Experimental evaluation of alumina nanoparticle additives in sunflower oil methyl ester for enhanced CI engine performance and emission control

This study experimentally investigates the performance, combustion, and emission characteristics of a compression ignition (CI) engine fueled with sunflower oil methyl ester (SOME) biodiesel–diesel blends, with specific emphasis on alumina (Al₂O₃) nanoparticle enhancement. Biodiesel blends ranging from 20% to 100% SOME were initially evaluated, among which the 40% blend (SOMED40) exhibited the most balanced fuel properties and combustion behaviour. Consequently, SOMED40 was further modified with 50 ppm of Al₂O₃ nanoparticles and tested under identical operating conditions. Engine experiments were conducted at a constant speed of 1500 rpm over varying load conditions, with key performance and emission improvements primarily observed at full engine load. At full load, the Al₂O₃-enriched SOMED40 blend demonstrated a 5.35% increase in brake thermal efficiency (BTE) and a 1.55% reduction in brake-specific fuel consumption (BSFC) compared to neat SOMED40. Emission analysis revealed substantial reductions, with carbon monoxide (CO) decreasing by 23.5%, hydrocarbons (HC) by 14.8%, nitrogen oxides (NOx) by 13.33%, and smoke opacity by 15.79% relative to SOMED40. When compared with conventional diesel at full load, the nano-enhanced blend achieved 25% lower NOx emissions and a 27.27% reduction in smoke opacity. These improvements are attributed to the catalytic activity and high thermal conductivity of Al₂O₃ nanoparticles, which promote improved atomization, enhanced combustion efficiency, and more uniform heat release. The findings demonstrate that alumina nanoparticle addition effectively mitigates the performance and emission limitations of biodiesel fuels. The SOMED40/Al₂O₃ blend emerges as a viable, cleaner alternative to conventional diesel fuel for CI engines without requiring any engine modifications.