What are the causes of knocking sounds in diesel engines?

1 Answers
HarleyLynn
07/30/25 9:03am
Diesel engine knocking sounds at medium speed can be attributed to the following reasons: 1. Premature fuel injection timing: When the diesel engine piston has not yet reached the specified injection position during its upward movement, the injector starts spraying fuel, causing premature combustion. The high-pressure gas in the cylinder impacts the piston, producing a rhythmic, crisp "click, click" knocking sound, which becomes more noticeable when the throttle is reduced. 2. Poor fuel combustion: Low injection pressure, injector dripping, poor fuel atomization, and delayed fuel injection timing can all lead to poor fuel combustion, resulting in knocking. 3. Worn fuel delivery valve: A worn fuel delivery valve increases the clearance between the decompression ring and the valve seat hole, reducing sealing performance and decompression effectiveness. Additionally, it causes excessively high residual pressure in the high-pressure fuel pipe, increasing fuel supply and leading to fuel detonation and knocking. The knocking sound is particularly noticeable when the throttle is reduced.
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