What does cetane mean?
Cetane is a colourless, waxy hydrocarbon — chemically known as hexadecane, C16H34 — that occurs naturally in petroleum and was first isolated from sperm whale oil, a fact reflected in its name, which derives from the Latin word for whale. Its chief importance lies not in the compound itself but in what it represents: because cetane ignites very readily under compression, it serves as the standard against which diesel fuels are graded. The resulting measure, the cetane number, expresses how quickly a diesel fuel ignites after being injected into an engine's cylinders; higher values mean smoother starting, quieter running, and less knocking, especially in cold weather. The term belongs chiefly to the vocabulary of chemistry, refining, and automotive engineering, appearing most often in the fixed phrases 'cetane number' and 'cetane rating'. For anyone comparing diesel fuels, understanding cetane is essential — it plays precisely the role that octane plays for petrol, only at the opposite end of the combustion process.
nounA colourless, waxy hydrocarbon (hexadecane, C16H34) found in petroleum and used as the standard reference in rating the ignition quality of diesel fuel; a high cetane number indicates fuel that ignites readily.
- The straight-chain alkane hexadecane (C16H34), a waxy component of petroleum originally identified in sperm whale oil.
- (In compounds such as 'cetane number' or 'cetane rating') A measure of the ignition quality of diesel fuel, expressed on a scale on which pure cetane scores 100.
"Diesel with a high cetane rating starts more smoothly in cold weather and produces less engine knock."
"Refiners blend additives into diesel to raise its cetane number before winter arrives."
"Pure cetane ignites almost immediately when injected into hot compressed air, which is why it serves as the top of the diesel rating scale."
As a mass noun referring to a chemical substance, 'cetane' is typically uncountable; a plural form exists only in rare technical contexts referring to distinct types or samples.
"The chromatograph separated several long-chain cetanes from the crude sample."
The name 'cetane' comes from the Latin for whale — it was first identified in sperm whale oil — yet today its name is stamped on every gallon of diesel sold worldwide.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cetane
Cetane was named in the nineteenth century by combining the Latin 'cetus' (whale), from Greek 'kētos', with the '-ane' suffix characteristic of saturated hydrocarbons, because the compound was first obtained from sperm whale oil. The same Latin root gives English 'cetacean' and related scientific terms such as 'cetology'. It thus shares its origin with words describing whales rather than with other alkane names like octane or propane, which derive from their chemical structures.
How cetane is actually used
Strictly a technical term used in chemistry, petrochemical engineering, and fuel specifications; rarely encountered outside these contexts except on pump labels and fuel datasheets. In everyday use it appears almost exclusively within the phrases 'cetane number', 'cetane rating', or 'cetane index'.
Easily confused with cetane
Octane is the hydrocarbon used to rate petrol's resistance to knocking (higher is better), whereas cetane rates how quickly diesel fuel ignites under compression.