The combustion of liquid fuels is of great interest in many practical applications, from industrial burners to diesel engines. Unfortunately, the combustion of a liquid feed in the form of a spray creates favorable conditions for the formation of soot particles, which represent a major concern because of their negative impact on combustion efficiency, global warming, and human health. The direct investigation of soot formation and evolution in spray combustion is a very challenging task, because of the multitude of the droplets and the interaction among numerous chemical and physical phenomena. In order to overcome these difficulties, in the latest decades significant experimental and modeling efforts have considered the combustion of simpler systems, like isolated droplets in microgravity conditions. Although the evident simplification with respect to spray combustion, microgravity droplets include most of the relevant physico-chemical processes occurring in practical combustors, including heat-up, phase-change, diffusion, radiation, and chemical reactions. From the modeling point of view, microgravity droplets represent an ideal system to study the sooting tendency for different fuels under transient conditions.
In this presentation we discuss and analyze the formation and evolution of soot from the combustion of isolated fuel droplets in microgravity conditions on the basis of a comprehensive numerical model, which includes detailed chemistry, non-ideal thermodynamics, detailed transport properties, and advanced radiative heat transfer models. Soot particles and aggregates are described using a Discrete Sectional Method validated on premixed and diffusion laminar flames, in a wide range of operating conditions. In particular, it is shown how the absence of buoyancy, combined with the effects of thermophoresis, leads to the formation and accumulation of soot clouds with concentrations significantly higher than those observed in conventional laminar flames, with impact on local temperatures, radiative heat transfer, and vaporization rates. The influence on soot tendency of addition of biofuels (such as ethanol and iso-butanol) to fossil fuels is also discussed.
Alberto Cuoci is Associate Professor at the Department of Chemistry, Materials, and Chemical Engineering of Politecnico di Milano. He holds a M.Sc. degree in Chemical Engineering and a Ph.D. in Industrial Chemistry and Chemical Engineering from Politecnico di Milano. He has been Invited Professor at Université Libre de Bruxelles in 2014 and at École Centrale de Paris in 2018. In 2020 he was awarded the Humboldt Research Fellowship for Experienced Researchers. The main scientific interests of Alberto Cuoci are in the field of numerical modeling of reactive flows with detailed kinetics, with special emphasis on formation of pollutants (NOx and soot) from laminar flames. He is also interested in the multiscale analysis of catalytic processes and numerical modeling of heterogeneous catalytic reactors.
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