The Intermolecular Interaction's Effect of Limonene as a Fuel Additive on the Exhaust Emission

Renewable fuel additives were selected as a solution to address the depletion of petroleum fossil fuels and associated environmental issues. Sweet orange peel oil (SOP) has a strong potential to be used as a fuel additive due to its unique characteristics resembling fuel oil. SOP contains 92.06% of limonene which has octane hyper-boosting characteristics. Limonene can enhance the research octane number (RON) beyond the octane rating of the primary fuel. This study aimed to understand the reported octane hyper-boosting effect of limonene by measuring RON and exhaust emissions through SI engines. Limonene was added to n-heptane as a representative of a low octane hydrocarbon in eight distinct volumetric concentrations (1-80%). The engine was tested at three different engine speeds (2000, 2500, and 3000 rpm). The RON test showed that limonene increased the RON of n-heptane from 0 to 91.5 (exceeding the original RON of limonene). The presence of limonene increased the bond stability of the fuel blends, thus preventing detonation. Furthermore, the exhaust emission test confirmed that carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions decreased across all fuel formulations and engine speeds. Limonene has a high sensitivity that can inhibit the reaction of n-heptane and stimulate complete combustion. However, the rise in NOx is detected with an increase in the limonene concentration in the fuel blends, but the value is still below the minimum requirements. Overall, experimental investigation demonstrated that limonene is an effective alternative octane booster to reduce exhaust gas emissions.