Diesel fuel is rated not by octane number but something called a cetane number. The cetane number gauges the ease with which the diesel fuel will autoignite when compressed. Higher cetane numbers indicate easier self-ignition and better engine operation, whereas a higher octane fuel would be more resistant to self-ignition under compression.
A numerical index designed to reflect the ignition quality of diesel fuels. The cetane number reflects the percentage of cetane in cetane/x-methyl naphthalene blend equal in ignition quality to a specific sample of tested diesel fuel.
Measurement of the ignition quality of diesel fuels. Higher cetane numbers provide a shorter ignition lag (better ignition quality). Cetane number is measured by a single cylinder engine in the laboratory.