Research of the mechanism and development of a model for the development of the process of combustion of pyrotechnic mixtures metal fuel + oxide of metal at external thermal actions
Abstract
The aim of the work is to establish the mechanism of combustion of two-component compacted mixtures of magnesium and aluminum powders with metal oxides and to develop a model of their combustion to determine critical ranges of combustion rate of mixtures taking into account external thermal influences. The analysis of experimental data on physical and chemical processes occurring in different combustion zones of the considered mixtures allows to establish the mechanism of their combustion according to which the process of conversion of the initial mixture into combustion products in the first approximation is stationary, one-dimensional and takes place in the following three most characteristic zones. Zone I is a heated layer in the mixture condensed phase, where chemical conversions can be neglected. Zone II is a reaction zone of the condensed phase of the mixture, in which the solid mixture is converted into a gas containing individual metal particles. Within this zone, oxidant decomposition and vigorous oxidation of metal fuel particles take place. The ignition of metal particles occurs on the combustion surface. Most of ignited metal particles, as a result of their agglomeration, are delayed on the combustion surface until their complete combustion. Heat from burning metal particles is transferred to the depth of the condensed phase. Zone III is a zone of heat release of the gas phase. In this zone, dispersed metal fuel particles are burned in the diffusion mode in the stream of oxidant decomposition products. The heat released is transferred to the condensed phase by thermal conductivity and radiation. A model of combustion of compacted two-component mixtures of magnesium, aluminum and metal oxides has been developed, which, in contrast to existing models of pyrotechnic nitrate-metal mixtures, takes into account kinetic characteristics of thermal decomposition of the oxidant and hightemperature oxidation, ignition and combustion of metal particles in decomposition products. This allows to more accurately calculate (relative error is reduced to 7… 9 % instead of 10… 15 % in existing models) the dependences of the combustion rate of mixtures on elevated heating temperatures and external pressures for different values of technological parameters (ratio of components, dispersion of metal fuel, nature of metal and oxidant, etc.). The model also allows to determine critical ranges of changes in the rate of combustion in these conditions, exceeding of which leads to accelerated mixtures combustion and explosive destruction of products
Keywords
fire safety; pyrotechnic mixtures; thermal influences; combustion processes; combustion models of metallized condensed systems
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