Combined effects of copper oxide nanoparticles and hydrogen enrichment on the performance and emissions of butanol enriched biodiesel in a diesel engine

• Butanol-enriched biodiesel with CuO nanoparticles enhances CI engine performance • RCCI with hydrogen enrichment achieves up to 36% brake thermal efficiency • Significant emission cuts: CO (−58%), NOx (−12%), smoke opacity (−55%) • Hydrogen + CuO synergy improves flame propagation and combustion stability • RCCI mode outperforms DI, offering a cleaner pathway for sustainable engines This study explores a multi-faceted approach to improving the combustion, performance, and emission characteristics of a single-cylinder, four-stroke, direct injection (DI) compression ignition engine through the combined effects of butanol enrichment, green-synthesized copper oxide (CuO) nanoparticles, and hydrogen supplementation. The baseline fuel was a B20 biodiesel blend, further enriched with 10% butanol to enhance oxygen availability and atomization. CuO nanoparticles were synthesized via an eco-friendly aloe vera extract-mediated method and dispersed into the fuel to promote oxidation kinetics and stabilize combustion. Experimental results revealed that the B20+But10%+CuO100 blend achieved the highest brake thermal efficiency (BTE) of 33.6% at full load, alongside notable reductions in carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and smoke opacity compared to neat B20. Reactivity controlled compression ignition (RCCI) trials further demonstrated that hydrogen enrichment at 5 LPM and 10 LPM improved flame propagation, Brake thermal efficiency (33.89% & 35.43%), and reduced brake-specific fuel consumption of nearly 10% (0.26 Kg/KWh) & 0.25 Kg/KWh). While excessive hydrogen supply (10 LPM) marginally increased HC emissions (110 PPM) at higher loads due to localized incomplete oxidation, overall results confirm significant emission mitigation. The findings highlight that the synergistic integration of butanol oxygenation, catalytically active CuO nanoparticles, and optimized hydrogen enrichment offers a viable pathway toward cleaner combustion, improved energy efficiency, and reduced pollutant emissions in biodiesel-fueled CI engines.