Vol 54, No 1 (2018)

This paper describes the study of evaporation and combustion of ethanol under a horizontal wall in a stratified shear gas layer in the case of the Rayleigh–Taylor instability. Data on the nature of flow are obtained with the use of particle image velocimetry (PIV), and temperature profiles are recorded by a thermocouple. It is shown that cells are formed in a narrow range of air velocity of 0.6 ± 0.05 m/s and does not depend on the height of the obstacle (backward ledge or an edge is 0–7 mm in height). The flow between the wall and flame front is an alternation of mushroom-shaped structures moving from one wall to another. In the cellular flame, the flow of substance (with respect to the air flow) exceeds its level in a standard laminar boundary layer three times. The averaged transverse velocity is directed away from the wall in the boundary layer with combustion without cells, and it is reduced and directed toward the wall in the cellular flame between the wall and flame front.

Estimates are obtained for the maximum efficiency of a system consisting of a heat recovery burner connected to an ideal Carnot heat engine. The burner serves as a heater of the ideal heat engine, and the cold side is at the ambient temperature. Combustion products heat the hot wall of the ideal engine and then transfer heat to the combustible mixture supplied to the combustion chamber. Recovery of the heat of the combustible mixture occurs through the heat-conducting wall of a countercurrent heat exchanger, in which the combustion products and the combustible mixture move toward each other in the channels connected by a heat-conducting partition. An estimate is obtained for the total efficiency of the system, which is defined as the ratio of the net power of the ideal engine to the chemical energy flux reaching the burner device. It is shown that the total efficiency of the system can approach the Carnot-cycle efficiency with the maximum possible temperature of the hot side of the ideal heat engine.

The effect of the thermocapillary flow of melt of inert components of gasless mixtures on the spinning combustion regimes of cylindrical samples has been studied numerically. The change in the structure of the spinning combustion wave due to a change in the sample radius is discussed, and new spinning combustion regimes are found. Increasing the melt flow velocity leads to stabilization of the combustion, i.e., to the transition from spinning regimes to the stationary propagation of the combustion wave.

This paper presents the results of mathematical modeling of the combustion of flow of a multifractional suspension of an aluminum powder in air taking into account the nonequilibrium nature of the process. The calculations were performed for air-to-fuel ratios α = 0.1–0.5. Time dependences of thermodynamic parameters, the completeness of metal particle combustion, and the relative residence time of the fractions in the flow were obtained. The adequacy of the nonequilibrium model for describing thermodynamic processes was validated by comparing with the equilibrium model for time tending to ∞. The necessity of taking into account the formation of Al₂O suboxide present in the range of the air-to-fuel ratio is analyzed and proved. The need to include nitriding reactions in the mathematical modeling for 0.1 ≤ α < 0.4 is shown by comparing the results of calculations based on equilibrium and nonequilibrium thermodynamics.

The sequence of phase formation in the oxidation of ASD-4 aluminum powder modified by vanadium pentoxide during heating in air in the temperature range 873–1073 K has been studied by synchrotron radiation x-ray diffraction. It has been shown that the sharp acceleration of the oxidation of the modified powder is related to the loss of the protective properties of the oxide shell on the particle surface due to the polyvalence of vanadium, which provides structural and phase changes on the surface and in the depth of the oxidized metal.

Propagation of a detonation wave in monodisperse suspensions of reacting particles (based on the model of the suspension of aluminum particles in oxygen) in channels with linear expansion is studied within the framework of mechanics of heterogeneous reacting media. Reduced kinetics is described with allowance for the transitional (from diffusion to kinetic) regime of combustion of micron-sized and submicron-sized spherical aluminum particles. The effects of the channel width, particle diameter, and expansion angle on propagation conditions and detonation regimes are determined. The critical channel width is found to be a nonmonotonic function of the expansion angle, which is associated with qualitatively different wave patterns behind an oblique step. Flow charts are constructed, and the results are compared with solutions of problems of heterogeneous detonation wave propagation in channels with a backward-facing step and with sudden expansion.

The standard enthalpies of combustion and formation of 7H-tris([1,2,5]oxadiazolo) [3,4-b:3′,4′-d:3″,4″-f]azepine, its bimolecular crystal with the γ-polymorph of CL-20, and the γ-polymorph of CL-20 have been experimentally determined. The standard enthalpies of formation of the bimolecular crystal and an equimolecular mechanical mixture of γ-CL-20 with azepine differ by less than 12.8 kJ/mol. This small difference is validated by quantum chemical calculations. It has been experimentally found that the presence of azepine in the bimolecular crystal inhibits the thermal decomposition of γ-CL-20 and increases the thermal stability of γ-CL-20 in the bimolecular crystal as compared to original γ-CL-20.

A gas explosion accident is often followed by a serious fire. In order to effectively prevent fire induced by a gas explosion accident, it is necessary to have some knowledge of the related explosion processes. The subject of the present study is to examine deflagration behaviors beyond the original cloud of the ethyne–air mixture and the fireball size in an ethyne–air explosion by means of numerical simulations. The explosion overpressure, flow velocity, and reaction rate distribution in an ethyne–air explosion are obtained. The peak explosion overpressure is found to reach its maximum beyond the original cloud for ethyne–air mixtures with ethyne concentrations greater than 13% (by volume). The explosion pressures beyond the original cloud may be higher than those within the cloud for these ethyne–air mixtures. The ratio of the combustion range to that of the original cloud is 1.4–2.7 in the radial direction on the ground and 1.5–4.0 along the axis of symmetry perpendicular to the ground.

The compression of ceramic (corundum) tubes by the detonation products of explosives have been studied experimentally and numerically. The formation of the shaped-charge jet of ceramic particles and its effect on steel witnesses targets has been investigated. The tubes were produced by detonation spraying. Ceramic particles were deposited on copper tubes, which were then dissolved in a solution of ferric chloride. In the experiments, a considerable penetration of the flow of ceramic particles was observed. During the interaction of the flow with the target, the target material was partially evaporated, as shown by metallographic analysis. Numerical analysis of the formation of the discrete shaped-charge jet showed that the maximum velocity of the jet head was about 23 km/s, and the velocity of the main part of the jet was about 14 km/s.