Octanagem

Octanagem, or octane rating, is a measure of a fuel’s resistance to knocking in spark-ignition engines. It indicates how well the fuel-air mixture resists premature detonation under compression, which can damage engines and reduce performance. Higher octane fuels resist knock better, allowing higher compression ratios and advanced ignition timing without pinging.

Two principal scales are used: Research Octane Number (RON) and Motor Octane Number (MON). In many markets, the posted fuel rating is the average of these numbers, known as the Anti-Knock Index (AKI) or (RON+MON)/2. Ratings are determined by standardized tests that simulate engine conditions using reference fuels and controlled compression.

Chemistry matters: fuels with higher octane typically contain more branched, cyclic, or aromatic hydrocarbons, which resist detonation. Straight-chain alkanes generally have lower octane. The octane rating measures anti-knock performance rather than energy content or emissions directly.

Practical use: engines with higher compression ratios, turbocharging, or advanced timing benefit from higher-octane fuel. Using a lower-octane fuel than required can cause knocking and reduced performance; using higher-octane fuel than needed usually yields no significant benefit under normal operation, though it may offer protection under heavy load.

Markets and labeling: gasoline is sold with octane ratings in most regions. Typical ranges include about 87 AKI in the United States and about 95–98 RON in many European markets, with premium grades sometimes exceeding 100 RON. Ethanol blends can influence the effective octane rating.

Standards and history: octane rating systems were developed in the early 20th century and are standardized by organizations such as ASTM and EN/ISO, with methods defining how RON, MON, and AKI are measured.