Techno-economic and environmental considerations of digestate oil enrichment via Aluminum oxide nanoparticles from beverage packaging waste

This study examines the performance of a diesel engine using digestate oil, Al2O3 nanoparticles, and biogas as additives. Higher digestate oil content reduced brake power and efficiency while increasing fuel consumption and exhaust temperature. Al2O3 nanoparticles slightly improved efficiency and fuel consumption while lowering exhaust temperature. Biogas further enhanced efficiency but raised exhaust temperature. NOx emissions increased with more oil, while CO and HC emissions decreased. Nanoparticle addition reduced NOx, CO, and HC emissions, whereas biogas increased NOx but further reduced CO and HC. In-cylinder pressure and heat release rate were decreased with increasing digestate oil content, with nanoparticles slightly increasing and biogas further decreasing both in-cylinder pressure and heat release rate. Molecular dynamics simulations reveal that Al2O3 promotes interactions between O2 and oil molecules, such as stearic and oleic acid, as well as soot precursors like coronene. Techno-economic analysis indicated a potential 20 % reduction in diesel use and up to 3 % CO2 emission reduction at farm scale. This catalytic effect facilitates soot oxidation and inhibits its formation, highlighting nano-Al2O3 as a promising combustion enhancer for reducing particulate emissions. These findings offer practical relevance for rural energy solutions by promoting circular economy practices through waste valorization.