Hacker News

Favorites Setup
Comment by MarkusWandel | original | Internal Combustion Engine (2021)
[−]MarkusWandel · 2026-07-01 Wed 17:40 UTC · link
Wonderful but it irritates me that so many descriptions of internal combustion engines refer to "explosions" of the fuel. You don't want that. It causes knocking and pinging and engine damage. You want a controlled burn that generates heat smoothly.
[−]stouset · 2026-07-01 Wed 18:02 UTC · link
You don’t want detonation, but you do want deflagration.
[−]Toutouxc · 2026-07-01 Wed 18:07 UTC · link
Not exactly. You do want a deflagration and not a detonation, but "explosion" is more loosely defined and, depending on who you're talking to, a self-sustaining subsonic flame front and a sharp pressure spike are a perfectly valid explosion.
[−]raffael_de · 2026-07-01 Wed 19:20 UTC · link
explosion/detonation causes engine knocking or pre-ignition which is both very bad. a properly working combustion engine is driven by controlled burning.
[−]Toutouxc · 2026-07-01 Wed 19:56 UTC · link
You’re replying to a post that says that “explosion” doesn’t imply “detonation”.
[−]raffael_de · 2026-07-01 Wed 21:10 UTC · link
and that is not strictly correct. it's called combustion engine and not explosion engine for a reason.
[−]kube-system · 2026-07-02 Thu 05:42 UTC · link
But it is strictly correct. Deflagration is the definition of low (i.e. subsonic) explosive.

Combustion is a broader term — combustion just refers to burning. And the reason it is called an internal combustion engine is to contrast it from its predecessor combustion engine designs - the external combustion engine.

More precisely, the type of combustion happening in an ICE engine is (low) explosive.

https://en.wikipedia.org/wiki/Explosive#Low

[−]rootusrootus · 2026-07-01 Wed 21:32 UTC · link
Even more confusing to anyone who doesn't know the lingo, detonation in the context of an internal combustion engine means something specific. It is a synonym for pinging and knocking, and happens when unburnt fuel/air mixture explodes after the spark plug has already fired. It can damage the engine, but typically takes some time. Preignition is when the mixture ignites before the spark plug fires, and is typically much more damaging, often destroying the engine in just a few revolutions. It can pound through the boundary layer between the mixture and the face of the aluminum piston and melt it, or break something else in the engine like a rod.

It's been a minute, but at one point GM had some pretty interesting videos up on YT where they talked about preignition testing on Cadillac Northstar V8s and how quickly it would grenade the engine. Fascinating stuff.

[−]userbinator · 2026-07-02 Thu 00:31 UTC · link
There are videos on YouTube of what the combustion actually looks like in slow motion. It's fast, but far less violent than an "explosion".
[−]00N8 · 2026-07-02 Thu 02:46 UTC · link
I don't think it's any slower than the dust explosions that occasionally happen in factories or grain silos. Although those do appear more violent due to the scale & damage.