Combustion Chemistry of Rich Methanol–Air Mixtures

Chain branching and heat release processes and their influence on the burning velocity of premixed rich and near-stoichiometric methanol–air flames were studied by numerical simulation and sensitivity analysis. The phenomenon of superadiabatic temperatures in these flames due to the kinetic mechanism of methanol combustion was first detected. Comparison of the simulation results of the structure of methanol and formaldehyde flames shows that the formation of water in superequilibrium concentrations in flames does not necessarily lead to superadiabatic temperatures, as believed earlier. It was first found that decreasing the dilution of the CH 3 OH/O 2 /N 2 combustible mixture with nitrogen at a constant equivalence ratio enhances the superadiabatic temperature effect. According to simulation results, in a rich near-limit methanol flame, the role of the chain branching reactions H + O 2 = O + OH and O + H 2 = H + OH is negligible due to their low rate. At relatively low temperatures, branching occurs mainly in reactions involving HO 2 and H 2 O 2 peroxide compounds, whose concentration is orders of magnitude higher than the concentration of the main chain carriers H, O, and OH. From the sensitivity analysis, it follows that the burning velocity of methanol flames is positively influenced mainly by the reactions of formation of chain carriers and is negatively influenced by the reactions of consumption of chain carriers. reactions having a major contribution to heat release but are not involved in the formation and consumption of radicals have small sensitivity coefficients.