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<< Lancair Builders' Mail List >>
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George,
Thanks so much for humoring a novice :-). Hope you'll entertain one more
along the lines of why poor distribution + LOP = roughness.
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If you are rich of peak, variations in fuel flow from one cylinder to the
next, make no difference in horsepower from one cylinder to the next.
...
BUT... on the contrary, when LOP, if cylinder 1 has 3% more fuel than
cylinder 6, then cylinder 1 will make 3% more power than cylinder 6. (see 2,
above) And THAT is why engines run rough when lean of peak.
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I figured this, more or less, but by what mechanism does roughness come in?
Is it simply due to the imbalanced forces from the combustion events
generating less power? I wouldn't think this to be the case because each
individual combustion event's forces (equal and opposite and all that Newton
stuff) are mostly contained within the engine.
Or, does it have more to do with changing the timing of the combustion
pressure peaks such that the cylinders are now beating against one another
as timed on the crankshaft's rotation rather than being well timed and all
pulling together?
I was trying to envision a scenario where if all cyls were at LOP (but by
different amounts), whether they would still push on the crank at the
appropriate rotational timing, just some harder than others. I would guess
if the timings were still right this wouldn't be all that rough (though this
is just a guess from envisioning in my head which directions the forces go).
However if the pressure timing was different amongst the cyls, then they'd
be banging against one another. I would guess this would be quite rough (and
terrible for the engine). And, I do remember you (or John Deakin?) showing
that leaner mixtures retarded the combustion event, so it got me wondering
which mechanism was more responsible for the roughness - the simple
difference in force magnitude between cylinders, or a change in their
relative timing.
I'm mostly just curious, at this point.
Thanks again - this has been quite informative!
-Jon C.
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Please send your photos and drawings to marvkaye@olsusa.com.
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