Enhanced performance and reduced emissions in compression-ignition engine fueled with biodiesel blends synthesized via CaO and MgO nano catalysts.

The rapid depletion of fossil fuel reserves has intensified the pursuit of sustainable alternatives for compression-ignition engines. Biodiesel, produced from renewable feedstocks such as waste cooking oil (WCO), offers an environmentally benign substitute that can be utilized either neat or in blends with conventional diesel. This study examines the comparative efficacy of nano-calcium oxide (CaO) and nano-magnesium oxide (MgO) catalysts in synthesizing biodiesel from WCO, emphasizing their physicochemical characteristics and subsequent effects on diesel engine performance and emissions. Distinct from prior investigations that focused on single catalysts or lacked engine-level validation, this work integrates detailed catalyst characterization (SEM, BET, XRD) with comprehensive combustion testing of various biodiesel blends. The synthesized biodiesel was blended with petroleum diesel at volumetric ratios of B10, B20, and B30 and evaluated in a single-cylinder diesel engine. Characterization results demonstrated superior catalytic activity of nano-CaO (average particle size: 67.1 nm; specific surface area: 80.7 m²/g) compared to nano-MgO (32.5 nm; 60.2 m²/g). Engine performance testing revealed that the NC(CaO)B10 blend reduced brake-specific fuel consumption by 8.3% and improved thermal efficiency at 75% engine load relative to baseline diesel. Furthermore, NC(MgO)B30 lowered CO₂ emissions by 4.2%, whereas NC(CaO)B30 achieved a 0.7% reduction in CO emissions and an approximate 3% increase in excess oxygen availability. These findings underscore the potential of CaO-based Nano catalysts, particularly at lower blend ratios, to enable cleaner and more efficient diesel engine operation. This work advances the case for nanotechnology-enhanced biodiesel as a viable component of sustainable fuel systems and highlights opportunities for optimization through higher blend ratios and synergistic catalyst combinations.