What is cetane and how does it impact combustion?

As the piston rises in a diesel engine, air is compressed to very high pressures, which also generates temperatures capable of igniting diesel fuel. Therefore, combustion timing is controlled by when the diesel fuel is injected into the combustion chamber. In reality, the combustion does not start instantaneously. There is a relatively short delay between the initial injection of fuel and the start of combustion. This time delay, or ignition delay, is essentially the effect of the cetane number of a diesel fuel.

Fuels with higher cetane numbers have a shorter ignition delay and combustion begins sooner, and as a general rule, offer better engine performance. This can lead to easier starting, less white smoke on start up, less noise, and lower emissions. All diesel fuels have a given cetane number from their basic formulation. But often, fuel marketers use cetane improving additives to increase the cetane number to further enhance the performance benefits of their higher quality diesel fuels.