Updated Reaction Rate Rules for the Construction and Derivation of Skeletal Chemical Mechanisms of Lightly Branched Isoalkanes

Iso-alkanes are found in large quantities in both novel and conventional fuels. Accurate kinetic models for these fuels are essential for numerical simulations of combustion engines. However, existing chemical kinetic mechanisms are insufficient to fully elucidate the combustion chemistry of alkane isomers. Additionally, the influence of molecular structure differences between iso-alkanes, specifically differences in the position and number of methyl branches on their low-temperature oxidation pathways has not been comprehensively studied. The relationship between fuel properties, such as auto-ignition behavior and flame characteristics, and molecular structure is still not fully understood. The present study proposes updated reaction rate rules to establish skeletal kinetic mechanisms for monomethyl and dimethyl iso-alkanes with different positions of methyl substitution. Firstly, the important reaction classes from the sub-mechanisms of the hexane isomers are identified using reaction-class-based global sensitivity analysis. Subsequently, skeletal chemical mechanisms for 2-methyl and 3-methyl pentane are constructed, following a comparison of their critical reaction pathways. It is observed that the location of the methyl group significantly influences the positions of the critical H-atom abstraction reactions. This work further extends the study to dimethyl hexane isomers, by considering 2,2- and 2,3-dimethyl butane, and 2,3- and 2,4-dimethyl pentane. By integrating the monomethyl and dimethyl alkanes, reaction rate rules are updated for the construction of skeletal chemical mechanisms for larger iso-alkanes with similar molecular structures. Using reaction rate rules, skeletal chemical mechanisms of monomethyl and dimethyl iso-alkanes up to C10 are constructed. Comparisons between experimental data and simulations show good agreement, demonstrating the robustness of the monomethyl and dimethyl iso-alkanes chemical mechanisms and the effectiveness of the proposed reaction rate rules.