In the years they were invented, Otto engines running on gasoline, kerosene, and alcohol saw a resurgence in the use of alcohol as fuel over time due to oil crises and the deterioration of the world's ecological balance. In this study, the performance and emission values of heavy and light alcohol mixtures, rarely researched in the literature, were evaluated in a single cylinder, carburetted, air-cooled engine at compression ratios (Cr) of 7 and 8.5. Following this, the energy and exergy analyses of the fuels were conducted according to the 1st and 2nd Laws of Thermodynamics. For MEB15, MEB30, and MEB45, the fuel exergy was calculated as −13.4 %, −5.3 %, and −0.4 %, respectively. The entropy production for MEB0, MEB15, MEB30, and MEB45 was calculated. Compared to gasoline data, HC and CO emissions decreased by more than 20 % in Cr:7. The highest sustainability index values were obtained for MEB15 (1.2–1.23) at Cr:8.5.