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.
 
From NASA Callback:

Increased frequency of maintenance [is] required on carburetors and fuel injector systems due to suspected cadmium particulate matter being found in float bowls, fuel injector nozzles, fuel screens, and fuel jets. This impacts fuel flow and metering, impacting engine performance due to restriction of fuel flow. This phenomenon was observed on aircraft during unscheduled maintenance due to complaints of loss of power and also during routine scheduled maintenance. Particulate accumulation [was] also found in check valves, auxiliary fuel pumps and mechanical engine pumps. Clumps and screen obstruction [were] observed. This has been observed over the past four months, since aircraft started using Unleaded 94 Octane (UL94). The exact source of the cadmium is not definitively determined at this time. We suspect the cadmium is held in suspension in the fuel, and in addition to accumulating and clogging the fuel system, some particles are entering the combustion chamber with unknown impacts on cylinders, valves, and exhaust systems. A simple experiment was conducted. Aviation cadmium bolts were placed in [100 Octane Low Lead] 100LL and UL94 for a few hours. The bolts in 100LL remained intact with no change. The bolts in UL94 showed flaking with particles suspended in the fuel, sparkling. Cleaning of all fuel parts in the fuel systems clears the problem, but it reappears. We are concerned since we have limited experience with UL94 and have not seen anything like this in our careers, which total over 50 years together as A&P and IA [Inspection Authority Mechanics]."

asrs.arc.nasa.gov

Everyday Heroes - NASA ASRS CALLBACK

This month, CALLBACK sends you Seasons Greetings as we present incidents that reveal some heroes who arguably deserve the spotlight.
asrs.arc.nasa.gov
 
I'be heard of paint stripper being used as fuel, but this is ridiculous.
How does a petroleum product remove a metal coating from a bolt?

Are we sure those were't fake bolts, hand-plated with the finest Chinesium?
 
An updated Callback went out, with a response from the UL94 manufacturer. They dispute the gas damaging hardware and explain a bit about the testing procedures.
 
AMENDED: The mission of ASRS is to de-identify and disseminate safety reports to the proper authorities who can investigate and determine if an action is warranted. In this case, after publication of the December 2024 CALLBACK, the fuel producer contacted us stating that they disagreed with the accuracy of the report and believed the fuel used by the reporter was not UL94. They stated that "UL94 has the same hydrocarbon chemistry as 100LL (absent tetraethyllead) and accordingly ASTM results show the fuel does not react to cadmium plated metals. ASTM requires every batch of UL94 to report a (more prone to react) copper strip corrosion test result - confirming there is no adverse reaction of UL94 to metals."
 
Sure, ASTM fuels might not react to cadmium plated metals. However, is there certainty that the fuel was unadulterated, either known or unknown by the school (alcohol?). Quality control, legit certificates of analysis?

There are studies that have shown cadmium coatings and fuels to react, so it's not implausible. Also, the fuel producer has a conflict in that their job is to protect the business; I would do the same as them, they are probably hurriedly trying to make sure they didn't mess up or find out someone outside the organization who did. It might be a weakness in the coatings too.

The Corrosion Behavior of Metals, Plated Metals, and Metal Coatings in Methanol/Gasoline Fuel Mixtures: "Government clean air regulations have prompted much interest in the automotive industry in alternative fuels for lower emission vehicles. Methanol fuels have become the primary focus of the auto companies in meeting these challenges. Even though the corrosiveness of methanol and commercial methanol fuel blends is well recognized, no systematic investigations on the relative corrosion behavior of metals and their coatings in these solutions are available. The purpose of the present study is to determine the relative corrosion rates for metals, plated metals, and otherwise coated metals that were exposed to ionic and water contaminated methanol/gasoline fuel mixtures. The results are described for samples that were immersed in M15 and M85 test fuels for between 2000 to 8000 hours under static laboratory conditions at 40°C. The primary measure of corrosion was mass loss, which was used to generate corrosion rates, where possible, for each of the specimens. The test results show that a high percentage of the materials tested display some measure of degradation in alcohol fuel blends. However, some metals and organics were shown to be viable barrier coatings for the protection of steel and aluminum in these fuels." (Ronald J. Lash; SAE Automotive Corrosion and Prevention Conference and Exposition, Technical Paper 932341, 1993).

Failure of Jet Engine Fuel Control Unit Originated by Corrosion of Cadmium Coating: "Since 2015 the barometric fuel units of the aircraft jet trainer fleet were featured by an anomalous increase in the rate of failures, all caused by the presence of debris in the jet fuel system. Cadmium and sulfur based composition of debris observed in the fuel control unit revealed that they were originated by a reaction of jet fuel’s sulfur compounds with cadmium protection coating of few components in the unit. Analysis carried out on jet fuel samples did not find any value out of the specification and therefore further investigations were conducted on the cadmium coating process. Two fuel pumps were examined: a degradation of cadmium coating was observed on every components of both pumps, proportionally to their flight hours.A brown-yellow gelatinous deposit was found into the pumps components, mainly composed by hydrocarbons, cadmium, sulfur and carboxylic salts. The investigation on the cadmium surface treatment process revealed the anomalous absence of the chromate conversion coatings: it was responsible of cadmium availability in the fuel flow, causing the cadmium plating detachment that finally resulted in the solid particles production." (Mirko Sgambetterra, Guido Zucca, Vincenzo di Francesco, Fabrizio De Paolis & Manuele Bernabei; Journal of Failure Analysis and Prevention, 11 September 2020, Volume 20, pages 1470–1478, (2020)).
 
455 Bravo Uniform said:
Sure, ASTM fuels might not react to cadmium plated metals. However, is there certainty that the fuel was unadulterated, either known or unknown by the school (alcohol?). Quality control, legit certificates of analysis?

There are studies that have shown cadmium coatings and fuels to react, so it's not implausible. Also, the fuel producer has a conflict in that their job is to protect the business; I would do the same as them, they are probably hurriedly trying to make sure they didn't mess up or find out someone outside the organization who did. It might be a weakness in the coatings too.

The Corrosion Behavior of Metals, Plated Metals, and Metal Coatings in Methanol/Gasoline Fuel Mixtures: "Government clean air regulations have prompted much interest in the automotive industry in alternative fuels for lower emission vehicles. Methanol fuels have become the primary focus of the auto companies in meeting these challenges. Even though the corrosiveness of methanol and commercial methanol fuel blends is well recognized, no systematic investigations on the relative corrosion behavior of metals and their coatings in these solutions are available. The purpose of the present study is to determine the relative corrosion rates for metals, plated metals, and otherwise coated metals that were exposed to ionic and water contaminated methanol/gasoline fuel mixtures. The results are described for samples that were immersed in M15 and M85 test fuels for between 2000 to 8000 hours under static laboratory conditions at 40°C. The primary measure of corrosion was mass loss, which was used to generate corrosion rates, where possible, for each of the specimens. The test results show that a high percentage of the materials tested display some measure of degradation in alcohol fuel blends. However, some metals and organics were shown to be viable barrier coatings for the protection of steel and aluminum in these fuels." (Ronald J. Lash; SAE Automotive Corrosion and Prevention Conference and Exposition, Technical Paper 932341, 1993).

Failure of Jet Engine Fuel Control Unit Originated by Corrosion of Cadmium Coating: "Since 2015 the barometric fuel units of the aircraft jet trainer fleet were featured by an anomalous increase in the rate of failures, all caused by the presence of debris in the jet fuel system. Cadmium and sulfur based composition of debris observed in the fuel control unit revealed that they were originated by a reaction of jet fuel’s sulfur compounds with cadmium protection coating of few components in the unit. Analysis carried out on jet fuel samples did not find any value out of the specification and therefore further investigations were conducted on the cadmium coating process. Two fuel pumps were examined: a degradation of cadmium coating was observed on every components of both pumps, proportionally to their flight hours.A brown-yellow gelatinous deposit was found into the pumps components, mainly composed by hydrocarbons, cadmium, sulfur and carboxylic salts. The investigation on the cadmium surface treatment process revealed the anomalous absence of the chromate conversion coatings: it was responsible of cadmium availability in the fuel flow, causing the cadmium plating detachment that finally resulted in the solid particles production." (Mirko Sgambetterra, Guido Zucca, Vincenzo di Francesco, Fabrizio De Paolis & Manuele Bernabei; Journal of Failure Analysis and Prevention, 11 September 2020, Volume 20, pages 1470–1478, (2020)).
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We have a strict rule of no yellow metals in the fuel systems in the test lab in which I work to avoid the potential for contamination. This includes any plated fittings.

IOW, everything that isn’t rubber or plastic is stainless.
 
I am reminded of a guy I used to work with - he was at war with the IT department but the IT department didn't know it. Harry was determined that the computer on his desk was going to be configured the way Harry wanted it, not how IT wanted it. Every once and a while, I would hear Harry grumbling - then it would build to cursing under his breath. His face would get red. Then the kicking of the file cabinet would commence. Finally, he couldn't stand it any more and would go storming out of the building. One day his boss walked into the area just in time to see Harry storming out waving his arms, cursing away. "What just happened? Where is Harry going?" "Oh nothing. He'll be back in a bit. He's just mad at his computer." She stands there looking at me like WTF? Finally, "Ummm.... OK, just tell him to come by my office when he gets back."

Be like Harry. Keep fighting for your leaded fuel.
 
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