Waste Cooking Oil (WCO) could become the alternative raw material for biodiesel production to sustain energy globally. Fossil diesel causes emissions of dangerous gases in compression ignition engines, and this had led to the use of biodiesel in the engines to reduce hazardous emissions. Researchers have also used nano additives with biodiesels to further improve CI engine performance and emission characteristics; behaviors are however Fuels-Nano additives combinations specific. This work therefore studied CI engines on the combination effects of blends of diesel, waste cooking oil-based biodiesel: B0 to B100 at 10 % incremental step, and
aluminum oxide (Al2 O3) nanoparticles additive with dosages of 5 g/l and 10g/l on each fuel blends. The biodiesel was produced through the transesterification process in the presence of potassium methoxide as a catalyst. All mixtures containing nano additives were ultrasonicated at a frequency of 25 Hz to prevent agglomeration. The experiment was carried out in a four-stroke, single-cylinder, air-cooled compression ignition engine at engine speeds of 500, 1000, 1500, and 2000 rpm. The result showed a decrease in the CO emissions, brake-specific fuel consumption, and an increase in NOx emissions, brake power, and brake thermal efficiency when the percentage of biodiesel increased for pure biodiesel-diesel blend at higher engine
speeds. Blends containing 5 g/l and 10 g/l aluminum oxide (Al2 O3) Nano-additive showed a significant increase in brake power, brake thermal efficiency and a significant decrease in brake-specific fuel consumption, CO and NOx emissions. For all blends tested, (B20+10 g/l) showed the best result for performance and emissions at all investigated speeds and torques; as it gave Highest BP of 8.5 % for low speed of 500 RPM and 9.7 % for high speed of 2000 RPM, Highest BTE of 19.4 % at high-speed of 2000 RPM and Highest NOx reduction of 42.9 % at low engine torque of 25 Nm and 32 % NOx reduction at high engine torque of 100 Nm; Highest CO reduction of 28.6 % at low engine torque of 25 Nm and 20.6 % NOx reduction at high engine torque of 100 Nm. In conclusion, for better performance and emission characteristics, waste cooking oil-based biodiesel blend with aluminum oxide; B20 +10 g/l can be used to fuel the compression ignition engine.