Experimental Study of Using Butanol or Octanol Blends as Alternative Fuels in Diesel Engines

Licentiate thesis, 2016

With the increased travel demand, the consumption of fossil fuels, as the main energy source for transportation, has risen sharply over the last few decades. Fossil fuels are considered a non-renewable resource. In addition, burning them in internal combustion engines can generate a large amount of greenhouse gas (GHG) emissions. According to the life-cycle assessment, use of renewable fuels as alternatives in diesel engines can help to dramatically reduce GHG emissions. Furthermore, the oxygen content in alcohols may help to suppress soot formation significantly. Therefore, mixing renewable alcohols in diesel fuel may offer a potential solution for reducing GHG emissions, soot emissions and fossil fuel consumption. Hence, it is important to investigate the possibility of using alcohol/diesel blends in existing diesel engines. To reproduce the characteristics of existing engines as closely as possible, a light duty (LD) single-cylinder engine, a heavy duty (HD) single-cylinder engine and a four-cylinder LD engine were employed with production engine settings. In both types of single-cylinder engine, engine performance and emissions were studied under steady-state conditions. In the four-cylinder LD engine, the cold start behaviour of the fuels was investigated. Four alcohols were selected to mix with diesel, i.e. n-butanol, isobutanol, 2-ethylhexanol and n-octanol. These alcohols were blended separately with one of two different cetane number (CN) improvers, either hydrotreated vegetable oil or di-tertiary-butyl peroxide, in diesel fuel. The mixtures were prepared to have the same CN as diesel fuel. With the same CN and engine settings, the alcohol/diesel blends and diesel fuel showed very similar heat release profiles. The blends generated slightly faster combustion, leading to slightly higher indicated thermal efficiency, than diesel fuel under most of the tested conditions in both types of single-cylinder engine. Soot emissions decreased sharply when changing diesel fuel to alcohol/diesel blends. Further, the n-butanol and 2-ethylhexanol diesel blends showed good cold start performance in the multi-cylinder LD engine. In conclusion, the results showed that from a combustion point of view, it is possible to use renewable fuels, such as n-butanol, iso-butanol, n-octanol or 2-ethylhexanol, mixed with diesel and ignition improver in existing diesel engines without any engine modifications.