© 2021 Elsevier LtdThis study was designed to analyses the performance and exhaust emissions of a direct-injection diesel engine fueled with multi-walled carbon nanotubes (MWCNTs) included in biodiesel-blended diesel fuel using response surface method (RSM). The influence of input parameters —engine load and MWCNTs concentration — on the response parameters (i.e., BSFC, BTE, CO, NOX, and UHC) were investigated and predicted. MWCNTs were added into B20 fuel (20% biodisesel+80% diesel) in various concentrations (25, 50, 75, and 100 ppm). The tests performed under varying engine load conditions (5, 10, 15, and 20 Nm) at a constant engine speed of 1800 rpm. Multi-regression models for BTE, BSFC, and CO, UHC, and NOX emissions were derived using RSM and were found to be statistically significant. Exhaust UHC and CO concentrations for the studied fuel blend decreases with the addition of MWCNTs into B20 fuel, while NOx emissions drastically increased. The optimal engine working conditions were found to be an engine load of 10 Nm and MWCNTs concentration of 98 ppm. Based on the optimized values, the most optimal results for BTE and BSFC along with CO, UHC, and NOX emissions were found to be 28.57 (%), 269.84 (g/kWh), 0.03 (%Vol.), 44.16 (ppm), and 458.81 (ppm).