An experimental investigation was done on diesel engines run on a blend of Karanja biodiesel and diesel in the ratio of 40:60 (B40) with different additive percentages (1.5%, 3%, and 4.5%). In this work, Picric acid dissolved in n-butyl alcohol (nBAPA) is used as an additive. The performance and emission tests were carried for three inputs-Load, compression ratio (CR) and B40 with different percentage of nBAPA and six outputs- brake specific fuel consumption (BSFC), brake thermal efficiency (BTHE) and Hydrocarbons (HC), Carbon monoxide (CO), Nitrogen oxides (NOX) and Carbon dioxide (CO2). A set of experiments were conducted by using the central composite design of response surface methodology (RSM) through Design Expert-10. The predicted and experimental maximum BTHE of 23.52% and 23.44 % were obtained at load 9.36 kg, CR 15, B40 with a 3% additive. The predicted and experimental minimum BSFC of 0.38kg/kWh and 0.37 kg/kWh were obtained load 9.36 kg, CR 15, B40 with a 3% additive. The predicted and experimental minimum CO2 of 2.13% and 2.29% were obtained at load 4 kg, CR 16, B40 with 1.5% additive. The predicted and experimental minimum HC of 3.33ppm and 4ppm was obtained at load 2.63 kg, CR 15, B40 with a 3% additive. The predicted and experimental minimum CO of 0.055% and 0.056% were obtained at load 8 kg, CR 16, and B40 with 4.5% additive. The predicted and experimental minimum NOx of 113.71ppm and 120ppm were obtained at load 2.63 kg, CR 15, B40 with a 3% additive.