Internal Combustion Engines
The fuels in order of decreasing knock tendency for spark ignition engines are

Napthene, aromatics, paraffin
Napthene, paraffin, aromatic
Paraffin, aromatic, napthene
Paraffin, napthene, aromatic

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

May open and close anywhere
Opens at 15° before top dead center and closes at 20° after top dead center
Opens at top dead center and closes at bottom dead center
Opens at 15° after top dead center and closes at 20° before bottom dead center

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