What Is Cetane and Why Does It Matter? Ed Newman | Feb 24, 2016 1:18:21 PM Cetane is a colorless, liquid hydrocarbon of the alkane series, C 16 H 34 , used as a solvent and in cetane number determinations. In the same way that octane number ratings are applied to rate the ignition stability of gasoline, cetane values are assigned to diesel fuel to rate its combustion quality. Cetane numbers are used to indicate the combustion speed of diesel fuel. Diesel fuels with higher cetane ratings have shorter ignition delays, providing more complete combustion and allowing engines to operate more effectively. We asked mechanical engineer Mark Nyholm, AMSOIL Product Manager – Heavy Duty, to elaborate on the importance of understanding cetane and