The electrical resistance of copper foil under multiple shock compression to a pressure of 40 GPa is studied experimentally in several explosive systems: in a reflected shock wave, under compression in a rigid shell, and in a layered system generating a sequence of waves of increasing amplitude. An improved design of the measuring cell is proposed, which significantly reduces the influence of parasitic eddy currents on the recorded voltage. Under shock compression, the electrical resistance of copper increases monotonically, but the growth rate depends on the loading history. Under compression by a sequence of shock waves, the electrical resistance of the metal is lower than under compression by a single shock wave (at the same incident shock pressure in the dielectric shell). In this case, the main change in the electrical resistance of copper occurs in the first shock wave. In subsequent waves, the electrical resistance also increases, but the final value is lower than in a single shock wave. The crystal structure defect concentration in a copper sample under complex loading is estimated. Under multiple compression, the defect concentration is lower than in the case of single compression (at the same wave pressure or deformation). This implies that during complex shock loading, defects are mostly generated in the early stages of compression, and subsequently there is only a relatively small increase in the number of defects. Qualitatively, the defect concentration during complex shock loading is determined by the deformation in the first shock wave.
The interaction of a shock wave with a near-wall gas bubble (transverse cylinder) filled with a hydrogen–oxygen mixture with added xenon is numerically investigated in a two-dimensional plane formulation using the Euler equations. Gas combustion is modeled using a detailed kinetic mechanism involving 19 reversible reactions. A high-order WENO finite difference method is applied. Shock wave refraction and reflection, as well as the focusing of secondary shock waves, are described. Various detonation initiation modes in the bubble are detected: direct initiation, initiation with shock refraction and reflection from the wall, and initiation with shock wave focusing on the symmetry plane near the wall. Based on a series of calculations, the dependence of ignition regimes and threshold Mach numbers of the incident shock wave on the bubble shape is determined. It is shown that the combination of shock focusing on the bubble and reflection from the wall leads to a significant decrease in threshold Mach numbers compared to both a plane layer of combustible gas in front of the wall and a free bubble without a wall.
This paper presents the most important gas-dynamic and kinetic parameters of combustion, explosion, and detonation for ammonia/oxygen combustible systems. Stoichiometric, lean, and rich compositions are considered with the addition of molecular nitrogen, which corresponds to the transition from fuel–oxygen mixtures to fuel–air mixtures. The same parameters are also reported for fuel-air mixtures across a range of concentrations from the lower to the upper flammability limit and as a function of initial pressure. From the perspective of explosion safety, the most critical data concern the critical initiation energy, which enables analysis of the relative hazard of different mixtures. Critical energy E_* is defined as the minimum initiator energy required to sustain the propagation of combustion and detonation waves in the mixture under study: the lower this energy, the more hazardous the mixture. Additionally, data on the detonation cell size are presented; this length scale is used to determine characteristic parameters of combustion chambers.
A coupled combustion model is used to study unsteady combustion of a metallized composite solid propellant with a harmonic pressure change above the propellant surface. The propellant combustion model includes chemical reactions in the condensed and gas phases. Above the propellant surface, the convection and diffusion of gas mixture components, the two-phase nature of the flow, the velocity and thermal nonequilibrium of phases, and aluminum particle combustion are taken into account. The boundary conditions of equality of mass and energy fluxes are specified on the propellant surface. The results of a theoretical computational study of the dependence of the propellant burning rate on the amplitude and frequency of pressure oscillations are presented. The study is carried out for two values of the gas-phase reaction order. The influence of the frequency of pressure oscillations on the amplitude of change in the propellant burning rate is determined.
We have studied the effect of preliminary mechanical activation (MA) of carbon black powder on the properties, densification, and combustion behavior of equiatomic Ti + C mixtures. MA has been shown to cause breakdown of the arched structure and disintegration of agglomerates of carbon black, leading to an increase in its bulk density by more than three times. During densification, carbon black powder behaves as a solid nonplastic material with a high elastic recovery value (up to 14
This paper presents the results of an experimental study of the ignition of electrode carbon samples heated by an integral flux of thermal radiation. The experiments were carried out using an Uran-1 radiant heating system in the range of heat flux density incident on the sample surface 75–314 W/cm2 in oxygen at different pressures (0.1 and 1.1 MPa). Ignition temperature values and the dependence of the ignition delay time on the heat flux density were obtained. The formal kinetic constants of the process were determined from the measured dependences using a heterogeneous ignition model.
The detonation of acetylene–oxygen mixtures diluted with helium or argon is studied in an extended channel with a flow-through supply of explosive mixture components at atmospheric pressure. The steady detonation velocity and the temperature and dynamic pressure of the products were calculated. The limits of existence of self-sustaining detonation in a channel with a diameter of 26 mm are determined for equimolar and stoichiometric mixtures diluted to 92
We have developed a reaction mechanism for the ignition and combustion of C3H8/nC4H10/iC4H10 three-component surrogates for liquefied petroleum gas-based alternative fuels. The mechanism describes the ignition of the surrogates at both high and low temperatures and also in the region of negative temperature coefficient. The mechanism involves 442 reactions for 84 components. We present results of testing the mechanism against experimental data for the ignition delay time of isobutane mixtures and petroleum gas mixtures containing propane, n-butane, and isobutane (T0 = 670–1478 K, p0 = 1–30 atm, ϕ = 0.3–2.0); for the laminar flame speed in isobutane–air mixtures; and for the concentrations of major isobutane oxidation products on a flat flame burner.
Continuous spin and multifront detonations of carbon-free ammonia/hydrogen–air mixtures are obtained for the first time in an annular cylindrical combustion chamber with a diameter of 503 mm. Binary ammonia/hydrogen fuel with a mass fraction of H_2 in the fuel ranging from 0.105 to 0.485 is investigated at specific mixture flow rates of 22- 347 kg/(s m2) and a fuel equivalence ratio ϕ = 0.47- 1.55 . Single-wave and double-wave continuous spin detonation regimes with a velocity of 1.15- 1.59 km/s and a wave rotation frequency of 0.73- 1.81 kHz at ϕ = 0.73- 1.2 are obtained in ammonia/hydrogen–air mixtures with three fuel compositions: NH_3 + 8H_2 , NH_3 + 4H_2 , and NH_3 + 2H_2 , and continuous multifront detonation with two opposing transverse detonation waves with a rotation frequency of approximately 1.0 kHz at ϕ = 0.72- 1.0 is achieved for the NH_3 + H_2 composition. The regions of continuous spin detonation and continuous multifront detonation regimes are determined as functions of the ammonia content in the binary fuel and the air manifold pressure. The pressure profiles in the air manifold and in the region of rotation of transverse detonation waves in the combustion chamber are measured using high-frequency sensors. Thrust forces and specific impulses are determined. The maximum thrust impulses obtained in the combustion chamber are 2300, 1500, 1350, and 900 s for binary fuel mixtures with a hydrogen mass fraction of 0.485, 0.32, 0.19, and 0.105, respectively.
In self-propagating high-temperature synthesis processes, one of the important problems is the predictability and reproducibility of the combustion regime. It is well known that different grades and even different batches of the same metal powders used in synthesis consist of particles of dissimilar shapes and sizes and contain various amounts of gasifiable impurities. Consequently, the burning rates of powder mixtures of the same composition prepared from such powders can exhibit a severalfold difference. Previously, we determined the burning rates of mixtures of titanium narrow fractions of a single grade over a wide range of particle sizes of the initial titanium powder for a granulated 5Ti + 3Si mixture. In the present work, we calculate the corresponding values for Ti + C . These values are well approximated by power-law functions with a determination coefficient R^2 > 0.97 . The resulting approximating dependences are adopted as baseline dependences. The burning rates of other titanium grades are compared precisely with these baseline dependences. For individual narrow fractions of other titanium grades, the burning rates of powder and granulated mixtures of 5Ti + 3Si and Ti + C are measured. Experiments have shown that the baseline dependences of the burning rate on the titanium particle size make it possible to predict the burning rates of granulated self-propagating high-temperature synthesis mixtures of the same composition for narrow fractions of other titanium grades with an accuracy of no worse than 30
This paper examines the influence of component ratio, mechanical activation, and preclamping of samples on the combustion speed and elongation of unclamped samples during synthesis and the phase composition and morphology of combustion products in the (5Ti + 3Si) + (Ti + 2B) system. The combustion front did not reach the lower end face of the sample prepared from a 5Ti + 3Si starting mixture. Preclamping, mechanical activation of the 5Ti + 3Si mixture, or the addition of a Ti + 2B mixture enabled complete combustion of the sample. Mechanical activation of (100 – x)(5Ti + 3Si) + x(Ti + 2B) mixtures increased the elongation and combustion speed of the samples. The combustion speed was shown to have a tendency to decrease with increasing 5Ti + 3Si content. Preclamping increased the combustion speed of the samples prepared from the mechanically activated mixtures and had little or no effect on the combustion speed of the samples prepared from the starting mixtures (except for the Ti + 2B mixture). For some starting mixtures, preclamping led to shrinkage of the samples. The samples containing 20
In order to determine the parameters of the Lee–Tarver trinomial ignition growth model of explosives, a method for determining the parameters of the Lee–Tarver trinomial ignition growth model using genetic algorithm and the relationship of reaction rate is proposed. This method first extracts the characteristic points of the test pressure, and then uses the self-programmed genetic algorithm program to analyze and process the physical information of the flow field and calibrate the parameters of the Lee–Tarver trinomial ignition growth model. The results show that the pressure curve calculated by the parameters of the Lee–Tarver trinomial ignition growth model obtained by the genetic algorithm is consistent with that calculated by the standard parameters, and the maximum peak error is 6.3
The excitation and propagation of exothermic reaction waves in a closed channel filled with gaseous oxygen at initial pressures of 0.1- 2 MPa are studied. The waves are excited by a heated Nichrome spiral coated with a small amount of VM-4 vacuum oil or render pork fat. The wave parameters and initial pressures at which flame propagation occurs in the channel are determined.
The mechanism of chain development during thermal gas-phase oxidation of methane was studied experimentally and theoretically. It has been established that the limiting stage, which determines the development of the process as a whole, depends on the conditions under which it is carried out. At a temperature of 728 K, the development of the process is determined by the interaction of peroxide radicals with each other. Increasing the temperature to 873 K leads to an increase in the role of reactions of peroxide radicals with formaldehyde, and then the limiting stage of the process becomes the interaction of peroxide radicals with methane. In this case, changes in pressure and temperature have the same effect on the ratio of concentrations of hydroperoxide and methylperoxide radicals, obtained both by calculation and experimentally.
Using an experiment with a lead shell as an example, a method for studying the quasi-isentropic compressibility of condensed substances was tested based on the use of multiframe radiography and explosive spherical loading devices with gas symmetrization. At the moment of maximum compression, the average density of the lead shell of ≈ 1pt 52.3 g/cm3 is reached and the compression ratio is ≈ 1pt 4.6 in this case. Total pressure in lead at the moment of maximum compression was ≈ 1pt 3.2 TPa, while the cold component was equal to ≈94
The energetic potential of ten fluorodinitromethyl-ONN-azoxy compounds as plasticizers of a binder in model solid composite propellants of various formulations, with a metal (aluminum hydride or metallic aluminum) and without it, was studied. The energetic potential of the specified plasticizers was compared with the potential of the most energetic known plasticizers (nitroglycerin, tetranitromethane, dinitrofurazan) in relation to model solid propellants intended for different stages of rocket systems. It has been shown that almost all of the studied fluorodinitromethyl-ONN-azoxyfurazans, when used as components of an active binder, provide higher energy indicators than nitroglycerin and tetranitromethane, and some of the fluorodinitromethyl-ONN-azoxyfurazans are superior in efficiency to dinitrofurazan. High-performance quantum-chemical calculations of the enthalpy of formation of new, not yet synthesized high-energy substances that are promising in various fields of application were carried out.
Despite numerous studies, many aspects of ignition and propagation of combustion and detonation waves in combustible mixtures remain insufficiently studied, which complicates the scientifically-based control of these processes. This paper presents new data on the various stages of ignition and a flame front propagation in a plane (two-dimensional) channel of constant cross section. The experimentally observed main flame instabilities (manifested in the significant nonuniformity and nonstationarity of the combustion front), the phenomenon of flame blowout (disappearance of glow), and the transition of the flame to a self-sustaining propagation mode are discussed. Attention is drawn to the problems of the occurrence of new ignition sources of the mixture in the flame front, including explosive microsources that contribute to the subsequent transition of combustion to detonation. A number of new features in the physics and dynamics of flame propagation have been identified.
The experimental and calculated results of the study of formation and growth of soot particles in a standard flat ethylene/air flame with the addition of dimethyl ether (DME) are presented. Two-dimensional laser-induced incandescence (2D-LII) was used as an experimental method to obtain data on the soot volume fraction in the flame. The time-resolved LII signal allowed us to obtain information on the mean size of soot particles depending on the height above burner (HAB). Kinetic modeling was carried out using a modern kinetic mechanism of pyrolysis and oxidation of hydrocarbons, including a sectional model of soot particle growth. DME additives have been shown to reduce soot volume fraction without significantly affecting final particle size. In addition, DME additives slow down the initial stages of soot particle formation but accelerate their subsequent growth.
The results of numerical modeling of experiments conducted using proton radiography and synchrotron radiation to record the process of movement of a flow of fine metal particles in gaseous media are presented. The emission of particles occurred as a result of the impact of a shock wave on the free surface of metal samples with small-scale profiled initial disturbances. Numerical modeling was carried out using a developed model of the evolution of a particle flow in a gas medium, which is based on a model of the source of shock-wave dusting of metals, based on the physics of the Richtmyer–Meshkov instability, and the laws of fragmentation of a single liquid droplet in a gas flow. It is shown that the proposed model has good agreement with the experimental results.
This paper presents an experimental study of the ignition and combustion of coal–water slurry fuel (CWSF) droplets in a high-temperature oxidizing environment at 700- 900 °C. The effect of adding waste motor oil as a component of CWSF and as a feedstock for generating syngas to be fed into the CWSF combustion zone is investigated. The feasibility of co-combustion of CWSF with syngas has been experimentally confirmed. The gas-phase ignition delay of CWSF droplets with the addition of syngas to the combustion zone is 1.1- 1.2 times shorter compared to CWSF combustion without adding syngas. Under these conditions, the heterogeneous ignition delay is reduced by a factor of 1.3- 1.7 and the combustion duration is shortened by a factor of 1.2- 1.5 . The use of waste oil as a component of CWSF provides a significant improvement in energy performance, which, combined with the increased combustion temperatures, makes this strategy the most attractive for practical implementation.
