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Development and implementation of multicomponent liquid wall film evaporation model

Various environmental regulations put ever stringent requirements on the automotive industry as a part of solution to the problem of global warming and climate change. Engine emissions are influenced, among others, also with quality of fuel and air mixing process. Auto ignitability of fuel in cylinder depends on detailed chemical composition of the fuel as well as on the evolution of the thermal and compositional state of the fuel mixture. The evaporation of wall film, formed by spray/wall impingement, is much slower than free droplets and has strong effects on engine emission. Multicomponent liquid evaporation is important phenomena encountered in droplets, but also in liquid films. Droplet evaporation is an area that has been thoroughly investigated and there are good numerical models taking into account all relevant phenomena. The same cannot be stated for the multicomponent evaporation of liquid wall films. Multicomponent evaporation modelling approach can be generally divided into two model groups: discrete multicomponent models and continuous multicomponent models. Discrete multicomponent evaporation models track individual fuel components and enable direct coupling of reaction kinetics to the individual fuel components, whilst continuous multicomponent models are based on the continuous thermodynamic method and describe fuel composition as continuous distributed function with respect to some parameter, such as the molecular weight. The latter approach decreases computational demands compared to the former one, but tends to be inaccurate if detailed chemical calculations are needed, or in the case of mixtures composed of large number of components. As current demands for computational simulation accuracy are relatively high, this research will only deal with discrete multicomponent evaporation models. From the stated above, it can be clearly seen that automotive industry faces great challenges which can be only met by designing new and improved engines using advanced designing tools, one of which is computational fluid dynamics (CFD). This works aims at further development of the numerical model of liquid wall film by implementation and validation of new mathematical models of multicomponent wall film evaporation. After state of the art literature review, suitable numerical models are going to be adjusted and implemented in the existing numerical framework of the commercial CFD code. Furthermore, implemented models will be compared with available experimental data in order to confirm its validity.

computational fluid dynamics; Eulerian approach; multicomponent evaporation; turbulent boundary layer; UNIFAC method; wall function; wall film

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