In recent years, biodiesel has gained popularity as an alternative fuel that can be used in place of conventional fuels. The main sources of biodiesel are tallow and oil. Dilution, pyrolysis, emulsification, and transesterification are some of the procedures used to create biodiesel. The main objectives of this work is to make biodiesel mixed together with the ratio of as a base fuel along with 20 PPM of copper oxide. The effect of mixed biodiesel with copper oxide is used to evaluate the engine characteristics. To measure the load on the engine, a water-cooled dynamometer is connected to it. Test results of B20C20 and B40C20 were compared with diesel. CO and UHC emissions increased as blend concentration increased, although brake thermal efficiency declined. The amount of nitrogen oxides (NOx) emitted was lowered by a small amount. © 2025 Elsevier B.V., All rights reserved.