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

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Internal Combustion Engines
Scavenging air in diesel engine means

Air used for combustion sent under pressure
Burnt air containing products of combustion
Air used for forcing burnt gases out of engine's cylinder during the exhaust period
Forced air for cooling cylinder

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