The effect of the addition of individual methyl esters on the combustion and emissions of ethanol and butanol -diesel blends

Biodiesel fuel is known to improve the properties of alcohol-diesel blends for use in compression ignition engines. In this work the effects on combustion characteristics and emissions of preselected methyl esters (i.e. biodiesel components) have been assessed. The most representative individual fatty acid methyl esters (FAMEs) were added to alcohol blends in order to understand the effect of carbon chain length and degree of unsaturation on combustion and emissions. The effects of alcohol addition on the properties of fuel blends were also investigated using ethanol and butanol. Relating to the physical properties, emphasis was given to both stability and lubricity of alcohol-diesel blends. The results showed that 15% of all methyl esters was enough to avoid phase separation of alcohol-diesel blends and keep the wear scar diameter of the blends below the limitation required by the lubricity standard. For combustion, the use of alcohol blends shows a clear benefit in terms of CO and soot emissions with respect to biodiesel blends with the same oxygen content. Short carbon chain length and saturated methyl esters are recommended to improve alcohol blends. Comparisons between the alcohols, show that butanol rather than ethanol produces lower CO, THC and soot emissions.

► Short chain length saturated FAMEs in alcohol blends show the highest emission benefits.
► Soot reductions of alcohol blends are higher than with biodiesel at same oxygen content.
► Alcohol blends show a better soot-NOx trade-off than biodiesel blends.
► Butanol-diesel-biodiesel blends show more potential to reduce exhaust emissions than ethanol-diesel-biodiesel blends.