Internal Combustion Engines
The knock in diesel engine occurs due to

Reduction of delay period
Delayed burning of the first part of the charge
Instantaneous auto ignition of last part of charge
Instantaneous and rapid burning of the first part of the charge

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

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
Starts at 30° before top dead center and ends at 50° before bottom dead center

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