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

Opens at top dead center and closes at bottom dead center
May open and close anywhere
Opens at 15° after top dead center and closes at 20° before bottom dead center
Opens at 15° before top dead center and closes at 20° after top dead center

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Internal Combustion Engines
Detonation is harmful due to

Increase in the rate of heat transfer, there is a reduction in the power output and efficiency of the engine
Excessive turbulence which removes most of the insulating gas boundary layer from the cylinder walls
None of these
High intensity of knock causes crankshaft vibration and the engine runs rough

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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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