The purpose of this project was to do research on a single-cylinder, four-stroke diesel engine that ran on biodiesel mixtures with nano additives. The diesel–biodiesel mixes are treated with varying concentrations of nano copper oxide (CuO). The flash point, fire point, and calorific value are all properties of the material. This fuel was discovered to boost the performance and lower emissions of a single-cylinder, four-stroke diesel engine. In this work, copper oxide (CuO) is used as a nano additive in the form of copper oxide, with tomato seed oil as the base oil (biodiesel) (CuO). The copper oxide (CuO) nano additives with a diameter of 50 nm were manufactured using a variety of tomato seed oil methyl esters and then blended in varied amounts with pure diesel fuel. Throughout the study, a modified single-cylinder 4-stroke diesel engine was evaluated to determine whether it could lower its specific fuel consumption, brake thermal efficiency (BTE), air–fuel ratio (AFR), exhaust gas temperature (EGT), NOx emissions, and hydrocarbons (HC) emissions, carbon monoxide (CO). When compared to normal diesel fuel, researchers discovered lower fuel consumption, improved performance, and lower emissions of hydrocarbons (HC) and carbon monoxide (CO), but greater emissions of nitrogen oxides (NOx).