Cetane

Cetane may refer to two related concepts in hydrocarbon chemistry and fuel engineering. It is the common name for the saturated straight-chain hydrocarbon with 16 carbon atoms, also known as n-hexadecane (C16H34), and it is the basis for the cetane number, a standard measure of diesel fuel ignition quality.

n-Hexadecane is a colorless, high-boiling liquid at room temperature with a boiling point near 287°C and a melting point around 18°C. It is a linear alkane used as a reference substance in diesel fuel research and testing, and it serves as a component in various hydrocarbon blends.

The cetane number (CN) is a dimensionless index that indicates how readily a diesel fuel will ignite under compression in a diesel engine. It is defined by comparison to a reference fuel blend composed of cetane (n-hexadecane) and α-methylnaphthalene, such that the test fuel’s ignition delay matches that of the reference. Pure cetane has a CN of 100, while the reference fuel with only α-methylnaphthalene has a CN of 0. In practice, commercial diesel fuels typically have CN values in the range of about 40 to 60; higher CN values generally correspond to shorter ignition delays and easier cold starting. CN is influenced by fuel composition: linear alkanes tend to raise CN, whereas branched alkanes, aromatics, and certain oxygenates can lower it. The cetane number is one of several factors considered in fuel formulation and engine performance, alongside other properties such as sulfur content, viscosity, and volatility.