In SI engines, maximum flame speed is obtained when the equivalence ratio is between
The highest flame speed (minimum time for complete combustion) is obtained with richer mixture (Point A).
All of the following factors promote detonation in SI engines, except
With increase in speed, the crank angle required for flame propagation
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.
With increase in compression ratio, flame speed
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 in a petrol engine is of the order of
The delay period is very short, about 0.002 sec. In high speed engines, this period will lead to significant crank movement.
Detonation is said to take place in the engine when
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.
Which aspect does not help to reduce the detonating tendency in a spark ignition engine?
The commercially available petrol in India has an octane rating of
9 Which of the following combustion chamber has inlet and exhaust valve placed on the opposite side of the cylinder?
The overhead valve engine is superior to a side valve or an L-head engine at high compression ratios. Which of the following characteristics of this type of valve arrangement is not favourable?
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.