V. G. Shevchuk

Flame Propagation in Two-Component Aluminum–Boron Gas Suspensions

Flame propagation in gas suspensions of boron particles, in boron–aluminum mixtures, and in aluminum–inert additive mixtures is experimentally studied. General features of the process are revealed, and flame-propagation velocities in two-component boron-containing mixtures are measured. It is shown that, in the considered range of parameters of the suspensions, addition of boron to aluminum retards flame propagation. The decrease in the flame-propagation velocity in boron–aluminum mixtures is more pronounced than in analogous aluminum–inert additive mixtures. The latter can be attributed to oxygen consumption by boron in relatively low-exothermal reactions yielding boron suboxides and, correspondingly, oxidant deficiency for the leading process of aluminum combustion. Key words: flame, velocity, gas suspension, aluminum, boron.

Laminar flame in fine-particle dusts

A simple conductive model of the laminar flame in fine-particle dusts, with particles burning in the diffusion mode, is presented. The model is based on the assumption about wide zones of combustion in dusts; therefore, the main contribution to the formation of the heat flux toward the pre-flame zone is made by the heat released on burning particles near the interface between the burning and pre-flame zones. The normal flame velocity is demonstrated to increase with decreasing particle size and with increasing fuel and oxidizer concentrations. The maximum velocities are reached under the condition of identical volume heat capacities of the solid and gas phases, which requires the fuel concentration to be several times higher than the stoichiometric value. The calculated results are validated by experimental data on the normal flame velocity as a function of the fuel concentration for gas suspensions of magnesium, aluminum, zirconium, iron, and boron particles.

High-velocity wave combustion regimes of an aerocolloidal mixture in open-closed tubes

This article is devoted to the continued experimental study of the nation of the laws governing the evolution of the unsteady flame-propagation process in aerocolloidal mixtures of aluminum particles. The general laws of the process and the influence of the concentration and grade of fuel on those laws are illustrated in a figure. It was observed that the laws of flame propagation in tubes are associated with its modulation by nonlinear unsteady acoustic oscillations generated by the unsteady flame; in the forward-motion phase, acoustic streaming is imposed on the motion of the flame front, increasing the apparent velocity.

Specific features of the emission and absorption characteristics of soot particles at combustion temperatures

The flames of solitary hydrocarbon drops (benzene, gasoline, hexane, and octane) are studied. A complex approach to the study of the combustion of these substances by spectral methods, which allow one to reveal the flame structure, the concentration and dispersivity of the condensed phase, the temperature in the combustion zone, and the radiation characteristics, is proposed. The emission characteristics of soot particles and their spectral features in the wavelength range λ=0.25−0.75 µm are also investigated.

Laminar flame in polydisperse aerosuspensions of aluminum particles

This work is an experimental and theoretical study of the dependence of normal flame velocity in polydisperse aerosuspensions of aluminum particles on the parameters of the particle size distribution function. It is shown that the velocity decreases with increasing dispersion of the distribution function as a result of reduction of the specific reaction surface.

Wave regimes of dust combustion

Experimental studies were performed to investigate the dependence of the laminar flame velocity in dust clouds of Al, Mg, Zr, Fe, and B particles on the physicochemical parameters (fuel concentration and composition, particle size distribution) and hydrodynamic conditions of the combustion process (semi-open tubes, free clouds of particle-air mixtures). Heat conduction was found to make a predominant contribution to the overall heat transfer in the combustion wave. The main causes of instability of laminar flames (acoustic disturbances, interfacial exchange, forced and natural convections), transient phenomena, and vibrational and turbulent combustion of dust were studied experimentally.

Conductive-radiative model of a laminar flame in dust suspensions

A mathematical model is proposed to describe a laminar flame in gas suspensions with particles burning in the diffusion mode. Conductive and radiative heat transfer in the combustion wave and also the differences in temperatures and velocities of the solid and gas phases are taken into account. An analytical expression for the normal flame velocity as a function of the fuel and oxidizer concentrations and the particle size is derived. Theoretical predictions are demonstrated to agree well with experimental data on the flame velocity dependence on the particle size in suspensions of magnesium particles in air. The relative role of radiative heat transfer and sedimentation of particles in the suspension is analyzed.