Detailed chemical kinetic mechanisms for combustion of oxygenated fuels

Thermodynamic properties and detailed chemical kinetic models have been developed for the combustion of two oxygenates: methyl butanoate, a model compound for biodiesel fuels, and methyl formate. a related simpler molecule. Bond additivity methods and rules for estimating kinetic parameters were adopted from hydrocarbon combustion and extended. The resulting mechanisms have been tested against the limited combustion data available ill the literature, which was obtained at low temperature. subatmospheric conditions in closed vessels. using pressure measurements as die main diagnostic. Some qualitative agreement was obtained, but die experimental data consistently indicated lower overall reactivities than the model, differing by Factors of 10 to 50. This discrepancy, which occurs for species with well established kinetic mechanisms as well as for methyl esters, is tentatively ascribed to the presence of wall reactions in the experiments. The model predicts a region of weak or negative dependence of overall reaction rate on temperature for each methyl ester. Examination of the reaction fluxes provides an explanation of this behavior, involving a temperature-dependent competition between chain-propagating uni-molecular decomposition processes and chain-branching processes, similar to that accepted for hydrocarbons. There is an urgent need to obtain more complete experimental data under well-characterized conditions for through testing of the model.