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Combustion, Explosion and Shock Waves

2018 year, number 6

Effect of the Wave Structure of the Flow in a Supersonic Combustor on Ignition and Flame Stabilization

M. A. Goldfeld1, Yu. V. Zakharova1, A. V. Fedorov1, N. N. Fedorova1,2
1Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
2Novosibirsk State University of Architecture and Civil Engineering, Novosibirsk, 630008 Russia
Keywords: сверхзвуковое течение, турбулентность, ударная волна, волна разрежения, камера сгорания, подготовленная смесь, воспламенение, supersonic flow, turbulence, shock wave, expansion wave, combustor, prepared mixture, ignition

Abstract >>
Results of numerical and experimental investigations of a high-velocity flow in a plane channel with sudden expansion in the form of a backward-facing step, which is used for flame stabilization in a supersonic flow, are presented. The experiments are performed in the IT-302M high-enthalpy short-duration wind tunnel under the following test conditions: Mach number at the combustor entrance 2.8, Reynolds number 30 × 106 m-1, and total temperature T0 = 2000 K, i.e., close to flight conditions at M = 6. The numerical simulations are performed by solving full unsteady Reynolds-averaged Navier-Stokes equations supplemented with the k-ω SST turbulence model and a system of chemical kinetics including 38 forward and backward reactions of combustion of a hydrogen-air mixture. Three configurations of the backward-facing step are considered: straight step without preliminary actions on the flow, with preliminary compression, and with preliminary expansion of the flow. It is demonstrated that the backward-facing step configuration exerts a significant effect on the separation region size, pressure distribution, and temperature in the channel behind the step, which are the parameters determining self-ignition of the mixture. The computed results show that preliminary compression of the flow creates conditions for effective ignition of the mixture. As a result, it is possible to obtain ignition of a prepared hydrogen-air mixture and its stable combustion over the entire channel height.

Flame Shape in a Nonstationary Flow of a HCHO PLIF Swirled Turbulent Jet

A. S. Lobasov1,2, S. S. Abdurakipov1,2, L. M. Chikishev1,2, V. M. Dulin1,2, D. M. Markovich1,2
1Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
2Novosibirsk State University, Novosibirsk, 630090 Russia
Keywords: форма пламени в закрученной струе, когерентные структуры, панорамная лазерно-индуцированная флуоресценция, флуоресценция формальдегида, метод главных компонент, flame shape in a swirled jet, coherent structures, panoramic laser-induced fluorescence, formaldehyde fluorescence, principal component method

Abstract >>
This paper describes the experimental study of the spatial structure of a chemical reaction zone in a turbulent flow of a jet swirled by means of panoramic laser-induced formaldehyde fluorescence. The burning of an air-methane mixture under atmospheric pressure and at different excess coefficients of fuel φ: the burning of an inverse cone shaped flame φ = 0.7- 1.4 and the burning of an elevated flame φ = 2.5. Aside from small-scale deformations, the changes in the shape of the chemical reaction zone is coupled with two types of large-scale coherent structures, namely the virtually axisymmetric deformation mode of the flame front, which is probably due to the action of Archimedes forces on the combustion products, and the rotation of the asymmetric mode due to the precession of the swirled flow.

Strongly Nonequilibrium Model of Thermal Ignition with Account for Space-Time Nonlocality

V. A. Kudinov, A. V. Eremin, I. V. Kudinov, V. V. Zhukov
Samara State Technical University, Samara, 443100 Russia
Keywords: локально-неравновесный теплообмен, время релаксации, нелинейный источник тепла, тепловое воспламенение, время задержки теплового воспламенения, численное решение, locally nonequilibrium heat exchange, relaxation time, nonlinear heat source, thermal ignition, thermal ignition time delay, numerical solution

Abstract >>
A modified Fourier law with account for heat flux relaxation and scalar value of the temperature gradient serves as a basis for the mathematical model of the locally nonequilibrium process of thermal ignition of systems with a hear source exponentially changing due to temperature. It is shown by the studies performed under the boundary conditions of the first kind that accounting for the space-time nonlocality increases the time delay of thermal ignition. Moreover, it is shown that, when the relaxation properties of the material are considered, the boundary conditions can only be accepted after a certain time rather than instantaneously. Consequently, the amount of heat fed to the system has a limitthat depends on the physical properties (including relaxation properties) of the medium.

Effect of Diffusion of Coal Pyrolysis Products on the Ignition Characteristics and conditions of Coal-Water Fuel Droplets

G. V. Kuznetsov1, V. V. Salomatov2, S. V. Syrodoi1
1Tomsk Polytechnic University, Tomsk, 634050 Russia
2Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: водоугольное топливо, зажигание кокса, воспламенение летучих, диффузия продуктов пиролиза, coal-water fuel, ignition of coke ignition of volatile, diffusion of pyrolysis products

Abstract >>
This paper presents a theoretical study of the thermal preparation and ignition of a coal-water fuel droplet under intense radiation-convective heating with diffusion of gaseous pyrolysis products of the solid fuel into the external gaseous medium. It has been found that gaseous pyrolysis products are ignited at a distance from the heating surface approximately equal to the radius of the droplet, after which the coke of the main fuel layer is ignited. The time between the ignition of volatiles and the coke residue is less than 0.5 s. Comparison of the ignition delays obtained by mathematical modeling and experimentally has shown satisfactory agreement between theoretical and experimental values.

Physicomathematical Modeling of Ignition of a Heterogeneous Mixture of Methane, Hydrogen, and Coal Microparticles

D. A. Tropin, A. V. Fedorov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Keywords: воспламенение, метановодородовоздушная смесь, микрочастицы угля, детальная химическая кинетика, математическое моделирование, ignition, methane-hydrogen-air mixture, coal microparticles, detailed chemical kinetics, mathematical modeling

Abstract >>
A physicomathematical model is developed for ignition and combustion of a methane-air mixture containg coal microparticles. The model takes into account the detailed kinetics of oxidation of the gaseous methane-hydrogen-air mixture and the processes of thermal destruction of coal particles with release of volatiles (methane and hydrogen) to the gas phase, ignition and combustion of these volatiles in the gas phase, and heterogeneous reaction of carbon oxidation. It is demonstrated that addition of coal particles to the methane-air mixture in the temperature interval from 900 to 1450 K reduces the ignition delay time. Moreover, addition of coal particles to the methane-air mixture leads to shifting of the ignition limit of the gas mixture toward lower temperatures. The calculated delay time of coal ignition in the air-coal mixture and the predicted delay times of methane and coal ignition in the methane-air-coal mixture are found to be in reasonable agreement with experimental data obtained in a rapid-compression setup.

Computational Fluid Dynamics Modeling of Combustion of Synthetic Fuel of Thermochemical Heat Regeneration Systems

D. I. Pashchenko
Samara State Technical University, Samara, 443100 Russia
Keywords: водород, горение, синтез-газ, термохимическая регенерация, CFD-моделирование, hydrogen, combustion, syngas, thermochemical regeneration, CFD modeling

Abstract >>
CFD modeling of the combustion of synthetic fuel formed in the systems of thermochemical heat recovery of waste flue gas due to steam reforming of methane was performed. The studies were conducted using the ANSYS Fluent software. Scientific justification and validation of the physicomathematical approaches underlying the ANSYS Fluent for the problems of modeling the combustion of multicomponent hydrogen-containing gas mixes. Numerical results were validated against experimental data. A visual comparison of the flame contours obtained by burning syngas at Reynolds numbers of 600, 800, 1000 was perfomed. In all cases there is obvious convergence of results. Change in the temperature of the fuel-air mixture at the entrance to the combustion chamber was found to have no significant effect on the temperature of the combustion products. The obtained results are of practical importance for the design of the burner units of heating plants with thermochemical heat recovery.

Influence of the Strain Rate, Particle Size, and Equivalence Ratio on the Combustion of the Premixed Air-Aluminum Microparticle Mixture with a Counterflow Structure

Ya. Pourmohammad, M. Sabzpooshani
University of Kashan, Kashan, 8731751167 I.R. Iran
Keywords: металлические частицы, микрочастицы алюминия, горение в противотоке, скорость деформации, предварительно перемешанная смесь, metal particles, aluminum microparticles, counterflow combustion, strain rate, premixed mixture

Abstract >>
The effects of the strain rate, equivalence ratio, and particle diameter on the combustion of a mixture of aluminum microparticles with air under fuel-lean conditions are studied in the counterflow configuration with an approximate analytical perturbation method. The flame structure is assumed to consist of three zones: preheating, flame, and post-flame zones. Reasonable agreement between the current results and experimental data is obtained in terms of the flame temperature. The dimensionless ignition and ultimate flame temperatures, place of the flame starting point, and flame thickness are obtained as functions of the strain rate for different particle diameters and equivalent ratios. The results indicate that the ignition and ultimate flame temperatures and also the flame thickness decrease with increasing strain rate. With a decrease in the strain rate, the length of the preheating zone increases. With increasing particle diameter, the flame thickness increases, whereas the ignition and ultimate flame temperatures decrease. An increase in the equivalence ratio causes an increase in the ultimate flame temperature and reduction of the preheating zone and flame thickness.

Ignition and Combustion of Condensed Systems with Energy Fillers

V. A. Arkhipov, A. S. Zhukov, V. T. Kuznetsov, N. N. Zolotorev, N. A. Osipova, K. G. Perfil’eva
Tomsk State University, Tomsk, 634050 Russia
Keywords: конденсированная система, комбинированный окислитель, перхлорат аммония, нитрат аммония, энергетические наполнители, алюминий, бор, бориды алюминия, борид титана, время задержки зажигания, скорость горения, condensed system, combined oxidizer, ammonium perchlorate, ammonium nitrate, energy fillers, aluminum, boron, aluminum boride, titanium boride, ignition delay time, burning rate

Abstract >>
This paper describes the results of an experimental study of ignition and combustion of condensed systems, containing energy fillers, i.e., powders of aluminum, boron, aluminum borides, and titanium. Compositions on a hydrocarbon or active fuel binder with a combined oxidizer (perchlorate and/or ammonium nitrate) are considered. Thermodynamic estimates for the ballistic characteristics of the compositions under study are given. It is shown that a unit pulse increases by 3.5% with the replacement of aluminum by boron in the compositions considered. It is experimentally determined that the time delay of ignition of boron-containing compositions decreases in conductive and radiant heat transfer and that the stationary burning rate of boron and aluminum boride containing compositions increases. The effectiveness of the impact of energy fillers on the characteristics of condensed systems as a function of the composition of a combined oxidizer is determined.

Optimization of the Binder Composition to Increase the Energy Potential of Polynitrogem Oxidizers in Non-Metal Compositions

E.M. Dorofeenko, S.I. Soglasnova, G.N. Nechiporenko, D.B. Lempert
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, 142432 Russia
Keywords: удельный импульс, температура горения, ракетное топливо, specific impulse, combustion temperature, rocket propellant

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The dependence of the specific impulse of non-metal energetic compositions based on high-enthalpy organic oxidizers on the elemental composition and enthalpy of formation of the oxidizer and the nature and volume content of the mixed binder consisting of hydrocarbon and active components. For a given volume content of the binder, it is possible to increase the specific impulse of compositions based on oxidizers with an oxygen ratio of 0.6-1.3 by finding the optimal mass ratio of the hydrocarbon and active components in the binder. The optimal content of the hydrocarbon component increases from 0 to 100% as the oxygen ratio of the oxidizer increases from 0.6 to 1.3.

The Use of the [H2O-CO2] Arbitrary Decomposition Assumption to Predict the Performance of Condensed High Explosives

D. Frem
FREM Co., Beirut, Lebanon
Keywords: бризантность, давление детонации, глубина отпечатка, метод Камлета , Джейкобса, brisance, detonation pressure, dent depth, Kamlet-Jacobs method

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The plate dent test is one of the simplest tools for fast determination of the detonation pressure. The test is based on the observation that the detonation pressure correlates with the depth of the dent produced by a detonating explosive on a metal witness plate. The present study is aimed at developing a model for estimating the dent depth, which is used not only to obtain the detonation pressure, but also to evaluate the brisance relative to a reference explosive. It is shown that the experimental dent depth values for CHNO and CHNOClF explosives can be successfully reproduced by a model based on few parameters, namely: loading density, number of moles of gaseous detonation products per gram of the explosive, and average molecular weight of the gaseous products, where the number of moles and the mean molecular weight of the gaseous products are calculated according to the [H2O-CO2] arbitrary decomposition assumption. Furthermore, the predicted values of the dent depth and the Kamlet-Jacobs method are used to estimate the detonation pressure for 37 explosives. The results show that the pressures obtained on the basis of the dent depth values are in better agreement with experimental/thermochemical code data than the predictions of the Kamlet-Jacobs method.

Thermal Emission from Water Behind the Front of a Reflected Shock Wave

S. A. Bordzilovskii1,2, S. M. Karakhanov1, K. V. Khischenko3,4
1Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
2Novosibirsk State University, Novosibirsk, 630090 Russia
3Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia
4Moscow Institute of Physics and Technology, Dolgoprudny, 141700 Russia
Keywords: вода, ударная волна, расчет температуры, уравнение состояния, двукратное сжатие, water, shock wave, temperature calculation, equation of state, double compression

Abstract >>
The thermal emission from a water layer shock-compressed by an incident wave and a wave reflected from a LiF window was recorded in the range of incident-wave intensity of 28-36 GPa. Losses of the luminous flux at the boundaries were estimated. The temperature of water compressed by one and two shock waves were calculated, and the calculation results are in good agreement with experimental data.

Experimental Study on the Dynamic Strain of a Thin-Walled Pipe in the Gas Cloud Explosion with Ignition Energy

N. Zhou1, Q. Yu1, G. Zhang1, X. Liu2
1Changzhou University, Changzhou, 213164 China
2Tianjin Fire Research Institute, Tianjin, 300381 China
Keywords: детонационная труба, взрыв облака газа, энергия зажигания, пик давления, динамическая деформация, detonation tube, gas cloud explosion, ignition energy, peak pressure, dynamic strain

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This paper describes an experimental study of the flame propagation mechanism for the combustible gas explosion in a closed pipe with a length of 12 m and an internal diameter of 0.125 m, which is carried out for different values of the ignition energy. The results show that an increase in the ignition energy results in greater explosive intensity, maximum peak pressure, and dynamic strain of the thin wall in the whole process. Moreover, the dynamic strain of the thin-walled pipe increases suddenly owing to arrival of a precursor shock wave and then vibrates for a long time, which is induced by the wave reflected back and forth. In addition, there is good agreement between the dynamic strain signals and pressure wave signals. These research results can provide a theoretical basis for industrial explosion accident assessments as well as explosion and shock resistance designs, which provides guidance not only for industrial safety, but also for prevention and mitigation of explosion accidents.

Breaking Through Double-Layer Targets with an Outer Ceramic Layer under the Action of an Impactor at an Angle

I. F. Kobylkin, A. A. Gorbatenko
Bauman Moscow State Technical University, Moscow, 105005 Russia
Keywords: пробивание, двухслойная керамико-металлическая преграда, воздействие под углом, предельная скорость пробития, breaking, double-layer ceramic-metallic target, action at an angle, limiting breaking rate

Abstract >>
Three-dimensional numerical simulation of interaction between an impactor directed at an angle and a double-layer target with an outer ceramic layer is performed. It is shown that the presence of a ceramic layer normalizes the breaking process: the main deformation and displacement of the target elements occur so as if the action of the impactor is carried out along a normal to the target surface. A quite intense rotation of the impactor remains at the final stages of interaction is observed. Experimental data and propositions on the transformation of the impact at an angle into an equivalent impact along the normal are used to develop an approximate analytical technique for calculating the limiting rate of breaking through the double-layer ceramic-metallic target under the action of the impactor at an angle.

Blast Load Model Generating Multiple Impulse Curves for Different Scaled Distances

B. S. Jang, S. H. Lee, Y. Lee
Chung-Ang University, Seoul, 156-756 Korea
Keywords: кривая импульса, взрывная нагрузка, взрыв, масштабированное расстояние, численное моделирование, impulse curve, blast load, explosion, scaled distance, finite element simulation

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This study proposes a blast load model that generates multiple impulse curves with appropriate shapes depending on the scaled distance and, thus, precisely calculates the blast load distribution over the structure surface. The suitability of the proposed model is examined by using the finite element simulation of a blast test with steel plates and comparing the predicted deflections with the measurements. The results reveal that the proposed model accurately calculates the blast load distribution over the structure surface. The predicted deflection profiles of the steel plates are closer to the measured deflection profiles when the proposed model is employed, as compared to the existing models, which produce only a single impulse curve.

Crack Propagation Law Affected by Natural Fracture and Water Jet Slot under Blast Loading

D. Su1, Y. Kang1,2, F. Yan1, D. Zheng3, X. Wang2, M. Wei1,4
1Chongqing University, Chongqing, 400030 China
2Wuhan University, Wuhan, 430072 China
3Dazhou Administration of Work Safety, Dazhou, 635000 China
4Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, 430071 China
Keywords: распространение трещины, естественный разрыв, водоструйная выемка, взрывная нагрузка, ANSYS/LS-DYNA, crack propagation, natural fracture, water jet slot, blast loading, ANSYS/LS-DYNA

Abstract >>
The natural fracture of rock has a strong effect on the law of explosion stress wave transmission and crack propagation during blasting. Based on the stress wave theory, the influential mechanism for both the law of transmission of the stress wave and of crack propagation due to natural fracture and water jet slot are analysed. Next, an experiment is conducted to understand the crack propagation law because of the effect of an explosion shock wave, and the evolution law of the blast stress wave and blast-induced crack propagation is simulated by ANSYS/LS-DYNA. The results indicate that the existence of the water jet slot not only promotes the generation of the main crack along its direction, but also promotes the generation of the secondary crack near the water jet slot because of the explosion shock wave. The direction of propagation of the secondary crack and the main crack are seriously affected by the natural fracture. In addition, if the distance between the blast hole and the natural fracture is too small, a smash area is formed; and with an increase in the distance between the blast hole and the natural fracture, the smash area becomes smaller, and the effect on the blast-induced crack becomes weaker.