Combustion and emission behavior of linear C 8 -oxygenates

Abstract

Alternative fuels have become of great importance in order to secure a sustainable mobility within the next decades. Within the Cluster of Excellence, “Tailor-Made Fuels from Biomass” at RWTH Aachen University, several possible fuel candidates could be derived from (hemi-)cellulose by selective catalytic conversion. The proposed fuel candidates include furans, ethers, alcohols, and ketones. Experiments with the isomers di-n-butyl ether and 1-octanol have proven their suitability for diesel-type combustion. With di-n-butyl ether being prone to auto-ignition, overall hydrocarbon, carbon monoxide, and soot emissions are reduced compared to diesel. In contrast, the prolonged ignition delay with 1-octanol causes an increase in HC and CO emissions particularly at low engine loads. However, soot emissions are even below those of di-n-butyl ether. With regard to particulate matter, an Exhaust Emissions Particulate Sizer Spectrometer (EEPS^™) has been utilized to investigate the particle size or number distribution. Compared to diesel, a reduction of the total particle number up to 80% was seen with the oxygenates next to a shift toward reduced particle mobility diameter. The HC emissions of both di-n-butyl ether and 1-octanol have been studied in detail by means of gas chromatography–mass spectrometry. As a main result, not only the general emission reduction potential of the biofuel alternatives 1-octanol and di-n-butyl ether can be shown with this work. Gas chromatography–mass spectrometry revealed that the composition of hydrocarbons emitted with the C₈-oxygenates is almost equal to those with diesel, except for the unburned fuel that is present in the exhaust gas. Quantification showed that the carcinogenic component 1,3-butadiene increased with the alternative fuel candidates, whereas particularly benzene and ethyl benzene reduced. Since both di-n-butyl ether and 1-octanol are found in high proportions in the exhaust gas, the effects on the aftertreatment system have to be investigated in a subsequent campaign.