Article pubs.acs.org/JPCA
Ab Initio Investigation of the Thermal Decomposition of n‑Butylcyclohexane Mohamad Akbar Ali, V. Tyler Dillstrom, Jason Y. W. Lai, and Angela Violi* Department of Mechanical Engineering, University of Michigan, 2250 Hayward Street - 2150 G.G. Brown, Ann Arbor, Michigan 48109, United States S Supporting Information *
ABSTRACT: Environmental and energy security concerns have motivated an increased focus on developing clean, efficient combustors, which increasingly relies on insight into the combustion chemistry of fuels. In particular, naphthenes (cycloalkanes and alkylcycloalkanes) are important chemical components of distillate fuels, such as diesel and jet fuels. As such, there is a growing interest in describing napthene reactivity with kinetic mechanisms. Use of these mechanisms in predictive combustion models aids in the development of combustors. This study focuses on the pyrolysis of nbutylcyclohexane (n-BCH), an important representative of naphthenes in jet fuels. Seven different unimolecular decomposition pathways of C−C bond fission were explored utilizing ab initio/DFT methods. Accurate reaction energies were computed using the high-level quantum composite G3B3 method. Variational transition state theory, Rice−Ramsperger−Kassel−Marcus/master equation simulations provided temperature- and pressure-dependent rate constants. Implementation of these pathways into an existing chemical kinetic mechanism improved the prediction of experimental OH radical and H2O speciation in shock tube oxidation. Simulations of this combustion showed a change in the expected decomposition chemistry of n-BCH, predicting increased production of cyclic alkyl radicals instead of straight-chain alkenes. The most prominent reaction pathway for the decomposition of n-BCH is n-BCH = C3H7 + C7H13. The results of this study provide insight into the combustion of n-BCH and will aid in the future development of naphthene kinetic mechanisms.
1. INTRODUCTION The major categories of hydrocarbons in jet fuels are alkanes, cycloalkanes and alkylcycloalkanes (naphthenes), aromatics, and alkenes.1 Alkanes are the most abundant components in real fuels and account for 50−60% of the fuel volume. Naphthenes make up to 20% by volume of jet fuels such as JetA, JetB, and JP-8 and ∼60% by volume of RP-1.2−4 Alkenes account for
