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

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

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Internal Combustion Engines
In a typical medium speed 4-stroke cycle diesel engine the inlet valve

Opens at 20° before top dead center and closes at 35° after the bottom dead center
May open or close anywhere
Opens at top dead center and closes at bottom dead center
Opens at 10° after top dead center and closes 20° before the bottom dead center

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