Citing Valve Damage, UND Drops Unleaded Fuel And Returns To 100LL

chemgeek said:
Isn't the fuel:air ratio set by adjusting the mixture knob? What does it mean that the carb runs "leaner" if the operator can adjust the fuel-air mixture to the desired setting for best economy or power by ear (onset of lean misfire or to max rpm) or EGT?
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Not if the full rich setting isn't rich enough.

There are a lot of different carburetor part numbers with different calibrations for different applications. Some have a richer full rich calibration than others. A carburetor calibration on the lean side may be exacerbated with a change in fuel.
 
If this is too far off topic, moderators can delete. Thanks.

Im about as confused by all of this as possible. I have 0-320 D2A carb engine. I use the lean assist on my G3x mostly to try and keep the plugs clean with the bonus of saving a bit of fuel. I use 100ll all except one tank of I think it was Swift just to give it a try. I would like to go to 94UL to keep the engine clean and lower the lead fouling problems. If just changing fuels could cause valve problems am I screwing up the engine by leaning? I thought the goal was to run as lean as you can as long as you are below 70% power. I am less concerned with cost than a clean engine that lasts at least to TBO.
 
When running 100LL in an O-360 or O-320, you can and should lean it any time you are less than 70% power. That's actually good for the engine, keeps the plugs and valves clean. Just make sure you have sufficient airflow for cooling. But if you don't and the engine temps start to rise, usually it's when climbing. In that case lowering the nose to climb at a shallower angle and higher airspeed brings the temps down effectively.
 
MRC01 said:
When running 100LL in an O-360 or O-320, you can and should lean it any time you are less than 70% power. That's actually good for the engine, keeps the plugs and valves clean. Just make sure you have sufficient airflow for cooling. But if you don't and the engine temps start to rise, usually it's when climbing. In that case lowering the nose to climb at a shallower angle and higher airspeed brings the temps down effectively.
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Thank you. That makes me feel better. My trouble is getting my oil temp up high enough!
 
Carburetors typically do not distribute fuel evenly. While most cylinders will be running properly, one or two may be running excessively lean or rich.
 
True, and this is even more so for carburetors having a full throttle enrichment circuit (sometimes called the "economizer") which distorts the mixture distribution even more. Put differently, at WOT it enriches all cylinders, but some more than others.
 
Uuuuh, at take off power, unless at high altitude, you run full rich mixture.
 
chemgeek said:
The fundamental problem with the UND trial of 94UL is that they did not conduct a proper control (say, dedicating a significant portion of their fleet to 100 LL for comparative analysis). This will make it more difficult to evaluate the cause of what they seem to be observing.
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Exactly. Anecdotal information is not a 'study'. Running a twin with a different fuel on each engine and operating the engines identically, such as GAMI is doing, would provide a single better data point. Doing this on multiple identical aircraft provides the basis for a proper study and statistical analysis. UND's information cannot prove any cause/effect.
 
robin ardoin said:
Exactly. Anecdotal information is not a 'study'. Running a twin with a different fuel on each engine and operating the engines identically, such as GAMI is doing, would provide a single better data point. Doing this on multiple identical aircraft provides the basis for a proper study and statistical analysis. UND's information cannot prove any cause/effect.
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The ideal experiment is a random controlled trial over a large number of airplanes, better yet blind so the people fueling, flying, and measuring valve clearances don't even know which fuel was used.

The UND study got one part right: a large number of airplanes. But they didn't randomize or control it.
The GAMI study got one part right: a controlled study. But it's only a single airplane.

So neither can prove any cause/effect. But that doesn't mean they aren't useful.
 
mondtster said:
Not if the full rich setting isn't rich enough.

There are a lot of different carburetor part numbers with different calibrations for different applications. Some have a richer full rich calibration than others. A carburetor calibration on the lean side may be exacerbated with a change in fuel.
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If this is the case and there are carb models that are too lean even at a full rich setting, the observed valve recession should be correlated with those carb models that are supposedly too lean at takeoff power. One would think it would be relatively easy to sort this out, and if this is indeed causal, those carbs would be at risk for causing similar issues for those operating with auto fuel STCs, if not 100LL as well.
 
chemgeek said:
If this is the case and there are carb models that are too lean even at a full rich setting, the observed valve recession should be correlated with those carb models that are supposedly too lean at takeoff power. One would think it would be relatively easy to sort this out, and if this is indeed causal, those carbs would be at risk for causing similar issues for those operating with auto fuel STCs, if not 100LL as well.
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That works well in theory, but as you have seen from the UND case, people won’t study it right. I fully expect a transition to unleaded fuel to go similar to the 1970s switch to unleaded fuel in automobiles, or more recently, the widespread adoption of ethanol blended fuels. There has been lots of unfounded and unproven finger pointing surrounding both and the aircraft fuel case will likely follow.
 
MRC01 said:
The GAMI study got one part right: a controlled study. But it's only a single airplane.
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GAMI has flown more than one airplane. And had a test with a flight school. Plus LOTS of hours on engines in the test cell.
 
Pinecone said:
It is the same formula. Just without the lead.

Not change in the chemicals used to make the 100LL and no change in the quantities of them
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Dear Pinecone:

Each of the other components increase as a percentage when you take one of them out. I’m too tired from work to explain it, but happy to do so later.

Whether or not the changes make a significant difference to the valve issue, I do not know.

Best Regards,
455 Buick
 
From a scientific perspective they started doing these checks when they switched to UL94 so there is no comparative data for 100LL use. It would appear that they are jumping to conclusions based on a very small number of anomalies.
 
455 Bravo Uniform said:
Dear Pinecone:
Each of the other components increase as a percentage when you take one of them out. I’m too tired from work to explain it, but happy to do so later.
Whether or not the changes make a significant difference to the valve issue, I do not know.
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How much the ratios of remaining ingredients changes, depends on the volume of TEL that was removed. We can quantify this. The data sheet for 100LL says it has 0.53 mL / L of TEL. By my calculations that's 0.053%. If you remove it, the total volume drops by that fraction, to 99.947% of what it was before. Thus the proportions of other ingredients increase by corresponding ratios, which seem to be so small that the differences are immaterial.

Perhaps I read the data sheet incorrectly and the volume of TEL is actually higher than that?
 
The applicable parameter is the mass of TEL. Max TEL quantity in 100LL is 0.56 grams/Liter. That's 2 grams/gallon. A gallon of 100LL weighs 6.02 pounds = a mass of 2733 grams. Pull out the 2 grams of TEL and its mass is 2731 grams or 99.93% of 100LL. This reduces the mass to volume ratio accordingly. I would guess this minute change is well within the error bars for all the other ingredients. Basically, the change in mass/volume is insignificant.
 
455 Bravo Uniform said:
Dear Pinecone:

Each of the other components increase as a percentage when you take one of them out. I’m too tired from work to explain it, but happy to do so later.

Whether or not the changes make a significant difference to the valve issue, I do not know.

Best Regards,
455 Buick
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Do you understand how much TEL is added?

About 2 grams per gallon. That is 1.21 milliliters.

The additive is around 61% TEL. So that makes it 2.98 ml.

A gallon of fuel is 3785 ml. So, deleting the TEL changes the overall volume by less than 0.1%. Yeap, that is a massive change.
 
As my late father told me: When a butterfly lands on a bridge, the bridge bends. But not very much.
 
Pinecone said:
Do you understand how much TEL is added?

About 2 grams per gallon. That is 1.21 milliliters.

The additive is around 61% TEL. So that makes it 2.98 ml.

A gallon of fuel is 3785 ml. So, deleting the TEL changes the overall volume by less than 0.1%. Yeap, that is a massive change.
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I do understand. I still work for the entity that owned Octel before we sold it in 1997.

I said whether it makes a difference or not, I do not know. And neither do you.

It’s not a massive change volume or mass-wise, but it doesn’t have to be to make a big performance change. That’s just logical. If you put it in and it affects one thing, and if you take it out it doesn’t affect another? Linear think much? If you know better, that’s excellent.

I’m done with ya. POA ignore function on.
 
455 Bravo Uniform said:
... It’s not a massive change volume or mass-wise, but it doesn’t have to be to make a big performance change. That’s just logical. ...
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Indeed. If adding as little as 0.05% of TEL makes a significant difference in performance, then removing it obviously does too.

Yet the original question was whether removing it significantly changes the ratios of the remaining ingredients, specifically octane boosters like Xylene and Toluene. That answer seems to be "no". Their mix/blend proportions remain essentially the same. Yet even so, this doesn't necessarily imply that the impact on performance must be as proportionally small as their ratio changes. Maybe? That's a chemistry question beyond my ken.
 
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