Cetane number

Cetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. Thus, it is the approximate equivalent of octane rating for gasoline (petrol). The CN is an important factor in determining the quality of diesel fuel, but not the only one; other measurements of diesel's quality include (but are not limited to) density, lubricity, cold-flow properties and sulphur content.
Definition
Cetane number or CN is a measure of a fuel's ignition delay, the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. Cetane numbers are only used for the relatively light distillate diesel oils. For heavy (residual) fuel oil two other scales are used CCAI and CII.
In short, the higher the cetane number the more easily the fuel will combust in a compression...