(654a) Automated Generation of Chemical Kinetic Reaction Mechanisms for Combustion of Large Alkanes

Large alkanes (paraffins) are of particular interest for use as hybrid rocket fuels. Understanding their oxidation and pyrolysis mechanisms is key for improvement of their performance in this growing application. Manual construction of detailed kinetic models for such large molecules is infeasible, while direct employment of the automated mechanism generation frameworks is unpredictable (terra incognita). Thus, we build from small authentic models. We first constructed a detailed yet compact mechanism for n-pentane combustion using the open-source Reaction Mechanism Generator (RMG) software, which we tested against available experimental (shock tube and RCM) ignition and flame speed data and prior modeling results to assess the validity of the automated model generation for small, most relevant, and well-tested fuels. This pentane mechanism then served as a seed mechanism for consistent generation of models for larger paraffins. Some modifications of reaction rate parameters in the n-pentane combustion mechanism were warranted, based on comprehensive analysis, reaction path analysis, and sensitivity analyses to improve model performance through scientifically justifiable changes. The new n-pentane model was next used as a sub-mechanism to generate a model for combustion of n-hexadecane. The present study presents ignition delay time predictions for both n-pentane and n-hexadecane across a wide range of temperatures, pressures, and equivalence ratios. Generated models show promising performance in comparison with experimental data and prior modeling studies.