C8-Oxygenates for Clean Diesel Combustion

Within this paper, the two possible alternative and biomass-based fuel candidates Di-n-butyl ether (DNBE) and 1-octanol are investigated with regard to their utilization in a diesel-type engine. In order to asses the fuels emission-reduction potential, both have been tested in a single cylinder engine (SCE) and a high pressure chamber (HPC) in comparison to conventional EN590 diesel at various load points. Due to its reduced reactivity 1-octanol features a longer ignition delay and thus higher degrees of homogenization at start of combustion, whereas DNBE ignites rather rapidly in both the HPC and the engine leading to a predominantly mixing controlled combustion. Thus, both fuels feature completely different combustion characteristics. However, compared to diesel, both fuels contribute to a significant reduction in Filter Smoke Number (FSN) up to a factor of 15. In addition to FSN measurements also size-number-distributions of particulates have been measured by means of an Engine Exhaust Particle Sizer Spectrometer (EEPS^™). With the oxygenated fuels a shift in the characteristic particle diameter distribution was observed in the higher engine load points. With DNBE, engine out emissions of unburned hydrocarbons (HC), carbon monoxide (CO) and combustion noise were below standard diesel fuel even without changing any engine hardware or calibration. In order to reduce HC-emissions and the maximum rate of heat release with 1-octanol the compression ratio (CR) has been increased from 15:1 to 17:1. By this, the ignition delay could be reduced leading to lowered CO- and HC-emissions and reduced heat release rates at low load operation.