The role of nanoparticles in combustion improvement: Performance and emission analysis of a DI diesel engine fuelled with water-in-biodiesel emulsions enhanced by mono and hybrid nanoparticles

The growing demand for cleaner and more efficient diesel engine operation has driven interest in alternative fuels and advanced additives. This study investigates the effects of incorporating mono and hybrid metal oxide nanoparticles aluminium oxide (Al₂O₃) and manganese oxide (Mn₂O₃) into a biodiesel blend (B10) and its water-emulsified form (B10W5) to enhance combustion performance, thermal efficiency, and emissions in a single-cylinder direct injection (DI) diesel engine under full-load conditions. Nanoparticles were dispersed into the fuel blends via ultrasonication, and their impacts on key engine parameters were experimentally evaluated. Al₂O₃ significantly increased the peak heat release rate (HRR) by 145 %, while Mn₂O₃ delayed ignition but enhanced post-ignition energy release. The hybrid Al₂O₃-Mn₂O₃ combination advanced ignition timing and increased peak in-cylinder pressure by 2.6–3 % compared to B10. The B10Al₂O₃-Mn₂O₃ blend with water achieved the highest indicated mean effective pressure (IMEP) of 12.2 bar, along with a 34.4 % increase in HRR, a 54.5 % rise in cumulative heat release, and 27.8 % faster combustion. It also recorded the highest indicated thermal efficiency (ITE) of 48.4 %, significantly outperforming B10. Both Al₂O₃ and Mn₂O₃ effectively reduced hydrocarbon (HC) and carbon monoxide (CO) emissions, though they slightly increased nitrogen oxides (NO_x) and carbon dioxide (CO₂) levels. B10Al₂O₃ increased NO_x emissions by 6.25 %, while B10Mn₂O₃, B10Al₂O₃-Mn₂O₃/B10W5, and B10W5Al₂O₃-Mn₂O₃ reduced NO_x by 7.21 %, 15.87 %, and 27.88 %, respectively. Overall, the findings demonstrate that integrating nanoparticles and water emulsification in biodiesel blends offers a promising strategy to enhance engine performance, boost thermal efficiency, and reduce emissions in diesel engines.