Cetane Number

Cetane number rates the ignition quality of a diesel-type fuel, the readiness of the fuel to auto-ignite under compression, on a scale where higher means a shorter ignition delay. Distillate marine gas oils carry a measured cetane number; for residual fuels, too opaque to test directly, the calculated cetane index or the CCAI stands in. Low cetane causes hard starting, knock, and incomplete combustion, so engine makers specify a minimum for the distillates they approve.