What do octane ratings in fuels measure?

Octane ratings in fuels measure the fuel's resistance to knocking, which is a type of abnormal combustion that can occur in engines when the air-fuel mixture detonates prematurely. A higher octane rating indicates that the fuel can withstand higher compression before igniting, which is important for high-performance engines that operate at higher pressures and temperatures.

This property is crucial for maintaining engine efficiency and preventing damage. When a fuel has a low octane rating and is subjected to high pressures, it may ignite too early, causing knocking which can lead to engine knock or pinging sounds and potential long-term damage. Therefore, fuels with higher octane ratings are preferred in many high-compression engines to ensure smoother operation and optimal performance.

Other options relate to different fuel characteristics that are important but do not specifically pertain to the measure of octane ratings. For example, viscosity refers to how easily a fluid flows, combustibility is about how easily a fuel can catch fire, and temperature stability relates to how a fuel performs under various temperature conditions. None of these directly correspond to the fundamental role that octane ratings play in the performance and safety of an engine.