The present research examined the usability of diesel-biodiesel and diesel-biodiesel-hexanol fuel blends as an alternative to diesel fuel in a compression ignition engine. Energy and exergy analyses were conducted using the
data obtained from the engine tests. In addition, the sustainability index was calculated. When selecting the most suitable fuel for diesel fuel, thermal and exergy efficiency and sustainability index values were compared. The
obtained results revealed that the most suitable alternative fuel for diesel fuel was the diesel-biodiesel binary fuel blend. In this fuel blend, thermal efficiency, exergy efficiency, and sustainability index values are 3.8, 5.18, and 1.44 % higher, respectively, compared to pure diesel fuel at an engine load of 100 %. As the alcohol ratio increases in diesel-biodiesel-hexanol ternary blends, the sustainability index value decreases compared to diesel fuel. As the hexanol ratio increases in fuel blends, the sustainability index decreases. The highest sustainability index for ternary fuel blends is 1.26 at 100 % engine load in B45H10 fuel. The increase in engine load increases the sustainability index and exergy efficiency in all fuel blends.