Blending n-octanol with biodiesel for more efficient and cleaner combustion in diesel engines: A modeling study

Biodiesel has become a popular alternative fuel to fossil diesel. However, compared to conventional diesel engines, the adoption of pure biodiesel often leads to higher NOx though soot emissions can be reduced. In this study, the alcoholic fuel n-octanol was chosen as the blending fuel in biodiesel. The modeling study was carried out to investigate the effects of blending n-octanol on the combustion characteristics and emissions formation process in a diesel engine. At first, a multi-component reaction mechanism involving 115 species and 489 reactions was constructed to better predict the combustion process of biodiesel and n-octanol. This mechanism was then coupled with KIVA-CHEMKIN to implement a three-dimensional simulation of the engine. The developed mechanisms and adopted models were validated under a variety of conditions. At last, to examine the effects of n-octanol, simulations were carried out by gradually increasing the percentage of n-octanol from 0% to 100% with an interval of 10%. Analysis of the simulation results revealed that blending more n-octanol with biodiesel could lead to a prolonged ignition delay. Due to the high latent heat of vaporization of n-octanol, the temperature at the initial stage of combustion can be reduced which subsequently mitigated the formation of NOx. The higher oxygen content of n-octanol was beneficial for the improvement in power output and the decrease of soot emissions. Overall, B20/O80 blends were found to be capable of achieving more efficient and cleaner combustion in the diesel engine at both speeds.