Home – Home – Jornals – Combustion, Explosion and Shock Waves 2020 number 2

An approach to studying the influence of the electric field on the flame with separate consideration of the effects of curving and extending of the plane flame is proposed. The degree of deformation can be used as a factor determining the action efficiency. Based on the results obtained by combined application of particle image velocimetry and spectral zonal registration, the change in the degree of deformation of the flame of a Bunsen-type burner located between flat electrodes is estimated.

The PIV and PLIF OH methods were used to experimentally study the structure of a jet impinging on a flat surface with swirl and combustion of a propane-air mixture with an equivalence ratio of 0.7 at distances between the nozzle and the surface H / d = 1 and 3 and in the absence of the impinged surface. The swirl parameter was 0.41 and 1.0, and the Reynolds number was 5000. It is concluded that for both values of the swirl parameter, the presence of the surface leads to the formation of an extended central cone-shaped recirculation zones. For H / d = 3 and 2, the intensity of OH fluorescence near the impinged surface and inside the recirculation zone significantly reduced. This effect is presumably caused by a decrease in the temperature of combustion products in the recirculation zone, including in the neighborhood of the flame front.

Combustion of FTi70 industrial ferrotitanium containing 65.9% of Ti and a model alloy of iron with 30.6% of Ti in nitrogen is described. It is shown that the degree of nitriding of the combustion products of industrial ferrotitanium is low. The distribution of nitrogen along the sample diameter is uneven. The dilution of the alloy with the final product increases in the degree of nitriding. The study of the combustion of the model alloy concludes that the degree of nitriding increases along with the melting point of the initial alloy. The composition of the combustion products of ferrotitanium is described.

The numerical simulation method is used to analyze the influence of a unit cell size on the burning rate of a donor-acceptor system. The cell size determines the fragmentation of a combustion wave. It is determined during calculations that, with an increase in the unit cell size, the average burning rate of the sample decreases. The combustion limits of a cellular system with external heat removal from the sample surface are determined: an increase in the unit cell size contributes to expansion of the combustion limits of the sample. The principal possibility of the synthesis in a chemical furnace for the cellular formation of the structure of the reacting system is shown.

Physicochemical changes occurring in an oxide shell of boron particles during heating are extremely important for the oxidation and combustion of boron, including those in solid propellant compositions. The Al₂O₃, MgO, MgF₂, Al, and Mg impurities were experimentally discovered in an oxide layer on boron particles obtained by various methods. The goal of this work is to determine the effect of these impurities on the thermal behavior of boron oxide, with particular attention paid to evaporation of B₂O₃. The temperature and thermal effects of reactions between the components are thermoanalytically determined, and the processes of dehydration, melting, and evaporation of boron oxide are analyzed in detail. The enthalpy of evaporation of boron oxide, starting at a temperature above 1 300^oC is experimentally determined, and is equal to 347 ± 3 kJ/mol. An interaction is observed between magnesium fluoride and boron oxide at a temperature of about 1 000^oC with a mass loss corresponding to the content of magnesium fluoride and the formation of gas-phase boron fluoride. It is established that boron dissolved in oxide has virtually no effect on the evaporation of the boron oxide melt, while the addition of Al₂O₃ or MgO significantly increases its thermal stability. Based on the analysis of the results obtained, an assumption is made about the effect of impurities on boron activity in the processes of boron ignition and combustion.

The effect of the modification of ASD-4 micron-sized aluminum powder with iron oxide on its oxidation in air is investigated. The modification consisted of coating the surface of metal particles with gel based on Fe(OH)(HCOO)₂ and ethylene glycol monomethyl ether, CH₃OC₂H₄OH, followed by heat treatment in air. It was found that the presence of iron oxide generally has a positive effect on the dynamics of oxidation ASD-4 powder when heated in air. The oxidation rate of modified powders increases with increasing content of iron oxide in them. X-ray diffraction analysis using a synchrotron radiation source under heating to 1 000 ^oC showed that the samples contained only the main phases γ-Al₂O₃ and α-Al₂O₃, γ-Fe₂O₃ and α-Fe₂O₃, and other iron oxides or intermetallic compounds were not found. At a mass concentration of 10 % Fe, an earlier appearance of the phase α-Al₂O₃ is observed and the exothermic peak of maximum heat release is shifted to lower temperatures (893 ^oC) compared to the unmodified ASD-4 powder (1 045 ^oC).

An approach to the mathematical modeling of the suppression of thermal decomposition and flame burning of forest fuels is proposed which is different from the well-known approaches in that a pyrolyzed FF layer is represented as a heterogeneous structure with high porosity and the thermophysical characteristics of this layer are described within the framework of additive mathematical models of thermal conductivity, heat capacity, and density. Experimental studies of the main thermophysical characteristics (thermal conductivity, heat capacity, thermal diffusivity) of typical FFs were performed. Mathematical modeling of heat- and mass-transfer processes under the conditions considered was performed, and the suppression characteristics of the destruction reaction of a typical FF were determined using the values of thermophysical characteristics established in the experiments. The ranges of the integral characteristics of FF flame suppression while varying the thermophysical characteristics of FF within the permissible limits were identified.

A comparative analysis of maximum pressures in a solid rocket motor obtained using exponential and real pressure dependences of the solid propellant burning rate on was performed. It is shown that at high exponents in the burning law, there is a large (tens of percent) difference between the maximum motor pressure obtained by the above two methods. In the case where the exponent is in the range of 0.3–0.4, the exponential pressure dependence of the burning rate overestimates motor pressure only by 2–3%.

This paper describes an experimental study pertaining to laser ignition of igniters of liquid rocket engines operating on such fuels as O_2g + kerosene, O_2g + ethanol, and O_2g + H_2g, and to how they ignite the fuel of a model combustion chamber. A quartz fiber based optical spark plug is described, which allows for multiple ignition of the igniter and the combustion chamber without replacing the spark plug. This study also touches upon possible types of pulsed lasers used in the laser ignition system, a fiber-optic laser igniter that remain insulated and efficient at a combustion chamber pressure of up to 10 MPa and more than 100 ignition cycles.

Cellular detonation in suspensions of two fractions of submicron and nano-sized aluminum particles is studied by numerical methods. Approaches of mechanics of heterogeneous media are used. The transition from the continuum to free-molecular regime of the flow around the particles is taken into account in the processes of interphase interaction. Particle combustion is described within the framework of the previously developed model of reduced kinetics. The results calculated for two-dimensional flows in a plane channel reveal significant differences from suspensions of two fractions of microparticles, where degeneration of transverse waves is observed. In the present study, weakly regular and irregular cellular structures are formed, which is also confirmed theoretically on the basis of the acoustic analysis based on the Barthel method.

Results of experimental investigations in a flow-type annular cylindrical combustor with an outer diameter of 503 mm are reported. The influence of air addition to products of continuous spin detonation of CH₄/mH₂-air mixtures on the parameters of detonation waves, pressure in the combustor, and specific impulse is considered. It is demonstrated that addition of air to detonation products increases the velocity of continuous spin detonation, the pressure in the combustor, and the thrust, whereas the specific flow rate of the fuel decreases.

A closed mathematical model of continuous spin detonation with the chemical kinetics equation correlated with the second law of thermodynamics is developed for a hydrogen-air mixture within the framework of quasi-three-dimensional unsteady gas-dynamic formulation. The model takes into account the reverse influence of the oscillation processes in the combustor on the injection system of the mixture components. For comparisons with experimental data, the numerical simulations are performed for the geometric parameters of the flow-type annular combustor with an outer diameter of 306 mm used in the experiments. For the flow rates of the mixture varied in the interval 73.1-171.3 kg/(s·m²), the one-wave, two-wave, and three-wave regimes of continuous spin detonation are calculated, the flow structure is analyzed, the specific impulses are determined, and comparisons with experimental data are performed. It is shown that the use of a simplified single-stage kinetic scheme of hydrogen oxidation, which was used in some investigations, for simulating continuous spin detonation leads to results that differ from the experimental data by several times.

Shock-wave initiation of chemical reaction in pressed pellets of a stoichiometric mixture of Al and CuO powders in a steel tube was studied. The dynamics of the chemical transformations in the heterogeneous flow of reaction products of the mixture during dispersion of the pressed pellet material in a rarefaction wave was investigated. From the results of pyrometric measurements, the maximum brightness temperature of chemical reaction products was ≈3 500 K.

This paper presents the results of measuring the thresholds of explosive decomposition of PETN-coal under the action of laser radiation pulses (λ= 1 064 nm and τ= 14 ns). Samples whose thickness is 1 mm and whose densities are 1.1 and 1.7 g/cm³ with inclusions of submicron particles of brown coal (750 nm) are investigated. A minimum explosive threshold of 1.8 J/cm² is reached with a concentration of inclusions of 0.5 % (by weight). The explosion is adiabatic. Composites with a density of 1.1 g/cm³ have a scattering matrix. A minimum explosive threshold of 2.3 J/cm² is obtained for a concentration of inclusions of 1 %. An extinction rate is estimated: k_ext = 135 cm^-1. Radiation is absorbed at a depth of <0.1 mm. Explosive decomposition in an unirradiated section develops according to the shock-wave mechanism of explosive combustion.

This paper describes an experimental study of the shock compression of samples simulating media with a given porosity using epoxy-based spheroplastics with filler made of glass microspheres with volume concentrations of 0.27 and 0.55. Shock adiabats in a pressure compression range of 0.1-1.2 GPa are obtained. The shock compression pressure at which the fracture of the used microspheres begins is estimated. The dependence between the nature of deformation and the concentration of microspheres in the sample is established.

This paper presents the results of metallographic analysis of the melting of C1 lead under shock-wave loading and unloading. Loading of lead samples in a titanium capsule was carried out by a plane shock wave using an aluminum projectile 6 mm thick, which was accelerated by detonation products of an explosive. The results of metallographic analysis of samples in the initial state, subjected to heat treated under normal conditions, and recovered after shock-wave loading are given. Melting traces were found in lead after shock-wave loading by a pressure of 25.6 GPa and subsequent unloading.