Application of Ab Initio Quantum Mechanical Calculations to Investigate Oxidation of C-7 and C-14 Methyl Esters: An Alternative Fuel

Using the GAUSSIAN 03 (Frisch et al., 2004, GAUSSIAN 03, Revision C.02, Gaussian, Inc., Wallingford, CT) program, the electronic structure of the C-14 and C-7 methyl esters, $C14H28O2$ (methyl tridecanoate) and $C7H14O2$ (methyl hexanoate), was estimated. For the electronic calculations, the density functional theory at the B3LYP/6-311G(d,p) level and the complete basis set (CBS-QB3) were applied. Bond dissociation energies for C-14 and C-7 esters were evaluated and compared with those of methyl butanoate, $C5H10O2$⁠. Using the KHIMERA program (2007, KHIMERA04, Version 1.1, Motorola Inc; Novoselov et al., 2002, “CHIMERA: A Software Tool for Reaction Rate Calculations and Kinetics and Thermodynamics Analysis,” J. Comput. Chem., 23, pp. 1375–1389), contributions from energies, harmonic vibrational frequencies, and moments of inertia were utilized to construct modified Arrhenius rate expressions for bimolecular reactions. $C7H14O2$ was selected as a surrogate for the $C14$ fuel in order to study the bimolecular reactions with flame radicals. In the present work, reactions of carbon numbers 4 and 5 of $C7H14O2$⁠, where carbon number 1 is the one single bonded to oxygen atom, with flame reactive radicals such as $CH3$⁠, $HO2$⁠, and H were studied where the rates for the reactions of other carbon sites can be obtained from studying methyl butanoate’s reactions. The rate expressions were estimated using transition state theory as implemented in KHIMERA over the temperature of 500–2000 K.