Oktanzahl

Oktanzahl, often abbreviated as ROZ (Research Octane Number) or MOZ (Motor Octane Number), is a measure of a fuel's resistance to knocking or pinging during combustion in an internal combustion engine. Knocking occurs when the fuel-air mixture in the cylinder ignites prematurely and uncontrollably, leading to a sharp metallic sound and potentially damaging the engine.

The octane rating is determined by comparing the fuel's performance against a mixture of two reference hydrocarbons: isooctane (2,2,4-trimethylpentane), which is assigned an octane number of 100, and n-heptane, which is assigned an octane number of 0. A fuel with an octane number of 95, for example, has the same anti-knock properties as a mixture of 95% isooctane and 5% n-heptane.

In Germany and many European countries, the displayed octane number on gasoline pumps is typically the Research Octane Number (ROZ). This is determined under milder laboratory conditions compared to the Motor Octane Number (MOZ), which simulates more severe engine operating conditions. The difference between ROZ and MOZ is known as the octane spread, and it can vary depending on the fuel's composition.

Higher octane fuels are generally required for engines with higher compression ratios, as these engines are more prone to knocking. Using a fuel with an octane number lower than recommended by the vehicle manufacturer can lead to engine damage and reduced performance. Modern engines often have knock sensors that can adjust ignition timing to prevent damage from lower-octane fuels, but optimal performance is achieved with the recommended fuel.