Experimental investigation of ZnO nanoparticle–enhanced pongamia biodiesel for performance, combustion, emission, and sustainability assessment in a CI engine

The present work explores the combustion behavior, engine performance, and exhaust emissions of a compression ignition engine operating on blends of Pongamia pinnata methyl ester (PPOME) with diesel fuel, supplemented with zinc oxide (ZnO) nanoparticles, with a focus on sustainable energy utilization. Biodiesel mixtures containing 20-100% PPOME were tested, and the blend with 40% biodiesel content exhibited the most favourable compromise between engine efficiency and emission control. When 50 ppm ZnO nanoparticles were dispersed into this blend (PPOMED40/ZnO), a further improvement in engine performance was observed, where brake thermal efficiency increased from 24.11% to 25.4%, while brake-specific fuel consumption decreased by 1.55% relative to the base blend (PPOMED40) under identical operating conditions. At full engine load, emission measurements demonstrated considerable reductions in major pollutants relative to conventional diesel operation under identical conditions, including decreases of 15.3% in NOₓ, 31.6% in CO, 15% in HC, and 27.3% in smoke opacity. A comprehensive thermodynamic evaluation incorporating energy, exergy, and sustainability analyses showed that the PPOMED40/ZnO blend achieved an exergy efficiency of 35% and a sustainability index of 1.54, indicating lower thermodynamic losses and improved system effectiveness. The findings suggest that the catalytic influence of ZnO nanoparticles promotes more efficient combustion while simultaneously lowering harmful emissions without compromising fuel economy. Additionally, the utilization of non-edible Pongamia oil as a renewable feedstock contributes to resource sustainability and supports circular bioeconomy strategies, in line with the United Nations Sustainable Development Goals related to affordable clean energy, responsible consumption, and climate action. Consequently, the PPOMED40/ZnO blend can be considered a promising, environmentally responsible substitute for petroleum diesel in CI engine applications.