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

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

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

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

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