Seperating alcohol from aviation gas

Dave Shepard · July 27, 2008, 01:06:56 AM

A friend of mine has a brother who builds and flys airplanes. Apparently using alcohol in avgas can have a pesky little glitch. It seems that your perfectly running airplane can vapor lock and fall out of the sky.

Well, this guy has developed a system for removing the alcohol. He first adds water, which goes into solution with the alcohol. He then pumps off the gas. Then, being rather frugal, he adds salt to the alcohol, which goes into solution with the water. He then pumps off the alcohol, which he is possibly burning in his car. And, lastly, having already been cited for frugality, he puts the saltwater in shallow pans in the yard to evaporate the water, so he can reuse the salt. :D

Dave

Fla._Deadheader · July 27, 2008, 02:46:48 AM

I've always heard it was near impossible to seperate Alcohol from Gasoline. That's why the Feds "Sweeten" yer homebrew, so's ya can't drink it. ??? IF this is true, and he DOES seperate it, I wan't verification. ??? ??? ???

John Mc · July 27, 2008, 09:36:22 PM

It's easy to separate the alcohol from gas... just add water, mix well, and wait for the water/alcohol to settle to the bottom. If you have a valve on the bottom of the settling tank (at the lowest point on the tank), you can then drain the alcohol water out. (Fla_Deadheader -- The separation is not necessarily 100% effective, but what's left is only a trace... however, there is enough trace gas left in the ethanol that you still don't want to be drinking it.)

In fact, this separation will happen in the aircraft's fuel tanks, if you leave an ethanol blended fuel in there. The ethanol will combine with the moisture in the air, or condensation in the tank and settle to the bottom.

There is one thing your pilot friend should be aware of: removing the alcohol lowers the octane rating substantially. Your friend is burning sub-regular octane gas in his aircraft. A great way to ruin the engine (not to mention ruining your whole day, if you happen to be up in the air when the engine finally craps out). That famous frugality could end up costing him and engine... or more.

BTW... vapor lock is not the only problem with running ethanol/gas blends in an aircraft. Ive been told the ethanol can attack the aluminum which is what many aircraft fuel tanks are. It will also attack some of the fuel system components. Though on a homebuilt aircraft, I supposed the builder could use materials compatible with ethanol.

John Mc

Ron Wenrich · July 27, 2008, 10:23:45 PM

Now you give me a couple of questions.

If moisture in the air can cause ethanol to settle out of aviation fuel, what's happening in all those tanks that sit underground and we pump gas out of them? How about our car fuel tanks?

If ethanol reacts with aluminum, why haven't they gone to plastic tanks? Static electricity?

And why don't beer cans and kegs fall apart from the ethanol in them? :D

Tom · July 27, 2008, 10:32:16 PM

QuoteAnd why don't beer cans and kegs fall apart from the ethanol in them?

Now, there is a good question. :D

Dan_Shade · July 27, 2008, 10:36:18 PM

i've never had a beer can or keg have ethanol in it long enough to find out!

John Mc · July 27, 2008, 11:07:48 PM

Quote from: Ron Wenrich on July 27, 2008, 10:23:45 PM
If moisture in the air can cause ethanol to settle out of aviation fuel, what's happening in all those tanks that sit underground and we pump gas out of them? How about our car fuel tanks?

Those underground tanks and car tanks are not made of aluminum, so are probably not attacked by ethanol... though now that you mention it, I'll have to see if I can find where I read that. It seems more likely that ethanol would attack the sealant used in the tanks than the aluminum itself. I know it attacks many of the "rubber" fuel lines and o-rings in various valves.

I've not seen any studies on this, but have heard from a couple of knowledgeable people that it can be a problem buying ethanol blend fuels from stations which don't sell enough to turn over their fuel relatively quickly. The settling is an issue. (OK, I know... I "heard it from a couple of knowledgeable people" is pretty weak. I can remember the conversation and the message exchange on-line, but I can't remember where or who it was.)

QuoteIf ethanol reacts with aluminum, why haven't they gone to plastic tanks? Static electricity?

Not sure if static electricity is an issue or not, but I would suspect so. The flow of gas through the fuel line builds up a static charge. For this reason, it's good practice when fueling an aircraft to keep the nozzle in contact with the metal rim of the tank fill port: that's not the place you want a spark to jump. Weight certainly is an issue. In many small aircraft, the fuel tanks are basically the wings... parts of the wing are sealed, to hold the fuel. Adding a plastic tank inside the wing adds weight, something that is at a premium in an aircraft. Also, what do you do when the plastic finally ages enough that it is not sound anymore? Tear the wing apart? Some models of aircraft did use rubber bladders inside the wings at one time. Replacement on those is an expensive proposition.

StorminN · July 28, 2008, 02:57:55 PM

Quote from: Ron Wenrich on July 27, 2008, 10:23:45 PMIf moisture in the air can cause ethanol to settle out of aviation fuel, what's happening in all those tanks that sit underground and we pump gas out of them? How about our car fuel tanks?

Most big underground tanks have a desiccant dryer on their air vent, at the very least... so only dry air gets into the tank. I think gasoline tanks have even more complex vapor recirculators and such. I installed a desiccant dryer on the vent of my small (300 gallon) biodiesel tank, after having a problem with condensation water emulsifying with the bio (no problems since).

Quote from: Ron Wenrich on July 27, 2008, 10:23:45 PM
If ethanol reacts with aluminum, why haven't they gone to plastic tanks? Static electricity?
And why don't beer cans and kegs fall apart from the ethanol in them? :D

When I was 16, I worked as a "line boy" at the local airport, taking care of the flight line of small aircraft. Static electricity is definitely a concern with aircraft. Next to our fuel pumps was a retractable reel with a grounding cable on it... any aircraft that had just come in from flying, we would ground with the cable before we started fueling. With helicopters, this was especially important (lots more static electricity).

Beer cans are lined with a coating, I think it's polycarbonate... kegs I'm not sure... but the ethanol is at max 8%, normally average maybe 5% in beer, right?

-Norm.

smoothED · July 28, 2008, 08:52:14 PM

Beer kegs are stainless steel,beer cans i think have a coating inside.

arojay · July 29, 2008, 11:41:49 PM

All this talk of beer has given me an idea!

bandmiller2 · February 16, 2009, 03:54:06 PM

Dave or outhers,have you ever tried this procedure to remove alky for your two cycle fuel??.Sorry to dredge this up but I just discovered this part of the forum,quess you'll have to put up with me here too.Frank C.

ely · February 16, 2009, 05:26:45 PM

the ethananol in gas will eat the resins out of some fiberglass tanks. evidently some of the older boats had these tanks. it will clog filters and gum up engines in the boats. costing thousands of dollars in repair work.
i read that out of a boating u.s. magazine last year.
some folks in fla. and calif. had class action lawsuit about that.

Dave Shepard · February 16, 2009, 06:00:34 PM

I haven't tried it, but I know it works, sounds like a pain in the butt to me. I'm told that high test doesn't have alcohol in it, and it's better for the saw anyway. I have a tiny tester from Bailey's. I've tested the regular gas around here, and never got more than 2% alcohol. If you had a way to measure the gas and alcohol accurately, you could just use a bottle to measure the alcohol content.