Development of Reduced Chemical Kinetics for Combustion Simulations with Transportation Fuels

In reacting flow simulations, detailed chemical kinetics for practical fuels is important for accurate prediction of flames and limit combustion phenomena, such as ignition and extinction in engines. However, detailed chemical kinetic mechanisms are typically large and computationally expensive to apply in practical computational fluid dynamic (CFD) simulations. To resolve this difficulty, various methods for mechanism reduction have been developed over the last few decades to generate reduced mechanisms that can accurately mimic detailed mechanisms. For instance, the method of directed relation graph (DRG) features linear reduction time and was fully automated, rendering it highly efficient for skeletal reduction of extremely large mechanisms. In the present work, DRG is improved to handle the reduction of mechanisms involving large isomer groups, e.g. those for large hydrocarbon fuels. Expert knowledge was further incorporated into DRG to allow flexible error control on each individual species and heat release. The revised DRG method and DRG with expert knowledge (DRGX) are further compared with other DRG-based methods on their reduction errors. A systematic approach for mechanism reduction, including DRGX, isomer lumping and DRGASA, is then applied to develop skeletal mechanisms for various engine fuels, such as biodiesel surrogates and n-dodecane for practical engine simulations. The reduction approach is also applied to study the effect of NO enrichment on the combustion of methane/ethylene mixtures. A reduced mechanism of ethylene was further developed for 3-D direct numerical simulation of a turbulent lifted ethylene jet flame in heated coflowing air. The recently developed method of chemical explosive mode (CEM) analysis (CEMA) was extended and employed to identify the detailed structure and stabilization mechanism of the lifted flame