Ruprecht-Karls-Universit├Ąt Heidelberg

Multiphase Flows and Combustion

Head: Prof. Dr. E. Gutheil

Flamelet Modeling of Turbulent Spray Flames

The modeling of chemical reactions in turbulent spray flames requires special attention since it is vital for the prediction of pollutants such as carbon monoxide and precursors of soot formation.

Flamelet models are suitable to include detailed chemical reaction mechanisms into complex models for spray combustion since the turbulent code requires the consideration of turbulent mixing and the scalar dissipation rate. The detailed chemical reactions are considered through use of precalculated laminar flamelet libraries.

The method requires the simulation of these laminar flamelet structures including detailed chemical reactions. In case of spray flames, the evaporation needs to be considered as well as its effect on the energy equation. Many researchers employ pure gas flamelets which is too big of a simplification. Figure 1 shows a comparison of a methanol spray flame in air where the LHS shows inclusion of a pure gas flamelet library and the RHS spray flamelets. In regimes where both evaporation and combustion occur, the consideration of spray flamelets is inevitable.

Figures 2 and 3 display contour plots of acetylene and formaldehyde, both have been obtained with laminar spray flamelet libraries for a turbulent ethanol/air and a methanol/air spray flame, respectively.

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Fig. 1 Structure of a methanol/air spray flame

Fig. 2 Mass fraction of acetylene

Fig. 3 Mass fraction of formaldehyde