Sustainable biodiesel production from waste cooking oil using NiO nanocatalyst with enhanced engine performance and emission reduction through hydrogen and antioxidant additives

Nickel oxide (NiO) nanoparticles were synthesized via a solution growth method and evaluated as heterogeneous catalysts for biodiesel production from waste cooking oil. Characterization using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy confirmed the crystalline cubic phase, functional stability, and well-defined morphology of the NiO nanoparticles, making them suitable for catalytic applications. The produced biodiesel achieved a high yield of 96.7% and was blended with diesel to form DWB20 (20% biodiesel + 80% diesel), which was tested in a single-cylinder, 5.2 kW Kirloskar CI engine. Engine performance, combustion behavior, and emission parameters were systematically assessed. The DWB20 blend showed only a marginal 3.2% reduction in brake thermal efficiency compared to diesel. Hydrogen addition further enhanced combustion, increasing efficiency by 8.4% and reducing emissions, except for NO, which was effectively mitigated through the incorporation of the antioxidant A-tocopherol acetate. Overall, this study demonstrates that NiO nanocatalysts enable high-yield biodiesel production and that the combined use of hydrogen and antioxidants improves engine performance and emission characteristics, supporting the development of cleaner and more sustainable fuel systems.