Analysis of the Effect of Bio-Fuels on the Combustion in a Downsized DI SI Engine

In this study the fuel influence of several bio-fuel candidates on homogeneous engine combustion systems with direct injection is investigated. The results reveal Ethanol and 2-Butanol as the two most knock-resistant fuels. Hence these two fuels enable the highest efficiency improvements versus RON95 fuel ranging from 3.6% - 12.7% for Ethanol as a result of a compression ratio increase of 5 units. Tetrahydro-2-methylfuran has a worse knock resistance and a decreased thermal efficiency due to the required reduction in compression ratio by 1.5 units. The enleanment capability is similar among all fuels thus they pose no improvements for homogeneous lean burn combustion systems despite a significant reduction in NO_X emissions for the alcohol fuels as a consequence of lower combustion temperatures. In general, 1-Butanol and 2-Butanol emit higher amounts of HC emissions in all operation points combined with significantly increased particle emissions at high loads indicating a worse mixture formation. Alcohol fuels lead under cold conditions to a higher oil dilution which is significantly depending on the boiling temperature of the fuel. Hence, the usage of 1-Butanol as a pure fuel is critical.