Transient flamelet modeling for soot formation and oxidation coupled with gas chemistry in laminar non-premixed flames

In general, the full transport equation approach for laminar non-premixed flame with soot formation, detailed chemistry and radiation has an advantage in accuracy and describing for emission pathway. But this approach requires the excessive computational cost especially for a higher-order hydrocarbon fuel flames. Thus, a novel flamelet model has been devised to circumvent these difficulties. The laminar flamelet model is one of the convenient and accurate methods in turbulent non-premixed flame. But in laminar non-premixed flame situation, this model is not suitable for simulating slow processor like soot and radiation. Thus in this study, we overcome this limitation by using the transient flamelet model. Also, for soot formation on laminar non-premixed flame, transient flamelet coupled with two-equation soot model has been adopted due to its inherent advantages in terms of accuracy and availability. The present two-equation soot model is able to account basic physical processes involved in soot formation and evolution mechanism. In this study, the soot mass fraction and number density are calculated on mixture fraction space by coupling the gas chemistry with soot formation. But only reaction rates are used in the flow field because soot formation is much slower than chemical reaction. To validate the present two-equation soot flamelet model, numerical results are compared with the full transport equation simulation data. Based on numerical results, the detailed discussion has been made for the precise structure and soot formation processes in the laminar non-premixed methane /air flames.