Fuel

[Ken]

HI Folks:

Just wondering what folks are doing with the ever increasing cost of fuel. I have three choices as we most do. 100 LL , non ethanol 91+ octane ( I only have 93 available) and ethanol unleaded. In my area 100LL and 93 non ethanol are getting close to the same price. 

I hate ethanol blends but at some point maybe that will be what I start using as it is much less expensive.

I would like any feedback from pilots that use an ethanol added fuel on what your experience has been. Any increased maintenance costs? If so, what areas of increased maintenance  should I keep a look out for?

 

Thanks   

 

[FlyingMonkey]

CTs run great with ethanol, literally no difference in running with 100LL.  Just run 93 octane pump gas with ethanol and save some money.

[Anticept]

They're designed to work with ethanol and non-ethanol fuels.

The catch to ethanol fuels is this: if you fly frequently, you'll never have water problems because any water will get burned in the engine. If it sits though, the fuel will be ruined. Ethanol is hygroscopic and will pull moisture right out of the air through the vents.

[FlyingMonkey]

16 minutes ago, Anticept said:

They're designed to work with ethanol and non-ethanol fuels.

The catch to ethanol fuels is this: if you fly frequently, you'll never have water problems because any water will get burned in the engine. If it sits though, the fuel will be ruined. Ethanol is hygroscopic and will pull moisture right out of the air through the vents.

I have heard that, but I have used 10% ethanol gasoline in my CT that sat for 6-8 weeks.  No water in the fuel, and it ran just fine.  I live in Georgia, so there is no lack of humidity.  I think you need to sump your fuel (you should every time anyway) and keep an eye on it, but my experience is that the horror stories of ethanol fuel being ruined if it sits a couple of weeks is overblown.

[sandpiper]

Flying in my local area, which is most of the time, I use ethanol free 92 octane. If I were to use premium with ethanol I could save about a dollar a gallon and it would run just fine and it is approved for use in our planes.

My reasoning is as follows: (please correct me if my beleifs are incorrect) 

1. Ethanol laced fuel gets its octane from the added ethanol. As it absorbs moisture from the air, it loses octane.

2. Until all the ethanol is used up from the moisture absorbed, you will not see water in your fuel although the fuel will appear cloudy as saturation is approached.

3. as water is absorbed, at some point the octane will be sufficiently reduced to cause detonation.

Again, please jump on this if any of this is incorrect.

Edited October 21, 2021 by sandpiper
added that fuel will appear cloudy as saturation is approached

[Anticept]

10% ethanol adds 2 points to octane.

#2 is correct, but the fuel will turn cloudy as it's approaching saturation.

Morden: Take a look in your carbs next time after it sits and then tell me that again

[sandpiper]

Thanks Corey. I will edit my post.

Edited October 21, 2021 by sandpiper
correct spelling

[FlyingMonkey]

18 minutes ago, Anticept said:

10% ethanol adds 2 points to octane.

#2 is correct, but the fuel will turn cloudy as it's approaching saturation.

Morden: Take a look in your carbs next time after it sits and then tell me that again

I've done it, have never had any issues.  No water, no cloudiness.  I'm not saying it's a non-issue, just that I think a lot of folks get the vapors (pun intended) about ethanol and it's really not an issue.  I'd probably put the gas in my car if it sat six months, but I would not sweat three months if the fuel looked okay.

I'd use ethanol free, but it's only 90 octane around here.  I don't want to have to mess with mixing fuel, so 93 octane pump gas it is. 

One true point about ethanol: it has lower fuel energy than gasoline, so your fuel consumption will be higher by a couple percent over pure gas to get the same power/speed.

[GrassStripFlyBoy]

I've been running all flavors of fuel over the past 2 years in CT, and hunted non-ethanol the last 20 years as stations slowly became more ethanol blended (for STC compliance with pure fuel).  I prefer pure mo-gas and fine to pay up to $4 a gallon, my local option is presently ~ $3.90 v/s 93 maybe 3.79, easy decision.

93 with ethanol is second choice, and I'd suggest learning how to test what % ethanol is within what you buy.  I use a simple glass mason jar, fill it 10% full to a line, then add in 90% remaining amount of fuel sample, shake it up and let the line resettle.  The amount of movement % wise is what corresponds to ethanol %, say it's now 12% of the value that equals 2% added ethanol. 

The lower octane fuels typically have greater %, 93 premium tends to be small %, at least around my area.  1-3% is the amount I see loaded in 93

I'm not against ethanol, but there are some risks to CT's in fuel tanks developing leaks, rubber degrading at a faster rate, sight tube clarity, carb floats becoming heavier, etc.  I don't think there will be an easily identifiable correlation to ethanol leading to these issues, but one must ask how much reward is there for potential greater risks.  Engine runs fine, and not worried about aging of the fuel, to me it's more of the long term side effects on non engine items that are harder to pin down. 

We're already enjoying some low fuel burn rates in these, I'd opt of the best fuel available.  All that said, there are owners who've used 93 for nearly a decade and not a single complaint.  This topic will forever remain an ongoing discussion.  Rarely do I see people touching on the % that is loaded.  I'd imagine there is a difference between a "premium" fuel with a low percentage added, and some crap brand with 10% added.  It's worth learning how to test and know what you're buying.

 

 

[Anticept]

37 minutes ago, FlyingMonkey said:

I've done it, have never had any issues.  No water, no cloudiness.  I'm not saying it's a non-issue, just that I think a lot of folks get the vapors (pun intended) about ethanol and it's really not an issue.  I'd probably put the gas in my car if it sat six months, but I would not sweat three months if the fuel looked okay.

I'd use ethanol free, but it's only 90 octane around here.  I don't want to have to mess with mixing fuel, so 93 octane pump gas it is. 

One true point about ethanol: it has lower fuel energy than gasoline, so your fuel consumption will be higher by a couple percent over pure gas to get the same power/speed.

The reason I bring it up is that I have. Bowls were full of "milk and water", and the fuel in the wings was not what I would trust with the cloudiness. Was about 3 months of sitting.

If you haven't had this issue, you might have a higher quality fuel than you think

[FlyingMonkey]

1 minute ago, Anticept said:

The reason I bring it up is that I have. Bowls were full of "milk and water", and the fuel in the wings was not what I would trust with the cloudiness. Was about 3 months of sitting.

If you haven't had this issue, you might have a higher quality fuel than you think

Sure, I don't doubt that it's a potential issue.  I grew up in the Northeast, and I think the fuel up there is generally pretty trashy.  Down here, I have not had any issues.  I tested the content in my fuel once, and it was something like 3-4%, so not bad.  If it's 9-10% or even higher, it probably would be much worse of an issue.

Just as an aside, I read once that in South Africa there were CTs flying on over 20% ethanol, because that is what is available.  Good thing it's a dry climate I guess! 

[Roger Lee]

Hi Corey,

"Ethanol is hygroscopic and will pull moisture right out of the air through the vents."

This isn't quite right for us. Because fuel off gases at very low temps and even more in warmer temps. This causes out gasing at the vents. This way no humidity can go back in. Even when it cools off gas still out gases. Gasoline has a flash point of about -45 °C. The flammable range of a liquid is the ratio of the flammable liquid to air that would create a volatile mixture. Plus the vents are so small that to get a cup worth of humid moisture through the vent might take years,. This isn't an issue with our planes. Plus the fuel with 10% ethanol can easily absorb 8.5 oz of water on a full 17 gal tank and still run.  10% ethanol can absorb 3.06 teaspoons of water per gallon.  

Unless you actually see water in the gascolator with ethanol fuel you're good. If you drain water out of the gascolator with ethanol fuel it's time to drain the tank.

[Roger Lee]

Hi Andy,

"Just as an aside, I read once that in South Africa there were CTs flying on over 20% ethanol, because that is what is available. "

Down in South America some are at 23%. They have pulled a couple 1500 hr. engines apart and they found no issues. The only reason Rotax limits it at 10% is that's all they tested.

 

[Madhatter]

Water absorption is minimal if container is mostly closed. Put ethenol gas in an open container in humidity and it with go bad fast. The small vents in the CT allows some airflow but not much especially when in a closed hangar. In SC on the coast an aluminum plane outside will corrode in the wings quickly due to constant air movement. In a closed hangar I never see this,  I've seen planes in hangars for 15 years wit no corrosion. I got this info on ethenol from someone who is in the gas.  business 

[Mike Koerner]

John,

I'm surprised by your first deduction, that water absorbed into the ethanol decreases the octane. I would expect water to increase octane.

Remember that octane is a measure of the resistance of the fuel to pre-ignition (knock). Water is not going to contribute to the combustion process at all. In fact, it seems like it's vaporization in the combustion chamber would lower combustion temperatures, inhibiting pre-ignition.

Of course, there is not enough water in our fuel for this effect to be significant. And we wouldn't want to use water to increase octane anyway, since it is not contributing energy to the process.

[John Vance]

It’s not that water reduces octane, but it pulls ethanol out of the gas.  Less ethanol, lower octane. 

[sandpiper]

15 hours ago, Mike Koerner said:

John,

 

Remember that octane is a measure of the resistance of the fuel to pre-ignition (knock). Water is not going to contribute to the combustion process at all. In fact, it seems like it's vaporization in the combustion chamber would lower combustion temperatures, inhibiting pre-ignition.

 

Mike - you are right about this. The later, big, radial engines had water injection for this purpose. My Dad flew B-47's in the USAF and, if I remember correctly, they also used water injection in their jet engines. Not sure for what purpose water was used in the jets but pretty sure it wasn't to stop detonation. 

[Towner]

In my area of California, 100ll or 91 with ethanol are my only options. So far, 91 with ethanol has been working great.

[Anticept]

On 10/21/2021 at 8:52 PM, Roger Lee said:

Hi Corey,

"Ethanol is hygroscopic and will pull moisture right out of the air through the vents."

This isn't quite right for us. Because fuel off gases at very low temps and even more in warmer temps. This causes out gasing at the vents. This way no humidity can go back in. Even when it cools off gas still out gases. Gasoline has a flash point of about -45 °C. The flammable range of a liquid is the ratio of the flammable liquid to air that would create a volatile mixture. Plus the vents are so small that to get a cup worth of humid moisture through the vent might take years,. This isn't an issue with our planes. Plus the fuel with 10% ethanol can easily absorb 8.5 oz of water on a full 17 gal tank and still run.  10% ethanol can absorb 3.06 teaspoons of water per gallon.  

Unless you actually see water in the gascolator with ethanol fuel you're good. If you drain water out of the gascolator with ethanol fuel it's time to drain the tank.

The way I said it makes it sound like it directly draws the air in, which was a bad choice of words.

It's called barometric breathing. As you get warm days and cold nights and pressure fluctuations, the temperature and pressure fluctuations will draw air into the wings. It's not much, but the lower the fuel level in the tank, the worse it gets. That is why there is a recommendation that if you ARE going to have an aircraft sit for a long time such as winterizing, either fill the tanks to just shy of the brim, or drain them completely (preferred). This is the same recommendation for boats.

This effect is also how lycomings and continentals end up with rusted interior engine parts, despite basically being a boiling temp and purging any water that would have been in it when it ran, the cooling draws in a LOT of air and moisture, and it will continue to breathe as it sits and temperatures and pressures fluctuate.

This is particularly bad for aircraft that sit outside, but for those in hangars, it's not that bad unless it sits for a long period. That's where my caution is.

[Mike Koerner]

Here's an interesting study from the university of Nebraska. In summary:

1) E-10 will hold up to 0.41% water (3 teaspoons per gallon) in solution. Below this threshold, the water will have no significant effect on combustion. There will be no loss of octane and no separation of the water or alcohol.

2) Higher concentrations of water in the fuel will cause a phase change with the water and alcohol mix separating from the fuel. The engine will undoubtedly run poorly when this separated alcohol & water mix is ingested. And, as suggested by the Johns, the separation of the alcohol and water will likely result in a reduction of octane in the rest of fuel.

3) Though E-10 draws moisture out of the air, it cannot absorb enough moisture to cause the phase separate over the course of a "winter storage season".

I don't see water ingestion as an issue with E10 fuel. In fact, I think the alcohol is helpful in avoiding the water separation issues common with aviation fuel. That said, I would prefer pure gasoline for its 3.3% higher energy content, but I wouldn't pay much extra for that.

[Anticept]

It should be pointed out that cold temperatures drop that phase separation limit considerably. Normal looking gas can go bad once exposed to the cold.

Your fuel is also not going to be water free even when you pump it at the station. It's not even water free when it gets pumped off the delivery truck to the station.

Unfortunately in Ohio, gasoline controls are terrible and some places have fuel that already has been sitting a long time (previous owner of my airplane found that out the hard way and the engine ran like crap). Another reason that region is important!

[GlennM]

On 10/23/2021 at 2:12 PM, sandpiper said:

My Dad flew B-47's in the USAF and, if I remember correctly, they also used water injection in their jet engines. Not sure for what purpose water was used in the jets but pretty sure it wasn't to stop detonation. 

My Dad was a crew chief on B-47s.  My understanding is the water injection is for more mass flow in the engine, which yields more thrust.  Power plants use water injection on their gas turbines for more power output, when needed.

 

I use Swift 94UL in my plane.  I get it delivered to the house and have a tank in the back of the truck.

[FlyingMonkey]

14 hours ago, GlennM said:

My Dad was a crew chief on B-47s.  My understanding is the water injection is for more mass flow in the engine, which yields more thrust.  Power plants use water injection on their gas turbines for more power output, when needed.

 

I use Swift 94UL in my plane.  I get it delivered to the house and have a tank in the back of the truck.

Water injection is used on supercharged and turbocharged engines to cool the air charge and offset some of the heating caused by compression through the forced air system.  It effectively increases density of the air charge and thus oxygen available for combustion.  It's similar to what an intercooler does, but without the pressure drop across it and the increased plumbing complexity of an intercooler.

I don't think water injection has ever been used on an NA engine, and if it has I'm not sure what the benefit would be.  At least on gasoline engines, I don't know about turbines.  Octane management is not the purpose of water injection. 

[Anticept]

The extra water content unfortunately also offsets any density changes from temperature.

What it does do though is increases stability of the fuel charge, allowing higher boost or aggressive timings without detonation.

[Tommy Mc]

Final_Report_EASA.2008-6-light-2.pdf

Hi Guys there is a whole heap of reading in this document if you have the time.  From my reading of it Ethanol is of no use in Aviation it is in fact dangerous as the percentage climbs.  You are not suppose to use it when Temps are higher than 23 degrees C due to Vapor locking or above 6000 feet.  You cannot use standard Icing charts as it can create Carb icing at 10 degrees C higher than the chart indicates for Avgas.  I'm pretty sure the British LAA (Light Aircraft Association) have not approved it for use at 10% yet.   You can not leave it in your Tanks for long periods it will draw in water as it is hydroscopic and it will phase separate given time.  Here we have found that "Milky" substance in the Carb Bowl after a week or so.  If/when the bowl starts to corrode it does not stop even with a change of Fuel type.  There are Aircraft here with leaking wings due to the Alcohol in the Fuel breaking down the Resin....... good new is my Wings are OK still after a long period of mogas use .......  there is so much more in this report...Final_Report_EASA.2008-6-light-2.pdf

Approx two months ago prices were as follows here in Ireland

Mogas  €1.55/ltr  

Avgas  €4/ltr

UL91  €3.50  (I have to import myself as it is not available in Ireland)

UL91 represents quite a hike in cost over mogas but I can't unread this report.