What causes rich detonation?

[rolls]

I've read multiple times that you can get rich detonation. I however cannot find a technical explanation as to WHY this occurs.

I understand why lean mixtures detonate as they are typically hotter. Richer mixtures tend to cool the cylinder bore/piston top due to excess fuel transferring heat out of the cylinder, same concept as water/meth injection.

How does a richer mixture again cause detonation? I understand a rich misfire, but I do not understand rich detonation.

Does anyone have an explanation?

edit: My hypothesis is as follows.

Excess fuel (eg running 12:1) causes a drop in temperature allowing more timing to be run, eg it decreases detonation.

Absurd amounts of fuel (eg running 10:1) whilst it drops the cylinder temp, it increases exhaust backpressure and exhaust temp (due to it burning there) which overwhelms any cooling ability the extra fuel brought along.

Thoughts?

[murfie]

I think a rich mixture allows "clumping" of fuel in the chamber. This leads to a slow broken flame front. Tuners some times increase fuel a little to run more ignition advance. The increase in fuel slows the flame front, but go to far and you get poor distribution.

[rolls]

I think a rich mixture allows "clumping" of fuel in the chamber. This leads to a slow broken flame front. Tuners some times increase fuel a little to run more ignition advance. The increase in fuel slows the flame front, but go to far and you get poor distribution.

I can see how it would kill power though how does clumping cause detonation?

[murfie]

The cylinder pressure raising faster than the flame front can propagate through the cylinder. The "clumps" ignite from the increased pressure and explode instead of a nice smooth flame front causing a knock sound. Lean condition is the same but the flame front goes out from gaps in fuel.

[4wheelinls1]

The cylinder pressure would be higher with considerably more fuel jammed in.

[rolls]

The cylinder pressure would be higher with considerably more fuel jammed in.

Perhaps this is the cause as the example I was giving was a ~900 hp E85 engine that was having dramas with the mixture too rich. The volume of fuel would be immense.

[4wheelinls1]

Thats been my feeling. If a top fueler missfires it hydraulics.

[murfie]

Perhaps this is the cause as the example I was giving was a ~900 hp E85 engine that was having dramas with the mixture too rich. The volume of fuel would be immense.

How big of an engine and what CR?

[murfie]

I've heard they start dieseling half way down the track. Not a very reliable source and I have no direct experience with them.

[rolls]

How big of an engine and what CR?

Aussie XR6T so a 6 cyl 4L 8.7:1 compression