Development of a reduced chemical kinetic mechanism for biodiesel/natural gas mixture

Abstract

Biodiesel as an alternative fuel for diesel in compression ignition engines cab be used directly to this type of engine without any significant changes in geometry. Some negative points of biodiesel in compression ignition (CI) engines such as high viscosity, injector carbonize and high NOx emissions cause to use this fuel with other fuels such as alcohol fuels and natural gas based on desired properties of second fuel. Numerical study of fuels such as biodiesel needs to have a chemical kinetic mechanism that can predict combustion characteristics and output emissions. In this study, a reduced detailed mechanism of biodiesel introduced by Zhang et al. is chosen to merged with natural gas GRI-Mech 3.0 mechanism to obtain a chemical kinetic mechanism of biodiesel/natural gas. Direct relation graph with error propagation (DRGP) method and consequently sensitivity analysis was employed to 525 reactions and 126 species that modified with highly sensitive reactions. At first, reduced mechanism of biodiesel/natural gas compared with merged mechanism of these fuels’ mixture with 0-Dimension simulation of ignition delay and 1-Dimension simulation of flame speed. Obtained results show error less than 1% for all intake temperatures and equivalence ratios. In the following, the reduced mechanism with zero percent of natural gas compared with original biodiesel mechanism. Yet again, results show errors almost near zero in lower equivalence ratio and acceptable error, in maximum condition about 10%, in moderate and high equivalence ratios (ERs) during predicting ignition delay with 0-Dimension simulation. Also, flame speed in this evaluation shows less than 2% error in 1-Dimension simulation.