Showing papers in "Combustion, Explosion, and Shock Waves in 2003"
TL;DR: In this paper, the principal possibility of organizing controlled combustion of a subsonic flow of a propellant in longitudinal pulsed and spin detonation waves is experimentally verified Conditions and reasons for the existence of detonation wave are considered.
Abstract: The principal possibility of organizing controlled combustion of a subsonic flow of a propellant in longitudinal pulsed and spin detonation waves is experimentally verified Conditions and reasons for the existence of detonation waves are considered
119 citations
TL;DR: The most relevant aspects of advanced experimental investigations of gas detonation and its mathematical simulation are presented in this article, along with some examples of the engineering use of gas explosion and its applications.
Abstract: The most relevant aspects of advanced experimental investigations of gas detonation and its mathematical simulation are presented. Examples of the engineering use of gas detonation are given.
85 citations
TL;DR: In this paper, the transition from reagent interaction involving a liquid phase in ordinary SHS powder mixtures to solid-state combustion after preliminary activation of these mixtures in an energy-intensive planetary mill was studied for Ni + 13 wt. % Al and Ni + 45 wt % Ti compositions.
Abstract: The factors responsible for the transition from reagent interaction involving a liquid phase in ordinary SHS powder mixtures to solid‐state combustion after preliminary activation of these mixtures in an energy‐intensive planetary mill were studied for Ni + 13 wt. % Al and Ni + 45 wt. % Ti compositions. The dependences of the burning rate and temperature on the duration and conditions of mechanical activation were determined. It is found that the occurrence of solid‐state SHS in a powdermixture is due to the formation of “laminated composites,” in which the reagents are ground to ultrafine size, the area of their contact increases severalfold, and the concentration of nonequilibrium defects is high. In activated samples, heat release proceeds in several stages and at lower temperature than in powder mixtures.
73 citations
TL;DR: In this article, the authors measured the ignition delay in methane-air mixtures within the range of temperatures of 1200-1700 K and pressures of 3-450 atm behind reflected shock waves in a shock tube.
Abstract: The ignition delay in methane–air mixtures ϕ = 0.5) within the range of temperatures of 1200–1700 K and pressures of 3–450 atm behind reflected shock waves in a shock tube is measured on the basis of emission of the electron‐excited OH radical (transition A2Σ+ – X2Π) at the wavelength of 306.4 nm and on the basis of absorption corresponding to the component F1
(2) (ν3 = 1) ← F2
(2) (ν3 = 0) of the P(7) line of the ν3 mode of the CH4 molecule at the wavelength of 3.3922 μm. The measured ignition delays are compared with those calculated by the GRI‐Mech 3.0 mechanism; good qualitative agreement of results is obtained in a wide range of pressures.
66 citations
TL;DR: In this paper, the effect of mechanical activation conditions in a planetary ball mill on the main parameters of SHS processes and combustion product composition was studied for Ni + 13 wt. % Al and Ni + 45 wt % Ti compositions.
Abstract: The effect of mechanical activation conditions in a planetary ball mill on the main parameters of SHS‐processes and combustion product composition was studied for Ni + 13 wt. % Al and Ni + 45 wt. % Ti compositions. From results of experiments at elevated initial temperatures, it is concluded that because of reverse quenching, the defects produced by mechanical activation are not annealed in the heating zone and are retained in the sample until the beginning of chemical interaction in the leading zone of the SHS wave. The process of annealing of the activated samples was studied in situ on a transmission electron microscope and a synchrotron radiation diffractometer. The energy stored in the samples as a result of mechanical activation is estimated by calorimetric studies.
61 citations
TL;DR: In this paper, a series of experimental studies addressing combustion of single metal particles was presented. But the experiments were aimed at identifying correlations between the burning particle temperature and composition histories, leading to phase changes coinciding with sudden changes in metal combustion regimes.
Abstract: This paper summarizes a series of experimental studies addressing combustion of single metal particles. Sets of free‐falling monodisperse molten metal droplets were formed at repeatable initial temperatures and velocities in a pulsed microarc discharge ignited between a cold tool cathode and a consumable wire anode. The droplets formed in oxygenated environments immediately ignited and burned, while their temperature histories were studied using optical pyrometry. Burning particles were quenched at different combustion times using techniques providing variable cooling rates. Analyses of the quenched samples were used to recover the evolution of burning particle compositions for different metals. Experiments were conducted with Al, Mg, Zr, Ti, Ta, W, Mo, Fe, and Cu particles. In addition, similar combustion experiments were carried out with boron particles produced using an oxygen‐acetylene torch melting an edge of a vibrating boron filament. Most of the combustion experiments were conducted in air, while argon–oxygen, helium–oxygen, and carbon‐dioxide environments were also used in some tests. A limited number of experiments on aluminum‐particle combustion were conducted in microgravity. The experiments were aimed at identifying correlations between the burning particle temperature and composition histories. Dissolution of oxygen and other gases was observed to occur within the burning metal, leading to phase changes coinciding with sudden changes in metal combustion regimes. Equilibrium metal–gas phase diagrams were used to interpret the experimentally observed metal combustion behavior. Based on the experimental results, an expanded mechanism of metal combustion was suggested, emphasizing reactions and phase changes occurring within the burning metal in addition to reactions occurring on and above the metal surface.
51 citations
TL;DR: In this paper, a mathematical model of ignition of a single aluminum particle under steady conditions is developed within the framework of Semenov's theory of thermal explosion, and the experimental dependences of the ignition delay on the radius and limiting ignition temperature are described.
Abstract: A mathematical model of ignition of a single aluminum particle under steady conditions is developed within the framework of Semenov's theory of thermal explosion. Based on this model, the experimental dependences of the ignition delay on the radius and limiting ignition temperature are described. The dependence of the preexponent in the empirical law of oxidation on the particle size, ambient temperature, and oxidizer content is determined.
44 citations
TL;DR: In this paper, the deformation instability of an explosive composition caused by local heating of optical microinhomogeneities was investigated, and an ignition mechanism was proposed based on the concept of local heating.
Abstract: Laser ignition of explosives based on di-(3-hydrazino-4-amino-1,2,3-triazole)-copper(II) perchlorate was investigated. Dependences of explosive sensitivity on the concentration of the transparent binder and on the radiation spot diameter and time dependences of the ignition delay were constructed. An ignition mechanism is proposed that is based on the concept of the deformation instability of an explosive composition caused by local heating of optical microinhomogeneities.
40 citations
TL;DR: In this paper, a model for gasless combustion is considered, based on the assumption that the medium consists of reaction cells whose exchange with heat proceeds much more slowly than heat transfer in each cell.
Abstract: A model for gasless combustion is considered, based on the assumption that the medium consists of reaction cells whose exchange with heat proceeds much more slowly than heat transfer in each cell. For various reaction rates and kinetic laws, temperature dependences of the burning rate are calculated and compared with available experimental data. Thermal and concentration structures of the combustion wave are revealed. Existence domains and stability boundaries of microheterogeneous and quasihomogeneous modes of gasless combustion are established, depending on the preexponent and activation energy of the chemical reaction. The effect of abrupt acceleration of the reaction at a critical point (for instance, at a phase‐transition point) on the combustion pattern is analyzed.
37 citations
TL;DR: In this article, the authors considered problems arising in the development of various devices with the use of detonation in a controlled frequency mode (pulsed detonation) are considered.
Abstract: Research problems arising in the development of various devices with the use of detonation in a controlled frequency mode (pulsed detonation) are considered. The frequency of cycles can be varied by independent initiation of detonation by a controlled system of ignition. Problems of detonation initiation concerning the frequency mode are considered: direct initiation, deflagration-to-detonation transition, and transition of a detonation wave formed in a narrow channel into a wide channel. The possibility of using thermochemical conversion in devices with pulsed detonation is considered. Examples of practical applications of devices with pulsed detonation are given (pulsed detonation engine, using pulsed detonation for drilling and crushing of rocks, and removal of metal cord from rubber in worn tires).
29 citations
TL;DR: In this paper, the dynamics of motion of the material in a gasless combustion wave was studied using high-speed video recording (500 frames/sec) with a spatial resolution of the order of 10 μm.
Abstract: Deformation during gasless combustion of 5Ti + 3Si and Ti + C samples was studied experimentally. The dynamics of motion of the material in a gasless combustion wave was studied using high‐speed video recording (500 frames/sec) with a spatial resolution of the order of 10 μm. It was shown that behind the combustion front, the medium was first expanded and then compressed. The dimensions of the expansion and compression zones were determined.
TL;DR: In this paper, a mathematical model of agglomerate formation is constructed for propellants whose typical feature is active burning of the metallic fuel in the surface layer, and the simulation is validated by the agreement of experimental and numerical data.
Abstract: The paper deals with mathematical simulation of dispersion of agglomerates formed in combustion of aluminized solid propellants. A substantial effect of the separation conditions of agglomerating metal particles from the surface of the burning propellant on the size of agglomerates is demonstrated. A mathematical model of agglomerate formation is constructed for propellants whose typical feature is active burning of the metallic fuel in the surface layer. Satisfactory quality of simulation is validated by the agreement of experimental and numerical data.
TL;DR: In this paper, the possibility of nonthermal initiation of chemical reactions by a uniform pulsed nanosecond discharge is demonstrated, and the main role in combustion initiation under conditions of a pulsed gas discharge in the case of moderate electric fields and low degree of ionization belongs to reactions of dissociation quenching of electron−excited levels of nitrogen.
Abstract: The possibility of nonthermal initiation of chemical reactions by a uniform pulsed nanosecond discharge is demonstrated. Dependences of variation of the ignition delay on initial conditions are obtained. It is shown that the main role in combustion initiation under conditions of a pulsed gas discharge in the case of moderate electric fields and low degree of ionization belongs to reactions of dissociation quenching of electron‐excited levels of nitrogen.
TL;DR: In this article, a mechanism is proposed to explain the autoignition of titanium alloys with formation of a juvenile surface of the metal in oxygen at elevated pressure, based on the assumption that the self-heating of failed sample fragments to the melting point of the alloy is due to the heat released during oxygen adsorption on the juvenile surface and its dissolution in the solid metal.
Abstract: A mechanism is proposed to explain the autoignition of titanium alloys with formation of a juvenile surface of the metal in oxygen at elevated pressure. It is based on the assumption that the self‐heating of failed sample fragments to the melting point of the alloy is due to the heat released during oxygen adsorption on the juvenile surface and its dissolution in the solid metal. In this case, the rate‐determining stage of the interaction is the adsorption process, whose rate depends on the oxygen pressure.
TL;DR: In this article, two stages of spontaneous formation of new disturbances and transverse waves on the expanding detonation wave front are observed, and the main mechanisms of reinitiation of detonation waves are discussed.
Abstract: Results of experimental investigations of an expanding multifront detonation wave are presented. Two stages of spontaneous formation of new disturbances and transverse waves on the expanding detonation‐wave front are observed. The main mechanisms of re‐initiation of detonation waves are discussed. Two‐dimensional numerical simulation of the dynamics of a multifront detonation wave in a linearly expanding channel is performed. The effect of spontaneous formation of new disturbances and new transverse waves is confirmed by computations, and the main mechanism of multiplication of transverse waves is the instability of detonation‐wave‐front elements at the stage they cease to be in the overdriven state and are attenuated during expansion.
TL;DR: In this article, the development of turbulent diffuse flame in a compartment with a vertical opening is studied experimentally and numerically, and the critical (minimum) flow rate of the fuel sufficient for flame projection is determined, as well as the delay between fuel ignition and flame projection.
Abstract: Development of turbulent diffuse flame in a compartment with a vertical opening is studied experimentally and numerically. Flame projection through the opening observed under conditions of limited natural‐convective ventilation is considered. The measurements are performed in a laboratory box designed for compartment‐fire simulation. The critical (minimum) flow rate of the fuel sufficient for flame projection is determined, as well as the delay between fuel ignition and flame projection with subsequent establishment of external combustion. Dimensionless variables for processing experimental data are proposed. A generic empirical dependence of the dimensionless time of flame projection on the dimensionless flow rate of the fuel is obtained for various opening sizes, burner positions, and box sizes. The dimensionless critical flow rate of the fuel obtained is in agreement with the previously published measurements performed for gaseous and condensed fuels. Unsteady stages of flame evolution before the projection and scenarios of flame projection through the opening are identified and analyzed. A three‐dimensional numerical model is developed for calculating turbulent diffusion combustion in a compartment with an opening. The model takes into account the conjugate radiative‐convective heat transfer on solid surfaces and the thermal conductivity of the wall and floor materials. The experimentally observed stages of flame development, flame projection through the opening, and stabilization of external combustion are reproduced in numerical calculations. The numerical values of flame‐projection time are in good agreement with the measurement results and proposed empirical relation.
TL;DR: In this article, a two-temperature mathematical model of steady filtration combustion is proposed, which takes into account the finite length of the reactor and the dependence of heat capacities of the phases on temperature and composition.
Abstract: A two‐temperature mathematical model of steady filtration combustion is proposed. The model takes into account the finite length of the reactor and the dependence of heat capacities of the phases on temperature and composition. The model describes the process of gasification of a solid fuel in a filtration regime. Calculation results for the gasification reaction of a carbon–nert component mixture are presented. The range of fractions of the fuel component is determined in which neither a purely normal nor a purely inverse wave is formed (an approach of a transitional wave is proposed for this interval). It is shown that the combustion temperature is finite within the entire interval of fractions of the fuel component.
TL;DR: In this paper, the effect of heat losses on solid flame combustion characteristics is considered and new steady-state three-dimensional periodic regimes are found that do not occur under adiabatic combustion conditions.
Abstract: The effect of heat losses on solid flame combustion characteristics is considered. New steady-state three-dimensional periodic regimes are found that do not occur under adiabatic combustion conditions. The essence of these regimes is explained using as an example the regime with six spots moving on helical lines in the near-surface layers of a cylinder. The spots are localized in the near-surface layers of a cylinder and do not intersect the central (located along the axis) zone of the sample. The interior of the cylinder (core) burns in a steady-state regime; i.e., along the cylinder axis, the front propagates at a constant velocity. An explanation is given for the existence of such regimes.
TL;DR: In this paper, the macrokinetics of combustion of agglomerates in a solid propellant flame using special samples of a model propellant generating monodisperse agglomers was investigated.
Abstract: The paper describes a procedure for studying the macrokinetics of combustion of agglomerates in a solid propellant flame using special samples of a model propellant generating monodisperse agglomerates Empirical dependences of the incompleteness of aluminum combustion in the combustion products of a propellant based on ammonium perchlorate and HMX on time and pressure were established The mass fraction of oxide accumulated on a burning agglomerate versus the degree of aluminum conversion was determined For fine agglomerates (310–350 μm), this fraction decreases with increase in the degree of conversion For large agglomerates (400–540 μmum), it increases, and, hence, the mass of large agglomerates increases as aluminum burns out Because of accumulation of oxide, the agglomerate size does not change markedly in the examined range of parameters
TL;DR: In this article, the problem of coal-particle lifting and ignition in a flow field formed by a shock wave passing along a dusty surface is considered, and particle dynamics are described on the basis of the previously developed and verified mathematical model, which takes into account the action of the Saffman forces and aerodynamic interference.
Abstract: The problem of coal‐particle lifting and ignition in a flow field formed by a shock wave passing along a dusty surface is considered. The particle dynamics is described on the basis of the previously developed and verified mathematical model, which takes into account the action of the Saffman forces and aerodynamic interference. Simulation of the coal‐particle reaction is based on the concepts of the surrounding film theory. Calculations that reveal qualitative and quantitative features of coal‐particle dynamics and ignition are performed. The combined mathematical model is verified by experimental data on trajectories and the dependence of the coal‐particle ignition delay on gas temperature behind the front of the transient shock wave.
TL;DR: In this article, the authors studied the parameters of transverse waves propagating over the surface of specimens pressed from colloxylin and double base propellants A and N. By means of microvideo-filming and thermocouple measurements, it was shown that the burning sites on the specimen surface are formed by a set of transversal waves.
Abstract: Parameters of transverse waves propagating over the surface of specimens pressed from colloxylin and double-base propellants A and N are studied. By means of microvideofilming and thermocouple measurements, it is shown that the burning sites on the specimen surface are formed by a set of transverse waves. Under atmospheric pressure, the transverse-wave front has the form of a step 0.5–1.1 mm high and decreases with increasing pressure or initial temperature of the specimen. The front propagates with variable velocities in the horizontal and vertical directions. The mean velocity of the transverse wave is three to eight times higher than the normal burning rate of the specimen as a whole (with a wide spread of local values) and increases with increasing pressure. Behind the front, combustion can be interrupted till the arrival of the next transverse wave. As in the SHS process, the reason for the emergence of the transverse waves is combustion-wave spatial instability.
TL;DR: In this paper, the process of nitration of aluminum and aluminum-containing mixtures in the regime of self-propagating high-temperature synthesis with a high pressure (up to 300 MPa) of the reacting gas (nitrogen) is considered.
Abstract: The process of nitration of aluminum and aluminum‐containing mixtures in the regime of self‐propagating high‐temperature synthesis with a high pressure (up to 300 MPa) of the reacting gas (nitrogen) is considered. The dependences of ignition temperatures and also burning temperatures and burning rates of these initial mixtures on test conditions (nitrogen pressure and composition of the initial mixture) are studied. The dependence of the burning rate of initial mixtures on factors affecting spreading of the liquid component (melt containing aluminum and nitrogen) over the surface of the second component (aluminum nitride or titanium diboride), such as the equilibrium wetting angle, interaction at the interface, and melting of the second component, is studied. The microstructure and some properties of materials obtained are examined. Based on these studies, the combustion mechanism is determined, a mechanism of phase formation in combustion of these mixtures is suggested, and the structure of the combustion wave is determined.
TL;DR: In this paper, the effects of heating and radiation on the properties of ultrafine diamonds are studied and quantitative assumptions on the kinetics of formation of ultra fine diamonds are made from analysis of IR spectra.
Abstract: IR spectra of ultrafine diamonds produced by different teams of researchers are studied. The effects of heating and radiation on the properties of ultrafine diamonds are studied. Quantitative assumptions on the kinetics of formation of ultrafine diamonds are made from analysis of IR spectra.
TL;DR: The plasmatron with gas-vortex stabilization of the arc, which was used in experiments, can provide, in a wide range of pressures and temperatures, a level of specific erosion of electrodes equal to 10-7-10-9 kg/C and a concentration of nitric oxide lower than 0.06 %, which has almost no effect on the flow structure and basic characteristics of ignition and combustion processes as mentioned in this paper.
Abstract: The quality of a high‐enthalpy air flow is considered in terms of simulating full‐scale flow parameters in studying supersonic combustion. It is shown that the plasmatron with gas‐vortex stabilization of the arc, which was used in experiments, can provide, in a wide range of pressures and temperatures, a level of specific erosion of electrodes equal to 10-7–10-9 kg/C and a concentration of nitric oxide lower than 0.06 %, which has almost no effect on the flow structure and basic characteristics of ignition and combustion processes.
TL;DR: In this paper, a flying steel plate against obliquely impacting tungsten heavy alloy long-rod penetrators was simulated using the NET3D code as a function of plate velocity ranging from −0.5 to 0.5 km/sec at an obliquity of 60°.
Abstract: The protection capability of a flying steel plate against obliquely impacting tungsten heavy alloy long‐rod penetrators was simulated using the NET3D code as a function of plate velocity ranging from −0.5 to 0.5 km/sec at an obliquity of 60°. The negativity in plate velocity was assigned if the plate had a velocity component in the direction of penetrator progress. Based on the residual kinetic energy of the penetrator after perforating the plate, the protection capability of the plate increased as the plate velocity decreased to a negative value at both a normal ordnance velocity (1.5 km/sec) and a hypervelocity (2.5 km/sec) impact. The defeat capability of the oblique plate increased as the impact velocity increased in the plate velocity range studied in this work. The interaction mechanisms between the penetrator and steel plate, responsible for these results, were investigated. The physical meaning of the results obtained in this work were discussed in the light of sensor‐activated and reactive armours.
TL;DR: In this paper, a physical mechanism responsible for the experimentally observed strong deceleration of the growth rate of the maximum skeleton temperature in a wave of filtration combustion of gases with increasing flow rate is established.
Abstract: A physical mechanism is established, responsible for the experimentally observed strong deceleration of the growth rate of the maximum skeleton temperature in a wave of filtration combustion of gases with increasing flow rate. The maximum temperatures of the gas and skeleton become commensurable, and the length of the thermal‐relaxation zone becomes much shorter. A classification of regimes based on the temperature‐heterogeneity criterion ϕ1 is proposed. Explicit analytical solutions are obtained for the wave for ϕ1≪1 and ϕ1→1. A correction to reverse reactions in combustion products is considered. The effect of composition on wave behavior is studied by means of numerical calculations with a detailed kinetic scheme. The activation energy for ultrarich and ultralean methane–air mixtures is evaluated. It is concluded that the limiting efficiency of the heat‐recuperation cycle in the wave is reached as ϕ1→1; methods for maximizing the efficiency are suggested.
TL;DR: In this article, it is shown that metal particles flying out into the gap due to the jet-formation effect can ignite in shock-compressed air, which can lead to chemical reactions with formation of TiO2 and TiN by the mechanism of internal combustion.
Abstract: Processes that occur in the welding gap during explosive welding are analyzed. It is shown that metal particles flying out into the gap due to the jet‐formation effect can ignite in shock‐compressed air. For most metals, the energy released thereby is small and has no significant influence on weld formation. In titanium welding on large areas, surface sections located far from the place of detonation initiation, which experience a long‐term action of a hot air flow, can dissolve a large amount of oxygen and nitrogen. If particles from these sections enter the gap, it can lead to chemical reactions with formation of TiO2 and TiN by the mechanism of internal combustion. The energy released in the gap per unit area is commensurable with and even greater than the kinetic energy of the accelerated (flyer) plate. Local bulging and rupture of metal observed in practice can be explained by ignition and combustion of gas‐saturated titanium particles in the welding gap.
TL;DR: In this article, the problem of a detonation wave propagating in a cylindrical column of a chemically active bubbly medium screened by a liquid from the tube walls is formulated and numerically solved within the framework of the Iordanskii-Kogarko two-phase model with allowance for energy dissipation due to acoustic radiation of bubbles.
Abstract: The problem of a detonation wave propagating in a cylindrical column of a chemically active bubbly medium screened by a liquid from the tube walls is formulated and numerically solved within the framework of the Iordanskii–Kogarko two-phase model with allowance for energy dissipation due to acoustic radiation of bubbles. The wave structure of the reaction zone and the detonation velocity of the bubbly medium column are calculated. It is found that the self-sustaining wave can propagate with a velocity greater than the velocity of one-dimensional bubble detonation by a factor of 1.5–2.5.
TL;DR: In this article, structural transformations have a pronounced effect on the propagation pattern of combustion waves and can either stabilize or destabilize combustion, and the major structural parameters appreciably affecting combustion wave stability are the initial porosity, particle size and pressure.
Abstract: Based on the two‐temperature, two‐velocity time‐dependent model of gasless combustion, taking into account structural transformations related to the force action of the gas filtering in the pores and vitrification and volume variation of the condensed phase during the chemical transformation, self‐oscillatory combustion modes are studied. Structural transformations are shown to have a pronounced effect on the propagation pattern of combustion waves and can either stabilize or destabilize combustion. The major structural parameters appreciably affecting combustion‐wave stability are the initial porosity, particle size, and pressure.
TL;DR: In this paper, the structure of heat release and the dynamics of formation of radicals and methane oxidation in a wave of filtration combustion of gases in fuel-rich methane-air compositions are studied with the use of skeleton diagrams and sensitivity analysis.
Abstract: The structure of heat release and the dynamics of formation of radicals and methane oxidation in a wave of filtration combustion of gases in fuel-rich methane–air compositions is studied with the use of skeleton diagrams and sensitivity analysis. Depending on heat release, the wave is divided into a preheating zone, an exothermic zone characterized by partial oxidation of methane in the reaction CH4 + 0.5O2 = CO + 2H2, and an endothermic zone with the conversion processes CO + H2O = CO2 + H2 and CH4 + H2O = CO + 3H2. It is shown that the composition of products in the wave front is essentially nonequilibrium. Several typical regions are also identified from the viewpoint of prevailing reactions of formation of the basic radicals in the wave. Thus, the dominating mechanism of chain branching is the reaction CH3 + O2 = CH3O + O in the “low-temperature” region, H2O2(+M) = 2OH(+M) and HO2 + CH3 = CH3O + OH in the “transitional” region, and H + O2 = O + OH in the “high-temperature” region. Two former regions correspond to the preheating zone and the latter region corresponds to the exothermic peak of the wave of filtration combustion of gases.