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

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

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Internal Combustion Engines
In a four stroke cycle petrol engine, the expansion

Starts at 30° before top dead center and ends at 50° before bottom dead center
Starts at 30° after top dead center and ends at 50° after bottom dead center
Starts at top dead center and ends at bottom dead center
May start and end anywhere

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