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Numerical analysis of mixture formation in fuel sprays using advanced turbulence modeling

  • Hindi, Gustavo de Queiroz
Publication Date
Sep 22, 2018
Repositório Institucional da UFSC
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Abstract : Emissions standards for internal combustion engines are becoming ever more stringent due to environmental concerns and the impact on health from pollutant s emissions. To meet these stringent targets, computational fluid dynamics simulation of engine in-cylinder processes has been extensively used for engine design in a faster and more cost effective way, allowing better understanding of the injection, evaporation and combustion processes to optimize the engine for lower emissions and higher efficiencies. However, spray combustion modeling is a very challenging task and a topic still open in literature with areas that require improvements. The review of current literature on fuel spray modeling approaches suggests that the usage of Large Eddy Simulation (LES) is of critical importance in order to represent the complex interactions between spray and turbulence, that affects all the physical processes related to mixture formation and combustion. However, some deficiencies have been identified relatedto the accuracy of non-reacting spray simulations, mainly related to the adequate setup of different models and numerical parameters and, in special, the mesh size, to adequately capture the interactions between spray and turbulence. This work presents the application of advanced turbulence modeling to the spray injection process in a static chamber, based on the implementation of a LES turbulence model in a Lagrangian spray based solver in OpenFOAM (open source code). Results that have been obtained hitherto for non-reacting sprays have proven that highly accurate results can be obtained for liquid and vapor length penetrations by correct modeling of spray phenomena and adequate mesh refinement to correctly capture turbulence-spray interactions. This work also contributes with a proposal for a new criterion based on the droplet Stokes number, for adaptive mesh refinement. This criterion also allows to assess to what extent the droplets turbulent dispersion is properly captured for a given mesh size, using LES approach. Complement this work a turbulence model comparison based on the averaged Navier Stokes equations (RANS), sensitivity analyses of ambient conditions in the static chamber and, the influence of the fuel s physical properties in important characteristics of non-reacting sprays.

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