Detailed Kinetic Mechanism for the Oxidation of Vegetable Oil Methyl Esters: New Evidence from Methyl Heptanoate

The oxidation of methyl heptanoate was studied experimentally in a jet-stirred reactor at 10 atm and a constant residence time of 0.7 s, over the temperature range 550−1150 K, and for fuel-lean to fuel-rich conditions. Concentration profiles of reactants, stable intermediates, and final products were obtained by sonic probe sampling followed by online GC and FTIR and off-line GC analyses. As previously shown for methyl hexanoate (Dayma, G.; Gail, S.; Dagaut, P. Energy Fuels 2008, 22, 1469-1479), the oxidation of methyl heptanoate under these conditions showed the well-known three regimes of oxidation observed for large hydrocarbons, namely, cool flame, negative temperature coefficient, and high temperature oxidation. The detailed chemical kinetic reaction mechanism built to model the oxidation of methyl heptanoate is an extended and revisited version of that previously developed for methyl hexanoate. This mechanism now involves 1087 species and 4592 reversible reactions. It was validated by comparing the present experimental results to the simulations. The main reaction pathways involved in methyl heptanoate oxidation were delineated computing the rates of formation and consumption of every species. Kinetic rate constants are proposed to model the oxidation of methyl esters.