In this study, the effects of adding graphene nanoplatelets (GNPs) into jatropha methyl esterediesel blended fuel (20% by volume jatropha methyl ester þ 80% diesel; symbolized by JB20) on the performance, combustion, and emission characteristics of a diesel engine were experimentally investigated. The GNPs were added at different concentrations of 25, 50, 75, and 100 mg/L of JB20. These blends were investigated under various engine loads and speeds. The results showed that adding GNPs at 50e75 mg/L of JB20 achieved an increase of 25% in the thermal efficiency and a reduction of 20% in the brake specific fuel consumption compared to those of pure JB20. The peak cylinder pressure, highest rate of pressure rise, and maximum heat release rate were also increased by 6%, 5%, and 5%, respectively. Furthermore, the engine emissions of NOx, CO, and UHC were reduced by 40%, 60%, and 50%, respectively, at a GNP dosage of 25e50 mg/L. The results showed that the dose level of 50 mg/L had the optimum enhancement in the overall characteristics of engine performance and emissions.