Oktaniluku

Oktaniluku is the Finnish term for the octane rating of gasoline, a standard measure of a fuel’s resistance to knocking in spark-ignition engines. Knocking is premature auto-ignition that can damage an engine, and a higher octane number indicates a greater resistance to such knocking.

Two main scales are used: the Research Octane Number (RON) and the Motor Octane Number (MON). The octane rating shown at pumps in many European countries is typically the RON value, while in the United States the rating is commonly given as the Anti-Knock Index (AKI), roughly the average of RON and MON. The scale is defined with iso-octane (100) as the high end and n-heptane (0) as the low end.

Higher octane fuels enable higher compression ratios and more advanced ignition timing without knocking, potentially improving engine power and efficiency under certain conditions. However, the octane number does not indicate energy content or fuel economy by itself, and it does not measure emissions directly.

Typical values vary by market. European fuels commonly range from about 95 to 98 RON, while the US uses AKI values from about 87 to 93, with premium grades achieving higher figures. Additives and fuel blends, including ethanol in many regions, influence octane performance.

Historically, tetraethyl lead was used to raise octane but has been phased out in most countries due to environmental and health concerns. Modern fuels rely on alternative additives and ethanol blends to achieve desired octane levels.