Home – Home – Jornals – Combustion, Explosion and Shock Waves 2017 number 1

Based on the previously developed model of detailed kinetics, the ignition delay time of hydrogen-silane/air two-fuel mixtures is calculated. The effect of the silane concentration and the temperature of the mixture on the ignition delay time is determined. It is shown that addition of a small (within 20%) amount of silane to the hydrogen-air mixture in the temperature range from 1200 to 2500 К leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations greater than 20%.

Possible scenarios of ignition and explosion development in coal mines are discussed. A principal possibility of complete quenching of detonation and combustion with the use of a sheet consisting of inert particles is experimentally demonstrated. As the detonation quenching process is rather complicated, it is recommended to focus the attention at the initial stage of ignition of the methane-air mixture, when it is possible to ensure effective quenching of the ignition site by using methods of advanced automatic monitoring and control with clear satisfaction of space and time requirements.

This paper presents the results of an experimental study of the ignition and combustion of pyrotechnic compositions based on microsized and ultra-nanosized aluminum particles in a model two-zone gas generator in which water is supplied as the oxidizer. The flow of the combustion products from the gas generator was video recorded, and the condensed products sampled behind the nozzle exit were studied by chemical and grain-size analysis. It was found that the replacement of aluminum microsized particles by ultra-nanosized particles in the samples led to »17% decrease in the active aluminum content in the condensed phase, a 10-15 % increase in the efficiency of the process in the gas generator (completeness of conversion of the pyrotechnic composition to the combustion products), and a factor of about three decrease in the ignition delay.

Results of an experimental study of a supersonic combustion chamber with a solid (continuous) and discrete (discontinuous) rear wall of the cavity are reported. The tests are performed in a short-duration wind tunnel with an attached pipeline at the input Mach number of 3, total temperatures of 2550-3140 К, and static pressures of 178-195 kPa. Heated kerosene is used as a fuel. Data on ignition conditions and kerosene combustion efficiency are obtained for different cavity configurations. The drag of internal elements of the combustion chamber, which form recess stabilizers, is estimated. An overall advantage of the combustion chamber with a discrete rear wall of the cavity over a solid rear wall is demonstrated.

Results of studying the influence of periodic application of a weak electric field on diffusion combustion of gaseous hydrocarbons are presented. The main attention is paid to investigating the effect of the electric field parameters on flame stabilization. Two types of electric fields are considered: 1) with a pulsed-periodic variation of the field strength in time and a constant configuration of force lines (pulsed-periodic electric field) and 2) with a change in the field configuration in time and a constant field strength (electric field with a time-varying configuration). Direct photo and video recording was used, as well as specrozonal detection of the natural luminescence of the flame (at wavelengths of emission of excited radicals OH* and CH*). It is shown that the region of flame stablization (ignition point) tends to the place with the maximum strength of the electric field. The action of the electric field with a time-varying configuration on combustion leads to flame stabilization in the plane of electrodes and to local intensification of combustion.

The effect of ignition conditions and the parameters of the melting of the inert component on unstable combustion modes was studied numerically using a model for the solid-state combustion of a disk. It is shown that the shape of the heated zone initiating combustion of the disk, determines the number and trajectories of zones of self-propagating combustion zone. The effect of the phase transition on the combustion characteristics is the more pronounced the closer the phase transition temperature to the combustion temperature. In this case, the combustion front takes the shape of a ring.

The synthesis of the composite material by thermal explosion of a reaction mixture of Ni + Al + Cr2O3 was studied. The thermodynamic parameters of combustion of the systems studied were estimated to predict the composition of the inorganic products (condensed or gaseous) of self-propagating high-temperature synthesis and calculate the adiabatic combustion temperature. It is shown that the synthesis process involves competing reactions in the sample volume which are responsible for the formation of a multiphase product. The influence of the content of Cr2O3 in the reaction system on the strength characteristics of the product synthesis. The microstructure of the synthesized samples, defined by their micro-hardness, toughness and residual porosity. The possibility of obtaining a homogeneous material based on NiAl intermetallic compound containing dissolved chromium and chromium oxide nanoparticles.

This paper presents the results of an experimental study of the dielectric relaxation of glycerol trinitrate in the temperature range of existence of the liquid-solid phase transition. The measurements were performed in the electric field frequency range of 1-1264 MHz. It is shown that the dielectric relaxation of glycerol trinitrate includes at least two relaxation process. Possible factors that determine the temperature and frequency dependence of the complex permittivity permeability of glycerol trinitrate are discussed.

Primary combustion products of B-based propellants are incomplete combustion products that are emitted from the gas generator of a solid ducted rocket. Studying the composition of primary combustion products provides valuable information about the primary combustion process and also helps to better understand the secondary combustion process. The particle size of the primary combustion products is analyzed by a laser particle size analyzer. The qualitative analysis of the sample composition is performed by using x-ray diffraction, x-ray photoelectron spectroscopy, and thermogravimetry-differential scanning calorimetry experiments. Based on these results, an integrated quantitative analysis of the sample composition is conducted. The quantitative analysis methods include tube furnace heating, ion chromatography, infrared spectroscopy, and inductively coupled plasma chromatography. In addition, scanning electron microscopy and energy dispersive spectrometry are also used to analyze the micro-morphology and distribution of different components in the sample. The primary combustion products mainly contain B, C, BmCn, H3BO3, B2O3, BN, Mg, MgCl2, and NH4Cl. BmCn (22-24%), H3BO3 (20%), and B (16.8%) are the three major components, while BmCn, B, and C (9.8-11.8%) are the three combustible components present in the highest amounts. The oxidant NH4ClO4 is completely consumed during the primary combustion, while the metal additive Mg does not show much reactivity. The micro-morphology and distribution of BmCn, H3BO3 (or B2O3), B, Mg, and C in the sample are investigated. Some components in the primary combustion products are found to be agglomerated, while some components are dispersed. Large particles in the sample mainly include B and Mg, while BmCn, H3BO3 (or B2O3), and C particles are small. In general, the combustion completeness of the primary combustion products is rather low. Therefore, better understanding and controlling of the secondary combustion process is very important to improve the performance of B-based propellants.

Pressure profiles in a transverse detonation wave propagating in a plane-radial vortex chamber during continuous spin detonation of a mixture consisting of lignite, syngas, and air are measured by specially designed and fabricated high-frequency pressure sensors based on TsTS-19 piezo-ceramics. Pressure levels in the detonation wave front relative to the mean static pressure are determined. It is demonstrated that these levels decrease toward the combustor center (by a factor of 20 and lower) as the wave intensity (velocity) decreases. Pressure oscillations behind the wave front testify to a complex gas-dynamic pattern of the processes in the wave region. A chemical reaction region is detected behind the wave front; its length is approximately 8% of the period between the waves.

A VISAR interferometer and a high-speed video camera are used to study the structure of detonation waves in bis-(2-fluoro-2,2-dinitroethyl)-formal mixtures with ethanol, whose mass concentration varied in the range of 0-35%. It is shown that the two types of instability existing in liquid explosives, which are the one-dimensional instability of the detonation front and the reaction failure wave instability on the edge of the charge, can be implemented in any combination. The reaction time of the studied mixtures are determined, and the varying nature of the dependence of the critical diameter of detonation and the reaction time on the diluents concentration is demonstrated.

The radiation transfer equation and the Mie theory are used in this paper to determine the optical properties of the PETN - aluminum nanoparticles compounds. In the case of laser initiation with a wavelength of 1064 nm, the illumination gain factor at a depth of 100 μm from the surface of the sample varies in the range from 1.070-3.308 for nanoparticles with the radius equal to 20-200 nm. The minimum dependence of the initiation energy density of explosive decomposition on the mass fraction of nanoparticles can be determined by the maximum value of the illumination gain factor in the sample. The dependences of the critical energy density of the initiation of the PETN - aluminum nanoparticles compound by pulses of the first and second harmonics of a neodymium laser on the nanoparticle radius with account for multiple scattering of light are determined. It is shown that account for the multiple scattering of light allows improving the agreement between theory and experiment.

The effect of the parameters of a charge of TNT and RDX alloys and their detonation conditions on the coagulation of carbon on the isentropes of detonation products. In the region of liquid nanocarbon, coagulation occurs by merging of nanodroplets and in the region of solid nanocarbon, by their joining (sintering) simultaneously with crystallization. Therefore, specific surface of nanodiamonds calculated from their sizes is always greater than the measured value. Separation of nanodroplets in the detonation products accelerates their coagulation and cooling due to the flow of cooler products around them. Evaluation of the distance between the surfaces of nanodroplets various alloys TG shows that they are small, smaller than nanodroplets. The conditions of rapid merging of nanodroplets during different deceleration of the products by rigid obstacles. An increase of up to five orders of magnitude in the size of diamond particles was established experimentally. The factors responsible for the change in the coagulation rate with the transition from heterogeneous to homogeneous TNT/RDX alloy with decreasing size of TNT/RDX particles.

A model for the spall fracture and compaction of a damaged material based on a description of the motion of a single pore is proposed. The model takes into account the strength properties, the effect of pressure, surface tension, and viscosity of materials and inertial forces. Equations describing the dynamics of growth and collapse of pores is presented. The proposed model can be used to calculate the spall fracture and compaction of liquids and metals, in both solid and liquid (molten) states.

A model for the penetration into a ceramic target with the formation of an expanding conical hole is proposed that can be used to determine the opening angle of the cone knocked out from the targets. The main cause of this fracture of ceramics is that the tensile strength of ceramic is much lower than its compressive strength. A method for calculating the maximum penetration velocity into a ceramic target without substrate was developed using the energy fracture criterion for ceramics. Two-dimensional numerical simulation of the impact of a steel projectile on a corundum plate showed satisfactory agreement between the calculated and experimental configurations of the resulting conical crack provided that the ratio between the compressive and tensile strengths is consistent with the recommendations of the developed model.

This paper describes the experimental and numerical study of the structures used for protection against the harmful effect of bullet and fission elements. A special place among them is taken by separated structures in which the gap between layers is filled with either air or various light materials with good damping, dissipative, and thermophysical properties. The results of the numerical simulation of the fragment of the separated protection are in good agreement with the experimental data on both residual forms and the size of deflections.