(700e) Automated Generation of a Chemical Kinetic Reaction Mechanism for Combustion of N-Hexadecane and Larger 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 that application. Manual construction of detailed kinetic models for molecules of this size is infeasible, while blind application of automated mechanism generation frameworks is not yet reliable. Thus, a combination of automated and manual approaches is required. In our first efforts toward this goal, a detailed kinetic model for combustion of n-pentane, the smallest relevant paraffin for this application, was generated using the open-source Reaction Mechanism Generator (RMG) software. Mechanism generation was tested with and without input from available libraries of thermochemical properties and rate parameters. In addition, some well-justified modifications to rate parameters of several key reactions were made based on comprehensive reaction path and sensitivity analyses to improve model performance. We then built upon this model, and the lessons learned in generating it, to produce compact kinetic mechanisms for n-hexadecane combustion, including by using the n-pentane mechanism as a seed mechanism for generating the n-hexane combustion mechanism. This talk will present ignition delay time predictions for both n-pentane and n-hexadecane across a wide range of temperatures, pressures, and equivalence ratios. We will also discuss lessons learned and the advantages and disadvantages of various approaches to creating compact yet useful mechanisms for large alkane combustion. Highly simplified models for the high temperature and high-pressure regime were also generated and tested for alkanes up to C₂₀H₄₂. These mechanisms show promising performance in comparison with experimental data and prior modeling studies. Our next step in this effort is to have a tractable mechanism for paraffin wax fuel (nominally C₃₂H₆₆), which is being investigated using multiple approaches.