Question

What are the effects of knocking?

(a) increase in heat transfer

(b) decrease in power output and efficiency

(c) preignition

(d) all of the mentioned

The question was posed to me in examination.

This key question is from Knocking in S.I. Engine in chapter Combustion and Combustion Chambers of IC Engine

Answer 1

The correct answer is:

(d) all of the mentioned

Explanation: Knocking in a Spark Ignition (S.I.) engine can have several detrimental effects:

• Increase in heat transfer: Knocking causes irregular combustion, which leads to excessive pressure and temperature fluctuations in the combustion chamber. These fluctuations can cause an increase in heat transfer to engine components, leading to overheating and potential engine damage.

• Decrease in power output and efficiency: Knocking results in incomplete combustion, reducing the engine's overall power output and efficiency. The irregular combustion process doesn't extract energy as effectively as normal combustion.

• Preignition: Knocking can be associated with preignition, where parts of the air-fuel mixture ignite before the spark plug fires. This early ignition disrupts the normal combustion cycle, leading to a loss of power and potential damage.

All of these effects make knocking undesirable in S.I. engines, and controlling it is essential for optimal engine performance.