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Combustion, Explosion and Shock Waves

2015 year, number 6

Numerical Study of the Combustion Chemistry of Fuel-Rich Mixtures of Formaldehyde and Air

V. M. Shvartsberg, V. A. Bunev, V. S. Babkin
Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: формальдегид, скорость распространения пламени, химия горения, численное моделирование, formaldehyde, flame speed, combustion chemistry, numerical modeling

Abstract >>
The combustion chemistry of formaldehyde in fuel-rich flames has been studied by numerical modeling and sensitivity analysis. It has been shown that the wide flammability limits of CH2O air mixtures are due to features of the combustion chemistry of formaldehyde at high equivalence ratios rather than to the superadiabatic temperature effect. In this case, the thermal decomposition reaction of hydrogen peroxide H2O2 plays a key role in the conventional branching reactions.

Combustion in Vortex Chambers with a Fluidized Particle Bed

N. A. Dvornikov
Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: вихревая камера, закрученный поток, псевдоожиженный слой, горение, vortex chamber, swirling flow, fluidized bed, combustion

Abstract >>
This paper is devoted to methods of estimating the combustion regimes of gaseous fuel in vortex chambers of various designs in the presence of a bed of inert particles in the chamber, which rotate with the gas flow. A simple geometric criterion for determining the possibility of fuel combustion in the particle bed without the formation of a flame above the bed is proposed.

Laminar Flame in Polydisperse Aerosuspensions of Aluminum Particles

A. S. Oparin, A. E. Sidorov, V. G. Shevchuk
Odessa National University, Odessa, 65082 Ukraine
Keywords: ламинарное пламя, нормальная скорость, полидисперсность, алюминий, laminar flame, normal velocity, polydispersity, aluminum

Abstract >>
This work is an experimental and theoretical study of the dependence of normal flame velocity in polydisperse aerosuspensions of aluminum particles on the parameters of the particle size distribution function. It is shown that the velocity decreases with increasing dispersion of the distribution function as a result of reduction of the specific reaction surface.

Thermal Explosion in a Binary Homogeneous Mixture

V. Yu. Filimonov1, K. B. Koshelev2
1Polzunov Altai State Technical University, Barnaul, 656038 Russia
2Institute of Water and Ecological Problems of the Russian Academy of Sciences, Barnaul, 656038 Russia
Keywords: саморазогрев, фазовые траектории, тепловой взрыв, бинарные смеси, вырождение, критические условия, self-heating, phase trajectories, thermal explosion, binary mixtures, degeneration, critical conditions

Abstract >>
Self-heating processes in binary homogeneous mixtures are studied based on the analysis of phase trajectories on the heating rate–temperature plane. The proposed approach allows determining the characteristic regions of exothermic reactions in the parametric diagram of the Todes criterion versus the Semenov criterion. Generalized strict criteria for the degeneration of thermal explosion are determined for reactions with low activation energy and reactions with a low thermal effect for any reaction orders. An approximating formula describing the dependence of the Todes criterion on the Semenov criterion is derived for calculating the critical conditions of thermal explosion up to its complete degeneration for reaction orders higher (or equal to) one. A criterion for the applicability of the classical thermal explosion theory as a special case of the proposed model is found. A diagram of the critical parameters in the introduced new variables is considered to predict and control the self-heating kinetics of mixtures.

Combustion of Iron Aluminum Thermite with Ammonium Chloride and Sodium Hydrogen Tarbonate

S. L. Silyakov, V. I. Yukhvid
Institute of Structural Macrokinetics and Materials Sciences, Russian Academy of Sciences, Chernogolovka, 142432 Russia
Keywords: железоалюминиевый термит, добавка соли, скорость горения, концентрационный предел, оксидная и металлическая фазы, iron aluminum thermite, addition of salt, combustion velocity, concentration flammability limit, oxide and metallic phases

Abstract >>
The effect of sodium hydrogen carbonate and ammonium chloride on the combustion of iron aluminum thermite in air at atmospheric pressure is experimentally studied. The effect of salt additives on the average linear velocity of combustion, the relative yield of the metallic phase in the ingot, and the relative weight loss during thermite combustion are investigated. The concentration flammability limits of the mixtures under consideration are determined.

Convective Combustion in the Slot of an Explosive Charge

L. A. Andreevskikh, S. A. Vakhmistrov, D. A. Pronin, E. V. Khaldeev, Yu. V. Sheikov
Institute of Experimental Physics, Sarov, 607190 Russia
Keywords: взрывчатое вещество, конвективное горение, термораспад, манометрическая бомба, заряд, детонация, explosive, convective combustion, thermal decomposition, constant-volume chamber, charge, detonation

Abstract >>
This paper presents the results of a study of the transition from layer-by-layer to convective combustion and to explosion for charges of advanced high-density explosives in a constant-volume chamber at a pressure of up to ≈60 MPa. Approximation of the results of the experiments with good correlation revealed a common parameter for explosives that characterizes the kinetics of convective combustion and made it possible to rank explosives according to their capability of transition from combustion to explosion. The results can be useful for computational modeling of explosion under accidental heating conditions.

Numerical Simulation of the Extinction of N Powder by a Pressure Drop Based on a Coupled Combustion Model

A. Yu. Krainov, V. A. Poryazov
Tomsk State University, Tomsk, 634050 Russia
Keywords: порох Н, скорость горения, сброс давления, погасание, N powder, burning rate, pressure drop, extinction

Abstract >>
This paper presents a physicomathematical model for the combustion of N powder which takes into account chemical reactions in the condensed and gas phases. On the burning surface, boundary conditions (coupling conditions) are specified. Results of calculation of the burning rate of N powder at constant pressure are in good agreement with available experimental data. The extinction of combustion of N powder by a sharp pressure drop pressure is simulates. Calculations of the boundary values of the degree and rate of pressure drop at which extinction of N powder occurs are in good agreement with published data of measurements.

Study of the Combustion Behavior and Kinetics of Different Types of Coal Gangue

Yu. Zhang, J. Li, F. Cheng, Ya. Guo
Shanxi University, Taiyuan 030006, Shanxi Province, PR China
Keywords: пустая угольная порода, характеристики горения, кинетические константы, coal gangue, strategy selection, combustion characteristics, kinetic constants

Abstract >>
Three types of coal gangue are compared systematically. The burnout index and the comprehensive combustibility index are found to increase significantly as the ash content decreases. The Arrhenius activation energy is obtained by using the Ozawa–Flynn–Wall and Vyazovkin models.

Shock Wave Structure in a Heterogeneous Medium with Two Pressures

A. V. Fedorov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: смесь газа и твердых частиц, давление фазы частиц, структура ударной волны, замороженные и дисперсионные ударные волны, mixture of a gas and solid particles, particle phase pressure, shock wave structure, frozen and disperse shock waves

Abstract >>
The shock wave motion of a mixture of a gas and fine solid particles is considered with allowance for the difference in velocities and the particle phase pressure, which is described by Anderson-type and other equations. Various forms of the equation of state for the particle phase are described. Graphical illustrations are given for the equation determining the composite type of this model with the particle phase pressure being neglected. Under certain assumptions, the complete model can be reduced to a hyperbolic system of equations. Types of shock waves formed in such a mixture are determined for this system of equations. The statements are illustrated by results of numerical simulations.

Effect of Combustor Geometry on Continuous Spin Detonation in Syngas—Air Mixtures

F. A. Bykovskii, S. A. Zhdan, E. F. Vedernikov, A. N. Samsonov
Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: непрерывная спиновая детонация, синтез-газ, воздух, поперечные детонационные волны, камера сгорания, структура течения, continuous spin detonation, syngas, air, transverse detonation waves, combustor, flow structure

Abstract >>
Regimes of continuous detonation burning of syngas–air mixtures in transverse (spinning) detonation waves in a flow-type annular cylindrical combustor are considered. Mixtures of carbon oxide and hydrogen in proportions of 1/1, 1/2, and 1/3 are used. The varied parameters are the combustor geometry and the fuel injection system, as well as the flow rates of air and syngas. The influence of additional supply of air to the products on the detonation wave parameters, pressure in the combustor, and specific impulse is determined. The range of realization of continuous spin detonation of the syngas–air mixture in terms of specific flow rates of the mixture is expanded from 25 to 786 kg/(s⋅m2). It is shown that additional supply of air increases the pressure in the combustor, the thrust, and the number of detonation waves, but decreases the detonation wave velocity. The flow structure in the domain of detonation waves is studied. For some values of the combustor expansion coefficient, a chart of detonation regimes in the coordinates of the fuel–to–air equivalence ratio and specific flow rate of air is constructed, and the specific impulse of the thrust force is calculated.

Physical Mechanisms of High-Enthalpy Initiation

A. P. Ershov, A. O. Kashkarov, E. R. Pruuel
Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: детонация, инициирование, конвективное горение, переход горения в детонацию, двухфазные среды, detonation, initiation, convective combustion, deflagration-to-detonation transition, two-phase media

Abstract >>
Injection of a hot gas flow produced by an external source into a powdered explosive allows very fast (within a few microseconds) deflagration-to-detonation transition. Under this high-enthalpy initiation conditions, the process begins with the stage of convective combustion, and the initial velocity of the wave is about 1 km/s. The combustion kinetics known from the literature does not provide the observed rapid development of the process. Various mechanisms of acceleration of the reaction are considered. Results of calculation for a two-phase gas-dynamic model are compared with data of synchrotron diagnostics (set of density profiles in the wave).

Some Aspects of Recording and Interpretation of Rotating Detonation Waves

A. A. Vasil'ev
Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: спиновая детонация, поперечная волна, детонационный двигатель, вращающаяся детонация, геометрическая акустика, spin detonation, transverse wave, detonation engine, rotating detonation, geometric acoustics

Abstract >>
Some important aspects of rotating detonation waves are discussed: specific features of recording and interpretation of trajectories of rotating transverse waves onto a moving film, relationship between the acoustic velocity of reaction products and the velocity of rotation of transverse waves, energy release and deficit of velocity of a rotating detonation wave, and multifront structure of rotating transverse waves.

Diaphragm Effect on the Detonation Wave Transmission Across the Interface between Two Mixtures

J.-M. Li1, K.-M. Chung2, Y.-C. Hsu2
1National University of Singapore, 119077 Singapore
2National Cheng Kung University, 711 Tainan, Taiwan
Keywords: переход горения в детонацию, детонация, распространение через границу смесей, диафрагма, пропан/кислород, deflagration-to-detonation transition, detonation, transmission across the interface, diaphragm, propane-oxygen

Abstract >>
An experimental study is conducted to investigate the effect of the diaphragm thickness on the transmission of an incident detonation wave from a propane–oxygen mixture (donor) to a propane-air mixture (acceptor). Quenching of the incident detonation wave near the interface is observed for all test cases. The presence of a diaphragm results in a longer distance required for re-initiating the detonation wave in the acceptor. In the presence of a diaphragm with a thickness smaller than 50 μm, the velocity of detonation wave propagation approaches that of the test case with a slide gate valve (no diaphragm).

Shock-Wave Processes in Wire Explosion in Water and Bubbly Media

I. I. Kochetkov, A. V. Pinaev
Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: электрический взрыв проволочки, плазменный пузырь, ударная волна, скорость звука, жидкость, пузырьковая среда, пузырьковая детонация, electrical wire explosion, plasma bubble, shock wave, sound velocity, liquid, bubbly medium, bubble detonation

Abstract >>
The structure of unsteady shock waves and bubble detonation waves generated by electrical explosion of a wire in water and chemically inert and reactive bubbly media was studied at a capacitor energy storage of 8÷81 J. The formation and expansion of a plasma bubble after wire explosion in water and bubble media was investigated using optical recording. The formation of cavitation zones and the breakdown characteristics of the liquid and bubbly media in short strong shock waves were established. It is proved that the initiation of bubble detonation by wire explosion occurs by a resonance shock–wave mechanism. A comparative frequency Fourier analysis of shock waves in an inert bubble medium and bubble detonation waves was performed.

Yield Stresses in a Ductile Metal at a High Strain Rate in Different Stress States

S.-W. Zhang, C.-L. Liu, G.-W. Ren, Q.-Z. Li
Institute of Fluid Physics, CAEP, P.O.BOX 919-101, fsp Mianyang, Sichuan, P. R. China
Keywords: предел текучести, упругий предвестник, высокая скорость деформирования, yield stress, elastic precursor, high strain rate

Abstract >>
The amplitudes of the elastic precursor in LY12 Al-based alloy samples under different pre-stress states are obtained. Even though the material does not undergo a brittle-to-ductile transition, the amplitude of the elastic precursor still increases with pre-compression. It is demonstrated that the amplitude of the elastic precursor is not only related to the yield stress, but also to the stress state. A method for obtaining a more accurate yield stress of materials under both uniaxial strain and uniaxial stress conditions is presented.