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Old 11-22-2021, 06:36 AM   #22 (permalink)
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Originally Posted by Piotrsko View Post
What about lean mixtures running hotter? Ever fry a piston top in a VW bug? In the diesel F250, you watch EGT on hard pulls because the aluminium stuff tends to melt.
Nope, the AFR gets so lean that there is not enough fuel to get it very hot in a diesel at it's most lean AFR, wich is usualy idle.
The more fuel you inject, the hotter it gets untill you reach the stochiometric AFR.
If you run it richer than that, you just produce lots of smoke.
So you'll get the highest EGTs under high load when the engine injects a lot of fuel.

On a sidenote:
The higher the combustion temperature, the more power you make.
But your engine doesn't like it when it gets too hot, it starts melting if your combustion temperatures get too high, and gasoiline engines start to knock/detonate when you push it too far.

The higher the difference between combustion and exaust temperature determines how efficient the engine is, higher expansion ratios can increase that.
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