Mixtures of n-butanol and iso-butanol blended with diesel: experimental investigation of combustion characteristics, engine performance and emission levels in a compression ignition engine

The isomers of butanol have slightly different properties, which can be exploited to improve combustion characteristics. To investigate the potential of this concept, normal-butanol (nB) and iso-butanol (isoB) were blended together in four different ratios (5% of each, 10% of each, and 7% plus 13% of each in both variations, by volume) with conventional diesel. The experimental data were analyzed via analysis of variance to evaluate significant differences between engine parameters. Brake power for the 5% isoB-5% normal-butanol-90% diesel blend was slightly improved while specific fuel consumption was increased with the increase in all dual blends. The high blend ratios of isoB (10% and 13% isoB) produced higher peak in-cylinder pressures and heat release rates as well as a substantial reduction in carbon monoxide emissions. The higher blend ratios of nB (10% and 13% nB) produced much lower unburnt hydrocarbon emissions because the energy required to crack the C-H bonds of nB is less than that required for isoB. Therefore, the hydrocarbons are more easily oxygenated. A slight reduction was found in NOx emissions when increasing either nB or isoB, with nB being slightly more effective. Therefore, a blend of n- and isoB could be a promising alternative to a single isomer additive (iso/nB) to optimize engine performance.