The performance and emission characteristics of a stationary four-cylinder, four-stroke, compression ignition (CI) diesel engine have been studied at 2000 rpm with pure diesel and watermelon seed oil methyl ester (WOME)-diesel (D80) blends with the additives acetoacetic ester, CuO and CuSO4 nanoparticles. A three-level factorial design was used to determine the quantity of WOME and the additives mixed with D80 in the experimental runs. The emission (H2S, NO2, CO and exhaust gas temperature (EGT)) and performance (fuel consumption (FC), brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE)) properties were very much improved above WOME20D80. The emission properties were also better than diesel, except NO2 that was higher by 6.3 %. The performance properties were much better than WOME20D80 but not as good as diesel. Compared with diesel FC was 11.4 % higher, BSFC 11.4% higher and BTE was 4.3 % lower. These emission and performance values are better than most of what had been reported in the literature; the acetoacetic ester provided additional oxygen to ease combustion. The experimental data have been fitted to a second-order polynomial equation and subjected to analysis of variance leading to some equations that may help predict the emission and performance properties of CI engines.