Octane Rating of Gasoline and Octane Booster Additives

Gasoline is a petroleum-derived liquid that is used primarily as a fuel in internal combustion engines (ICE), particularly spark ignition Otto Engine. Gasoline is a blend of hydrocarbons with some contaminants, including sulfur, nitrogen, oxygen, and certain metals. The four major constituent groups of gasoline are olefins, aromatics, paraffins, and napthenes. Octane number (ON) is measure of the ignition quality or flammability of gasoline. The ONs are Research Octane Number (RON) and Motor Octane Number (MON). RON is measured relative to a mixture of isooctane and n-heptane. Antiknock Index (AKI) is a measure of a fuel's ability to resist engine knock or octane quality. The AKI is an arithmetic average of RON and MON. The ON decreases with an increase chain length in the hydrocarbon molecule. The ONs increase with carbon chain branching. Another way of increasing the ON is used gasoline octane boosters as additives, such as tetraethyl lead (TEL), methyl tertiary-butyl ether (MTBE), and ferrocene. Aromatic alcohols, ethanol, and methanol also increase the ON of gasoline. The advantage to adding oxygenates, such as MTBE, methanol, and ethanol, to gasoline is that they cause very little pollution when they burn and are cleaner fuels.