A Reduced Mechanism for High-Temperature Oxidation of Biodiesel Surrogates

Abstract

A skeletal mechanism with 118 species and 837 reactions was developed from a detailed LLNL mechanism that consisted of 3329 species and 10806 reactions for a tricomponent surrogate mixture, consisting of methyl decanoate, methy-9-decenoate, and n-heptane, which is suitable for combustion modeling of biodiesel derived from various feedstocks. The method of directed relation graph (DRG) for skeletal mechanism reduction was improved for mechanisms with large numbers of isomers. The improved DRG together with isomer lumping and DRG-aided sensitivity analysis (DRGASA) were subsequently applied to obtain a minimal skeletal mechanism from the detailed mechanism for the given error tolerance. The reduction was performed within a parameter range of pressure from 1 to 100 atm, equivalence ratio from 0.5 to 2, and temperature higher than 1000 K in autoignition and perfect stirred reactors (PSR). Although reduced in size almost by a factor of 30, the skeletal mechanism features high accuracy for high-temperature applications both in predicting the global system parameters, such as ignition delay and extinction time, and detailed profiles of species concentrations. Furthermore, numerical simulations of jet stirred reactors were compared with experimental measurements for rapeseed oil methyl esters. The temperature and species profiles in one-dimensional atmospheric counterflow diffusion flames were well predicted as well compared with experimental data in the literature.