The octane rating of petrol is a measure of its tendency to pre-ignite. Click here to find out more about octane ratings.
Controlling Octane Numbers
The octane rating of a fuel can be increased with relatively small quantities of additives. This is cheaper than refining the whole fuel. Additives in past/current use include:
In 1900 at the World Exhibition (Paris) Rudolph Diesel demonstrated an internal combustion engine that ran on peanut oil. His intention was to design an engine that would run on whatever fuel was locally available. When he died in 1913 his engine continued to be developed, but until recently "diesel" fuel has frequently been petrochemical in origin.
Diesel engines require no spark. The fuel is injected into the cylinder and it ignites when compressed. There is therefore no octane rating, but the ease with which the fuel ignites under compression can be measured, and this is called the cetane rating. A higher cetane number means the fuel ignites easier, and this is preferable.
Ethanol and E85