Internal Combustion Engines
Detonation is harmful due to

High intensity of knock causes crankshaft vibration and the engine runs rough
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

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Internal Combustion Engines
The correct sequence of the decreasing order of brake thermal efficiency of the three given basic types of engines is

Two stroke S.I. engine, four stroke S.I. engine, four stroke C.I. engine
Four stroke C.I. engine, two stroke S.I. engine, four stroke S.I. engine
Four stroke S.I. engine, four stroke C.I. engine, two stroke S.I. engine
Four stroke C.I. engine, four stroke S.I. engine, two stroke S.I. engine

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