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2016 year, number 1

1.
High Speed OH PLIF Applied to Multiphase Combustion (Review)

T. D. Hedman, K. Y. Cho, M. A. Pfeil, A. Satija, H. C. Mongia, L. J. Groven, R. P. Lucht, S. F. Son
Purdue University, West Lafayette, Indiana 47906, USA
Keywords: плоскостная лазерно-индуцированная флюоресценция, многофазное горение, композитное топливо, капля горючего, гелеобразное горючее, planar laser-induced fluorescence, multiphase combustion, composite propellant, fuel droplet, gelled propellant

Abstract >>
Multiphase reactive systems can exhibit highly dynamic combustion phenomena that could be better understood by using recently developed high-repetition-rate optical diagnostic and imaging approaches. Here, we present an overview of recent activities using high-speed (5 kHz) OH planar laser-induced fluorescence to visualize and make measurements in several multiphase reactive systems. This technique is used to visualize the dynamically changing OH concentration in the gas phase near the surface of solids, liquids, and gels. In addition to gas-phase OH imaging, condensed phases of various solid propellants, gels, and liquids are found to fluoresce when exposed to the laser radiation centered at 283.2 nm. Simultaneous imaging of condensed phases and gas-phase OH radical fluorescence has proven to be particularly useful for various measurements, and several examples are presented.



2.
Combustion of Methane Injected into an Air Flow with High Subsonic Velocities by Different Methods

R. V. Albegov, V. A. Vinogradov, Yu. M. Shikhman
Baranov Central Institute of Aviation Motors, Moscow, 111116 Russia
Keywords: метан, схемы впрыска, инициирование и стабилизация горения, эффективность процесса, methane, injection methods, combustion initiation and stabilization, efficiency of the process

Abstract >>
An important stage of the development of promising engine and propulsion systems is provision of an effective process of hydrocarbon fuel combustion. There are many publications with numerical and experimental data on combustion of various gaseous hydrocarbons under laboratory conditions, but there is a lack of data on effective combustion of hydrocarbons in short combustion chambers with a large number of injectors. Results of systematic experimental studies of natural gas (methane) combustion in a high-velocity subsonic air flow in an air-breathing model combustor with a rectangular cross section are presented in this paper.



3.
Thermal and Dynamic Structure of an Ethanol Flame in the Boundary Layer near an Obstacle

R. Kh. Abdrakhmanov, B. F. Boyarshinov
Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: стабилизация горения, пограничный слой, ребро, обратный уступ, тепловыделение, хемилюминесценция, stabilization of combustion, boundary layer, rib, backward-facing step, heat release, chemiluminescence

Abstract >>
The distribution of the dynamic and thermal parameters of a gas in the immediate vicinity of a flame stabilizer (behind a rib and a backward-facing step 3 mm high) are studied. Data on the longitudinal and transverse velocity components, velocity pulsations, and correlations of pulsations in the boundary layer with combustion and without combustion are obtained using the PIV equipment. Temperature is measured with a thermocouple. Flame is visualized in the visible and ultraviolet regions. It is shown that in the flow attachment region near the leading edge of the flame, the gas velocity is close to the normal burning velocity. Heat release is estimated from the results of measurements. The presence of regions of volume and frontal combustion and kinetic and diffusion reaction is established. With increasing distance from the stabilizer, the heat-release rate decreases by more than an order of magnitude.



4.
Enthalpy Distribution at the Front of an One-Dimensional Laminar Flame

V. A. Bunev, A. A. Korzhavin, V. M. Shvartsberg
Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: энтальпия, водород, формальдегид, пропан, метанол, фронт пламени, численное моделирование, enthalpy, hydrogen, formaldehyde, propane, methanol, flame front, numerical modeling

Abstract >>
The enthalpy distribution at the front of one-dimensional flames of homogeneous mixtures of hydrogen, propane, formaldehyde, and methanol with air was numerically investigated. It is shown that the enthalpy distribution is more complex than the classical concepts: the enthalpy can both increase and decrease relative to the initial value. The specific form of the distribution is determined, in particular, by intermediate components formed at the flame front as they are also carriers of chemical energy and transfer it due to diffusion.



5.
Calculation of Flammability Limits of Silane-Oxygen and Silane-Air Mixtures

D. A. Tropin, A. V. Fedorov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: силановоздушная смесь, время задержки воспламенения, детальная химическая кинетика, математическое моделирование, silane-air mixture, ignition delay time, detailed chemical kinetics, mathematical modeling

Abstract >>
The upper and lower flammability limits of silane-oxygen and silane-air mixtures at pressures of 0.05-1.1 atm and temperatures of 350-640 K are found on the basis of Westbrook's detailed chemical kinetics. It is demonstrated that the death of OH radicals has a minor effect on these limits (their stability) within the framework of the Arrhenius kinetic model. The effect of the silane-air mixture composition on the flammability limits is found. It is shown that the behavior of the ultimate temperature of ignition is nonmonotonic as the fraction of silane increases.



6.
Combustion of Lean Methane-Air Mixtures in a Slot Burner with Adiabatic Outer Walls

A. Yu. Krainov, K. M. Moiseeva
Tomsk State University, Tomsk, 634050 Russia
Keywords: щелевая горелка, метановоздушная смесь, внутренняя вставка, тепловое расширение, устойчивое горение, slot burner, methane-air mixture, inner insert, thermal expansion, stable combustion

Abstract >>
The problem of the combustion of a methane-air mixture in a slot burner with adiabatic outer walls is solved. The problem is investigated numerically in a one-dimensional formulation and dimensional variables. The range of existence of stable high-temperature combustion of the methane-air mixture is determined as a function of gas flow rate and methane content in the mixture. The mechanism of failure of stable combustion is determined. The effect of heat transfer of the gas insert with an inner insert on combustion stability is shown.



7.
Model of Oxygen Cutting of a Metal Plate with Chemical Heat Release

M. A. Anisimova1, A. G. Knyazeva2,3
1Tomsk Polytechnic University, Tomsk, 634050 Russia
2Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences, Tomsk, 634021 Russia
3Tomsk State University, Tomsk, 634050 Russia
Keywords: кислородная резка, математическая модель, режимы резки, распределение температуры, реакция окисления, oxygen cutting, mathematical model, cutting modes, temperature distribution, oxidation reaction

Abstract >>
A model for the process of oxygen cutting of a metal plate is proposed which takes into account heating by external and internal heat sources, heat release from the cutting zone and reducing the thickness of the cutting geometry. The model was implemented numerically. It is shown that the model can describe different cutting modes: surface cutting, severing, and cutting in the kinetic and diffusion regimes. From the calculations results, the temperature field was constructed and the effect of the parameters on the thickness of the workpiece and the shape of the cutting edge was studied. The results are qualitatively consistent with experimental data.



8.
Gasless Combustion of a System of Thermally Coupled Layers

B. G. Prokofiev1, V. K. Smolyakov2
1Tomsk State University, Tomsk, 634050 Russia
2Tomsk Scientific Center, Siberian Branch, Russian Academy of Sciences, Tomsk 634021 Russia
Keywords: безгазовое горение, термически сопряженные слои, химическая печка, gasless combustion, thermally coupled layers, chemical furnace

Abstract >>
This paper presents the numerical simulation of gasless combustion of a sample as a combination of thermally coupled flat layers consisting of two different chemical compounds, which represent the model of a chemical furnace. The critical combustion conditions are established, depending on the volume ratio of mixtures in the sample or the content of reaction products. The time, velocity, and combustion modes of the layer composition are determined, depending on the volume content of the mixtures, the thickness, and the number of layers. The combustion wave propagation in view of “homogenization” of the sample with layer thickness decreasing at a fixed concentration of the components is considered.



9.
Negative Erosion Effect and the Emergence of Unstable Combustion. 1. Analysis of the Models

K. O. Sabdenov, M. Erzada
Gumilyov Eurasian National University, Astana, 010008 Kazakhstan
Keywords: горение твердых ракетных топлив, обдув поверхности горения, эрозионный эффект, combustion of solid propellants, blowing of the combustion surface, erosion effect

Abstract >>
This paper presents the analysis of different hypotheses and models related to the physical nature of the negative erosion effect. The influence of various factors on the emergence of this effect is estimated, and the most significant of them are mentioned. A system of equations for the study of the negative erosion effect is proposed. The new useful properties of the Bulgakov-Lipanov number are found.



10.
Axisymmetric Expanding Heterogeneous Detonation in Gas Suspensions of Aluminum Particles

Yu. V. Kratova, T. A. Khmel’, A. V. Fedorov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia 630090
Keywords: численное моделирование, газовзвесь, детонация, дифракция детонационной волны, numerical simulation, gas suspension, detonation, detonation wave diffraction

Abstract >>
A problem of expansion of heterogeneous detonation in a suspension of aluminum particles in gaseous oxygen from a circular tube and its propagation in a semi-bounded or unbounded space is studied by numerical methods. The effects of the particle diameter in monodisperse suspensions and of the composition of bidisperse suspensions on detonation propagation regimes are studied. The calculated results are compared with data on heterogeneous detonation of gas suspensions in a plane channel and on gas detonation. The critical values of the channel width and the tube diameter are found to differ by a factor of 2-2.5, as it is also observed in gas detonation. However, the ratio of the critical diameter to the detonation cell size in the case of heterogeneous detonation can be smaller than that in gas mixtures by an order of magnitude.



11.
Initiation of a Gas Volume above the Boundary of a Gas-Liquid Medium by a Bubble Wave Detonation

A. V. Pinaev, I. I. Kochetkov
Lavrentyev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: взрыв проволочки, плазменный разрядный пузырь, ударная волна, пузырьковая детонация, воспламенение пенистой среды, инициирование газовой смеси, wire explosion, plasma discharge bubble, shock wave, bubble detonation, foam ignition, initiation of gas mixture

Abstract >>
It is shown that detonation can be transmitted from a reacting bubble medium into an explosive gas volume located above the interface. Experiments were performed in which bubble detonation was initiated by wire explosion in a gas-liquid medium. The dynamics of the boundary of the gas-liquid medium after the arrival of the bubble detonation wave at it was studied. The distance between the wire and the boundary of the bubble medium was decreased to 1 cm, at which the gas volume was initiated by the hot products from the wire explosion and the discharge plasma. The probability of detonation transmission from the bubble medium to the volume of the gas mixture depending on the depth of immersion of the wire is determined, and the mechanisms of ignition of the explosive gas volume are described.



12.
Influence of the Thickness and Absorption Coefficient of a Copper Oxide Film on the Ignition Delay of PENT by a Laser Pulse

A. V. Khaneft1,2, V. A. Dolgachev1, A. S. Zverev1,3, A. Yu. Mitrofanov1,3
1Kemerovo State University, Kemerovo, 650043 Russia
2Tomsk Polytechnic University, Tomsk, 634050 Russia
3Yurga Technological Institute, Yurga, 652055 Russia
Keywords: моделирование, поглощающая пленка, лазерный импульс, зажигание, тэн, modeling, absorbing film, laser pulse, ignition, PETN

Abstract >>
Numerical modeling of PETN ignition by a copper oxide film absorbing laser radiation has been performed. The calculation results showed the presence of a minimum in the curve of the dynamic delay of PETN ignition by a rectangular laser pulse versus thickness of the absorbing film. This effect is due to the fact that when the film thickness is commensurate with the reciprocal of the absorption coefficient, the amount of heat generated in the thin film due to the multiple reflection of the light flux is proportional to its thickness. Therefore, the smaller the film thickness, the more time is required to heat it to the ignition temperature of PETN. In the case of a thick film, additional energy and time are required to heat its cold part to the ignition temperature of PETN.



13.
Initiation of PETN Detonation by an Impactor and a High-Enthalpy Gas Flow

A. P. Ershov, A. O. Kashkarov, E. R. Pruuel
Lavrentyev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: инициирование, детонация, горение, переход горения в детонацию, initiation, detonation, combustion, deflagration-to-detonation transition

Abstract >>
This paper compares two methods of near-threshold initiation of a loose-packed PETN charge: by impact of a plate and by injection of an intense flow of hot gases into the powder. Synchrotron diagnostics of material density was used. Both methods lead to the development of detonation in about 10  s, but the nature of initiation differs sharply. Initiation by an impermeable piston involves the formation of a dense plug of compressed material. After some delay, a wave is formed at the front of this plug which initiates chemical reaction and accelerates to normal detonation. For high-enthalpy initiation by a hot gas flow, the compression of the powder is low and the process develops in the gas-permeable material, starting from the stage of rapid convective combustion followed by transition to detonation.



14.
Detonation Propagation in Thin Explosive Layers with Inert Partitions

I. F. Kobylkin
Bauman Moscow State Technical University, Moscow, 105005 Russia
Keywords: тонкие слои ВВ, передача детонации, критическая толщина перегородки, десенсибилизация, детонационный диод, thin explosive layers, detonation transfer, critical partition thickness, desensitization, detonation diode

Abstract >>
This paper describes the experimental results in the study of detonation transfer in thin layers of a PVV-12M plastic-bonded explosive (90% of RDX and 10% of bond) through solid and perforated partitions. The critical thicknesses of steel or Plexiglas partitions, exceeding which makes detonation transfer impossible, are determined for the explosive layers with a thickness of 2-12 mm. It is shown that shock waves in the plates, which bound the explosive charge, can stay ahead of the initiating shock wave in the passive part of the explosive charge and load the explosive charge from the lateral surface. Thus, the peripheral desensitized layers of the explosives are formed, which reduce the layer thickness of the detonable explosive and complicate the detonation transfer. Detonation transfer through the partitions whose thickness is greater than the critical thickness can be carried out with the use of holes in the partition, closed by thin plates. The plate thicknesses at which detonation propagates through the hole either in forward and reverse directions or in the forward direction only, are determined.



15.
Electrical Resistance of Copper under Shock Compression: Experimental Data

S. D. Gilev, V. S. Prokop’ev
Lavrentyev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: электросопротивление, электропроводность, медь, ударное сжатие, высокая плотность энергии, высокое давление, electrical resistance, electrical conductivity, copper, shock compression, high energy density, high pressure

Abstract >>
The electrical resistance of copper foil under shock compression is measured. The electrical resistance and electrical conductivity are plotted as functions of the shock pressure in the interval up to 20 GPa. These dependences are monotonic and have no visible inflections or singularities. A qualitative dependence of the electrical resistance of the metal on the shock impedance of the material of the block containing the sample is found. A comparison of the data obtained in this study with results of other authors shows that it is important to take into account the block material, the shape and thickness of the sample, and the procedure of determining the state of the sample.



16.
Explosion Characteristics of Nano-PMMA Particles

W. Gao, J. Li, Yu. Li, X. Yan, J. Yu, X. Zhang
Dalian University of Technology, Dalian, 116024, China
Keywords: взрыв пыли, наночастицы ПММА, максимальное давление взрыва, индекс дефлаграции, эффект агломерации, dust explosions, nano-PMMA particles, maximum explosion pressure, deflagration index, agglomeration effects

Abstract >>
Explosion characteristics of PMMA particles with three different diameters (100 nm, 800 nm, and 30 μm) are studied experimentally. The explosion severity including the maximum explosion pressure and the pressure rise rate of 100-nm PMMA particles significantly exceed those of 800-nm and 30-μm PMMA particles at low concentrations due to a greater specific surface area. However, the explosion severity of 100-nm PMMA particles gradually decreases below that of 800-nm PMMA particles once the dust concentration reaches 250 g/m3 and above because 100-nm PMMA particles are prone to agglomerate, but it is still higher than that of 30-μm PMMA particles. In addition, the maximum explosion pressures increase with increasing concentrations of PMMA particles of all sizes, peaking at 250 g/m3, while they do not change significantly as the concentrations go beyond 500 g/m3. According to the explosion classification based on the deflagration index, nano-PMMA particles indicate a higher explosion risk and more serious explosion severity than those of micro-particles.