The critical conditions for the transformation of a plane detonation wave into a cylindrical detonation wave are experimentally found. For mixtures of oxygen with hydrogen or methane, the geometric conditions are determined for detonation initiation in a cylindrical gap at various diameters of the orifice through which the plane detonation enters the gap. To identify features of observed explosive processes, the results of two-dimensional numerical modeling are analyzed.

Определены минимальные энергии инициирования горения газообразного тетрафторэтилена (ТФЭ) при различных начальных давлениях и температурах, а также его смесей с азотом, аргоном и гелием. Исследован переход горения из газовой фазы ТФЭ в жидкую. Показано, что детонацию в жидком ТФЭ возбудить практически невозможно. Бедные пределы детонации и горения смесей ТФЭ–воздух при нормальных условиях составляют 12.2 об. %. Измерены скорости детонации воздушных смесей ТФЭ.

Experiments show that the combined e ̈ect of acceleration of the §ow due to the passage of the combustion wave from a larger-diameter tube into a smaller-diameter tube and through turbulizing obstacles signi¦cantly reduces the run-up distance of the strong shock wave€ reaction zone complex in a stoichiometric methane€air mixture: such a complex can be formed in a tube with turbulizing obstacles within a distance of ∼ 1 m (∼ 14 diameters of the test section) from the ignition source and can propagate in such a tube at a velocity of 1300€1400 m/s. After the passage of the shock wave € reaction zone complex from the tube portion with turbulizing obstacles into the smooth portion, it propagates there at a velocity of 850€900 m/s, without substantial attenuation, at least over a distance of 0.5€1 m.

The minimum energies required to initiate the combustion of gaseous tetrafluoroerthy1ene (TFE) and mixtures thereof with nitrogen, argon, and helium at various initial pressures and temperatures are determined. Flame transition from the gas to the liquid phase of TFE is investigated. Liquid TFE is demonstrated to be virtually nondetonable. The fuel-lean flammability and detonability limits of TFE-air mixtures under normal conditions are demonstrated to be identical, 12.2 vol %.

The dynamics of the combustion of stoichiometric methane-air mixtures during the passage from a larger-diameter to a smaller-diameter tube is experimentally studied. The combined effect of increases in the velocity and duration of the gas flow and in the degree of its turbulization due to a decrease in the cross sectional area of the tube and installation in it of turbulizing obstacles considerably enhance the probability of onset of combustion mode with the formation of strong shock waves. Combustion waves led by a shock wave that ignites the mixture at obstacles and propagates at a velocity of up to 1400 m/s within a distance of ∼14 tube diameters are produced.

This paper studies the effects of small additives of propylene and isopropanol on the hydrogen-air flame speed in the predetonation regime, deflagration-to-detonation transition, and burning rate. It is shown that the difference in the effects of these additives on the combustion is determined primarily by their ability to terminate reaction chains. In hydrogen flames, the additives are consumed as a result of their reactions with the active intermediate products of H2 combustion in which these species are replaced by inactive radicals.

Minimum energies of direct initiation of detonation in hydrogen-, propane-, furan-and sylvan-air mixtures in a tube by explosion of gaseous charges at different initial pressures are determined experimentally. The minimum energies of detonation initiation by explosions of gaseous mixtures at pressures above a certain threshold value are shown to be identical with the appropriate energies of detonation initiation by charges of condensed explosives.

Propagation of flames and detonation waves in fuelair mixtures with inhibitor additives is studied. Propane and hydrogen are chosen as fuels and tetrafluorodibrorooethane as an inhibitor. Experiments are performed in a tube. The detonation and flammability limits are determined as functions of the inhibitor concentration in the mixture. For propane-air mixtures the additive decreases the detonation velocity beyond the value characteristic of detonation limits of noninhibited mix* tures.The flammability limits narrow faster than the detonability limits as the inhibitor concentration grows, so that detonation propagates in mixtures that can not support flame, / I n inhibited hydrogen-air mix tures detonation limits are narrower than the flammability limits. A comparison of the calculated and measured detonation velocities reveals that the inhibitor additives enhance to some extent the heat release !behind the detonation wave. For hydrogen-air mixtures the measured velocities exceed the calculated ones at Copyright © 1992 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. *Head of Laboratory, N. Semenov Institute of Chemical Physics. fGraduatc Student, Moscow Physical Engineering Institute, t Junior Researcher, N. Semenov Institute of Chemical Physics. §Engineer, Moscow Physical Engineering Institute. fSenior Researcher, N. Semenov Institute of Chemical Physics.