Fuels derived from biomass will most likely contain oxygen due to the high amount of hydrogen needed to remove oxygen in the production process. Today, alcohol fuels (e. g. ethanol) are well understood for spark ignition engines. The Institute for Combustion Engines at RWTH Aachen University carried out a fuel investigation program to explore the potential of alcohol fuels as candidates for future compression ignition engines to reduce engine-out emissions while maintaining engine efficiency and an acceptable noise level.
The soot formation and oxidation process when using alcohol fuels in diesel engines is not yet sufficiently understood. Depending on the chain length, alcohol fuels vary in cetane number and boiling temperature. Decanol possesses a diesel-like cetane number and a boiling point in the range of the diesel boiling curve. Thus, decanol was selected as an alcohol representative to investigate the influence of the oxygen content of an alcohol on the combustion performance. To gain knowledge about the underlying processes of such fuels, experiments in a single cylinder research engine were carried out. Engine results for decanol (alcoholic compound) are compared to regular diesel fuel and rapeseed oil methyl ester (B100) in different load points with respect to all regulated emissions.
The soot emissions when using decanol are significantly reduced up to 90% depending on the load point. In order to better understand the ongoing processes inside the cylinder, the experimental results were confirmed by 3-D CFD calculations with n-dodecane and 1-decanol.
Furthermore, the experimental results indicate an additional potential for future diesel combustion concepts such as HCCI with respect to soot and NOx emissions in the part load range when using oxygenated fuels. Overall, the low particulate matter emissions of alcohol fuels provide justification for their consideration as fuels in future diesel engines.