oktan

Oktan, a term used in several languages such as Indonesian and Turkish, refers to the octane rating of gasoline. It is a measure of a fuel’s resistance to knocking (premature ignition) in spark-ignition engines. Higher oktan numbers indicate greater resistance to knocking, allowing higher compression ratios and potentially higher efficiency in engines designed for those fuels.

In practice, octane rating is determined by standardized tests that produce different values: the Research Octane Number (RON) and the Motor Octane Number (MON). The octane rating displayed at many pumps is an average of these, known as the Anti-Knock Index (AKI), typically calculated as (RON + MON) / 2. Market labeling varies, with common values such as 87, 89, 91, and 93 in the United States, and RON values like 95 or 98 in many European countries.

Chemically, octane relates to a family of eight-carbon hydrocarbons (C8H18). The reference high-octane component is iso-octane (2,2,4-trimethylpentane), assigned a rating of 100. Gasoline is a blend of numerous hydrocarbons, and octane is influenced by molecular structure as well as additives. Historically, additives such as tetraethyl lead were used to raise octane in some regions, but leaded gasoline has been phased out in most markets in favor of cleaner alternatives, including ethanol blends and other octane-boosting compounds.

Usage and implications: engines designed for higher-octane fuels can run with higher compression and more advanced timing without knocking, which can improve performance and efficiency. However, using a fuel with an octane rating below what an engine requires can reduce performance and increase wear over time.