An Experimental Study on the Use of Butanol or Octanol Blends in a Heavy Duty Diesel Engine 2015-24-2491
Global warming driven by “greenhouse gas” emissions is an increasingly serious concern of both the public and legislators. A potentially potent way to reduce these emissions and conserve fossil fuel resources is to use n-butanol, iso-butanol or octanol (2-ethylhexanol) from renewable sources as alternative fuels in diesel engines. The effects of adding these substances to diesel fuel were therefore tested in a single-cylinder heavy duty diesel engine operated using factory settings. These alcohols have better calorific values, flash points, lubricity, cetane numbers and solubility in diesel than shorter-chain alcohols. However, they have lower cetane numbers than diesel, so either hydrotreated vegetable oil (HVO) or Di-tertiary-butyl peroxide (DTBP) was added to the diesel-alcohol mixtures to generate blends with the same Cetane Number (CN) as diesel. Blends containing 10 and 20% of n-butanol or iso-butanol, or 30 % octanol were tested at four operating points from the European Stationary Cycle. The same engine settings were used in all cases.
The average engine performance in tests with the blends was similar to that achieved with pure diesel but the blends generated less cycle-to-cycle variation. The brake thermal efficiency was similar for all the fuels but the brake specific fuel consumption was slightly higher for the blends due to their lower calorific value. Because of their oxygen content, the blends produced much lower emissions of soot and carbon monoxide than were achieved with diesel. Blends yielded slightly higher NOx emissions than pure diesel and all the fuels produced similar hydrocarbon emissions. Possibly because of its branched molecular structure, the iso-butanol blends yielded slightly higher soot emissions than the n-butanol blends. Because HVO contains no aromatics, its addition to fuel blends reduced soot emissions. Overall, these results confirm the substantial potential of renewable longer-chain alcohols as components of blended diesel fuels.