Detonation leads to which of the following?

Explanation:

Detonation:

• Detonation is due to the auto-ignition of the end portion of the unburned charge in the combustion chamber.
• As the normal flame proceeds across the chamber, the pressure, and temperature of the unburned charge increase due to compression by a burned portion of the charge.
• This unburned compressed charge may auto-ignite under certain temperature conditions and release energy at a very rapid rate compared to the normal combustion process in the cylinder.
• This rapid release of energy during auto-ignition causes a high-pressure differential in the combustion chamber and a high-pressure wave is released from auto ignition region.
• The motion of high-pressure compression waves inside the cylinder causes vibration of engine parts and pinging noise and it is known as knocking or detonation.
• Detonation leads to a knocking sound.

Cause of detonation:
Compression ratio:

• Increasing the compression ratio increases both the temperature and pressure.
• An increase in temperature reduces the delay period of the end charge. Hence tendency to knock increases.
• Therefore, in order to reduce the possibility of detonation, it is essential to keep the compression ratio as low as possible.

Lean fuel mixture:

• A lean mixture burns slower than a rich mixture.
• This longer burning time causes higher combustion chamber temperature, which promotes the tendency for unburned fuel in front of the spark ignition flame to detonate.

Engine Overheating:

• Even the excessive intake air temperature or overheating of the engines can cause pre-ignition because the mixture in the cylinder will be at a higher temperature and so closer to the ignition point.