Vol 52, No 3 (2016)

The propagation of fuel-rich hydrogen–air flames with added ethanol has been studied using numerical methods. It has been shown that the inhibition by ethanol is less effective compared to propane and propylene. The addition of ethanol leads to the effect of superequilibrium temperatures, but it takes place only at ethanol concentrations above a certain value. At the flammability limit of fuel-rich mixtures of hydrogen, ethanol, and air, determined by the Le Chatelier rule, the estimated maximum flame temperature is constant. The exception is mixtures with a small addition of ethanol.

The paper describes the formation of the combustion zone structure of a titanium powder layer in inclined rectangular air channels with natural gas filtration. It is shown that heterogeneous combustion near the critical conditions of its existence with limited supply of gaseous reagent in the reaction zone and under the effect of gravitational forces is accompanied by rearrangement of the plane homogeneous front into more complex wave structures: cellular, cross-cellular, and heterogeneous. The features of the process under study is the presence of gaseous impurities affecting the gas exchange in the reaction zone, the destabilization of the plane front, and the formation and propagation of heterogeneous and cellular wave structures.

Basic characteristics of combustion of the diesel fuel in a novel autonomous burner with injection of superheated steam into the combustion region are studied. The temperature distribution in the flame is obtained. Calorimetric measurements of heat release and gas analysis of combustion products are performed. The environmental effects of fuel combustion are compared for regimes with injection of a steam jet and an air jet. It is demonstrated that the combustion regime with steam gasification ensures high combustion intensity and combustion efficiency; moreover, the combustion process becomes more environmentally friendly.

This paper presents the experimental study of ignition and combustion of micro- and nanoparticles of aluminum diboride as part of pyrotechnic energy-saturated compositions in a gas generator with an air afterburner chamber and the thermodynamic calculations of combustion of pyrotechnic compositions based on aluminum diboride in air. The discharge of the combustion products from the afterburner chamber is recorded on video. It is shown that replacing micron aluminum diboride by powdered diboride with a mass-average diameter of particles equal to ≈270 nm in the pyrotechnic composition and increasing the pressure in the afterburner chamber cause the combustion efficiency in air to increase by 5–20%.

The thermal effect of the phase transition on unstable regimes of gasless combustion is numerically studied within the framework of the model of solid flame combustion of a cylindrical sample. The closer the phase transition temperature to the burning temperature, the more pronounced the effect of the phase transition on the combustion character. In this case, the combustion front surface is noticeably smoothed owing to reduction of temperature gradient values. A relationship between the change in the combustion modes considered in the study and the change in the phase transition parameters is found. An unsteady periodic symmetric mode of combustion with ring-shaped trajectories of motion of combustion sites over the side surface is obtained.

Experiments aimed at studying the ignition of coal dust obtained by coal disintegration in high-energy mills are performed in a tubular furnace. Effective kinetic constants of ignition of coal dust ground in a vibrational–centrifugal mill and in a disintegration mill under conditions of rapid heating are determined for the first time. It is shown that the volatile release rate depends on the method of coal grinding.

To better understand the detonation characteristics of ammonium nitrate (AN) and activated additives mixtures, potassium chloride (KCl) and monoammonium phosphate (MAP) are mixed with AN by different mixing methods. The UN gap test and scanning electron microscopy are applied to study AN and AN-additive mixtures. For the mechanical mixing method, the detonation velocity of AN-additives decreases with increasing the additive proportion, while the detonation velocity of modified AN prepared by the solution mixing method shows the opposite tendency. It is proved that the sensitivity to shock waves increases as the size of AN particles decreases. The type of additives, the mixing methods, and the particle size distribution are important parameters that affect the detonation characteristics of AN.

The optical thermal radiation arising from the shock collapse of glass or polymer microballoons in a transparent condensed medium (water or polymerized epoxy resin) was detected. The temporal characteristics of the detected radiation in the pressure range 0.5–29 GPa at different viscosities of the material surrounding the pore were determined. The brightness temperature of hot spots was estimated to be 1600–3200 K at a pressure of 2–29 GPa. The length of the leading edge of the radiation pulse corresponding to the time of hot-spot formation increases from 2 · 10⁻⁸ to 30 · 10⁻⁸ s, depending on the shock-wave intensity and the viscosity of the material surrounding the pore. Analysis of the data shows that in the pressure range 5–29 GPa, hot-spot formation is dominated by the hydrodynamic mechanism of collapse and in the range 0.5–5 GPa, by the viscoplastic mechanism.

The analysis of the dynamic response of a circular tunnel in three types of soil at different depths under surface detonation of a 250-kg TNT charge reveals that the tunnel peak particle velocity and the failure zone length are sensitive to the soil type and material properties. The buried tunnel in silty clay sand has the least damage; the length of the failure zone is 5 m in the longitudinal direction and 0 to 60° at the top arch.

Regimes of continuous spin detonation of two-phase kerosene–air mixtures with small addition of hydrogen are obtained for the first time in a flow-type annular cylindrical combustor 503 mm in diameter.