(712c) Theoretical Studies of HO2 Radical Reactions of Relevance to Ethanol Combustion

A detailed chemical kinetic mechanism has been assembled for the combustion of ethanol. While there are no surprises in the mechanistic initiation and propagation routes, the uncertainties in the rate coefficients and branching ratios for many of these primary routes have inhibited an accurate description of the high temperature combustion of ethanol. One specific class of propagation reactions that is particularly important at high pressures are reactions of HO₂ with the fuel and intermediates, in the present case ethanol and acetaldehyde. These are reactions that cannot be experimentally isolated, particularly at combustion temperatures (>700 K), and consequently we have initiated theoretical studies on these reactions.

Ab-initio electronic structure theory has been used to characterize the energetics for the various abstraction channels in Ethanol + HO₂ and Acetaldehyde + HO₂. The energetics for the saddle points were characterized at the CCSD(T)/cc-pV∞Z level of theory using B3LYP/6-311++G(d,p) geometries. Rate coefficients for the various abstraction channels were estimated using Transition State Theory. These results and their implications for ethanol combustion modeling will be discussed.

This work was supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract no. DE-AC02-06CH11357 as part of the Argonne-Sandia Consortium on High-Pressure Combustion Chemistry, FWP# 2009 ANL 59044.