Development of a reduced biodiesel combustion kinetics mechanism for CFD modelling of a light-duty diesel engine

A reduced chemical kinetics mechanism has been developed and validated under zero-dimension and multi-dimensional engine simulations for a range of engine operating conditions and types of biodiesel fuel. The mechanism is first constructed by reducing a detailed MB/MB2D mechanism consisting of 301 species and 1516 reactions to 77 species and 212 reactions. The ignition delay periods and temporal evolutions of important species are in good agreement with those produced using detailed kinetics. The reduced mechanism is then combined with a skeletal modified n-heptane mechanism to account for actual biodiesel energy content and molecular structure when fuel blends are introduced. Two additional global reactions are also included to cater for the change in ratio between saturated and unsaturated methyl esters in the fuels. The combined mechanism (BOS-V2) consists of 113 species and 399 reactions with integrated nitrogen oxides (NOx) reaction kinetics. This mechanism is then further validated using OpenFOAM for the computational fluid dynamics (CFD) engine simulations. Here, neat and B50 blends of coconut, palm and soy methyl esters are used. Good agreements in ignition delay, peak pressure, pressure trace, heat-release profile and emission trends are achieved between experimental and predicted data for all the tested fuels and engine operating conditions. The results show that the proposed mechanism gives reliable predictions of in-cylinder combustion and emission processes.