Internal Combustion Engines
Detonation is harmful due to

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

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

Starts at 40° before bottom dead centre and ends at 30° after bottom dead centre
Starts at bottom dead centre and ends at top dead centre
May start and end anywhere
Starts at 40° after bottom dead centre and ends at 30° before top dead centre

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