Robert J. Donahue wrote:
> While on the topic of carbs, I always wondered why a lean mixture makes an
> engine run hot.
Ok, this is off the top of my head, no references, so I'm open to other
opinions.
When you run lean every gas molecule can easily and QUICKLY find a
oxygen atom to bond/burn with. This promotes a efficent and clean engine,
as all the gas will be burned. But the quicker it burns the hotter it
will be because it will reach peak combustion sooner, therefore peak
heat sooner, therefore the cylinder will be at peak heat soak for a
longer period.
When you run rich it takes longer for all the gas molecules to find the
oxygen atoms, so the combustion peak is later, therefor less time at
peak heat. Some gas molecules may never find a oxygen atom and just
be thrown out with the exhaust- bad as it's a waste of fuel and dirty
emissions too. This is what air pumps are for, to inject air into the
exhaust manifold to burn the left over gas molecules.
There is also the physical cooling process of the cooler gas molecules
cooling the cylinder, the more cool gas the more cool cylinder.
> A friend of mine says air cooled
> engines are run extra rich to help keep them cool, fact or fiction?
Fact. It's easier to burn a hole in a piston (or burn a valve) with a
too lean running air cooled engine. Many air cooled three or four
cylinder motorcycles will run the middle cylinders richer for the
better cooling.
-Aron Travis-
"always in a automotive frenzy"
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