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<< Lancair Builders' Mail List >>
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Jon,
Your question:
>>One thing that is not obvious to me is why LOP operation seems to be
predicated on having a very balanced fuel/air mixture to all the cylinders,
i.e. why are GAMIjectors necessary? Why can carburated or non-GAMI'd engines
run ROP (presumably also with poor mixture distribution) but not LOP? What
is it that causes them to run rougher LOP than ROP?<<
Excellent question.
1) When ROP, there is an excess of fuel. 3% more fuel will not make any
additional horsepower. Subtracting 3% from the fuel flow, if it remains
well rich of peak, will not hurt the horsepower. Why? Because all of the
available O2 is already burned up and there is no available O2 to burn the
extra fuel to make more heat.
2) By contrast, when LOP, there is a universal surplus of "AIR" (O2).
Thus, if you add 3% of fuel, you will get almost exactly a 3% increase in
horsepower. Subtract 3%, you drop 3% in horsepower.
NOW... assume you have an engine that has uniform air flow to each cylinder
(most IO-520/550 and TSIO520 engines do, with the exception of the so called
"tuned" induction engines which are less than perfect).
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. (see
1, above)
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. The cylinder to
cylinder variation in fuel flow causes a corresponding cylinder to cylinder
variation in baseline horsepower and that is perceived as roughness by the
pilot and his significant other!
Does that help?
Regards, George
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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