Combustion Characteristics for Partially Premixed and Conventional Combustion of Butanol and Octanol Isomers in a Light Duty Diesel Engine
Journal article, 2017
Reducing emissions and improving efficiency are major goals of modern internal combustion engine research. The use of biomass-derived fuels in Diesel engines is an effective way of reducing well-to-wheels (WTW) greenhouse gas (GHG) emissions. Moreover, partially premixed combustion (PPC) makes it possible to achieve very efficient combustion with low emissions of soot and NOx. The objective of this study was to investigate the effect of using alcohol/Diesel blends or neat alcohols on emissions and thermal efficiency during PPC. Four alcohols were evaluated: n-butanol, isobutanol, n-octanol, and 2-ethylhexanol. The alcohols were blended with fossil Diesel fuel to produce mixtures with low cetane numbers (26-36) suitable for PPC. The blends were then tested in a single cylinder light duty (LD) engine. To optimize combustion, the exhaust gas recirculation (EGR) level, lambda, and injection strategy were tuned. The measured emissions and thermal efficiencies for PPC with the blends were compared to those for conventional combustion with production engine settings. The study showed a viable way to achieve PPC by low CN alcohol/Diesel blends in a single cylinder LD engine. Because of its lower combustion temperature and increased fuel-air mixing, PPC produced very low soot and NO emissions, independently of the fuels used. High HC and CO emissions were observed when the ignition dwell cross zero from negative to positive value. Properties of the individual component would influence the combustion behavior even compare to the fuel with similar CN. Compared to conventional diffusion-controlled combustion, PPC generated a high indicated thermal efficiency up to 50% in all tested conditions for both low CN level blends.