Comparison of Different Chemical Kinetic Models for Biodiesel Combustion

The current study compares the predictions by four different published mechanisms in literature which have been used for 3 dimensional compression ignition engine simulations. These four mechanisms use two different sets of surrogates: (a) methyl decanoate, methyl 9-decenoate, and n-heptane, (b) methyl butanoate and n-heptane. The mechanisms include: (1) 115 species and 460 reactions [1] using surrogate mixture (a); (2) 77 species and 209 reactions [2] using surrogate mixture (a); (3) 145 species and 869 reactions [3] using surrogate mixture (b); (4) 41 species and 150 reactions [4] using surrogate mixture (b). The different reduction techniques implemented to obtain the reduced mechanisms from the detailed mechanisms are briefly described. The surrogate mixture compositions are then modified to match the cetane number of the real biodiesel fuels. The experimental data for comparison include jet-stirred reactor data for species concentrations for biodiesel derived from rapeseed oil and 3 dimensional constant volume combustion data (for ignition, combustion, and emission characteristics), engine data (for pressure, heat release rate, and emission characteristics) for soy-derived biodiesel. 0-D and 3-D constant volume simulations with all the mechanisms can capture the general experimental trends quite well. Large surrogate models and mechanisms tend to provide better predictions at the expense of increased computational costs. The 115 species and 460 reaction mechanism was observed to perform the best among the mechanisms in predicting the jet-stirred reactor and 3-D constant volume data. It was observed that all the mechanisms are able to qualitatively capture the engine performance and emission characteristics.