ДЕСТРУКЦИЯ АЛКАНОВ В НИЗКОТЕМПЕРАТУРНОЙ ЗОНЕ БУНЗЕНОВСКИХ АТМОСФЕРНЫХ ПЛАМЕН
Keywords:
hydrocarbons, combustion, flame, flame structure, modeling.Abstract
The article discusses the problems of modeling processes for alkane conversion in flames and comparison of the obtained results with experiment. The criterion of correctness of the choice for proposed model with real conditions is usually considered to be the closeness of the calculated and experimental results with the most frequently used integral parameters: the burning rate, flame temperature, the ignition delay time, etc. The scatter of results for 10%, and even more for some practical applications is often considered to be quite reasonable. More reliable should be considered to compare simulation results with the real flame structure, monitoring of gradual changes of the initial substances with their transformation into intermediate and final products. A thorough identification of the structure of the flame, especially at the initial stages allows us to better understand the processes, and in the future to specifically inhibit or promote combustion. One can assume that laminar Bunsen type premixed flames, burning at atmospheric pressure, with the fuel excess coefficient close to stoichiometry or slightly more give the picture close to reality of the chemical transformations of fuel and oxidant when compared with other devices of burning and conditions of the process realized. Developed mathematical models differ from each other include a different number of reactions, and take into account the most important combustion parameters. But there is no single universal model for all combustion conditions. Modern computational capabilities do not allow for yet a full accounting of all particles, reactions, parameters of combustion mixtures. Therefore, simplified models based on a relatively small number of reactions and particles, though give results faster but with less accuracy. In all models the primary reactions include, above all, the destruction of fuel molecules. Further, depending on the content of the fuel, the fragments of molecules in lean mixtures can undergo further fragmentation with the formation of some intermediate and final substances, or in rich mixtures they can lead to the growth and combining particles up to formation of cyclic, aromatic compounds, carbon agglomerates of different structure and solid particles of soot. Involved radicals include particles such as H, OH, НО2, R, RO, RO2. The most interesting fact for flames of hydrocarbons without soot ranging from butane and more, is the absence of the intermediate particles with the number of carbon atoms more than 3 in conversion zone. We can assume that at the initial stages with active participation of atoms and molecules of oxygen occurs the formation of unstable oxygencontaining cyclic intermediate structures from 5-6 atoms, which are rapidly converted into smaller structures due to the bonds breaking. In rich mixtures with lack of oxygen, the cyclization is carried out with the participation of acetylene and similar particles, forming benzene derivatives, other carbon compositions, and the soot particles.
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