Experimental Studies on Using Butanol and Octanol Isomers as Drop-in Fuels for Diesel Engines

Doctoral thesis, 2019

The increasing importance of transportation in modern societies has caused fossil fuel consumption to increase greatly in recent decades. However, burning fossil fuels in internal combustion engines can lead to high emissions of greenhouse gases, which cause climate change. Because of this, there is great interest in using alcohols and other renewable fuels in Diesel engines to reduce vehicles’ lifecycle greenhouse gas emissions. It is therefore important to investigate the possibility of using alcohol/Diesel blends, or even fossil-free blends, in both existing Diesel engines and new engines employing advanced combustion concepts.

This thesis explores the use of four alcohols (n-butanol, isobutanol, 2-ethylhexanol, and n-octanol) and two bio-Diesels (hydrotreated vegetable oil, or HVO, and rapeseed methyl ester) as drop-in fuels in Diesel engines. Their effects on the performance and emissions of compression ignition engines were assessed by performing experiments using light- and heavy-duty single cylinder engines under steady-state conditions.

To test the compatibility of alcohol-containing blends with existing engines, HVO and the commercial cetane number (CN) improver DTBP were used to compensate for the alcohols’ low CN values and prepare oxygenated blends with CN values similar to fossil Diesel. Blends with and without fossil Diesel were tested. Two single-cylinder engines were operated at four standard load points using production calibrated engine settings. Experiments were also performed using an advanced combustion strategy (partially premixed combustion) in which the alcohols were blended with fossil Diesel fuel directly to produce mixtures with low cetane numbers (26 or 36). The blends’ effects on spray penetration, flame development, and soot characteristics were investigated in the constant volume combustion chamber.

The results show that from a combustion point of view, the tested alcohol blends with Diesel-like CN values can be used in unmodified existing Diesel engines. Compared to conventional Diesel fuel, the oxygenated blends yielded slightly higher indicated thermal efficiencies, significantly lower soot emissions, and similar heat release profiles. Moreover, partially premixed combustion was shown to further increase thermal efficiency while reducing soot and NOx emissions.