<![CDATA[The development of environmentally friendly bioadditives has attracted growing attention for improving diesel fuel quality. This study comparatively investigated the role of oxygenated compounds in essential oils from Cymbopogon nardus and Cymbopogon citratus as natural bioadditives. The essential oils were obtained by hydrodistillation and characterized for yield, moisture content, density, kinematic viscosity, and volatile compound composition using gas chromatography–mass spectrometry. The essential oils were then blended with diesel fuel at five additive concentrations (0.2, 0.4, 0.6, 0.8, and 1.0% (v/v)), with neat diesel (0% (v/v)) serving as the control. The resulting blends were evaluated for density, kinematic viscosity, distillation characteristics, and ignition quality, as indicated by the Calculated Cetane Index (CCI). The results revealed that C. citratus essential oil contained a higher proportion of oxygenated compounds than C. nardus. The optimal bioadditive concentration was determined to be 0.8% (v/v) for C. nardus and 0.6% (v/v) for C. citratus, based on a balance between statistically significant CCI improvement and maintaining density and kinematic viscosity within diesel fuel specifications. At these optimal concentrations, the CCI increased from 45.5 for neat diesel to 46.3 for C. nardus and to 46.9 for C. citratus, respectively, while density and kinematic viscosity remained within diesel fuel specifications. These findings suggest that variations in essential oil composition may contribute to the observed differences in fuel properties and support the potential use of essential oils rich in oxygenated compounds as sustainable bioadditives for diesel fuel applications.]]>
