Pengzhi Wang, Sirio Brunialti, Máté Papp, S. Mani Sarathy, Tamás Turányi, Henry J. Curran, Tibor Nagy

Proc. Combust. Inst., 40, 105408 (2024)

The core chemistry and thermodynamic data of large alkanes in the NUIGMech mechanism were recently updated. In the present work, the set of rate rules for large alkanes is optimized against experimental data to improve the predictivity of the mechanism. As a starting step of developing a consistent set of rate rules for any larger alkane, we optimized the mechanism of pentane isomers, whose mechanism was generated based on 185 rate rules in 24 reaction classes using code MAMOX++. Including the core chemistry, the mechanism contained 1427 species and 6676 reactions. For the efficient optimization of such a large mechanism, the Optima++ code was extended to rate rules and was linked with the Zero-RK simulation code. As reference data, first-stage and total ignition delay times measured in shock tubes and rapid compression machines, and species concentrations measured in jet-stirred reactors were collected in wide ranges of conditions. The prior uncertainties of the Arrhenius equations of the 185 rate rules were determined based on a review of alkanes’ rate constant studies. The PCA-SUE method was used for the selection of the influential rate rules. This method identified 94 important rate rules, whose Arrhenius parameters were subsequently optimized within their prior uncertainty ranges using Optima++ against a representative subset of the data collection with a moderate computational effort. The optimization significantly improved the accuracy of the mechanism, which now performs significantly better even than the Bugler et al. mechanism (PROCI, 2017). The present study has demonstrated the effectiveness of the proposed methodology, thereby paving the way to the optimization of a complete set of rate rules that can be used for the generation of a reliable combustion mechanism for any larger alkane, and with some extensions even for unsaturated fuels or oxygenated fuels such as biodiesels. 

Optima++ v2.5.0 (26 April, 2024)