Enhancing agricultural engine efficiency with Pongamia biodiesel: A case study in thermal performance and emissions

Non-edible biodiesel reduces petroleum diesel use in compression-ignition engines, yet efficiency and NOx emissions depend on the blend fraction and load. Validated response models that couple the Pongamia blend ratio and load for the joint control of brake thermal efficiency (BTE) and NOx remain limited. This study aimed to model and optimize the BTE and NOx emissions of Pongamia biodiesel–diesel blends. Pongamia methyl ester was produced by base-catalyzed transesterification and tested at 1500 rpm across 25–100% load using a 13-run central composite design and response surface methodology. At full load, BTE was 30.4% for diesel and 24.9% for B100, while NOx was 9.1–11.8 g/kWh, indicating an efficiency loss due to elevated thermal NOx formation at high substitution. The desirability optimum was 69% load, BTE was 26.6%, and NOx was 843 ppm with a desirability of 0.664, supporting dual-response condition selection. The results provide an operating solution for fuel and load selection for off-road engines. Future research should focus on calibration and EGR-assisted strategies that restrain NOx emissions at higher blend ratios.