Adding n-butanol, n-heptanol, and n-octanol to improve vaporization, combustion, and emission characteristics of diesel/used frying oil biodiesel blends in DICI engine

Diesel engines play a vital role in the transportation sector. Ternary blends of alcohol, biodiesel, and diesel have the potential to improve diesel engine combustion and emissions. In the current work, three different types of alcohols; n-butanol, n-heptanol, and n-octanol were added to biodiesel/diesel blends to improve diesel engine performance, combustion, and emissions. The biodiesel was produced from used frying oil (UFO) by ultrasonic enhanced transesterification to achieve the highest yield, lowest viscosity, and minimum production time. Three ternary fuels containing 10 vol% (n-butanol or n-heptanol or n-octanol), 10 vol% UFO biodiesel, and 80 vol% diesel were tested using diesel engine at 25%, 50%, and 75% load conditions. Thermogravimetric analysis of the ternary blends proved the enhancement in the vaporization characteristics compared with biodiesel and diesel fuels; the lighter the alcohol, the faster the vaporization rate but with longer ignition delay which enhanced the premixed burning mode. The specific fuel consumption increased by up to 6% with a slight reduction in thermal efficiency (approximate to 1%) when n-octanol was used while n-butanol and n-heptanol showed comparable values to neat diesel. Ternary blends showed a reduction in smoke opacity, NOx, CO, and CO2 by up to 38%, 11%, 35%, and 14% compared with diesel, while the lowest emissions were attained for the addition of n-heptanol.