Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2‑Methylhexane

Accurate chemical kinetic combustion
models of lightly branched
alkanes (e.g., 2-methylalkanes) are important to investigate the combustion
behavior of real fuels. Improving the fidelity of existing kinetic
models is a necessity, as new experiments and advanced theories show
inaccuracies in certain portions of the models. This study focuses
on updating thermodynamic data and the kinetic reaction mechanism
for a gasoline surrogate component, 2-methylhexane, based on recently
published thermodynamic group values and rate rules derived from quantum
calculations and experiments. Alternative pathways for the isomerization
of peroxy-alkylhydroperoxide (OOQOOH) radicals are also investigated.
The effects of these updates are compared against new high-pressure
shock tube and rapid compression machine ignition delay measurements.
It is shown that rate constant modifications are required to improve
agreement between kinetic modeling simulations and experimental data.
We further demonstrate the ability to optimize the kinetic model using
both manual and automated techniques for rate parameter tunings to
improve agreement with the measured ignition delay time data. Finally,
additional low temperature chain branching reaction pathways are shown
to improve the model’s performance. The present approach to
model development provides better performance across extended operating
conditions while also strengthening the fundamental basis of the model.