Why do Diesel engines have that distinctive sound to them when compared to gasoline engines?

Question

Why do Diesel engines have that distinctive sound to them when compared to gasoline engines?

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Answer 1

Have you heard of ‘pinging’ and ‘knocking’ in petrol engines? It is called ‘pre-ignition’, where a hot engine has some contaminants in the cylinders that ignites the petrol before the spark does. If ignition happens a bit before the piston reaches the top, you have a pressure pulse. You also have shocks caused when the flame front from the spark meets the flame front from the secondary ignition.

With a diesel engine, with no spark plug, pinging and knocking is the normal running condition! So the engine always sounds like it is knocking.