Originally Posted by The Evil Twin
I had the same thought until PS corrected me. I started thinking about it in the sense of thermodynamics. To put it simply, if the cylinder temperatures got hotter as the mixture was leaned out then the absence of any fuel would result in infinite heat
Now we know that won't work. Unfortunately.
Thinking of small aircraft, as you ascend you would lean the mixture to account for less dense air. As you do so the exhaust gas temp increases, yes. Not because lean= hotter, but because the excess fuel acts as a coolant. It absorbs the heat. As the mix is leaned out there is less "coolant" (vaporizing fuel) and the EGT goes up.
However, only so far. If the mix is leaned further then it starts dropping (less fuel, less work, less heat) until combustion can no longer be supported.
Two ways of stating same thing...lean mixture = less fuel = less "coolant"....therefore, lean mixture does result in increases of EGT or in my case the cylinder/engine temp on my boxer. More fuel in response to an ambient temp sensor that registers lower than actual ambient temps [hence air density is less than temp sensor would indicate] results in the fuel management putting more fuel [more coolant] into the cylinders resulting in a richer mixture. Sorry I know this not complicated, but I will be damned if I can see it...thanks for patience.
Kinda ...less fuel more temp [lean] : more fuel less temp [richer]
2007 R1200GS Adventure " ...to explore off-road, alone in my case, way out in the boonies...that feeds the soul!"