Internal Combustion Engines
The knock in diesel engine occurs due to

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

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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
None of these
High intensity of knock causes crankshaft vibration and the engine runs rough
Excessive turbulence which removes most of the insulating gas boundary layer from the cylinder walls

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