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  #31  
Old 01-12-2014, 09:47 AM
Mike S's Avatar
Mike S Mike S is offline
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Originally Posted by N395V View Post


Now if I can just keep low sulfur diesel from destroying my Superduty Powerstroke by adding ATF to every tank of fuel. Several mechanics have told me this is the problem and the cure.
10% bio fuel.
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Rv-10, N210LM.

Flying as of 12/4/2010

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  #32  
Old 01-12-2014, 10:31 AM
BillL BillL is offline
 
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Originally Posted by Toobuilder View Post
If Lycoming endorses running at peak EGT (factory endorsed = "good"), then how can running cooler (LOP) be "bad"?
Not saying there is a problem, but . . .

There is more to the discussion that just temperatures. Oxygen content of the exhaust goes up with leaning. Cars are limited to 3% due to keep the catalytic converters functioning properly. We can run higher (oxygen and much cooler) if the lean combustion stability remains good. IF and IF there were an exhaust valve material that was sensitive to oxidation at those temps then it could be worse.

I don't know what exhaust head materials are being used, but Continental always recommended the leaner the better, as long as the engine remained running smooth.

Large natural gas engines greatly extended their life by going very lean and getting near diesel exhaust temps. Valve materials last much much longer with cooler operation.

Just for the record. I plan on running LOP, as much as I can get it.
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RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
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  #33  
Old 01-12-2014, 10:38 AM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by rocketbob View Post
No because the exhaust valve has a stellite-coated rotator cap.

Hence the name!
Bob... the rotator cap rotates though... correct?
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  #34  
Old 01-12-2014, 10:45 AM
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Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.

Of course with no cats on aircraft, I'd like to hear if there is any composition of the exhaust gasses that is harmful to exhaust valves. If it is something other than simply a matter of temperature and contaminants, I'd like to know. Both of which are lower at LOP than the peak setting endorsed by Lycoming.
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  #35  
Old 01-12-2014, 11:07 AM
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My pea brain has accumulated some facts over the years and here's what I believe to be true concerning LOP:

1) Lycoming does not list an upper limit for EGT on non-turbo engines (turbo is 1600, but that is limited to keep the turbo alive)

2) Lycoming allows running continuously (in cruise) at "peak" EGT (in other words, as hot as your engine will make the EGT go)

3) lead, carbon, trash in the fuel and poor machining will prevent the exhaust valve from seating fully and limit the transfer of thermal load to the head, causing local overheating of the valve and failure.

4) LOP EGT is by definition cooler than allowed by the factory, results in less fuel (and by default, less lead, carbon and trash in the exhaust), and because of the lower energy of combustion, lower CHT.

If the above 4 factors are true, what additional factors make LOP ops "bad" or "damaging"? I'm not talking about poor engine management skills, I'm talking specifically "LOP causes damage because of..."
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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1984 L39C
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  #36  
Old 01-12-2014, 11:24 AM
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Quote:
Originally Posted by Toobuilder View Post
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.
Probably more so to keep the pistons alive. Usually over rich mixtures cause higher Cat temps as the fuel lights off inside. There is a tricky balancing act between piston and Cat life with regards to WOT AFRs.
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  #37  
Old 01-12-2014, 12:43 PM
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What else has changed?

My sincerest apologies to Mr. Freitag. While trying to post a reply, watch NFL TV and type on an iPad, I somehow deleted most of his post. Would Mr. Freitag please re-post as best as he can remember? Again, my apologies to Mr. Freitag, Sincerely and feeling like a dunce, Don Hull
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it is a change that goes on, deep and permanent, in the ideas of living." Miriam Beard
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  #38  
Old 01-12-2014, 01:00 PM
BillL BillL is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.

Of course with no cats on aircraft, I'd like to hear if there is any composition of the exhaust gasses that is harmful to exhaust valves. If it is something other than simply a matter of temperature and contaminants, I'd like to know. Both of which are lower at LOP than the peak setting endorsed by Lycoming.
Sorry not to be crystal clear - it is OXYGEN OXYGEN OXYGEN is the difference as the hot mixture goes LOP. The fuel burn goes from a carburizing flame to oxidizing flame.

Full load enrichment on the Vett is for power. More fuel across the catalyst will not BURN because there is NO OXYGEN. Many cars have this. It is not to "protect" the catalyst. Lets not get off track.
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Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”

Last edited by BillL : 01-12-2014 at 03:17 PM.
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  #39  
Old 01-12-2014, 02:04 PM
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Toobuilder Toobuilder is offline
 
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So, does the gaseous makeup of the exhaust contribute to valve distress, or is it simply temperature (and/or the impurities which prevent the physically prevent the valve from transferring its heat load to the head/fins/air)?
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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1940 Taylorcraft BL-65
1984 L39C
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  #40  
Old 01-12-2014, 02:50 PM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by az_gila View Post
Bob... the rotator cap rotates though... correct?
Yes it does, and so does the spring, seat, keepers, etc.
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