TiO2 and CuO nanoparticles are investigated as potential additives to diesel fuel to reduce emissions and enhance engine performance. Various concentrations of nanofuels are examined under different loads to accurately determine their influence in combustion process. The measured emissions are CO, CO2, NO, O2, unburned HC meanwhile the mechanical parameters are BSFC, brake power, RPM, thermal efficiency and exhaust temperature. It is worth mentioning that the experimental work was conducted on two conditions; cold start and hot start.