Abstract
<title>Abstract</title> <p> This study investigates the effect of various nanoparticles on the performance and emission characteristics of a diesel engine fueled with waste plastic oil (WPO) blends. Five fuel samples were prepared and tested: diesel, WPO20, WPO20 + 50 ppm MgO, WPO20 + 50 ppm RuO <sub>2</sub> , and WPO20 + 50 ppm La <sub>2</sub> O <sub>3</sub> . Experiments were conducted on a single-cylinder, four-stroke, water-cooled, direct-injection diesel engine coupled to an eddy-current dynamometer under controlled-load conditions. The nanoparticles were characterized using TEM analysis, confirming their morphology. At peak load, the WPO20 + 50 ppm MgO blend exhibited a 3.53% increase in BTE and a 15.5% reduction in BSFC compared to WPO20, indicating improved combustion efficiency. Emission results showed significant reductions of 20.97% in CO, 27.96% in HC, and 13.76% in smoke opacity, while NO <sub>X</sub> emissions increased slightly by 7.07% due to higher in-cylinder combustion temperatures and enhanced oxidation activity. Tribological performance was evaluated using a four-ball tribometer under a 40 kg load, 1200 rpm, and 75°C for 3600 s. The WPO20 + 50 ppm MgO blend showed a 12.1% reduction in COF and a 22.9% reduction in WSD, indicating improved lubricity and anti-wear performance. SEM analysis of worn surfaces revealed smoother tracks with fewer grooves and reduced surface deformation in nanoparticle-doped fuels, confirming the formation of a protective tribo-film. Overall, the results demonstrate that the addition of MgO nanoparticles significantly enhances engine performance, reduces emissions, and improves tribological behaviour, making WPO-based blends a promising sustainable fuel for diesel engines. </p>