of the coolant toward the flow of gaseous products makes it possible to recuperate a significant part of the thermal energy released, which has a significant effect on the temperature and composition of combustion products. It is shown that the gasification characteristics can be purposefully changed by varying three main parameters: air flow rate, steam flow rate, and coolant flow. As an example, the dependences of the main gasification characteristics (combustion temperature, product composition, and process efficiency) on control parameters are calculated. Calculations make it possible to estimate possible modes and select an optimal set of control parameters for gasification.
PubDate: 2021-09-01

• Combustion Modes of Mixtures of Nickel (II) Oxide with Titanium

Abstract: The effect of the ratio of the components of mixtures of nickel (II) oxide with titanium on the combustion modes and burning rate of compositions based on them is studied. It is found that under normal conditions, a change in the mass content of nickel oxide from 75 to 30% leads to a regular change in combustion mode: a flame, a multi-hotspot mode, and a self-oscillating mode with a periodic separation of combustion products from the burning surface. It is shown that the maximum burning rate of such mixtures (82 mm/s) is achieved at equal mass proportions of nickel oxide and titanium. In the condensed combustion products of a mixture of nickel oxide with titanium, Ti2Ni intermetallic and Ni2Ti4O $$_{x}$$  binary oxide were identified.
PubDate: 2021-07-01

• Simulation of Synthesis of Matrix–Inclusion Composite Materials
during Combustion

Abstract: A model for synthesizing a composite during combustion is proposed and numerically investigated. It is assumed that a set of chemical conversions can be described by a kinetic scheme with two total parallel reactions. One of the reactions corresponds to the matrix synthesis, and the other one to the inclusion synthesis. It is taken into account that the mixture components melt in a certain temperature range rather than at a fixed melting point. The possibility of the reaction front propagation in a self-oscillating mode is shown. The critical values of the parameters that separate the stationary and self-oscillating modes of the reaction front propagation are revealed. Computational results in limiting cases correspond to known theoretical concepts.
PubDate: 2021-07-01

• Flame Spread over a Liquid Fuel Film on a Low-Thermal-Conductivity
Substrate

Abstract: The spread of a flame over the surface of a liquid fuel on a substrate with low thermal diffusivity is studied. It is shown that the fuel–substrate system is not thermally thin. Heat transfer ahead of the flame edge due to the motion of the liquid under the temperature gradient in the liquid layer (the Marangoni effect) is analyzed. The temperature gradients in the condensed phase and the thickness of the liquid fuel layer ahead of and under the flame front are given. The velocity of the fuel diffusion flow in the gas phase at the flame edge is estimated. It is shown that the temperature gradient along the surface of the liquid film determines the velocity of the film and the rate of diffusion of the evaporated fuel to the flame edge.
PubDate: 2021-07-01

• Shock Compression of Titanium Hydride and Titanium, Tantalum, and
Zirconium Deuterides

Abstract: This paper presents the results of an experimental study of shock compression of titanium hydride (TiH2) and the deuterides of zirconium (ZrD2), tantalum (TaD0.8), and titanium (TiD2, TiD1.6, and TiD1.1) in the pressure range 30–220 GPa. The synthesis of titanium and zirconium deuterides from titanium and zirconium powders and tantalum deuterides from tantalum rods is described. Experiments to determine the Hugoniots of deuterides and hydrides were performed using the well-known reflection method. Shock-wave generators with explosive charges of different power were used for compression of samples. A description of the obtained experimental data using simple equations of state is proposed.
PubDate: 2021-07-01

• Block Diagram of Chemical Transformation in an Fe2O3/Al/AlN Wave
Combustion in Nitrogen

Abstract: The stages of chemical transformation in the combustion wave of an Fe2O3/Al/AlN exothermic mixture in nitrogen atmosphere is studied using an original method for stopping a combustion front. It is revealed that, in an Fe2O3/6Al stoichiometric mixture diluted with 35% (wt.) AlN, the combustion front is stopped following the combustion of a (30–40)-mm mixture column. The zones of a stopped combustion wave are investigated by the local analysis methods. It is shown that the alumothermal reduction of iron (III) oxide to iron aluminide proceeds in stages via the formation of a (FeAl) $$_{x}$$ O $$_{y}$$  double oxide of varying chemical composition. The final synthesis products include aluminum oxynitride, iron aluminide, and unreacted aluminum nitride.
PubDate: 2021-07-01

• Modal Stability of a Cylindrical Flame Front in an Annular Combustion
Chamber in the Presence of Entropy Waves

Abstract: An initial (linear) stage in the development of rotating transverse detonation waves in a flat-radial annular combustion chamber is determined and simulated. The problem of linear modal stability of the cylindrical front of Chapman–Jouguet deflagration combustion in a radially diverging subsonic flow with a small Mach number in the presence of perturbation waves of the flow entropy is solved. The steady flame front is described by discontinuity of the gas-dynamic parameters provided that the combustion products are in chemical equilibrium. It is revealed that the flame front is unstable for some types of small perturbations of the main flow of the combustible mixture and the flame front. Instability is determined under the condition of a constant flow rate in the mixture injection system. The spatial forms of oscillations and perturbation waves of the combustion front in the annular combustion chamber are obtained by numerical and analytical methods.
PubDate: 2021-07-01

• Modeling of Ignition and Combustion of a Coflowing Hydrogen Jet in a
Supersonic Air Flow

Abstract: Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a supersonic (M = 2) flow of an inert gas mixture/humid hot air are reported. The computations are performed with the use of the ANSYS CFD Fluent commercial software by means of solving transient Favre-averaged Navier–Stokes equations supplemented with the $$k$$ – $$\omega$$ SST turbulence model and several kinetic schemes of hydrogen combustion. Two single-step schemes and three detailed kinetic schemes including 16, 38, and 37 forward and backward reactions are considered. The goal of the study is to choose a computation method and kinetic mechanism that ensure good agreement with experimental data on supersonic combustion of a coflowing hydrogen jet. In the case of a non-reacting flow, it is demonstrated that the computational algorithm can accurately predict the parameters of mixing of the hydrogen jet and external flow. In the case of a reacting flow, the flow characteristics are significantly affected by large vortex structures developing at the interface between the combustion layer and the external flow. If the flow unsteadiness is taken into account and a detailed kinetic scheme with 37 reactions is used, good agreement of the mean characteristics of the flow with experimental data on the distributions of pressure, temperature, Mach number, and species concentrations at the combustor exit is provided.
PubDate: 2021-07-01

• Numerical Simulation of Fracture of Titanium and Aluminum Nanocrystals by
the Molecular Dynamics Method

Abstract: Results of numerical simulations of fracture of titanium and aluminum nanocrystals by the molecular dynamics method are reported. The nanocrystals are subjected to uniaxial tension in a wide temperature range (300–1270 K). It is demonstrated that tension of titanium nanocrystals heated to temperatures above 0.7 of the melting temperature in a non-stressed nanocrystal first leads to a phase transition from the crystalline to liquid state, followed by fracture. This effect is not observed in the case of tension of the aluminum nanocrystal.
PubDate: 2021-07-01

• Mathematical Simulation of Volume and Gasless Wave Combustion in a Hybrid
Mixture of Activated and Inactivated Powders

Abstract: Mathematical models constructed in the macroscopic approximation are used to perform a theoretical study of volume and wave synthesis in a hybrid mixture consisting of nonactivated and activated powders of the same composition. Synthesis dynamics depending on the fraction of activated powder at different values of the preliminary mechanical activation parameters is considered. Analytical formulas are obtained for approximate estimates of the temperature and time of synthesis in nonactivated and activated compositions.
PubDate: 2021-07-01

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