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Class 4 (4th Engineer) MEKM 📅 Jun 2024

Exam Question

A very sudden rise in pressure during combustion accompanied by a metallic, hammer like sound is called knocking of the unit or detonation and usually occurs (16)

(a) Near the end of the pressure rise after ignition of fuel charge

(b) Just before the fuel charge is about to ignite

(c) Immediately after the unit reaches peak pressure and before ignition of fuel

(d) At any stage of the combustion process.

State the correct answer and explain why the other reasons given are not justified.

Reference Answer

The correct answer is **(a) Near the end of the pressure rise after ignition of fuel charge.**
### Detailed Explanation of Correct Answer (a)
Knocking, also known as detonation, in a Compression Ignition (CI) engine is an abnormal combustion phenomenon characterized by an extremely rapid rate of pressure rise, creating a shockwave that is heard as a distinct metallic, hammering sound. This occurs due to the uncontrolled and explosive combustion of a significant portion of the fuel that has accumulated in the combustion chamber during the ignition delay period.
The process can be broken down into key stages:

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