Micro mixing time in the Eddy Dissipation Concept

The turbulent micro mixing in the Eddy Dissipation Concept (EDC) has been investigated. The EDC is a model for turbulence-chemistry interaction modeling that allows for the use of multi-step reactions. The EDC was originally developed assuming that the reaction kinetics is fast compared to the turbulent mixing. With a more detailed description of the chemistry the interaction between turbulence and chemistry becomes more complex which may call for a revision of the model. Three ways to estimate the turbulent mixing times have been investigated. The first is the time scale proposed in the EDC, i.e., the time scale related to the Kolmogorov time scale. The second is a time scale based on the geometrical mean of the Kolmogorov time scale and the time scale given by k/epsilon. The third time scale is the time scale given by 4k/epsilon. The fuel chemistry was modeled with a three-step simplified mechanism. A separate model based on calculations with a comprehensive reaction mechanism was used for estimating the chemical time scale at which extinction occurs. Tn the study a natural gas-fired sudden expansion reactor was modeled. The use of the Kolmogorov related time scale resulted in an overestimation of the extinction effects, whereas best result was obtained when the mixing time was modeled with the time scale given by 4k/epsilon.