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“A series of experiments to research the growth of polycyclic aromatic hydrocarbons was conducted at the combustion process kinetics research plant. We have studied chemical reactions of PAH growth in visual detail, stage-wise – the way they occur e.g. in engine combustion chambers. These are typical reactions, there is no scientific discovery here; but these reactions were previously studied and confirmed experimentally at temperatures only up to 700 kelvin, whereas we have advanced much higher up the temperature scale – our experiments were conducted at 1200 kelvin. In Russia, such experiments are unprecedented; in such studies, every extra hundred degrees is a struggle,” says LPI Samara Branch director, Samara University Professor Valery Azyazov.
According to him, such experiments confirm and refine the existing models of combustion processes by practical testing of theoretical calculations. In a split second, thousands of interconnected reactions occur in the combustion chamber of an engine, like a huge complex clockwork of a thousand spinning cogwheels each affecting the other. Learning how each “cogwheel” works (by effort of the Samara University test plant) helps better understand the work of the “clockwork” as a whole. Besides, the Samara plant can measure chemical reaction speeds – that is, to continue the analogy, it can determine how fast each of the “cogwheels” rotates at any given moment. This data is necessary to refine kinetic models of combustion that inform scientists and developers in what time interval and how fast certain substances form and are consumed in the course of the reaction. By examining the reactions individually, scientists make a “snapshot” of the instant in which many chemical events occur in the engine, and “dissect” each event, checking it against the theoretical calculations.
“The reactions that are involved in the formation of PAHs are quite numerous, and only a small fraction of them have been studied experimentally. Data for the vast majority of reactions is obtained by using constantly evolving theoretical approaches. Calculation results are validated by comparison with experimental data for the most critical reactions. Obtaining experimental data for all reactions involved in the PAH growth process is very costly, both in terms of time and resources. In practice, the main bulk of data is obtained by calculation, and only a small fraction of data for the most important reactions is measured at the plants as unique as ours. We use our plant to, so to say, ‘dissect under the microscope’ the chemical reaction we choose, and study the peculiarities of its course in practice. Theorists use our data to cross-check their computational methods. With this combined approach, we can untangle the mechanisms of formation of soot which begins to grow from simple cyclic hydrocarbons. Full understanding of these mechanisms can minimize harmful, carcinogenic engine emissions,” emphasizes Valery Azyazov.
For referenceThe unique research plant to study the reaction dynamics and kinetics of combustion processes was designed and assembled at Samara University, in the international scientific laboratory “Physics and Chemistry of Combustion” under the Mega Grant issued by the Government of the Russian Federation “Elaboration of Physically Justified Models of Combustion”. The plant commissioned in 2022 should help engineers in solving import substitution problems, namely in development of efficient and eco-friendly domestic aircraft engines.
The plant creation had been in progress since 2017. An entire room in the laboratory was allocated for components and supporting equipment of the plant. The central component of the plant – a vacuum chamber – weighs one and a half tons; a construction crane was used to lift it to the third floor where the University laboratory is located.
The size of the plant matters because it allows boosting sensitivity of the unit by placing a large number of scientific recording instruments in it. This helps significantly improve selectivity and sensitivity in determining reaction products, which, in turn, helps build more accurate models of combustion processes and better understand what needs to be done to increase efficiency of fuel combustion, simultaneously reducing harmful emissions.
Combustion products of hydrocarbon fuels have carcinogenic activity, as they contain polycyclic aromatic hydrocarbons (PAHs), which can cause cell mutation and cancer in living organisms. Therefore, identifying PAH formation mechanisms during fuel combustion is critical in development of new aircraft engines.
