Lean burn engines

[Seth]

There is petrol engine lean, and there is diesel engine lean. 

Gasoline engine lean is like 15-20:1 gravimetric AFR. And if you get
this lean, combustion temps are falling off in a big way. Lean and
burning things is more like just lean of stoich (~14.7) **and** full
throttle. I contend you can still burn things even rich of stoich until
you add enough fuel to create a more reducing atmosphere and the
combustion temps fall off. I *speculate* this has something to do with a
non-homogenous charge in the cylinder resulting in local packets that
are oxygen or fuel rich.

Diesel engine lean is more like greater than 100:1 gravimetric AFR. If
you have all air and almost no fuel burning, then you aren't going to
burn anything. (but a little fuel) Even at full power, many diesels
don't go fuel richer than 40:1 You probably won't find this to be the
case at the tractor pull, though.


-Seth

Stephen Webb wrote:
> 
> >
> > 60-80% of the heat absorbed into the engine from the reaction is thru the
> > exhaust valve, and it's guide.   Depending on the amount of heat generated
> > you can exceed the thermal limits of the metal, and then it just blows off,
> > similiar to the dome of a piston when detonation is present.   Also, when
> > running that lean you might be in trace detonation, and localized heating of
> > some components is even worse.
> 
> So is this to say "lean mixtures run hotter, locally, because of
> detonation"?
> 
> Why is this not a problem with diesel engines, as they run lean most of
> the time.
> 
> -Steve
> 
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