system
Given the following post, respond as if you're commenting on Reddit:
human
what's all the extra noise in a diesel engine?

I've driven both kinds of cars. I understand that diesel fuel is made up of longer hydrocarbon molecules. I think. But is the engine shape really that different? What a racket? What is it exactly that's making such a louder noise than a petrol engine?
gpt
Higher compression and knock.

In diesel the combustion is closer to detonation. In otto cycle it's deflagration.

In the old days you could hear car engines knocking under high load/hot temperature/low octane fuel.