Chemical mechanism reduction and derivation for C7-C16 n-alkylbenzenes using integrated global sensitivity analysis and reaction rate rules

Coupled with reduced/skeletal chemical mechanisms, computational fluid dynamics simulations have been carried out to increase thermal efficiency and reduce hazardous emissions of combustion devices. n-Alkylbenzenes up to C16 are the primary compounds in transportation fuels and are responsible for polycyclic aromatic hydrocarbons and soot yield. However, their combustion chemistry is rather complicated, with various resonance stabilized intermediate radicals, which significantly affect both auto-ignition behaviors and flame propagations. This makes it extremely difficult to decouple the species and reactions from the reduction targets, during the reduction of the relevant detailed mechanisms, especially for the C0-C7 sub-mechanism. This study proposes an integrated global sensitivity analysis method for the reduction of complicated chemical mechanisms, in which the fuel-specific sub-mechanism is simplified through the reaction class-based global sensitivity analysis and the trial-and-error method, whereas the base sub-mechanism is reduced by the species global sensitivity analysis. The final mechanism is obtained by merging the skeletal fuel-specific sub-mechanism and the reduced base submechanism. A case study is conducted for n-butylbenzene, and the acquired skeletal mechanism can well characterize its global combustion parameters. Then, by considering the molecular structures, the skeletal submechanisms for C8-C16 n-alkylbenzenes are derived according to reaction rate rules. Last, the whole set of skeletal mechanisms is extensively validated. It is found that the model predictions are in good agreement with the experimental data, including species concentrations in jet-stirred reactors and laminar premixed flames, ignition delay times in shock tubes and rapid compression machines, and laminar flame speeds over the working conditions of p = 0.04-50 atm, phi=0.25-2.0, and T = 500-2000 K.