Cetane from :
http://en.wikipedia.org/wiki/Cetane_number
Quoted from one of the paragraphs: "Cetane number is actually a measure of a fuel's ignition delay; the time period between the start of injection and start of combustion (ignition) 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."
A quote from anothe paragraph with me doing the Bolding:"Generally, diesel engines run well with a CN from 40 to 55. Fuels with
higher cetane number which have
shorter ignition delays provide more time for the fuel combustion process to be completed. Hence, higher speed diesels operate more effectively with higher cetane number fuels."
Cetane is a
measure of the ignition delay; but higher cetane fuels have a shorter ignition delay.
I interpret this to mean shorter the ignition delay the less likely it will knock.
I interpert the sentance; "Fuels with higher cetane number which have shorter ignition delays
provide more time for the fuel combustion process to be completed." to mean ignition has more total time to burn due to ignition starting sooner than with lower Cetane fuel.