Test: Combustion & Combustion Chambers of IC Engine - 1 - Mechanical Engineering MCQ

The highest flame speed (minimum time for complete combustion) is obtained with richer mixture (Point A).

The time required for the flame to traverse the combustion space would be halved, if the engine speed is doubled. Double the engine speed and hence half the original time would give the same number of crank degrees for flame propagation.

Increased compression ratio reduces the clearance volume and therefore increases the density of the cylinder gases during burning. 
This increases the peak pressure and temperature and the total combustion duration is reduced. Thus engines having higher compression ratio have higher flame speed.

The delay period is very short, about 0.002 sec. In high speed engines, this period will lead to significant crank movement.

The rate of pressure rise is high per degree of crank rotation for knocking combustion and finally causes heavy vibrations in the engine due to pressure waves.

Apart from (a), (b) and (c):
• Confinement of thermal failures to cylinder head by keeping the hot exhaust valve in the head instead of the cylinder block.