In the 2t example, I've never been able to find actual AFRs for them. But yer, when they lean to destruction they are probably still way richer than stoich, so rich on a stoich scale and even richer than max power when they heat the piston enough to seize it.Erland Cox wrote: ↑Thu Feb 02, 2023 3:11 am Some engines like power adders or two strokes are partly fuel cooled.
They cannot take leaning out to best power AFR without overheating.
Maybe they could with less ignition lead?
21% of the air is oxygen and that burns with the fuel.
The nitrogen expands when heated together with the parts taking part in combustion.
Highest charge heat gives most expansion and most pressure.
So it is when going towards maximum pressure you can burn stuff, richer or leaner runs cooler.
There can be some surfaces like 2 stroke pistons that need the extra fuel cooling though.
Erland
Of course a 2t gets no rest, not only does it have to fire every time the pistons up top but the crankcase is a non intercooled blower so the piston is already hot from compressing the next charge.
Of course the other thing with taking fuel out of a 2t running on premix, you're taking lube out as well.