Effects of ethanol addition on biodiesel combustion: A modeling study

The present study aims to numerically investigate the impacts of ethanol blend ratio together with advanced fuel injection timings on biodiesel's performance, combustion and emission characteristics. Simulations were conducted using coupled KIVA-CHEMKIN code for neat biodiesel and its blend fuels with 5%, 10% and 20% (vol.%) of ethanol at a fix engine speed of 2400rpm under 10%, 50% and 100% engine load conditions, with and without advanced fuel injection timings of 2°, 3° and 5° crank angle. A skeletal reaction mechanism was constructed to include the significant oxidation and emission formation kinetics of biodiesel and ethanol fuels, and it was validated by performing the 0-D ignition delay predictions, as well as 3-D numerical simulations against the experimental results. The results indicate that peak cylinder pressure and indicated thermal efficiency generally decrease with the increasing ethanol blend ratio due to its prolonged ignition delay and reduced heating value. In terms of emissions, the CO emissions generally increase as the ethanol blend ratio increases, while the NO_x emissions are reduced. The soot emissions increases under 10% load conditions, but reduced under 50% and 100% load conditions. With advanced fuel injection timings, the combustion process seems to be improved under 10% and 100% engine load conditions. For the efficient use of biodiesel/ethanol blend fuels, it is suggested that the ethanol blend ratio and advanced fuel injection timing should be carefully selected based on the engine operating conditions.