41. A mixture of 45% cetane and 55% alpha-methyl-naphthalene is found to have the same ignition delay as a sample of diesel oil. The sample can be described as having a/an __________.

The cetane number of a diesel fuel is defined as the volume percentage of cetane in a reference blend that matches its ignition delay; therefore, a mixture containing 45% cetane has a cetane number of 45.