In the present experimental study, the influence of copper oxide (CuO) nanoparticles on emissions and performance of a 4.4 kW diesel engine powered by palm oil biodiesel have been analyzed. Palm oil biodiesel of 20% by volume was blended with diesel fuel and the resulting blend is termed as B20. The B20 test fuel blends were doped with CuO nanoparticles with concentrations of 25 ppm, 50 ppm, and 75 ppm. Experiments were carried out at 0%, 25%, 50%, 75%, and 100% engine loads at a constant speed (1,500 rpm). Performance parameters such as brake thermal efficiency (BTE) and brake specific energy consumption (BSEC), emission parameters such as carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), nitrogen oxides (NOx), and smoke opacity were analysed. It was observed that when CuO nanoparticles were used as additives for the B20 blend, BTE increased significantly by about 1.18%-7.69% and BSEC decreased considerably by about 4.12% - 6.76%. In addition, when CuO nanoparticles were added, there were also substantial reductions in CO (2.21% - 8.86%). Furthermore, there was a noticeable increase in HC (0.3% - 9.78%), CO2 (2.38% - 5.97%), and NOx emission levels (1.75% - 5.27%) when compared to the B20 blend. However, in comparison to diesel fuel, all the emission levels were lower for all biodiesel blends except for NOx emissions. Overall, it was concluded that CuO nanoparticles could be considered as an appropriate petroleum additive for palm oil biodiesel blends.