Comparative performance and emission analysis of waste animal fat and palm oil biodiesel in direct injection diesel engines

This study investigates the feasibility of using waste-derived biodiesel as a substitute for conventional diesel in direct-injection (DI) internal combustion engines. Three biodiesel formulations were evaluated: waste animal fat biodiesel (WAFB), palm oil-derived biodiesel diluted with D-limonene (PODL20), and a mixture of palm oil, waste oil biodiesel, D-limonene, and ethanol (PWBDE). Experimental investigations of combustion, engine performance, and exhaust emission characteristics were conducted on a single-cylinder, air-cooled, four-stroke Lister Petter TS1 direct injection diesel engine at 1500 rpm under variable load conditions. Results indicate that brake-specific fuel consumption (BSFC) is strongly influenced by fuel composition, with WAFB exhibiting performance closest to neat diesel owing to its superior physicochemical properties. Brake thermal efficiency (BTE) was highest for WAFB among the tested biofuels, whereas PODL20 and PWBDE exhibited reduced efficiency due to higher viscosity and lower energy content. Exhaust gas temperature (EGT) trends reflected fuel oxygen content and combustion quality across load conditions. Biodiesel blends generally reduced total hydrocarbon (THC), nitrogen oxide (NOx), and carbon dioxide (CO₂) emissions. However, carbon monoxide (CO) emissions increased for certain blends, indicating incomplete combustion under partial-load conditions. The transesterification and dilution process significantly influenced the fuels' compatibility and combustion properties. Based on the results, biodiesel derived from waste, especially WAFB, has the potential to serve as a cleaner source compared to conventional diesel fuel.