Modelling of Turbulent Spray Flames with Variable Degrees of Fuel Pre-Evaporation

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During the first funding period, we developed novel closures that account for the unresolved (sub-grid) interactions between spray evaporation and turbulence and between evaporation and combustion. The modelling is based on large-eddy simulations (LES) coupled with a conditional moment closure (CMC) method for the modelling of the combustion process. The predictions of non-reacting spray jets and spray flames with significant pre-evaporation of the fuel are very good. A reduction of the amount of the pre-evaporated fuel, however, leads to partially premixed combustion if the gaseous mixture in the jet is within the flammability limits. The partially premixed combustion cannot satisfactorily be described by LES-CMC in its current implementation. We now suggest several approaches for the modelling of a wide range of spray flames with variable degrees of pre-evaporation. The approaches are based on different definitions of an additional progress variable that ensure the accurate modelling of non-premixed, partially premixed and -to a certain degree- premixed flames.