Vol 53, No 1 (2017)

Based on the previously developed model of detailed kinetics, the ignition delay time of two-fuel hydrogen–silane–air 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 K leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations higher than 20%.

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 using water as oxidizer. The flow of combustion products from the gas generator was video recorded, and the condensed products sampled behind the nozzle exit were studied by chemical and particle-size analyses. It was found that the replacement of microsized aluminum particles by ultra-nanosized particles in the samples led to a ≈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 combustion products), and a factor of about three decrease in the ignition delay.

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); (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 spectrozonal registration 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 stabilization (ignition point) tends to the place with the maximum strength of the electric field. The effect of the electric field with a time-varying configuration on combustion is the flame stabilization in the plane of electrodes and local intensification of combustion.

The synthesis of a composite material by thermal explosion in 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 was studied. The microstructure of the synthesized samples was examined, and their micro-hardness, toughness and residual porosity were determined. The possibility of obtaining a homogeneous material based on NiAl intermetallic compound containing dissolved chromium and chromium oxide nanoparticles is shown.

Primary combustion products of boron-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, B_mC_n, H₃BO₃, B₂O₃, BN, Mg, MgCl₂, and NH₄Cl. B_mC_n (22–24%), H₃BO₃ (20%), and B (16.8%) are the three major components, while B_mC_n, 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 B_mC_n, 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 B_mC_n, 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.

A VISAR interferometer and a high-speed streak camera are used to study the structure of detonation waves in bis-(2-fluoro-2,2-dinitroethyl)-formal (FEFO) mixtures with methanol, 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 is determined, and the different character of the dependence of the critical diameter of detonation and the reaction time on the diluent concentration is demonstrated.

The effect of the parameters of a charge of TNT/RDX alloys and their detonation conditions on the coagulation of carbon on the isentrope of the detonation products is analyzed. In the region of liquid nanocarbon, coagulation occurs by coalescence of nanodroplets and in the region of solid nanocarbon, by their joining (sintering) simultaneously with crystallization. Therefore, the specific surface area of nanodiamonds calculated from their sizes is always larger than the measured value. Separation of nanodroplets in 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 in various TNT/RDX alloys shows that they are small, smaller than nanodroplets. The conditions of rapid coalescence of nanodroplets during different deceleration of the products by rigid barriers are analyzed. 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 are discussed.

A model for the penetration of a ceramic target with the formation of an expanding conical hole is proposed that can be used to determine the apex angle of the cone knocked out from the target. The main cause of this fracture of ceramic targets is that the tensile strength of a ceramic material is much lower than its compressive strength. A method for calculating the maximum penetration velocity in 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 corresponds to the recommendations of the developed model.