Some New Observations on Methanol Oxidation Chemistry

New experiments conducted in a turbulent flow reactor show kinetic characteristics of methanol oxidation that have not been observed previously. Data are presented for methanol oxidation at equivalence ratios in the range of 0.6−1.6 and initial temperatures or 1025-1090 K at atmospheric pressure. At intermediate extents of reaction, a marked deceleration in chemical reaction rate is observed to cause a "plateau" in the energy release and species concentration profiles. This effect becomes considerably more pronounced with increasing equivalence ratio and is not predicted by the earlier comprehensive kinetic mechanism of Westbrook and Dryer. A revised mechanism incorporating numerous recent reaction rate and thermochemical data provides both a significant improvement in agreement with flow reactor data and an improved understanding of the important reactions involved in methanol oxidation. Reaction path flux analyses reveal the importance of HO 2 chemistry, the decreasing role of chain-branching reactions during fuel decay, and the inhibiting effect of H 2 . The ratio of the rates of the reactions CH 3 OH + H = CH 3 + H 2 O and CH 3 H + H = CH 2 OH + H 2 is confirmed to be only 1/40 at 1000 K, in agreement with recent fundamental measurements, but much lower than the value of 1/2.5 used in most recent methanol mechanisms. The importance of continued updating and hierarchical re-validation of kinetic mechanisms is emphasized by these results.