what is octane number of petrol

The octane number of petrol is a measure of its ability to resist "knocking" or "pinging" during combustion, caused by the air/fuel mixture detonating prematurely in the engine. Octane ratings are measures of fuel stability and are based on the pressure at which a fuel will spontaneously combust (auto-ignite) in a testing engine. The octane number is actually the simple average of two different octane rating methods—motor octane rating (MOR) and research octane rating (RON)—that differ primarily in the specifics of the operating conditions. The higher the octane number, the more stable the fuel. Retail gasoline stations in the United States sell three main grades of gasoline based on the octane level: regular (the lowest octane fuel–generally 87), midgrade (the middle range octane fuel–generally 89–90), and premium (the highest octane fuel–generally 91–94) . Some companies have different names for these grades of gasoline, such as unleaded, super, or super premium, but they all refer to the octane rating.