The increasing prices and depletion of fossil fuels underscore the urgency of finding alternative fuels derived from renewable natural resources, such as biodiesel. This study examines the performance and emission characteristics of a single-cylinder diesel engine using a combination of diesel and biodiesel made from cardanol oil (B20M10), enhanced with oxygen enrichment and CuO nanoparticles (600 PPM). Initial tests on a compression ignition (CI) engine operating at constant parameters—1500 rpm, 200 bar injection pressure, and a compression ratio of 17.5—focused on performance metrics like efficiency, brake specific energy consumption and emissions including oxides of nitrogen (NOx), unburnt hydrocarbon (HC), and carbon monoxide (CO), all varying with brake power. In the experiment the effects of oxygen enrichment at different percentages (0%, 2%, 4%, and 6%) on engine efficiency and emission parameters were examined. This comprehensive experimental design aims to compare results with neat diesel, optimize oxygen flowrate in CI engine for B20M10 biodiesel blends, and investigate performance and emission characteristics under various load conditions. Results revealed that B20M10 fuel blend with 600PPM CuO nano particle with 4% of oxygen addition is optimized on the basis of emission and performance characteristics of the engine.