Energy efficiency and renewable energy solutions: Nano-additized algal biodiesel for cleaner marine engine applications

Marine compression-ignition engines are being pushed toward lower particulate emissions and higher fuel sustainability. Algal biodiesel offers a renewable, low-sulfur option, and catalytic nano-additives have been investigated to enhance combustion. An experimentally validated dose–load optimization for AgNP-dosed algal biodiesel remains unavailable. This study evaluates the addition of AgNPs to algal biodiesel and optimizes performance–emissions responses using response surface methodology. Silver nanoparticles were synthesized using Murraya koenigii leaf extract, blended into algal biodiesel at 50 and 100 ppm by weight, and tested in a direct-injection engine at 1500 rpm and 200 bar across 25–100% load. Brake thermal efficiency (BTE) increases and brake specific fuel consumption (BSFC) decreases; BTE rose by 8.5%, and BSFC fell by 9.0% at full load, indicating improved energy conversion. An optimal desirability is obtained; the optimum was identified at 53.78 ppm and 64% load, and this condition defines a practical dosing window. CO, HC, and smoke opacity decrease, while NOx increases at higher load, indicating that oxidation benefits are achieved and NOx control is required. The findings support the use of AgNP-dosed algal biodiesel for marine-relevant CI operations. Future research targets endurance durability, energy efficiency, Ag partitioning along exhaust and deposit pathways, and NOx mitigation maps under EGR and injection-timing variation.