Everybody says ethanol in auto gas is a bad idea. But, it's a fact. I have a question about what could be done specifically to an engine installation to make E10 safe to run, if you were going to run an experimental Lycoming. I'm not interested in talking about clear fuel availability, or if it's better or worse than 100LL. I'm interested in what happens to the engine.

Rotax says up to 10% ethanol is okay for their little 4-strokes. More conventional aircraft engine manufacturers are saying that 91 octane unleaded auto fuel is ok for low compression engines, but ethanol is still not allowed. Even the line of experimental Lycomings sold as "[url=http://www.xp-series.com/]XP Series[url]" by Superior state that while 91 auto fuel is fine, that ethanol is not.

What's technically different about these two engines, save for the amount of test data they can present if challenged, that would make E10 okay for the small displacement carbureted 4-stroke, but not for the larger displacement carbureted 4-stroke?

As far as I know, the issues with ethanol enriched fuel are 1) its ability to hold water in suspension until...it doesn't, thus fuel contamination, and 2) fuel system corrosion. What if you're designing your own fuel system and you harden it to solve these things?

Considering that a guy had a fuel system that was exactly like his Rotax-powered light sport, and wanted to run E10 because that's all that was available, what is going to fail? I'm interested in specific fuel system components, or empirical data on water contamination pathology. Thanks.

I built Long eze Lyc O-235 L2C with EI and ran it on all aspects of auto fuel and 100LL. I had the JPI w/FF to monitor and record the data. I had the engine driven pump rebuilt by an auto re-builder and was told that the diaphragm was ethanol safe. I drilled out the main metering jet in the carb, started small and kept making it bigger and was finally running E-85 auto in it. I found that the engine performs great on the fuel. The ethanol pulls heat out of the oil pan sump and the engine runs cooler. I found if I let the airplane sit for a couple of weeks after running E-85 some of the internal Al parts in the carb and cyl intake ports would be so clean they had corrosion. To run 100LL you just cant use full rich, pull the mixture back to a good egt and it runs normal. That engine will pull 3000 rpm 11gph on 100LL and 3200 RPM and 15gph on E-85. I put E-85 in an old truck and the fuel pump diaphragm went out within minutes. After the pump rebuild, and drilling out the main metering jet it got better fuel economy than 87UL. The engine in the truck was a Chevy 292 inline 6 with high compression. The timing was 5 ATDC with 87UL and I could bump it up to 10 BTDC with E-85.

I've been using E50(50% ethanol)in an unmodified 1992 Toyota 4x4 with 22R-E engine for a little over 11 years now with no problems. I have a mixture meter tapped int the oxygen sensor to prove it isn't running lean. I've never changed the fuel filter yet and it has an aluminum runner that the fuel injectors tap into. Fuel pump is original also.

If you want to use AGE-85 (88% ethanol,11% pentane and 1% biodiesel)in a Texas Skyways O 470 UTS in a 180 or 182 the only change is to increase the size of the jet in the carb and make sure you have nitrile rubber fuel bladders in the wings. The biodiesel is to coat the cylinders and lines to prevent corrosion when not in use. If you're using E10, the combustion chamber of a Lycoming really shouldn't know the difference.

I know of a Marvel carburetor that was taken apart after several years of E10 use and the shop said it looked great inside. They replaced the older metal float with one of the new blue ones.

One of the big issues has to do with rubber components, seals, etc. If a fuel system does not have the right materials in it you will start finding leaks, plugged up filters, fuel bladders dissolving , plugged jets or injectors, etc.

Lycoming and Continental know that the fuel systems in most of the aircraft flying today were not built with materials meant to handle ethanol and that the introduction of fuel with ethanol in an airplane not ready for it can cause major issues. Even the experimental guys have discovered that if they are running a Rotax 912 which is approved for ethanol they have to watch out for unlined fiberglass fuel tanks and bad hoses that can clog up fuel systems. The problem has more to do with material degradation than the engines ability to burn it.

My answer has to be, why take the chance? Over my typical year, I would save $1150 in fuel costs if I burned regular mogas instead of 100LL. As long as I sump my tanks every time I fly, I'm unlikely to take off with contaminated fuel. While that's not a guarantee that I won't have an engine failure, if that happens, it won't be because of contaminated fuel or because the fuel damaged any of the fuel system components.

Do I like paying that additional amount? No, but what would it cost me to buy mogas? I'd have to truck it in somehow, or I'd have to fly to one of the only 2 airports in eastern Colorado to buy it, neither of which makes much economic sense. I suspect I'd burn up whatever I saved, flying to those airports or purchasing equipment to tanker the mogas to my airplane--and then I'd have the risk that my 50 year old airplane's pieces and parts would start to disintegrate under the effects of the mogas, so that I'd have to pay my IA to fix those. There goes any savings!

The other piece of "why take the chance" is that many of the places I fly have limited places to land enroute. I'd just as soon that my engine didn't hiccup along the way. If it costs me an extra thou each year to minimize that possibility, I'd rather pay it.

Cary

some older continental engines were originally equiped with a rubber tipped needle valve in the carb. ethanol will cause this rubber tip to soften and swell up untill it sticks in place.

Long-chain carbon molecules have complicated reactions with each other - fuels come plastics come synthetic rubbers come polymers. Some will disolve others in 5 seconds flat, like mixing petrol and polystyrene, and others are fine forever.

Unless you know all the bits in your system are, that are ultimately made from oil products, it's really hard to say what will happen if you get ethanol on them. Even then, who knows exactly reacts with what, except some very clever chemists.

In the Precision/Marvel-Schebler carburetor itself, the float should be updated to the purple indestructible one and it is a recommended update anyway plus the seat valve needs to be brass. For more specific questions on effects of ethanol on aircraft engines you cannot do better than the experience of the Vanguard Squadron at Tea South Dakota who have been doing airs shows for the better part of two decades on 100% ethanol. Here is a good discussion by one of the members. http://www.vansairforce.com/community/s ... hp?t=58334

Thanks for posting the Van Guard article---I hadn't seen it before. I remember talking to a guy at Tea about ten years ago. He said he ferried the planes to shows once in a while for the team and said they preferred ethanol right from the plant instead of AGE-85.

Ethanol is fine, but there are a couple drawbacks. First, it is hydrophilic, and can introduce water to components. I've seen ferritic fuel system components rust when a user switched to alcohol blends (cars). In addition, alcohols are not particularly innocuous to a lot of elastomers. Viton replacements yield good resistance to swelling or deterioration to even straight up alcohol. Some other types swell up into fat cheerios and slowly turn to a gooey mess. You can change the elastomeric components and packing to compatible types. It's a fixable problem.

I'd like to hear from folks running ethanol with bladders though...the examples I have seen are expensive crackly messes, and the owners were running ethanol fuels (legitimately or not). I would be gun shy personally unless I heard success stories with bladders.

Second, the energy density of alcohol is lower, and you'll have to burn significantly more to generate the same HP in most cases. The heat of vaporization also means the mixture burns cooler, leading to lower efficiency (some people claim the cooler inlet charge is an efficiency advantage, but thermodynamics and dyno tests quickly get rid of that idea). For carbureted engines, there is a greater potential for carb ice from this problem as well. Vapor pressures are higher, and this means some machines might be able to vapor lock more easily. We already know that some mogas blends present vapor lock issues in some certificated installations, and ethanol blends in experimental ships have led to a lot of gray hair flying up at higher altitudes.

On the other hand, a pure alcohol or specifically blended fuel can be used in an engine with a much higher compression ratio, and can be operated with a better ignition advance ratio. These items *can* increase efficiencies to more than overcome the vaporization (enthalpy) and energy density issues by simply improving thermodynamic efficiency. Alcohol also burns cleaner. Gasoline/alcohol blends, even high alcohol blends, seriously detract from the potential gains alcohol offers...the petroleum fractions limit compression and advance ratios.

I hope someday that we'll be able to fly our older certificated planes with the range of available mogas fuels, even if we had to use supplements.

If you get water in your fuel and fly into freezing conditions it can freeze in the line. Now you are a glider. Or so I have been told.

G'Day...Rob

Couple of interesting comments----ethanol has a high vapor pressure. It has a very low vapor pressure by itself and the reason the Van Guard team needs a little tank of gasoline to prime and cold start. The other is that ethanol carrying a little water will freeze in the lines----ethanol is like anti freeze. Diesel 911 contains alcohol to try and get a frozen fuel line on a big truck flowing again--it doesn't add to the problem.

See the Parker Seals Compatibility Tables in Section 7 here:

http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

Ethanol scored 'unsatisfactory' for use with:
Polyacrylate ACM
Polyurethane AU, EU (some floats?)

...and 'doubtful' for use with:
Nitrile NBR (some needles?)
Hydrogenated Nitrile HNBR
Fluorocarbon FKM (many o-rings?)

...and 'fair' for use with:
Silicone MQ, VMQ, PVMQ (many o-rings?)

To me, 'fair' is not acceptable.

Other materials, like leather (primers?) are not covered in the Parker table, but we've had collective negative experience with already.

180Marty wrote:Couple of interesting comments----ethanol has a high vapor pressure. It has a very low vapor pressure by itself and the reason the Van Guard team needs a little tank of gasoline to prime and cold start. The other is that ethanol carrying a little water will freeze in the lines----ethanol is like anti freeze. Diesel 911 contains alcohol to try and get a frozen fuel line on a big truck flowing again--it doesn't add to the problem.

Vapor pressure: the vapor pressure of alcohol by itself is the same as when in a blend (the partial pressure isn't the same of course). The issue is temperature vs vapor pressure. Ethanol has a non-linear vapor pressure vs temp function. As it warms, its vapor pressure rises quite fast. The vapor pressure of alcohol blended fuel at 100F is roughly 15% higher than the gasoline blend alone...in fact, the fuel has to get a waiver from the laws meant to reduce air pollution from evaporation. It's called the 1 psi waiver, I believe. It is significant enough that it sometimes has to be blended as late as possible to avoid lock problems in distribution centers. And yes, alcohol is stubborn to start with when cold. Butane and other lighter petro fractions are often used in winter blends to help with starting at the lower vapor pressures.

Ethanol won't cause the water entrained in it to freeze...but that isn't the problem. The enthalpy of vaporization causes the induction system to cool down...a lot. Carb ice is is generated from the intake of atmospheric moisture, not significantly from fuel moisture entrained in the fuel. Folks frequently comment on carb ice when converting an old muscle car to pure alcohol....the problem is real, but vulnerability depends on the specific case.

OregonMaule wrote:If you get water in your fuel and fly into freezing conditions it can freeze in the line. Now you are a glider. Or so I have been told.

G'Day...Rob

Isn't this true of any fuel?

But I guess you are saying that the potential to have water held in, and then come out of suspension is greater with ethanol enriched fuel?

In a Cessna Owner magazine article back in the 1990's, Texas Skyways using AGE-85 in their O-470 UTS said carb ice was a non-issue. On the vaporization and temp comment, ethanol is very low VP when cold but goes up a bunch when hot??? is this where the term heat of vaporization comes in?

180Marty wrote: On the vaporization and temp comment, ethanol is very low VP when cold but goes up a bunch when hot??? is this where the term heat of vaporization comes in?

I believe "heat of vaporization" refers to the net heat energy that's released or taken in during the process of vaporization or condensation.

jet966 wrote:See the Parker Seals Compatibility Tables in Section 7 here:

http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

Ethanol scored 'unsatisfactory' for use with:
Polyacrylate ACM
Polyurethane AU, EU (some floats?)

...and 'doubtful' for use with:
Nitrile NBR (some needles?)
Hydrogenated Nitrile HNBR
Fluorocarbon FKM (many o-rings?)

...and 'fair' for use with:
Silicone MQ, VMQ, PVMQ (many o-rings?)

To me, 'fair' is not acceptable.

Other materials, like leather (primers?) are not covered in the Parker table, but we've had collective negative experience with already.

If you look at the row for "gasoline," it also scored several fair and unsatisfactory ratings for various O-ring materials. Some materials scored "satisfactory" (Hifluor FKM, Perfluoroelastomer FFKM) both both gasoline and ethanol. Why not use those components in your fuel system?

Viton is a fluorelastomer that ranks as "adequate" or "marginal" with alcohol/gas blends. It works, but I think you are right about it being less than ideal. Alcohols are really rough on a lot of plastics and elastomers...it is hard to design with. Vitons are among the best materials to use around gasoline/alcohol blends it seems though. Teflon cold flows and is asking for trouble unless it is used a bit more carefully.

Treefeller wrote:But I guess you are saying that the potential to have water held in, and then come out of suspension is greater with ethanol enriched fuel?

The water in the fuel really doesn't seem to be an issue for carb ice. I mentioned it was an issue for corrosion...it's fairly common in the car world. That is a minor issue in my mind, given that it hasn't pulled airplanes out of the sky. The larger issues for me are:

1) vapor pressure.
70 degree F alcohol boils nearly a couple thousand feet lower than mogas, and several thousand feet less than avgas. We know there are folks out there with vapor lock issues burning alcohol blends at moderate altitudes, and even some with issues burning alcohol free mogas (hence the lack of stc's for some birds). Avgas is formulated with a lower vapor pressure than mogas to help with this issue.

2) elastomer compatibility.
This is a fixable problem for most folks I would hope, but perhaps not for sure...I have bladders and am skeptical.

3) Carb ice.
The alcohol blends drop the temp of the carb a lot more than gasoline alone, and this means that atmospheric moisture can form more readily. My 182 makes ice...which sucks, but it really does as soon as the carb temp needle is well into the yellow zone and there is visible moisture/haze. I think it might make more ice if I used alcohol.