I'm just curious as I've never been able to figure it out. Why does an engine run hotter when running lean?
Until you overfuel, then they run cooler. Same principle, use more fuel than you can burn and it cools things down. Diesels start cooling down at about 80% of stoic.quote:
Originally posted by tom slick:
only gas engines run hotter, it's because there is more oxygen to burn up. diesels and turbine engines are the opposite, they run hotter when you add fuel.
The way it was explained to me, there's an insulating/cooling layer of unburned fuel during the combustion cycle when you're at 'stoic balance (not ust at a fuel enriched condition) If you run leaner then that ..this cooling/insulating layer is spent.quote:
Originally posted by TallPaul:
How is it that running lean can burn a hole in a piston (at least I have heard that can happen)?
Its my understanding as far as gasoline engines. Under ideal conditions (not excessively lean) a boundary layer of gasoline/air mixture just above the metal surfaces keeps the flame front from actually touching the metal surfaces.quote:
Originally posted by Palut:
I'm just curious as I've never been able to figure it out. Why does an engine run hotter when running lean?
Correct, this boundary layer is a dozen microns thick. This thin boundary layer keeps the 2000dF burn temperature from reaching the combustion chamber walls.quote:
Under ideal conditions (not excessively lean) a boundary layer of gasoline/air mixture just above the metal surfaces keeps the flame front from actually touching the metal surfaces.