Minimized Skeletal Mechanism for Methyl Butanoate Oxidation and Its Application to the Prediction of C3–C4Products in Nonpremixed Flames: A Base Model of Biodiesel Fuels

Abstract

Kinetic database of methyl butanoate (MB) combustion has been widely used as a base component for formulating kinetic mechanisms describing oxidation of larger methyl esters for biodiesel fuel surrogates. In this study, the detailed mechanism of Dooley et al. (Dooley, S.; Curran, H. J.; Simmie, J. M. Combust. Flame 2008, 153, 2–32) is minimized without empirical adjustment of rate constants in elementary reactions, using a combination of methods including a path flux analysis, removal of individual species, and peak molar concentration analysis. In the first phase, a basic skeletal mechanism with 38 species and 170 reactions for the oxidation of MB is developed, toward understanding the capability and limits of the reduced descriptions on high-temperature ignition delay times and major species profiles in 1-D counterflow flames. A comprehensive analysis of the decomposition pathways associated with preserved and removed reactions provides a scheme for mechanism developers with a clear foundation for creating new skeletal mechanisms of large methyl ester combustion. In the second phase, the MB skeletal mechanism takes into account additional 10 species and 33 reactions in order to predict experimentally measured products in a coflow nonpremixed methane/air flame doped with methyl butanoate. This 48-species skeletal mechanism combined with a 2-D computational fluid dynamic (CFD) flamelet model, for the first time, is able to predict the magnitude and shape of seven C3–C4 intermediate products, which are comparable to the experimental results. Moreover, the present skeletal mechanism, compared with published skeletal mechanisms, not only features a significant reduction in computational cost but also retains more significant products mass-spectrometrically determined.