Evaluation and Development of Chemical Kinetic Mechanism Reduction Scheme for Biodiesel and Diesel Fuel Surrogates

The aim of this study is to evaluate the existing chemical kinetic mechanism reduction techniques. From here, an appropriate reduction scheme was developed to create compact yet comprehensive surrogate models for both diesel and biodiesel fuels for diesel engine applications. The reduction techniques applied here were Directed Relation Graph (DRG), DRG with Error Propagation, DRG-aided Sensitivity Analysis, and DRG with Error Propagation and Sensitivity Analysis. Nonetheless, the reduced mechanisms generated via these techniques were not sufficiently small for application in multi-dimensional computational fluid dynamics (CFD) study. A new reduction scheme was therefore formulated. A 68-species mechanism for biodiesel surrogate and a 49-species mechanism for diesel surrogate were successfully derived from the respective detailed mechanisms. An overall 97% reduction in species number and computational runtime in zero-dimensional closed homogeneous batch reactor simulations was achieved for both reduced mechanisms. Accordingly, the reduced n-hexadecane mechanism was integrated into a CFD solver to simulate spray combustion in a constant volume bomb. However, the ignition delay was underestimated by 0.04 ms owing to its high cetane number. This corresponds with recent study which demonstrates that n-hexadecane alone is unsuitable as a single-component diesel surrogate. Thus, fuel blending is recommended here to match the diesel fuel kinetics and compositions. As such, the reduced n-hexadecane mechanism is expected to be a better representative of surrogate component for various transportation fuels such as biodiesel. Additionally, it can be applied to predict the reactivity of other n-alkane or interchange with one another for kinetic and CFD simulations.