The usage of petroleum fuels in IC engines is hazardous to humans, plants, and agriculture since they exhaust poisonous pollutants into the environment. Substantial research is now being conducted to identify an alternative to petroleum fuel and to enhance its quality. Nanoparticles are a relatively new technology that may be used to improve the properties of fuel. Engine tests were performed on conventional CI engines using a diesel and biodiesel blend under different running circumstances. The purpose of this study is to investigate the performance, emissions, and combustion characteristics of a pumpkin seed oil methyl ester diesel blend (PSOME20) in a diesel engine with the help of a copper oxide nanoparticle. CuO nanoparticles in varying concentrations (50 and 100 ppm) were dispersed in the PSOME20 fuel. The results showed that the BTE of the PSOME20CuO100 fuel is 2.3% higher than that of the PSOME20 fuel, but the reduction in BSFC is 6.4%. Engine HC, CO, and smoke emissions were being significantly minimized when CuO nanoparticles were mixed with PSOME20. The addition of CuO nanoparticles to PSOME20 enhanced combustion behaviors such as HRR and cylinder pressure. © 2022 Elsevier B.V., All rights reserved.