The Effect of Additive Polarity Levels on the Bond Stability and RON of Low-octane Hydrocarbons

Sweet orange peel has a strong potential to be used as a biofuel to substitute for conventional fuels. However, it contains polar and nonpolar compounds such as limonene and eugenol, which have different polarities, molecular structures, and physical characteristics. These differences affect fuel reactivity at low temperatures. Therefore, this study was conducted to understand the role of different polarities of additives in enhancing the research octane number (RON) and hydrocarbon stability of the fuel blends. The research was conducted using molecular modelling simulation software and experiments. The simulation was carried out using HyperChem software 8.0 to calculate the hydrocarbon stability of the fuel blend through the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap analysis and the orbital and binding energy analysis. Meanwhile, the experiments were carried out by varying the concentration of additives (1%–80% (v/v)) to measure the RON and the formation of new hydrocarbons through gas chromatography and mass spectrometry (GC-MS). HOMO LUMO analysis showed that new hydrocarbons in fuel blends added with limonene have a higher energy gap than fuel added with eugenol. Eugenol increased the RON of n-heptane from 0 to 92.7 and peaked in the formulation of 80%. Meanwhile, limonene increased the RON of n-heptane from 0 to 91.5 (exceeding the original RON of limonene), reaching the peak at 50% formulation addition. The increase was due to the different polarities of additives, which caused a change in the fuel blend's molecular structure and hydrocarbon stability.