Internal Combustion Engines
The two reference fuels used for cetane rating are

Cetane and alpha-methyl naphthalene
Cetane and iso-octane
Cetane and tetra ethyl lead
Cetane and normal heptane

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Internal Combustion Engines
The expansion of fuel in a four stroke cycle diesel engine

Starts at 15° after top dead center and ends at 30° before bottom dead center
May start and end anywhere
Starts at top dead center and ends at 30° after top dead center
Starts at 15° before top dead center and ends at 30° after top dead center

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