Internal Combustion Engines
Compression ratio of I.C. Engines is

Volume displaced by piston per stroke and clearance volume in cylinder
Ratio of pressure after compression and before compression
The ratio of volumes of air in cylinder before compression stroke and after compression stroke
Swept volume/cylinder volume

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Internal Combustion Engines
In a four stroke cycle diesel engine, the inlet valve

Opens at 20° after top dead center and closes at 20° before bottom dead center
Opens at 20° before top dead center and closes at 40° after bottom dead center
May open and close anywhere
Opens at top dead center and closes at bottom dead center

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