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Alcohol induces vapor lock?

TXFlyGuy

Well Known Member
I just read where any fuel that contains alcohol must be avoided in aircraft. The reason stated was the alcohol will easily cause vapor lock.

True? Not true? I had just made up my mind to born 93 Octane MoGas. Might back off on that decision now.

Environmental regulations sometimes require the addition of oxygenates to gasoline. Reformulated gasoline (RFG) contains oxygenates. Although there are other differences between RFG and standard gasoline, the percentage of oxygenates are what we, as pilots, need to be primarily concerned about.

The most widely used oxygenate today is ethanol. Ethanol cannot be legally or safely used with the STCs
 
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I have used E10 Mogas in a variety of aircraft. If the limitations of its characteristics are well understood, it provides safe / efficient use as a fuel.

Items to be thoughtful of are; E10 Mogas has a low vapor pressure and will boil off at mush lower temp than Avgas. Temps over 90 F are kind of a threshold for my IO-320. In the winter months, I can run straight E10 without issue. If you keep it pressurized with the boost pump, one can reduce this tendency. On a hot day, it will absolutely cause a rough running engine due to boiling the fuel lines, primarily at low fuel flow settings such as idle and taxi RPMs. At high altitudes where the atmospheric pressure is lower, this can also manifest itself if you don't keep it pressurized. E10 does attract water if you are not careful. E10 also has a lower Specific Fuel Consumption than 100LL, so 42 gallons of E10 may not provide the same SFC as 42 gallons of 100 LL, which may affect your range.

Why use it? As a "filler / mixer" with 100LL, it provides a little lower cost over straight use of 100LL. I typically will top off my tanks of 100LL with 93 E10 for a 60 / 40 mix with 100LL. It does provide a cleaner burning mixture as well as less lead by-products in the oil / engine / spark plugs.
 
Pretty sure this is accurate: it's Mogas that causes vapor lock problems. Ethanol has less energy density and attracts water, which are separate issues.
 
When most people refer to MOGAS, they mean non-ethanol auto fuel.

Ethanol will vaporize much easier than AVGAS at altitude. Don Rivera provided a nice chart and summary on the topic in his Fuel Injection 101 course. To paraphrase, he said he would never run fuel with ethanol in any airplane engine. Carbureted engines fair better in this realm because the float bowl will always remain full as long as fuel is getting to the carb. The problem with FI is that the line pressure past the flow divider is only about 2 PSI.

Apparently lots of people run Ethanol fuel and have had no problem so YMMV.
 
I never had any issues running ethanol free mogas in my RV-10, but then I planned for it and installed a cooling shroud around my fuel pump and took care to use heat shields, insulation, and reflective tape wherever I could FWF. I kept 1 tank pure ethanol free mogas and the other 100LL. I used the 100LL for take-off and landing and the mogas for cruise. Worked like a charm and saved a lot of money. Never used the ethanol laced stuff as I found lots of places to purchase the ethanol free fuel here: https://www.pure-gas.org/ I was saving about $2 per gallon at the time using the mogas as apposed to 100LL. I had an IO-540V4A5 260 hp engine with low compression pistons.
 
Well, no, not exactly. Our fuel systems are usually not optimal, hydraulically speaking. Hydraulically, it's almost always better to "push" than to "pull". Pulling reduces pressure in the line, and if the pressure is low enough, the liquid will boil. Alcohol has a lower boiling point than pure gasoline and so it boils more quickly. Temperature, of course, also plays into this.

Putting the fuel pumps in the tank to "push" the fuel to the engine, like automobiles do, would be a step towards this. Almost as good (and equivalent in practice) is putting electric fuel pumps at the wing roots - several people here have done just that.
 
https://www.pure-gas.org/
Use the link (posted above) to find the closest source of Ethanol Free MoGas.
Use your Mogas fairly quickly, it breaks down during storage. Maybe limit it to less than 6 months. Don't use winter Mogas in your plane during summer. Winter mogas has a lower vapor pressure, which helps cars start better in the winter, but vapor locks more easily in you plane in the summer. This happened to me once in my T-18. I flew to a summer air show with the winter cover on the oil cooler and winter mogas in the tank. The plane sat in the hot sun all day. The Take-off was *OK* but the engine ran progressively worse as the oil heated up and the fuel pump added more heat to the fuel. I landed short of my destination and drained some mogas, then topped off with 100LL. The rest of the flight was uneventful. Later in the week I realized the relationship between the oil temp indicating 210 instead of 170. Realize the oil temp sender is mounted after the oil cooler. The oil temp inside the engine is hotter. This hot oil splashes into the fuel pump & transfers heat into the fuel. Add this to the sun-heated fuel tank + hot air in the engine compartment + radiant heat from the exhaust pipes....
Eventually I gave up and now I use 100LL in my RV-8.
 
Fuel pumps in wings

I've got automobile fuel pumps in my wings in the rv8 and have had no issues in more than two years of operation. They are mounted to the round access cover and are removable without pulling the tank.

I use the Superior fuel injection system, and an electronic controller keeps the pressure to about 20 psi. This also reduces the current requirement from about 4 amps to 1.2 amps, and I run it continuously at that level. No problems with ethanol even at our field elevation of 8000 MSL and 90Degree days.

I'll try to find some pictures to post. Fuel float sender and pump mount onto the cover plate, and the original pump "Sock" filter is retained.

Roger Bloomfield
RV8 N51BL
RV9-A 711 ED
 
The ethanol free gas is a 80 mile roundtrip for me to purchase, by car.

Plus, it is only 91 octane, where we really desire 93 octane.

Our fuel system has dual boost pumps, located down in the wheelwell, below the center tank. This area is always cool, so heating the fuel should not be an issue.
 
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I have been running mostly 91E10 in my 9A with IO360 for the last 150-ish hours, and there have been some "adjustments" made to combat the vapor pressure but it's been working just fine.

First, I eliminated the engine-driven pump (during the initial build) and put in dual electric pumps pulling cool fuel from the wings and pushing it forward to the servo at about 42-44 psi. These are the AFP pumps, and switching tanks for me is now accomplished by turning one on and the other off. My fuel selector is now just 2-position, on and off, between the output of the pumps and the firewall. After the servo at the fuel divider, I went down to .022" orifices on the injectors and a 4-pound spring for the flow divider itself, in order to bring the pressure in the spider lines up just a little bit, that definitely helped for low-power operation. I also double-wrapped all my FWF fuel lines with firesleeve for additional insulation.

I have noticed a couple times when running 91E10 during a rapid climb to altitude with fuel at the ground ambient temps in the summertime (here in the 90's and low 100's) that somewhere around 10-11,000 and climbing my fuel pressure will sag into the high 30's as the fuel pump begins to cavitate due to the warm fuel and low ambient pressure. One time only I actually got a "low fuel pressure" warning from my Dynon at 30 psi at around 13,000 and climbing. As the fuel in the tanks cool down with ambient air this problem generally goes away about 10-12 minutes after takeoff, even with flight in the mid-teens. I don't think I've ever seen the low pressure persist long enough into flight to still be present at the time I leveled off from a climb direct to 16,500 or 17,500, which is my normal cruise altitude.

One other big problem you'll have with 91E10 fuel is boiling out during a shutdown, and the subsequent very difficult hot-start. With an injected engine on 100LL it's common for the fuel divider to boil dry after heat-soaking on shutdown, but usually the fuel servo does not get hot enough to boil itself dry. When running 91E10 it will - and then during a hot start the body of the fuel servo and divider are hot enough that incoming fuel will heat and flash into vapor bubbles for 4-5 minutes until they cool down, causing a loping rough-idle condition during taxi to the runway that your passengers will NOT like. Usually by the time I got to the end of the runway and completed 20 seconds of partial power runup this was complete and normal cool fuel was present, but it was still a problem I wanted to solve... so I installed an AFP purge valve on the inlet to the fuel divider. Now my hotstart routine is to go full rich and full throttle, activate the purge valve, and turn on a fuel pump for long enough to boot my Dynon screens (about 45 seconds usually), then pull the throttle closed and open it a crack. This will recycle cool fuel from the tanks through the fuel servo and up to the divider, cooling off those components, and then back to the tank. Start cranking (still with the purge valve activated, the engine is flooded from the shutdown boiloff event at this point an no more fuel is going to the divider with the purge valve active) and at about 4-5 seconds the engine will finally be lean enough to fire - as it does I deactivate the purge valve and the engine very smoothly catches to about 700 rpm - when I do it right you would swear it was a standard cold start. Since the fuel in the system, and the system itself, is now cooled off you don't get the vapor bubbles and loping idle, and life is good.

SHIPCHIEF is right about not storing it long - I fly enough that storage is not an issue but I don't think I would be comfortable with more than 6 months on autofuel. Don Riviera will also warn you about running straight 91E10 due to the boiloff in the fuel divider on shutdown, and possibility of accumulating varnish in the divider over time. I have not yet seen any of that, and I have been checking for it - maybe because I run a little 100LL occasionally on a long cross-country, or maybe because it's not really a big problem, I can't say. What I can say is that my engine (with the fuel system mods I've done) is quite happy with 91E10, and I'm quite happy with $3/gal.
 
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SHIPCHIEF is right about not storing it long - I fly enough that storage is not an issue but I don't think I would be comfortable with more than 6 months on autofuel.

How fuel could last that long completely baffles me. How can 40-ish gallons of fuel sit unused in an RV for such an extended period of time? I think I made three trips to the gas station in the last 10 days, each time bringing back 18 gallons of mogas to replace the stuff I burned. :confused:
 
With regard to ethanol and vapor lock, when I was experimenting with Subby engine and mogas, I tested every load of fuel with Hodges Vapor tester.

One day bought a gallon of E85 fuel and tested it with Hodges. It had same vapor lock numbers as 100LL. It does not cause vapor lock.
 
With regard to ethanol and vapor lock, when I was experimenting with Subby engine and mogas, I tested every load of fuel with Hodges Vapor tester.

One day bought a gallon of E85 fuel and tested it with Hodges. It had same vapor lock numbers as 100LL. It does not cause vapor lock.

Now, this is interesting, and reassuring information.
 
Now, this is interesting, and reassuring information.

Well, maybe maybe not since it will vary from station to station. I also have a test rig for vapor pressure, and have found that even ethanol-free mogas varies based on where it came from. Kwik Trip has different numbers than the Sinclair station does, for example. The Holiday station's numbers are so bad I won't use it - it's significantly worse than either of those other two.
 
Talking about Reid vapor pressure is hair-pulling and non-intuitive for most of us who aren't engineers or chemists.

I'm certainly not an authority, but I think some have made mis-statements about it. (I have to look this stuff up again, every time I start to think about it.)

Here's the definition of RVP, from Wikipedia:
"Reid vapor pressure (RVP) is a common measure of the volatility of gasoline. It is defined as the absolute vapor pressure exerted by a liquid at 37.8 °C (100 °F) as determined by the test method ASTM-D-323."

I spent a few minutes communing with 'the google', and got these numbers:

100LL (Shell brand): 6.38psi (Various other sources mention a range of something like 5.5-7 psi; one document says 100LL is ">5.5psi.")

Pure Ethanol: 2 psi

Generic auto fuel: can range from 7-15 psi

10% ethanol auto fuel: EPA-limited to 10 psi *maximum* (Higher RVP evaporates more pollutants into the atmosphere.)

Note that auto fuel universally has a *higher*, not lower, Reid vapor pressure than gasoline. Yes, it vaporizes easier, so a higher number means that it vaporizes easier.

Note also that pure ethanol has a MUCH LOWER Reid vapor pressure (much harder to vaporize) than avgas.

From various readings on the always believable interwebs, a small % of ethanol blended to mogas seems to raise the RVP of mogas by about 1 psi, but much higher percentages seem to lower it, or at least not change it much (see the references here and elsewhere, to E85).

Hope I didn't make any mis-statements, and the above will be food for though. A really interesting data point is the contrast between the *range* of RVP for mogas, and the actual number for E10 mogas.

Charlie
 
Talking about Reid vapor pressure is hair-pulling and non-intuitive for most of us who aren't engineers or chemists.

I'm certainly not an authority, but I think some have made mis-statements about it. (I have to look this stuff up again, every time I start to think about it.)

Here's the definition of RVP, from Wikipedia:
"Reid vapor pressure (RVP) is a common measure of the volatility of gasoline. It is defined as the absolute vapor pressure exerted by a liquid at 37.8 °C (100 °F) as determined by the test method ASTM-D-323."

I spent a few minutes communing with 'the google', and got these numbers:

100LL (Shell brand): 6.38psi (Various other sources mention a range of something like 5.5-7 psi; one document says 100LL is ">5.5psi.")

Pure Ethanol: 2 psi

Generic auto fuel: can range from 7-15 psi

10% ethanol auto fuel: EPA-limited to 10 psi *maximum* (Higher RVP evaporates more pollutants into the atmosphere.)

Note that auto fuel universally has a *higher*, not lower, Reid vapor pressure than gasoline. Yes, it vaporizes easier, so a higher number means that it vaporizes easier.

Note also that pure ethanol has a MUCH LOWER Reid vapor pressure (much harder to vaporize) than avgas.

From various readings on the always believable interwebs, a small % of ethanol blended to mogas seems to raise the RVP of mogas by about 1 psi, but much higher percentages seem to lower it, or at least not change it much (see the references here and elsewhere, to E85).

Hope I didn't make any mis-statements, and the above will be food for though. A really interesting data point is the contrast between the *range* of RVP for mogas, and the actual number for E10 mogas.

Charlie

Correct. Ethanol content in 10% ethanol autofuel (E10) does not raise the vapor pressure due to the ethanol. The vapor pressure is higher due to the different blend of the base-stock gasoline that the ethanol is ADDED to, and the resultant total mix does have a higher vapor pressure, at least considerably higher than 100LL. The base stock is a different mix because the goal of the final mix is to hit a target octane number without exceeding it by much, and ethanol is an octane booster.
 
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Looking at the data posted online for each state, it lists Texas as having an RVP of 9.0 for 10% Ethanol gasoline blends.

So does this indicate that Ethanol gas has a 60% greater (vs. 100LL) likelihood of causing vapor lock?
 
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Aaaand, the fact that ethanol is an octane booster, combined with its affinity for water, makes that the *potentially* biggest drawback. *Not* because it attracts water. But because if water gets a the tank, when you sump the tank & pull off the water, you're pulling off some of the ethanol, with it, lowering the octane of the fuel. If you have an engine that cares (rotaries don't), then you may have a knock issue.

The only other significant downside I've seen, is that if you fly in the nosebleed altitudes *and* at extremely low temps, the E can separate from the G, giving an alternately high & low octane fuel to the engine. (I never fly high or cold enough to worry about that.) You do need to make sure that the 'soft' stuff in the fuel delivery path is compatible with ethanol, but just about all current production a/c parts seem to be, now. Lyc mechanical fuel pumps used to be vulnerable, but the mfgr told me (off the record) that current production is compatible.

From the reading I've done, all the talk about corrosion seems to have been driven by some very early chemical plant processing carelessness (or plain intentional corner cutting), where the acid used in their ethanol production wasn't completely removed from the blend stock. Methanol is a different animal, but I don't recall any commercial road fuel that uses methanol in its blend. (It *is* found in racing, though.)

As others have indicated, there seems to be no real risk of vapor lock if you're running an auto style fuel injection and keep all fuel lines on the hot side of the firewall at injection pressure (fuel pumps aft of the firewall).

Again, hoping for no mis-statements...

Charlie
 
Looking at the data posted online for each state, it lists Texas as having an RVP of 9.0 for 10% Ethanol gasoline blends.

So does this indicate that Ethanol gas has a 60% greater (vs. 100LL) likelihood of causing vapor lock?

Don't know the answer, but how'd you arrive at 60%? Avgas is typically between 6 & 7, and Egas is a 9, for you.
 
Using Shell's published 6.38 psi number, 9-6.38=2.62 2.62/6.38=0.41

Using best/worst of 5.5 & 10, you'd get 4.5/5.5=0.818, but it's unlikely you'd ever see that spread.
 
The only other significant downside I've seen, is that if you fly in the nosebleed altitudes *and* at extremely low temps, the E can separate from the G, giving an alternately high & low octane fuel to the engine.

First time I've ever heard this, and I've done an awful lot of research on the matter. What is your source?

From the reading I've done, all the talk about corrosion seems to have been driven by some very early chemical plant processing carelessness (or plain intentional corner cutting), where the acid used in their ethanol production wasn't completely removed from the blend stock.

Correct. Old wives tales are hard to kill.
 
Aaaand, the fact that ethanol is an octane booster, combined with its affinity for water, makes that the *potentially* biggest drawback. *Not* because it attracts water. But because if water gets a the tank, when you sump the tank & pull off the water, you're pulling off some of the ethanol, with it, lowering the octane of the fuel. If you have an engine that cares (rotaries don't), then you may have a knock issue.

The only other significant downside I've seen, is that if you fly in the nosebleed altitudes *and* at extremely low temps, the E can separate from the G, giving an alternately high & low octane fuel to the engine. (I never fly high or cold enough to worry about that.) You do need to make sure that the 'soft' stuff in the fuel delivery path is compatible with ethanol, but just about all current production a/c parts seem to be, now. Lyc mechanical fuel pumps used to be vulnerable, but the mfgr told me (off the record) that current production is compatible.

From the reading I've done, all the talk about corrosion seems to have been driven by some very early chemical plant processing carelessness (or plain intentional corner cutting), where the acid used in their ethanol production wasn't completely removed from the blend stock. Methanol is a different animal, but I don't recall any commercial road fuel that uses methanol in its blend. (It *is* found in racing, though.)

As others have indicated, there seems to be no real risk of vapor lock if you're running an auto style fuel injection and keep all fuel lines on the hot side of the firewall at injection pressure (fuel pumps aft of the firewall).

Again, hoping for no mis-statements...

Charlie

My only concern about using fuel with ethanol is its incompatibility with fuel system parts.

It is not an issue with any auto engine because the engine was designed to use it, including the source tank, pump, and fuel lines. Also fuel injection is universal with pressures running 20 psi and higher. Vapor lock does not happen when fuel is under these pressures.

With Lycoming installation it is a risk because there may even be a compatibility issue with aluminum tank. For sure the engine fuel pump (they won't say if parts are compatible) and certainly with an old carburetor installation.

FWIW Airflow Performance fuel injection system is impervious to ethanol.

I might be using mogas with ethanol except for the unknown with the engine fuel pump. But as is I won't.
 
Airguy,

I wish I could find the reference for high altitude cold temps, but it's escaping me at the moment. I doubted it too, but someone posted a link (probably on this forum) several years ago to a paper documenting the numbers. I can't remember specific numbers, but they were high enough to need O2 & the temps were very, very low. So far away from where I'll ever fly that I didn't make an effort to record the info, but figured it was worth mentioning for those who like to go really high. Perhaps a search here will turn up a hit, or just start a thread asking the question. IIRC, there's at least one or two petroleum engineers on the forum.

David,

The only references to *ethanol* and aluminum corrosion (other than old hangar tales) talk about the risk of corrosion from *water* that might be attracted and held by the ethanol. If tanks are kept more or less full and sumped regularly, it should be a non issue. If they are left almost empty in high humidity environments, water will condense in them even with avgas.

If you have technical references that document a danger from ethanol, I'd be grateful if you'd share them. I can tell you that I know multiple alt engine flyers that have run E5, E10, etc mogas for over a decade in RV's with no recorded issues.

I'd encourage doing your own research, but I spoke with a technical advisor at Aero Accessories (Tempest) several years ago about Egas & fuel pumps, because I had heard of documented issues with the pump diaphragms & seals. I was considering the use of E-gas in my Lyc powered -4. At that time, he told me that any pump made or rebuilt in recent history used E-compatible soft parts. He more or less indicated that they could no longer get the soft parts made from the old materials. (As a FWIW, my take on that is that they are buying bits & pieces from the auto/agricultural world, where everything runs on Egas now. The Lyc pump is basically a 50+ year old automotive design.) The same tech advisor split his time between Tempest and Marvel Schebler; they're in the same small town and apparently owned by the same people/group, though I can't document the ownership. In the course of our conversations, he told me that the carbs have always been E-compatible, FWIW.

As I said, do your own research. But Tempest is a phone call away.

Now, one thing that *could* bite your butt is if you have an older build. Some of the really old 'proseal' tank sealants don't seem to stand up well to mogas, E-blended or not, but obviously a bigger risk with ethanol. My 25 year old -4 springs leaks from time to time running a steady diet of E-free 91 mogas. I'm not sure whether its mogas related, or just a symptom of 25 year old sealant. I've been seeing a few accounts of others with sealant going soft, too, in planes that are running 100LL.

Charlie
 
My tanks are sealed with Flamemaster - CS3204. They claim to be resistant to almost everything, including ethanol, as well as other chemicals.

As we plan to fly between 9,000 and 11,000 (+/-) on x-country trips, the concern is vaporization. Maybe that is not high enough to have it be an issue.
 
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My tanks are sealed with Flamemaster - CS3204. They claim to be resistant to almost everything, including ethanol, as well as other chemicals.

As we plan to fly between 9,000 and 11,000 (+/-) on x-country trips, the concern is vaporization. Maybe that is not high enough to have it be an issue.

A friend of mine regularly flies from near sea level and tropical temps to lower O2 levels (12k-15k ft) in the mountains, running a rotary with auto style injection, with the fuel pumps on the cold side of the firewall. No issues with whatever 87 octane E-gas is available at the moment.

I've had vapor lock cause a precautionary landing in my carb'd, Lyc powered -4, at barely a thousand feet above sea level. But it was 'winter' blend non-Ethanol high octane mogas, on a 100+ degree day, after a 30 minute flight and an hour+ heat soak on a ramp. I knew better; just didn't pay attention to my own knowledge.

Fuel system type and configuration (and driver intellect) matter.

Charlie
 
It has been a lively discussion with lots of questionable information.
I can't dispute the findings of chemical engineers and statements issued by
Folks worried about the legal consequences of "approving" mogas with ethanol.
What I do know and have is nearly 500 hours on my Rv-10 flying mostly on
Mogas 91E10 in any and all conditions without so much as a hick up.
For those looking for mogas advice, I can only encourage you to take the advice
From those who actually have experience flying on mogas rather than
Those who simply read or heard that " alcohol causes vapor lock".
Some effort and minor modifications to your fuel system are necessary to
Keep your engine running well on lower octane fuel.
The benefits are worth it in my opinion, lower cost ($2) per gallon
And a very clean running engine to name just a couple.
 
It has been a lively discussion with lots of questionable information.
I can't dispute the findings of chemical engineers and statements issued by
Folks worried about the legal consequences of "approving" mogas with ethanol.
What I do know and have is nearly 500 hours on my Rv-10 flying mostly on
Mogas 91E10 in any and all conditions without so much as a hick up.
For those looking for mogas advice, I can only encourage you to take the advice
From those who actually have experience flying on mogas rather than
Those who simply read or heard that " alcohol causes vapor lock".
Some effort and minor modifications to your fuel system are necessary to
Keep your engine running well on lower octane fuel.
The benefits are worth it in my opinion, lower cost ($2) per gallon
And a very clean running engine to name just a couple.

This is good to know. My engine manual says to burn "premium pump" gas.
The options for us are:

1. 100LL
2. 91 Octane E-Free MoGas
3. 93 Octane 10% Ethanol

The airport that I manage (3TX2) does not have fuel available. This means I would have to make a 1.5 hour round trip to tanker the 91 Mogas in my truck. Or, fill up my tanks locally (tanker) with the 93 E10. Or, fly 5 minutes to 52F and top off with 100LL.

The easiest (and cheapest) would be to buy the local premium 93 E10.

This is my temptation, but there are so many people telling me that "you can't burn Ethanol in your airplane", thus the reason for this thread.

Thanks to everyone who has replied.

edit: During the mid 80's, I ran 87 Octane pump gas through my Lycoming-320 for hundreds of hours. At that time, people were saying the same thing. Vapor lock. After getting off 100LL, my Lyc ran like a top. The plugs never fouled like they used to. It ran so smooth, especially on decent with reduced (or idle) power settings. Plus is saved $$. The only problem was having to fill up 5 gallon cans, and truck them to the airport.
 
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The only other significant downside I've seen, is that if you fly in the nosebleed altitudes *and* at extremely low temps, the E can separate from the G, giving an alternately high & low octane fuel to the engine. (I never fly high or cold enough to worry about that.)
Charlie

This page talks about phase separation occurring at lower temps, but only because of water saturation. Does this ring a bell?

http://www.lcbamarketing.com/phase_separation_in_ethanol_blen.htm
 
Sumps drained. Check.

Takeoff from 650' MSL at 80 degrees, and climb to 11,000' MSL, temp 45 degrees.

Will this alone cause phase separation (91E-10)?
 
This page talks about phase separation occurring at lower temps, but only because of water saturation. Does this ring a bell?

http://www.lcbamarketing.com/phase_separation_in_ethanol_blen.htm
No; the paper I recall dealt with actual aircraft, at high altitudes and extremely low temps. I don't recall water even being a factor.

The water/ethanol separation from gas happens regardless of temps/pressures; that's how I check for alcohol in mogas before using it in my non-E-compatible -4's fuel system. Just add put a teaspoon or so in a test tube, mark the level, add a couple of ounces of gas, and shake. If there's ethanol present, it will bind with the water, and when you let it settle out, the apparent water level in the tube will rise a noticeable amount.

I really hate that I didn't save that paper. I don't like unsubstantiated 'stuff' on the interwebs, and I hate being one of those who add to the problem. But as I mentioned earlier, I didn't save it because the altitudes and temps were so outside the realm of where I'd ever take an RV, and I know others (others have already posted here) who regularly operate higher and colder than I do, with no problems. IIRC, if you're not breathing O2 in a turbo'd a/c, and wearing thermal underwear+superinsulated clothing, it's not really a factor.

Charlie
 
This is downright scary.

And is designed to be so.

This source has an axe to grind - dig deeper and sniff in the corners and you'll see it. I won't throw mud on a public forum but I'll say that all is not what it appears to be. He uses the solubility of water in ethanol-laced gasoline without regard to the SOURCE of the water - you would have to leave a small amount of fuel in your tanks and actively vent them (not passively with ambient pressure changes) with very humid air over an extended period of time to expose them to that quantity of water. Yes, it's technically accurate - but it's nowhere near realistic.

I will advocate keeping an open mind and doing your own research - both online and physical hands-on - to determine a viable fuel source. Knowledge is power and hearsay is worthless.
 
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And is designed to be so.

This source has an axe to grind - dig deeper and sniff in the corners and you'll see it. I won't throw mud on a public forum but I'll say that all is not what it appears to be. He uses the solubility of water in ethanol-laced gasoline without regard to the SOURCE of the water - you would have to leave a small amount of fuel in your tanks and actively vent them (not passively with ambient pressure changes) with very humid air over an extended period of time to expose them to that quantity of water. Yes, it's technically accurate - but it's nowhere near realistic.

I will advocate keeping an open mind and doing your own research - both online and physical hands-on - to determine a viable fuel source. Knowledge is power and hearsay is worthless.

I have personal experience refuting this. I had to replace two gas tanks on my boat. Both were completely rotted on the bottom. The air in the tank will quickly match the ambient humidity level even with passive venting. Don't believe me, drill a 3/8" hole in your humidor and see if it holds your 70% RH. As the air cools down at night and drops below the dew point, condensation is produced, just like on your grass in the fall and spring. All that water coalesces via gravity and drips into the gas where it immediately sinks to the bottom. After a fall season, you can have an 1/8" of solid water on the bottom of your tank.

This can only be avoided by keeping the gas tank full. Then there is very limited air and therefore very limited condensation. Modern cars avoid this with closed venting systems and corrosion resistant tanks, usually plastic.

Granted this is somewhat seasonal and limited to certain climates.

Larry
 
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Do you sump the boat's tanks before every use, like your plane,
or is that a season's worth of condensation?

Boat stored inside, or out?

Ethanol doesn't reach out through the vent and pull moisture into the tank; it will come in, ethanol or not; even gas or not. And it will still corrode the tank, regardless of fuel, just like it does in a wing or fuselage. Unrelated to ethanol.

FWIW, I live in central MS, my RV is always hangared, and I've never found more than a couple of drops of water in the tanks. And there have been times, sad to say, that the plane has sat for a month or more at a time.
 
How about you just fill up one tank with whatever you choose to use.
It a great way to experiment and have 100 LL available if those vapor lock demons show up. I have also mixed and filled my tanks with whatever
Gasoline is available.
You'll find plenty of scary information on mixing 100LL with mogas and yet hundreds of us are doing just that. Just like the phase separation stories
Consider the source. Boats are in a different category all together,
Get your info from airplane owner who have successfully used
Mogas.
 
The statement above that Ethanol does not "reach out" and pull water into your fuel tank is true. Moisture will form inside your tank, regardless of what type of fuel you have.

Here is what is interesting, perhaps all of you already knew this (I did not)...

Ethanol is hydroscopic. This simply means that the ethanol will "absorb", or hold the H20 in solution, up to the point of saturation. This allows the very small percent of actual water to pass through the engine without any issues. Ethanol can hold up to 0.41% water, or roughly 3.06 tablespoons per gallon of gas. That is the maximum amount. Go above this, and you get the phase separation. It would appear that phase separation is not dependent on temp or pressure, but more so on the volume of water present.

Pure gasoline is hydrophobic. Meaning that any water in the fuel will simply drain to the lowest point in the fuel system, and collect at that point.

Here is a pull quote from the following paper:

"Articles from Frazier at Oklahoma State Extension and Korotney at U.S. EPA disagree stating an E10 blends cannot absorb enough moisture from the air to phase separate over a storage season."

To read more, click on this link: https://cropwatch.unl.edu/documents/Ethanol and Water Contamination 09052014.pdf
 
The statement above that Ethanol does not "reach out" and pull water into your fuel tank is true. Moisture will form inside your tank, regardless of what type of fuel you have.

Here is what is interesting, perhaps all of you already knew this (I did not)...

Ethanol is hydroscopic. This simply means that the ethanol will "absorb", or hold the H20 in solution, up to the point of saturation. This allows the very small percent of actual water to pass through the engine without any issues. Ethanol can hold up to 0.41% water, or roughly 3.06 tablespoons per gallon of gas. That is the maximum amount. Go above this, and you get the phase separation. It would appear that phase separation is not dependent on temp or pressure, but more so on the volume of water present.

Pure gasoline is hydrophobic. Meaning that any water in the fuel will simply drain to the lowest point in the fuel system, and collect at that point.

Here is a pull quote from the following paper:

"Articles from Frazier at Oklahoma State Extension and Korotney at U.S. EPA disagree stating an E10 blends cannot absorb enough moisture from the air to phase separate over a storage season."

To read more, click on this link: https://cropwatch.unl.edu/documents/Ethanol and Water Contamination 09052014.pdf

You are doing your homework - excellent !!
Keep it up.
 
This is my temptation said:
The Vanguard squadron from South Dakota runs their formation planes on straight ethanol. South Dakota state university did extensive testing on ethanol fuel and airplane fuel systems in the 90's. With slight modification it works great. According to the university you should shy away from 10% ethanol, it is the butane that is added to the blend that will cause vapor lock as you gain altitude.
 
Do you sump the boat's tanks before every use, like your plane,
or is that a season's worth of condensation?

Boat stored inside, or out?

Ethanol doesn't reach out through the vent and pull moisture into the tank; it will come in, ethanol or not; even gas or not. And it will still corrode the tank, regardless of fuel, just like it does in a wing or fuselage. Unrelated to ethanol.

FWIW, I live in central MS, my RV is always hangared, and I've never found more than a couple of drops of water in the tanks. And there have been times, sad to say, that the plane has sat for a month or more at a time.

I wasn't trying to draw parallels with aviation (very different use cases) only to debunk the notion that the moisture laiden air cannot make it into a fuel tank with active ventilation.

Larry
 
Larry,

I suspect we're collectively talking past each other on this. Yes, moisture will collect in a fuel tank without active air circulation. But it won't collect any more, or less, in an E-gas laden tank than a E-free mogas tank, or an avgas tank, at least to a degree that's detectable with our fuel checkers. So it's not a relevant data point.

Moisture gets in fuel tanks. We drain it before flight. Done.

The only issue I see is if there's a truly significant quantity, from say, leaky fuel caps in a long rainstorm, and you're draining off a significant percentage of the ethanol with the accumulated water. *Then* you might be affecting the octane of the fuel, because blenders use the alcohol as an octane enhancer, replacing other chemical additives that were octane enhancers, or using lower octane gas stock than they would have otherwise been able to use.

I'm not qualified to give an answer, but I'd bet it would take the very nebulous quantity of "a lot" of water in a typical full fuel tank to draw of enough ethanol with it to have a significant octane altering effect.
 
A boat story......being a pilot and learned about this subject a long time ago, had an argument with a coworker about winter fuel storage in our boats, I kept mine full he did not, long story short, first trip to Catalina after winter he launches, gets halfway out of the channel and boat engine dies, will not restart. After he loads up and goes home he drains a portion of his tank and told me right there he cursed me.....because I was right. Ended up with a 2 liter soda bottle of water to show me on that next work day. Now this was on the coast, humid, over several months of storage with a 1/4 full tank. :rolleyes:
 
More good information, especially for those in Texas, and the Dallas/Ft.Worth area...

The RVP for TX is specified by the EPA not to exceed 7.0, or 7.8 from May through October. This would be what they call "boutique fuels".

RFG is mandated in many counties, including where I live in the North Texas area. It has a lower volatility rating so as to not evaporate as readily as the standard fuels.

Here is some interesting data -

14.7 psi at sea level, 100 degrees F. That will give you this: At 12,000 MSL, the psi will be 9.68.
 
More to the point is how close that 7psi number is, to the avgas number of around 6.3 (can be as high as 7.0). So your summer mogas has effectively the same RVP as avgas.

And to re-emphasize: If you're running auto style injections with your fuel pumps on the cool side of the firewall, all discussions of vapor lock are irrelevant, because hot fuel will always be at ~40psi. Even running 'dribble' injection, if you run electric pumps on the cold side of the firewall, hot fuel will always be at ~20+psi all the way to the spider.
 
if you run electric pumps on the cold side of the firewall, hot fuel will always be at ~20+psi all the way to the spider.

Where it will drop to as low as 2psi in the nozzle lines (according to people on here smarter than I). Fortunately there's lots of cooling air here during flight but not so much when starting/taxiing.

Bevan
 
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