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Numerous previous studies have reported that the reduction of emissions by adapting oxygenated bio-fuels chiefly depend on the overall oxygen percentage of the blended oxygenates. However, the effect of molecular structures of the fuels has sometimes only been attributed to differences in auto-ignition quality (i.e. cetane number). In this paper, fuels with two kinds of molecular structures, namely linear and cyclic, have been studied. It reports on emissions tests on a modified in-line 6-cylinder DAF HD Diesel engine with several selected oxygenates mixed with diesel. Fuels in question here are from the non-oxygenates group: n-hexane and cyclohexane, and the oxygenate group: 1-hexanol and cyclohexanol. In order to isolate the effect of molecular structure, the blend compositions are chosen such that the overall oxygen fraction of all blends is the same.

In this paper, the soot-NOx trade-off and fuel efficiency of various aromatic oxygenates is investigated in a modern DAF heavy-duty diesel engine. All oxygenates were blended to diesel fuel such that the blend oxygen concentration was 2.59 wt.-%. The oxygenates in question, anisole, benzyl alcohol and 2-phenyl ethanol, have similar heating values and cetane numbers, but differ in the position of the functional oxygen group relative to the aromatic ring. The motivation for this study is that in lignin, a widely available and low-cost biomass feedstock, similar aromatic structures are found with varying position of the oxygen group to the aromatic ring. From the results it becomes clear that both the soot-NOx trade-off and the volumetric fuel economy (i.e. ml/kWh) is improved for all oxygenates in all investigated work points.