Environmental valorization of agro‐waste into nano‐enhanced biodiesel: <scp>ZnO</scp> ‐assisted orange peel fuel for low‐emission diesel operation

Abstract This study examines the conversion of orange peel waste into low‐emission biodiesel enhanced with zinc oxide (ZnO) nanoparticles. Turning agricultural residues into sustainable fuels cuts environmental pollution and reduces reliance on fossil diesel. Orange peel oil was extracted by solvent‐assisted distillation and converted to biodiesel via transesterification. ZnO nanoparticles were added to the biodiesel at 25 and 50 ppm by ultrasonic dispersion. The blends were tested in a single‐cylinder diesel engine. Emissions of carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and smoke opacity were analyzed. Thermal efficiency was also measured to assess environmental impact and energy performance. The biodiesel with 50 ppm ZnO (B100 + ZnO 50 ppm) achieved a 6.06% higher brake thermal efficiency (BTE) than neat biodiesel. It also produced substantial emission reductions: CO decreased by 61.7%, HC by 38.1%, and smoke by 42.3% compared with diesel. However, NOx emissions increased moderately by 14.7%, likely due to enhanced combustion efficiency and higher peak oxidation temperatures from ZnO nanoparticles. This nano‐enhanced orange peel biodiesel shows strong environmental potential as a low‐emission, renewable diesel substitute. It supports waste valorization and pollution abatement. This approach promotes circular bioeconomy principles by transforming agro‐industrial residues into eco‐efficient energy carriers compatible with current diesel infrastructure.