As
a renewable source of energy, ethanol has been widely used in
internal combustion engines as either a gasoline alternative fuel
or a fuel additive. However, as the chemical source term of the computational
fluid dynamics simulation of combustors, there remains a disagreement
in understanding the chemical kinetic mechanism of ethanol. The reaction
mechanism of ethanol + HȮ2 is a well-known crucial
reaction class in terms of predicting the reactivity of ethanol as
well as ethylene formation under engine-relevant conditions. However,
the kinetic parameters of the reactions are basically extrapolated
by analogy to the n-butanol + HȮ2 system calculated by Zhou et al. (Zhou et al. Int. J. Chem.
Kinet.
2012, 44 (3), 155–164).
The reliability of such an analogy remains to be seen because no direct
theoretical or experimental evidence is available in the literature
to date. In this study, thermal rate coefficients of H-atom abstraction
reactions for the ethanol + HȮ2 system were determined
by using both conventional transition-state theory and canonical variational
transition-state theory, with the potential energy surface evaluated
at the CCSD(T)/cc-pVTZ//M06-2x/def-TZVP level. The quantum-mechanical
effects were corrected by the zero-curvature tunneling method at low
temperatures (<750 K), and difference schemes of two Eckart functions
were fitted to optimize the minimum energy path curves. Torsional
modes of the −CH3 and −OH groups were treated
by using the hindered-internal-rotation approximation. Furthermore,
the rate coefficients of the title reaction were calculated at both
the CCSD(T)/cc-pVTZ//M06-2x/def-TZVP and CCSD(T)/CBS//M06-2x/def-TZVP
levels of theory with uncertainty of a factor of 3. Similar to the n-butanol + HȮ2 system, the title system
is dominated by α-site H-atom abstraction, but the rate coefficients
of the three channels are slightly slower than that of the n-butanol + HȮ2 system. In general, the
new calculations show only a limited effect on the ethanol reactivity
at low pressures and high temperatures (>1300 K), but they prevent
the kinetic mechanisms from overpredicting ignition delay times under
engine-relevant conditions.