Newsgroups: rec.aviation.student
From: trisoft@realtime.net (James M. Knox)
Subject: Re: Another silly question:  why do leaner engines run hotter?
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In article <19980924070234.27577.00000924@ng21.aol.com>, wendybg@aol.com (Wendy B G) wrote:

>By contrast, "leaner" engines run hotter because all the fuel is burning.
>However, if there is too much air, the ratio is too lean, and not enough fuel
>to keep the engine running. It will let you know instantly by complaining. You
>should develop a sensitivity to your engine that will tell you (in your gut and
>in the soles of your feet) if any cylinders are firing out of synch. Then
>immediately give a little more richness (push in the little red knob about
>1/4"). The roughness should go away.

Good explaination, Wendy.  But the GAMI folks would never let me live it down 
if I let that last part get by.  

The reason the normal GA opposed 4 or 6 cylinder engine tends to "complain" 
when you get "too lean" is not because there is too much air, but because the 
fuel-air mix from one side to the other is not even.  The cylinders aren't 
"out of synch" - they are "out of power balance."  Balance the left-right 
fuel/air mix and the engine will run smooth all the way from very rich through 
peak and on down to virtually idle cutoff.  [A nice side effect of this is 
that it lets you use AIR for cooling instead of FUEL.]

Now, for the interested student:  If the fuel/air mix is uneven at 100 LOP, 
then wouldn't it also be uneven at 100 ROP?  Yes, it would.  So why doesn't 
the engine run rough 100 ROP?  Answer - because although the fuel/air mix is 
different, the ROP *power* level is still similar;  the LOP *power* level has 
considerable difference with relatively small fuel/air differences.  [Poor way 
of saying that the power curve is steeper on the lean side of peak than it is 
on the rich side.]

                                                jmk
