Himičeskaâ fizika

The results of kinetic analysis are presented taking into account the rates of chemical reactions and heat release when solving problems of spontaneous ignition and laminar combustion of hydrogen-air reactions with a 1% addition of propylene. The solution was obtained using computer modeling. It has been shown that the addition of propylene to hydrogen-air mixtures significantly slows down the course of chemical reactions due to the recombination of atomic hydrogen during spontaneous combustion in the entire range of initial temperatures from 800 to 1400 K, as well as during the propagation of laminar combustion waves in rich and stoichiometric mixtures. However, propylene is a flammable substance, and during its decomposition and oxidation, heat is released, which increases the rate of temperature increase. As a consequence, under certain conditions, in particular at an initial temperature of 800 K, with the reduced rates of chemical reactions of hydrogen oxidation, as well as in the case of lean mixtures, the addition of propylene leads not to an increase, but to a decrease in the ignition delay, and to a significant increase in the temperature and speed of propagation of the combustion wave. Additional data were obtained on the important role played in laminar flames of hydrogen-air mixtures by reactions involving the HO₂ radical: the branching reaction HO₂+H => OH+OH and the trimolecular reaction H+O₂(+M) => HO₂(+M), as well as the maximum concentration of the HO₂ radical. These reactions proceed at high rates in the low temperature area due to the participation of atomic hydrogen diffusing from the high temperature area of the flame and provide a significant contribution to the release of heat. The maximum concentration of the HO₂ radical is achieved at the temperature that presumably corresponds to the “leading zone” of combustion. When propylene is added, the change in the maximum concentration of the radical correlates with the change in the velocity of normal combustion.

Highly dispersed initiating explosives and igniting compositions based on them in the form of an aqueous suspension and paste have been obtained, which can significantly improve the safety of the technological process of equipping pyrotechnic initiation devices. The properties of the obtained explosives are analyzed, and the scope of their application in the form of film pyroelements is proposed. A visual - thermal analysis of the exothermic transformation in film pyroelements under normal conditions has been performed. It has been shown that high-temperature exothermic reactions do not occur in the form of a detonation wave, but in the form of stationary layered combustion at the rate of 20 to 200 mm/s under normal conditions, with intense release of dispersed products and flames.

The combustion in a free cylindrical gas charge caused by detonation transmission from the initiating tube was experimentally investigated. The dependences of the combustion velocity change along this charge for stoichiometric mixtures of ethane, ethylene and propane with oxygen were obtained. A pulsating combustion pattern along the charge was observed, as a consequence of the damped oscillatory process. The speed of this process varied from the detonation velocity at the section of the initiating tube to 200–350 m/s at the end of the gas charge.

The paper presents the results of modeling the conversion of a lean non-combustible propane-air mixture with initiation by a high-frequency corona discharge at a pressure of 5 bar and an initial temperature of 300 K for different equivalence ratios. The discharge creates non-thermal plasma in filament channels. Experiments on the development of such a discharge in air for different conditions were carried out. At pressures of 1 and 2 bar, the discharge has a complex morphology with branching of discharge filaments. At pressures above 3 bar, the glow region has the shape of a straight spoke. The paper presents a kinetic analysis of the conversion. The key component for propane decomposition is the O atom produced in the discharge as a result of O₂ dissociation by direct electron impact and excited N₂ molecules. In the afterglow, after completion of discharge, the source of the O atom is the reactions of ozone decomposition with N₂ and O₂. For the formation of NO, it is necessary to take into account the production of N atoms in the excited and ground states. Intermediate oxidized hydrocarbons play a major role in increasing the concentrations of C₃H₆, C₂H₄, and CO over time. The decomposition of O₃ occurs to a greater extent in a cycle involving NO₃. The heating of the discharge-activated zone did not exceed 600 K. The composition of the conversion products obtained as a result of modeling was compared with known experimental literature data.

Using a multichannel laser interferometer, a series of experiments with recording of particle velocity profiles have been carried out to determine the dynamics of shock initiation of detonation in the mixtures of nitromethane with microballoons, which are heterogeneous explosives with a controlled charge structure. It is shown that the addition of 5–8 wt.% microballoons to nitromethane reduces the shock wave amplitude required to initiate detonation by almost an order of magnitude. At 8 wt.% of microballoons, depending on the initiation conditions, the realization of both steady Chapman-Jouguet detonation and weak detonation is observed.