Avgas/Fuel Prices/Ethanol in auto fuel

hecilopter · #1 04-11-2006, 02:03 PM

I saw on the news yesterday that fuel prices at the pump were increasing again due to several reasons. The most interesting was a change in chemical composition of the fuel to eliminate MTBE and replace it with ethanol.

One of the reasons I went with the Superior XP-360 engine in my airplane was its ability to use super unleaded auto fuel if aviation fuel ever became unavailable/unreasonable to obtain. One of the warnings in the owner's manual, however, was that auto fuel with any ethanol content was forbidden. Any other auto gas 91 octane and above with no ethanol was fine in any mixture with avgas or straight.

Has anyone else seen this/have any insight? Are they really about to put ethanol in ALL auto fuel? This completely eliminates is usability as an aviation fuel. Very disappointing.

tin man · #2 04-11-2006, 02:13 PM

$4.42 gallon for 100LL @ KSQL this morning

Tom

Ironflight · #3 04-11-2006, 02:30 PM

Quote:

Originally Posted by hecilopter

Has anyone else seen this/have any insight? Are they really about to put ethanol in ALL auto fuel? This completely eliminates is usability as an aviation fuel. Very disappointing.

That certainly seems to be the way I interpret it - they are going to be putting ethanol in all the auto gas - at least that is what they are saying! Last fall, when the price of gas spiked in Houston at $3.00/gallon, they blamed it on the hurricane. Now the excuse is Ethanol....

I always heard the reason to fly with Mogas was to save money! Right now, you can get 100LL at Anahuac or Liberty (TX) for $2.70 a gallon. Regular Unleaded autogas as Kroger (here in Houston? $2.70 per gallon. Go figure....

Paul

cobra · #4 04-11-2006, 02:39 PM

MBTE is a good octane booster that replaced lead additives, but it also is a serious water polluter once it gets spilled on the ground or flushed into storm drains.

Methanol and ethanol are small molecules that attack some kinds of rubber. Ill bet the problem with your motor involves "cheap" seals and o-rings in the fuel pump- something that can likely be substituted for better materials if a widespread changeover in fuels is mandated. Ethanol adds oxygen to the fuel, which reduces ozone generation. It also increases the octane rating, which slows down the fuel burn rate and reduces detonation.

scard · #5 04-11-2006, 02:48 PM

Quote:

Originally Posted by cobra

Methanol and ethanol are small molecules that attack some kinds of rubber. Ill bet the problem with your motor involves "cheap" seals and o-rings in the fuel pump- something that can likely be substituted for better materials if a widespread changeover in fuels is mandated.

I'll pretend to know something about this... Ethanol is an alcohol that will (and does) boil at a surprisingly low tempature at altitude, hence turning to vapor in the lines. Not good. Mogas with ethanol in it has no business in a general aviation application unless you really know what you're doing. Be careful.

cobra · #6 04-11-2006, 03:47 PM

Gasoline is a blend of many different hydrocarbons, and most of them are as or more volatile than alcohols. The gas companies have added ethanol additives (they call them oxygenates) during the summer to control ozone and carbon monoxide emissions in many urban areas for years- no reports of excessive vapor locking that Ive seen to date.

RVbySDI · #7 04-11-2006, 03:55 PM

Come on guys! Ethanol is another fuel source that you may have problems with now because you live in the 19th century. If it can work in a car driving up a mountain road like Pikes Peak at 14,000' don't you think you can figure out a way to make it work in your airplane flying at 8,000'?

Quote:

Originally Posted by scard

Ethanol is an alcohol that will (and does) boil at a surprisingly low tempature at altitude, hence turning to vapor in the lines. Not good. Mogas with ethanol in it has no business in a general aviation application unless you really know what you're doing. Be careful.

If vapor lock scares you then figure out a solution to get the vapor out of the engine (hmmmm, those Andair fuel valves with the vapor return lines sound awfully handy).

Oh, I suppose if you do that you might also have to give up that most wonderous of other engine components called the carburator too. Wouldn't that be a horrible thing in deed?

I wonder if any of those racers who enter the annual Pikes Peak Race use ethanol in any of their engines? If so, I wonder if they have figured out how to avoid the dreaded vapor lock at 14,000'?

Quote:

Originally Posted by hecilopter

One of the warnings in the owner's manual, however, was that auto fuel with any ethanol content was forbidden.

Why is it "forbidden"? Because the manufacturer of that engine is looking at those old rubber gaskets, seals, o-rings, etc. that he has always used since he began building engines in 19 ott something or other and knows that alcohol can and does destroy the rubber. If he would spend his 1.50 per part on an Ethanol friendly gasket, seal or o-ring rather than the "I've always done it this way" gasket, seal or o-ring I don't think he would "forbid" Ethanol any longer. My guess is that he would all of a sudden be touting the wonders of Ethanol and charging a premium for the "new" 1.50 per part Ethanol widget that he has "added" to his engine.

Again, why does such a "high performance" industry like aviation have to play catch up to the rest of the internal combustion world? The engine can handle the Ethanol just fine. If the subsequent other components cannot do so then find a replacement for those other components. Problem solved. You don't have to give up your favorite pasttime of burning holes in the sky. The world will not come to an end.

I don't see why we can't make the necessary changes to our engine designs to allow for this cleaner burning fuel choice even in our airplanes. Every problem has a solution. This one will too. I, for one, believe that 99.999% of problem solutions do not need to involve any kind of government regulation. That goes for regulations designed to "save" aviation from the ghastly horrors of an ever changing world. So, I sure hope we do not beg and bargain for government regulation in this fuel issue either.

Build your airplanes to new standards and you might find out that those new standards may be better than the old ones.

RVBYSDI
Steve
RV9A Slow Build

rv8ch · #8 04-12-2006, 01:56 AM

Quote:

Originally Posted by RVbySDI

...I don't see why we can't make the necessary changes to our engine designs to allow for this cleaner burning fuel choice even in our airplanes. Every problem has a solution. This one will too. I, for one, believe that 99.999% of problem solutions do not need to involve any kind of government regulation. That goes for regulations designed to "save" aviation from the ghastly horrors of an ever changing world. So, I sure hope we do not beg and bargain for government regulation in this fuel issue either.

Build your airplanes to new standards and you might find out that those new standards may be better than the old ones.

Right on, Steve! The solutions to vapor lock are known, and can be applied to aviation. Gasoline with ethanol works fine in aircraft if you use the right rubber, FI, and take care of vapor lock. Ask anyone flying with an auto conversion.

All it will take is one sensationalist TV report that says that we are spraying lead into the air and avgas could be gone very quickly. We must adapt.

mahlon_r · #9 04-12-2006, 05:02 AM

If alcohol boils off with less ambient pressure, I think it will boil off at altitude more readily vs. sea level. If that happens will the octane of the fuel change because there is less alcohol in it? May be a non issue, may be an important one ? Will the quantity of fuel in the tanks be affected? Some fuels around here has as much as 15% ethanol, a small percent change in fuel consumption due to the alcohol venting off at 10,000 feet might negate the lesser cost of the fuel. Again maybe a non issue but maybe an important one. Another issue is, the blends of automotive fuel vary greatly with season and climate. It is very easy to change climates during aircraft operation on the same tank of fuel but difficult to do in a car. Just thinking out loud...
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Ironflight · #10 04-12-2006, 05:35 AM

I am perfectly willing to acept what I believe to be the very small potential for vapor lock. That only leaves the problem with the fuel system's material incompatability with alcohol - seals and O-rings, I would guess. I have asked this before, and no one has brought forth the answer, so here again is the question - can someone show me a parts list of what needs to be replaced in a stock carb'ed engine to make it compatible? Think fuel tank to throttle body, and everything in between. Honestly, it can't be that many pieces - but do the proper O-rings and gaskets (in the right materials) exist? I don't know.

Disolving seal material is going to potentially give you gunk, and that is worse in my opinion than vapor lock anyway - becasue it doesn't go away. Prevent that, and I'd be a lot more inclined to run Mogas! To me, in order for a risk to aceptable, you need to be able to understand it, to quantify it. Once you've done that, it is a known risk, and you buy off on it with an educated opinion - not a guess...

Paul