Tribological and Environmental Performance of Diesel Engines Using Hybrid Metal Oxide Nanoparticles in Algae Biofuels

Abstract This study evaluates the performance, combustion, and emissions characteristics of a diesel engine fueled with spirulina microalgae methyl ester (SMAME), enhanced with magnesium oxide (MgO) and ruthenium oxide (RuO2) nanoparticles. Nanoparticles were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Experiments were conducted on a single-cylinder, four-stroke CI engine at a constant speed of 1500 rpm under varying loads, using SMAME20, SMAME20 + 50 ppm MgO, SMAME20 + 50 ppm RuO2, and SMAME20 + 50 ppm (MgO + RuO2) blends. The SMAME20 + 50 ppm (MgO + RuO2) blend achieved the highest in-cylinder pressure (71.35 bar) and peak heat release rate (39.93 J/°CA). It also showed a 10.16% increase in brake thermal efficiency and a 5.3% reduction in brake-specific fuel consumption compared to SMAME20. Emission analysis revealed reductions in carbon monoxide (CO), hydrocarbon (HC), and smoke opacity by 12.8%, 10%, and 11.22%, respectively. Furthermore, tribological behavior was assessed using a four-ball tribometer, following ASTM-D4172 standards, at a 40 kg load, 1200 rpm, and 75 °C. The SMAME20 + 50 ppm (MgO + RuO2) blend showed improved wear resistance, with a 13.61% reduction in wear scar diameter and a 39.2% decrease in the coefficient of friction. SEM analysis confirmed reduced wear and smoother surface morphology in nanoparticle-enhanced biodiesel blends.