quote: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. Diesels alway run way on the lean side of stoic. They can't use the air as efficiently as gas engine which run great at stoic. That's why a naturally aspirated diesel is doing good to devlop 80% of the torque of a naturally aspirated gas engine of the same displacement.
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.
quote: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.
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)?
quote: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. If for what ever reason such as detonation and or not enough gasoline in the mixture this boundary layer gets blown away. Metal parts would be unguarded, thus exposed to the actual flame. Hence the hotter running.
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?
quote:Correct, this boundary layer is a dozen microns thick. This thin boundary layer keeps the 2000dF burn temperature from reaching the combustion chamber walls. When detonation occurs, the pressure rise is rapid enough to wipe this film away from the combustion chamber walls and allow the 2000dF+ gas temperatures to 'interact' with the aluminum and steel surrounding them. This leads to a lot of heat arriving in the cooling systems.
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.