What’s the difference between engine knocking and detonation?

Question

[Wikipedia](https://en.wikipedia.org/wiki/Engine_knocking) isn’t clear, seeming to say they’re synonymous, then later implying they’re not.

What’s the difference, if any, between the two?

In: 3

Answer 1

You seem to know a bit about gasoline engines, stop me if you need some further clarification.

You understand that the air/gasoline mixture in an engine needs to be compressed to generate power, but also that compressing the air/gasoline mixture creates heat. That heat might be enough to spontaneously ignite the mixture before the engine is ready for it.

The process of having a mistimed combustion of the air/gasoline mixture is called “detonation” it might have a few different causes or effects, but as a lump term, mistimed ignition is called “detonation”.

Regardless of whether you have detonation, or even in a properly timed spark-ignition of the cylinder, sometimes the air and the gasoline aren’t mixed evenly within the cylinder to begin with. This means pockets of the air/gasoline with ignite *before others*. Normally the entire cylinder burns at once, like a bomb, in the case I’m explaining now the burn is more like wave. It starts in one place and travels to another. This wave is sort of like an ocean wave crashing into a concrete wall, it hits with a powerful smack. That “smack” creates the noise we call “knocking”.

Short Version – A mistimed combustion is called “detonation”. An improper combustion, regardless of timing, can result result in the creation of pressure waves that smack the metal in the engine creating the noise we call “knocking”.