cetane number | cetane rating | CN
DEFINITION grade of the combustion quality of diesel fuel during compression ignition, or more specifically, a measure of a fuel's ignition delay, i.e. the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel REFERENCE Wikipedia > Cetane number. http://en.wikipedia.org/wiki/Cetane_number [16.5.2013]
COMMENT 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.<BR>In short, the higher the cetane number the more easily the fuel will combust in a compression setting (such as a diesel engine). The characteristic diesel "knock" occurs when the first portion of fuel that has been injected into the cylinder suddenly ignites after an initial delay (once ignition occurs, all the remaining fuel burns smoothly as it leaves the injector nozzle). Minimizing this delay results in less unburned fuel in the cylinder at the beginning and less intense knock. Therefore higher-cetane fuel usually causes an engine to run more smoothly and quietly. This does not necessarily translate into greater efficiency, although it may in certain engines.