Cetane number

Cetane number measures how readily diesel fuel ignites after injection into hot, compressed air. Higher values generally indicate shorter ignition delay.

Ignition delay: The time between fuel injection and the start of combustion in an engine. Cetane number chiefly indicates how long this delay will be.
Diesel fuel: A liquid fuel used in compression-ignition engines, commonly produced from petroleum or renewable feedstocks. Cetane number characterizes the ignition behavior of this fuel class.
Cetane improver: A fuel additive that shortens diesel ignition delay and raises measured ignition quality. Additives such as 2-ethylhexyl nitrate can raise a fuel’s cetane rating.
Octane rating: A measure of gasoline’s resistance to premature autoignition in spark-ignition engines. It concerns resistance to ignition, nearly the opposite fuel behavior cetane measures.
Compression ignition: Combustion initiated by heat from compressing air rather than by a spark. Diesel fuel’s ignition quality matters because compression initiates combustion.
ASTM D613: A standard method that determines diesel fuel cetane number using a calibrated single-cylinder test engine. It defines the direct engine test behind conventional cetane-number measurements.
2-Ethylhexyl nitrate: An organic nitrate commonly added to diesel fuel to improve ignition quality. It is a widely used chemical means of increasing cetane number.
Research octane number: A standardized measure of gasoline knock resistance under specified engine test conditions. Its test and purpose differ from diesel ignition-quality measurement.
Cetane: A straight-chain hydrocarbon, hexadecane, used as the high-ignition-quality reference fuel. Its assigned value of 100 anchors the traditional cetane-number scale.
Ignition quality tester: An instrument that estimates fuel ignition quality by measuring combustion in a constant-volume chamber. It offers an alternative laboratory route to ignition-quality assessment.

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