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2015 year, number 4

On the Boundaries of the Transitional Regime of Mass Transfer during Ethanol Combustion on Horizontal Rear Walls of a Rib and a Step

B. F. Boyarshinov
Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: mass transfer, flame blow-off, laminar--turbulent transition, combustion, boundary layer
Pages: 401408

Abstract >>
Mass transfer in the boundary layer on the surface behind a rib and a backward-facing step during combustion of evaporating ethanol on the horizontal top and bottom walls of the channel is studied. It is shown that there are two values of the air flow velocity at which flame blow-off occurs for each configuration. For a backward-facing step 3 mm high, two critical combustion modes are observed near the boundaries of the laminar-turbulent transition region. For a rib and for a backward-facing step, flame blow-off may occur at a low velocity of the air flow 6 m/s) if the flow regime approaches or deviates from the laminar mass transfer mode. At elevated velocities of the air flow (19 m/s in experiments with a backward-facing step), flame blow-off is induced by the change from the transitional to turbulent mass transfer mechanism.


Numerical Simulation of Ignition of Particles of a Coal-Water Fuel

G. V. Kuznetsov1, V. V. Salomatov2, S. V. Syrodoy1
1Tomsk Polytechnic University, Tomsk, 6340050 Russia
2Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: hydrocarbon fuel, ignition, vaporization, thermal decomposition, filtration, volatiles, ignition delay
Pages: 409415

Abstract >>
The problem of particle ignition of coal-water fuel has been solved. The simultaneous processes of water vaporization and thermal decomposition of the solid fuel are taken into account. The conditions and characteristics of particle ignition of coal-water fuel under typical furnace conditions were determined by numerical simulation. The obtained values of the ignition delay time are in good agreement with published experimental data.


Measurements of the Visible Flame Height of a Swirl-Stabilized Kerosene Jet Diffusion Flame

S. K. Birwa, D. P. Mishra
Indian Institute of Technology, Kanpur, 208016 India
Keywords: kerosene, spray combustion, design of experiments, momentum flux ratio, pressure swirl atomizer
Pages: 416423

Abstract >>
An experimental investigation of the structure of a kerosene-based Jet A1 unconfined flame is conducted for different fuel flow rates and momentum flux ratios (MFRs). A pressure swirl atomizer is used to atomize the fuel jet. It is found that the flame height increases with increasing MFR for a fixed fuel flow rate. However, the flame height first decreased and then increased with increasing fuel flow rate for a fixed MFR. A correlation of the flame height with the power level and MFR is developed in a dimensionless form by using the response surface optimal design method. Variations in the lean blowout limit with the fuel flow rate are also studied. The lean blowout limit first increases to a peak value and then subsequently decreases, in agreement with the behavior of the flame height at the lean blowout limit. A blue region at the top of the flame is observed for high fuel flow rates. The flame characteristics obtained in the study are explained with the help of the spray characteristics of the kerosene fuel.


Influence of Flow Swirling on the Aerothermodynamic Behaviour of Flames

M. T. Parra-Santos1, V. Mendoza-Garca2, R. Szasz3, A. N. Gutkowski4, F. Castro-Ruiz1
1University of Valladolid, 47011 Valladolid, Spain
2University of Tarapac
3Lund University, 22100 Lund, Sweden
4Lodz University of Technology, 90924 Lodz, Poland
Keywords: reactive flow, recirculation zone, CFD, swirling flows, stretched flames
Pages: 424430

Abstract >>
The present work focuses on the numerical simulation of diffusive flames in a confined high-swirl burner. Navier-Stokes equations expressed for a time-dependent, compressible, and three-dimensional flow with finite-rate kinetics are solved for lean methane/air mixtures. A simplified mechanism is used to model the combustion. Non-reactive and reactive cases are contrasted for a swirl number of 0.95. Three flames for swirl numbers of 0, 0.6, and 0.95 are analyzed. In swirling flows, the inner recirculation zone is mainly composed of reaction products, which help in ignition of the incoming fuel. Moreover, the forward stagnation point plays an important role, leading to an azimuthal deflection of the flame front.


Physicomathematical Modeling of Ignition and Combustion of Silane in Transient and Reflected Shock Waves

D. A. Tropin, A. V. Fedorov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: silane-hydrogen-air mixture, ignition delay time, detailed chemical kinetics, mathematical modeling
Pages: 431438

Abstract >>
A model of nonequilibrium gas dynamics is proposed to describe ignition and combustion of a mixture of silane, hydrogen, oxygen, and an inert gas (nitrogen or argon). The model is based on detailed chemical kinetics of nonequilibrium chemical reactions. The model adequately describes the behavior of experimental data on the ignition delay time for this mixture versus the temperature behind the reflected shock wave in accordance with three criteria of ignition. The detonation wave velocity and equilibrium parameters of the mixture (pressure and temperature) are calculated as functions of the fuel-oxidizer equivalence ratio. Based on the dependences of the ignition delay time on the temperature behind the reflected shock wave calculated by this model, an approximation formula for the silane-oxygen-nitrogen/argon is derived.


Combustion of Chemical Transformations in Thermite Systems with Two Active Reducing Agents

V. I. Yukhvid, P. A. Miloserdov, N. V. Sachkova, V. A. Gorshkov
Institute of Structural Macrokinetics and Materials Sciences, Russian Academy of Sciences, Chernogolovka, 142432 Russia
Keywords: combustion, SHS, auto-wave synthesis, parallel reactions, thermite mixtures, refractory oxides
Pages: 439443

Abstract >>
The combustion and chemical transformation of a Fe2O3/Al/Zr mixture has been studied. From the results of thermodynamic calculations and experiments, it has been found that the ratio of Al and Zr affects the phenomenology and features of the combustion and the composition of cast combustion products. The range of obtaining oxide materials (Al2O3 and ZrO2) is determined. A qualitative model for the combustion of thermite systems with two parallel reactions is proposed.


Firmation of Condensed Combustion Products in Dust Flames of Metals: Coagulation Stage

N. I. Poletaev
Mechnikov Institute of Combustion and Nonconventional Technologies of Odessa National University, Odessa, 65082 Ukraine
Keywords: metal dust flames, coagulation kinetics, thermal ionization of flame, ionized additives, nanoparticles of metal oxides
Pages: 444456

Abstract >>
The coagulation dynamics of condensed products of vapor-phase or gas-phase combustion of gas mixtures of microdispersed metal particles in dust laminar flame considered taking into account the ionization of the combustion zone due to additives of electronegative and electropositive atoms and due to thermionic emission. The influence of the degree of ionization of a monodisperse coagulating aerosol and the charge of the particles on the coagulation rate constant is studied. It is shown that the rate of coagulation of the aerosol is most significantly affected by the Coulomb interaction of like-charged condensed-phase particles, which, under certain conditions, leads to an early stop of this stage in the condensation of combustion products. Ionization of the coagulating particles gives rise to a dependence of the size of primary particles of combustion products on the environmental parameters affecting their electric charge, and can be used for targeted control of the degree of dispersion of the combustion products.


Combustion of TiAl Alloy in Nitrogen

B. Sh. Braverman, O. K. Lepakova, Yu. M. Maksimov, Yu. V. Tsybul'nik, V. D. Kitler
Department of Structural Macrokinetics, Tomsk Scientific Center, Russian Academy of Sciences, Tomsk, 634021 Russia
Keywords: self-propagating high-temperature synthesis, forced filtration, nitrides, MAX-phases
Pages: 457461

Abstract >>
It has been shown that Ti-Al-N ternary compounds, belonging to MAX phases (ceramic materials that can be processed as metals) can be produced by combustion of a granular powder of T65Yu35 (TiAl) alloy in nitrogen flow at a pressure close to atmospheric pressure. Combustion is accompanied by transfer of part of the aluminum through the gas phase. The propagation velocity of the combustion zone and the maximum temperature increase with increasing flow rate.


Combustion and Thermal Decomposition of Hydrazine Borane

G. B. Manelis, V. V. Zakharov, G. N. Nechiporenko, V. A. Strunin, A. V. Raevskii, V. V. Yakovlev
Institute of Problems of Chemical Physics, Chernogolovka, 142432 Russia
Keywords: hydrazine borane, combustion, kinetics
Pages: 462466

Abstract >>
Burning rates of hydrazine borane at a pressure of 20-100 atm have been measured. Spectroscopic and electron microscopic studies have demonstrated that the condensed combustion product is a fine powder of boron nitride. Thermal decomposition of hydrazine borane has been studied. The obtained kinetic data and physicochemical properties of the materials and the foam combustion model have been used to calculate the pressure dependence of the burning rate of hydrazine borane, which agrees with the experimental one. The obtained degree of conversion of the material to boron nitride indicates the possibility of using hydrazine borane and similar compounds in high-performance systems.


Effect of the Time of Mechanical Activation of a Ti + 2B Mixture on Combustion of Cylindrical Samples and Thin Foils

N. A. Kochetov, S. G. Vadchenko
Institute of Structural Macrokinetics and Material Science Problems, Russian Academy of Sciences, Chernogolovka, 142432 Russia
Keywords: SHS, mechanical activation, combustion mechanism, burning rate, convective-conductive model of combustion
Pages: 467471

Abstract >>
The effect of the activation time of the Ti + 2B mixture on the burning rate of cylindrical samples and thin foils is studied. For cylindrical samples, combustion of samples activated in argon is compared with combustion of samples activated in air. The burning rates are almost identical in these two cases. It is demonstrated that the burning rate of cylindrical samples continuously increases with increasing activation time. The burning rate of thin foils remains almost unchanged as the activation time increases up to 4 min and then drastically increases and reaches a value twice greater than the burning rate of cylindrical samples. For the titanium and boron powders used in this study, the time needed to reach the maximum burning rate is 7 min in the case of activation in air and 5 min in the case of activation in argon; if the activation time is longer, then the product of combustion is formed. The features of combustion observed in this study can be explained from the viewpoint of convective-conductive model of combustion wave propagation.


Influence of the Size of Inclusions of Ultrafine Nickel Particles on the Laser Initiation Threshold of PETN

B. P. Aduev, D. R. Nurmukhametov, A. A. Zvekov, I. Yu. Liskov
Institute of Coal Chemistry and Chemical Materials Science, Siberian Branch, Russian Academy of Sciences, Kemerovo, 650000 Russia
Keywords: laser, PETN, nanoparticles, extinction coefficient
Pages: 472475

Abstract >>
We investigated the probability of explosion of tetranitropentaerythrite (ρ = 1.73 g/cm3) containing 0.1% (by weight) ultrafine nickel particles of size 270-300 and 140-175 nm at the distribution maxima depending on the energy density of the initiating laser pulse (1064 nm, 14 ns). In the first case, the critical energy density corresponding to a 50% the probability of explosion was 1.4 J/cm2, and in the second case, 0.7 J/cm2. Dependences of the light absorption cross section and the absorption coefficient on the inclusions particle size were calculated using the microhotspot theory of laser ignition. The calculation results are consistent with the microhotspot model of the initiation of thermal explosion.


Instability of a Detonation Waves in Nitromethane and FEFO

A. V. Utkin1,2, V. M. Mochalova1,2, S. I. Torunov1, S. A. Koldunov1
1Institute of Problems of Chemical Physics, Chernogolovka, 142432 Russia
2Tomsk State University, Tomsk, 634050 Russia
Keywords: detonation, instability of detonation front, waves of reaction failure, pulsations of detonation front, nitromethane, FEFO, nitromethane/diethylenetriamine mixture
Pages: 476481

Abstract >>
The stability of detonation waves in nitromethane and FEFO was studied in experiments using a VISAR laser interferometer and an SFR high-speed photorecorder. It is shown that the relationship between various types of instability of the detonation front in liquid explosives is not strictly deterministic. Waves of reaction failure exist in the case of a stable detonation front (no cellular structure) and are absent in the case of an unstable detonation front.


Electrical Resistance of High-Pressure Phases of Tin under Shock Compression

S. D. Gilev, V. S. Prokop'ev
Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: tin, phase transition, shock compression, electrical resistance, melting
Pages: 482487

Abstract >>
The normalized electrical resistance R/R0 of tin for different pressures of shock compression p is measured. The resultant dependence R/R0(p) differs significantly from the known dependences for static and quasi-isentropic compression and demonstrates the growth of the electrical resistance with increasing pressure. The dependence has an inflection testifying to a phase transition. The inflection corresponds to pressures of 4.7-5.3 GPa in the dielectric embracing a thin sample and to pressures of 8.4-9.6 GPa in the first shock wave. The latter parameters qualitatively agree with the characteristics of the phase transition β-n → γ-n. The first shock wave in tin determines the final electrical resistance of the sample after wave reverberation. The experimental data obtained in this study are indicative of the kinetic behavior of the electrical resistance in the transition β-n → γ-n, which is accompanied by generation of crystalline structure defects with a characteristic time greater than 1 μs. A drastic increase in the electrical resistance of the sample in the expansion wave is observed. This increase is attributed to tin melting.


Air Explosion Characteristics of a Novel TiH2/RDX Composite Explosive

B. Xue, H.-H. Ma, Z.-W. She
Modern Mechanics Department, University of Science and Technology of China, Hefei, Anhui, P.R. China
Keywords: titanium hydride, RDX, composite explosives, air explosion, particle size
Pages: 488494

Abstract >>
An explosive mixture of cyclotrimethylenetrinitramine (RDX) and titanium hydride (TiH2) is introduced. To investigate the explosion characteristics of the composite explosive, charges with various contents of the TiH2 powder are prepared and tested in air explosion experiments. Results show that the peak overpressure, positive duration, and positive specific impulse increase as the content of TiH2 increases from 10 to 20%, as compared to passivated RDX. The peak overpressure, duration, and specific impulse have the largest increase of 6, 9, and 23%, respectively, as compared to passivated RDX, when the TiH2 content is 20%. The effect of the TiH2 particle size is also considered. The charge containing the TiH2 powder with a mean particle size of 4.6 mm shows higher values of the three parameters than that containing 45-mm TiH2 particles under the condition of the same content of TiH2. However, the relationship between the detonation velocity and TiH2 content is a linear inverse proportion, and the particle size of TiH2 has a minor effect on it. Solid explosion products of the TiH2/RDX composite explosive are analyzed by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX). TiO2 is found in explosion products, which is believed to form due to TiH2 oxidation.


Hydrogen and Air Detonation (Deflagration) Synthesis of Carbon-Encapsulated Iron Nanoparticles

H. Yan, T. Zhao, X. Li, Ch. Hun
State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, Liaoning 116024, China
Keywords: gaseous detonation, carbon-encapsulated iron nanoparticles, detonation tube, hydrogen, air
Pages: 495501

Abstract >>
With ferrocene as a precursor, carbon-encapsulated iron nanoparticles are synthesized through detonation of a gas mixture of hydrogen and air in a titanium detonation tube. XRD and TEM characterization shows that a downward trend in the size of particles can be observed with increasing amounts of the precursor. However, no further decrease occurs when the size of nanoparticles reaches approximately ≈40 nm, after which they remain in the range of 30−50nm. The initial temperature of the detonation tube at 353 K is the optimal initial temperature for the synthesis. The average grain size of the synthesized products becomes larger as the temperature of detonation increases.


Smoothed Particle Hydrodynamics Simulation of the Submarine Structure Subjected to a Contact Underwater Explosion

Z. Zhang, L. Sun, X. Yao, X. Cao
College of Shipbuilding and Ocean Engineering, Harbin Engineering University, 150001 Harbin, China
Keywords: damage characteristics, contact underwater explosion, cylindrical shell, SPH method, water interlayer
Pages: 502508

Abstract >>
In this paper, a modified smoothed particle hydrodynamics (SPH) formula is deduced to solve the problem of interfaces with a high density ratio. Simplified SPH models for single and double cylindrical shells (abbreviated as single-hull and double-hull models, respectively) are established to study shock wave propagation and to conduct the damage analysis. The SPH results for the single-hull model are verified by AUTODYN. In addition, the damage analysis indicates that the single-hull model is damaged more severely than the double-hull model. The inner shell in the double-hull model is protected by a water interlayer.