Lee's personal website, blog, and FAQ's
RSS icon Email icon Home icon
  • Can ethanol be an aviation fuel?

    Posted on August 15th, 2007 Lee Devlin 22 comments

    A few months ago I bought an engine for the Cozy that is a 200 HP version of the Lycoming IO-360. This engine produces about 20 HP more the standard 180 HP O-360 engine. In order to get to 200 HP, it has higher compression ratio and that requires the use of 100 octane fuel. Today, 100 octane fuel is available at most U.S. airports, but I worried about its continued availability in the future. Aviation fuel, or 100LL as it’s called, uses tetraethyl lead to increase the octane rating of fuel. Adding lead to auto fuel to enhance its octane used to be quite common but fell out of favor when it was found to distribute the lead, now recognized as a poison, into the atmosphere. Just about all countries in the world have discontinued the use of lead as an octane enhancer for auto fuel.

    I began to wonder what I might use for fuel in the future should leaded aviation fuel be outlawed, and my attention turned toward alcohol, ethyl alcohol, to be specific. It’s also called ethanol or grain alcohol and is used as an octane enhancer. It also makes gasoline burn more cleanly. Ethanol is the form of alcohol that you find in alcoholic drinks. Because of this, it is subject to liquor taxes. The only way to avoid paying liquor taxes is to add poison to it. If fuel was drinkable and available for a few dollars per gallon, it’s assumed that no one would bother buying beer, wine, or spirits. With that logic, it’s hard to understand why anyone would buy an 18-year-old bottle of scotch for $75 when Everclear can be had for $10. :-) This poisoning is called ‘denaturing’ and as long as it makes the alcohol undrinkable, just about anything can be used.

    It’s not unusual for auto fuel in the U.S. to contain 10% alcohol since most cars can run on fuel with this concentration of alcohol. It’s beginning to become available at 85% concentrations, called E85, but that requires that the fuel system is compatible with that level of alcohol concentration. Only a small number of vehicles manufactured over the past 10 years or so claim compatibilty with E85 and you can look up whether yours is compatible by searching for “E85 compatibility” on the Internet. Each year, more vehicles are introduced that will run on E85 or regular gasoline and these are referred to as ‘flexible-fuel’ vehicles. There’s even an effort underway to make an aviation grade ethanol called AGE-85 that is not without controversy.

    Back in the 1980s and 1990s when aviation fuel cost about twice as much per gallon as auto fuel, several efforts to qualify auto fuel in aircraft were conducted. They were targeted at older aircraft with low compression engines which were able to run on an aviation fuel called 80LL whose octane rating was close to regular unleaded auto gas. Quite a few aircraft were eligible to burn auto fuel, provided they purchased a placard called an ‘STC’ for about $200. Some airports actually began carrying it as a less expensive alternative to 100LL after 80LL went out of production. However, the tests to get approval for the STC were conducted before alcohol became a common additive to auto fuel. After it became commonplace to use alcohol as an additive, it was found that some aircraft had problems with it attacking the rubber seal materials in the fuel system. The entities that granted the STC, namely Peterson Aviation and the EAA, do not allow the use of auto fuel that contains alcohol. The octane enhancer of choice back in the 1980′s was MTBE, methyl teriary butyl ether, and it had no issues with fuel system compatibility. But it has subsequently fallen out of favor because it has environmental and health concerns. It has largely been replaced by ethanol. Adding ethanol has now become so common with auto fuel, and the difference in price between auto fuel and avgas is not as significant as it was in the 1980s so the popularity of using auto fuel in aircraft is beginning to wane.

    The IO-360 engine I mentioned earlier would not be a candidate for an auto fuel STC anyway because the octane rating of auto fuel available in the U.S. runs about 85-91 octane which is much too low and would damage an aircraft engine designed to run on 100 octane fuel. To get a fuel that had an octane rating around 100 would require using some additive. Otherwise, engine knock, also known as auto-ignition, would create multiple flame fronts that collide in the engine’s cylinders, increasing pressures and temperatures that over stress and damage the engine.

    It would appear that a solution to my concern would be to make the plane compatible with ethanol because it has an octane rating of 105. I recall seeing a group of experimental aircraft showing up at Oshkosh for many years now that all run on ethanol. They are known as the Vanguard Squadron and are shown in the image above. I tracked down one of their members, Dick Pearson, and he generously allowed me to pick his brain regarding his experience of using ethanol in an airplane. Dick has nearly 14 years of experience of using ethanol in 2 separate experimental aircraft that he flies as well as that of the other 4 aircraft in the Vanguard Squadron. He is quite a proponent of the fuel. He told me that there is a lot of controversy and misinformation floating around regarding ethanol. For example, there is a persistent belief that the energy that it takes to grow corn and convert it into ethanol exceeds the energy content of the resulting ethanol, giving it a negative energy balance. This is not true. The reason that this misconception persists is because natural gas is often used in the conversion process to provide heat for making alcohol from corn. But there’s a good reason for using natural gas for heat. The value of natural gas per BTU is much lower than it is for ethanol per BTU. It’s about a third the cost per BTU as ethanol. So even though one could use a portion of the ethanol to provide heat in the process that makes it, it’s not as economical as using natural gas for heat. It’s this business of using a fuel other than ethanol to help make ethanol that leads people to believe that it has a negative energy balance. It actually has a positive energy balance widely accepted to be around 1.34, or getting a third more energy out of the process than is put into it. That takes into consideration the energy required to fertilize, plant, irrigate, spray, harvest, transport, and convert the corn into alcohol.

    Energy balance is only part of the equation, since when you talk about energy you must consider more factors that the energy balance or cost/BTU. It’s also important to consider factors such as energy density, convenience, and fuel compatibility. This is particularly true when it comes to transportation fuels since there is high value to having a fuel that is compatible the existing engines. If energy balance and cost/BTU were the only measures of concern, we might see coal-fueled vehicles since its cost per BTU is about 10% of what we pay for gasoline.

    In Brazil where they make alcohol from sugar cane, they are able to burn the waste parts of the sugar cane called bagasse to generate the heat needed for the process. As a result, they get 10 times more energy from the sugar cane than is required to grow and convert the sugar cane to ethanol. This is similar to the energy balance expected with cellulosic alcohol.

    A number of companies are working on deriving ethanol from cellulosic plants instead of corn kernels. These materials include waste products such as wood chips, corn and wheat stalks, and other organic waste materials that have limited use today. In most cases, you have to pay someone to dispose of them. The processes that convert cellulose to alcohol are currently not mature enough to be cost competitive with making ethanol from higher-value materials like corn. However, there are a number of companies working to improve the processes and if they become competitive, it could reduce the cost of ethanol to be lower than gasoline in a direct fuel mileage comparison, and when that occurs, it has the potential to change everything.

    Some cellulose-to-alcohol processes are based on enzymes that can unlock the sugars in cellulose and convert it into alcohol using conventional fermentation. There is an ethanol plant in Canada already doing this as well as a few more under construction. There is a also a non-fermentation process developed by Range Fuels of Broomfield, Colorado that can convert cellulosic materials to alcohol. Range Fuels is building a cellulose-to-ethanol plant in Georgia that will be capable of producing 100 million gallons of ethanol a year from wood chips. I think this will substantially change the perception that ethanol is nothing but a farm subsidy, which is the view a lot of people have about it today. Can you imagine a lawn service where they reduce the fee if you let them take away the lawn clippings, leaves, and other yard waste? I think that would be a huge step in the direction of energy independence because recovering energy from local waste materials would reduce an energy supply chain that currently extends around the globe to a short loop within your own neighborhood. It would also reduce CO2 emissions because plants generally release their carbon back into the atmosphere in a relatively short time, and so instead of digging up carbon that has been buried for millions of years, we’d be able to use carbon that was essentially on its way back into the atmosphere anyway. [UPDATE 2014-02-26] Range Fuels burned through $234M in capital, about a third of it from taxpayers, before shutting down operations in 2011.

    There are a lot of competing and complementary renewable energy technologies under development including wind, solar, and biomass. I don’t think that there will be a single winner in the race to replace our convenient yet exhaustible fossil fuels. I feel a lot more optimistic about it after doing my own investigation of alternatives like ethanol instead of listening to pundits arguing for or against it, because it doesn’t take long for people to get emotional about their point of view when it comes to renewable energy. I guess that’s because mixing politics with science can be such a volatile combination. Now if only that volatility could be converted into usable energy our future would be secure!


    22 responses to “Can ethanol be an aviation fuel?”

    1. So, are you going to convert your IO-360 to use E85? After reading your article I got the impression you are considering it.

      I’m building a RV9 and considering using a O320 with E85, or a Delta Hawk Bio-Diesel engine. I haven’t decided at this point in time.

      Anyhow, great article.

    2. Hi Allen,

      Thanks for your comment on the Ethanol article. The conversion only involves resizing the jets on the fuel injectors so that it will have more range with respect to the mixture. Ethanol requires approximately 30% higher stoichiometric ratio than gasoline. You can still use gasoline as long as you remember to lean the engine. That’s not a problem for me since I live at nearly 5,000 feet and I never run full rich anyway.

    3. Lee:

      I’ve been researching the effects of auto fuel with enthanol in my 0320 RV4 and came upon your blog. I’m still a bit confused about whether it could be used in my carburated engine. I’m currently using auto fuel without ethanol mixed with 100LL. What are your thoughts on using auto fuel with ethanol? Will it cause a probem with the carburetor? You have certainly come a long way in aviation since those long ago days at N57. Do you remember the Long EZ ride? Look forward to hearing from you.


    4. Hi Allen,

      It’s truly a small world. Imagine getting a blog comment from the man who changed my life by giving my very first LongEZ ride about 15 years ago.

      I will send you an email with the my questions on your O-320 setup because I’d like to know if it’s a high or low compression model. I know that in order to use a high concentration of ethanol, the stoichiometric air-to-fuel ratio has to be able to be adjusted to about 9.8:1 vs. 14.7:1 on a regular engine. I’m not sure that you can manage that with the mixture control alone.

      In the case of fuel injected engines, they re-jet them and then the only issue is that it’s possible to have them so rich at sea level with AVGAS that you have to lean them to get them to idle correctly. So rejetting may also be required for a carburetor to get full HP at sea level when running high concentrations of ethanol.

    5. I to am very interested if you can run e85 in IO-360. I have a Piper Arrow and I know I would have to wait to an STC to be approved.

      I am cosidering a homebuilt and the thought of a more affordable (and better)fuel heightens my interest.

      I need more information to help with $$$ decisions.

    6. Jocke Berglund

      Hi Lee, I`m flying a Enstrom 280 helicopter in sweden. In europe 100LL cost about at least 3 dollars per liter. So here we are very interested in any alternative. For me, an alternative would be to run my HIO-360 on auto fuel mainly due to the few places that has 100LL. Whit an helicopter there`s no big problem to land next to a auto gas station and carry a couple of fuel cans to fill the chopper up. Whats interesting is, that I read on http://www.verticalmag.com that Lycoming this fall, is announcing stc:s targeting on IO-360:s to run on autofuel. So look out for Lycomings news in august. I actually was looking if Lycoming said anything about Ethanol, but nothing came out on there webpage. Strange if all aircraft engines one day must be grounded only because Lycoming disregards the fact that fossil fuel is coming to an end….
      Joakim Berglund Stockholm Sweden

    7. Hi Joakim,

      I believe that in Europe, auto fuel is 95 octane which may be sufficient for aircraft engines. In the U.S., sometimes the highest fuel octane available is 91 octane, especially around Colorado where I live, and they often use ethanol to get it to that level. Ethanol in low concentrations can have problems, because it prevents you from being able to drain water from the tank. If enough water gets in, it can cause the alcohol to combine with the water and to separate from the gasoline, and so there’s concern that it might cause the engine to run rough or stop because the ethanol/water combination may not be very flammable with only 10% ethanol concentration to start with in the tank. If the alcohol is in high concentrations, like 85%, then this problem isn’t likely, because it would take a lot of water to make the fuel non-flammable.

      I saw an announcement from Lycoming last week through Avweb, which described a ‘paperwork process’ with the FAA to approve a 93 octane autofuel that will be compatible with Lycoming engines. It’s not just any 93 octane unleaded auto fuel, but rather one that is based on Euro Norm EN228 (in Europe) or ASTM D4814 (in the U.S.) with some additional specification. This is actually very good news. They expect approval this fall.

      Airframe approval would have to be separate.



    10. I’ve been burning “high test” auto fuel in my Cozy since completing it in 1996. It has a low compression Lycoming O-320 E2D. I, too, have had concerns about dissolving anything, but at this point, the only problem I’ve seen is the fuel site gauges are somewhat cloudy. Otherwise, auto gas burns cleaner and there is no plug fowling. My auto fuel of choice has always been BP (British Petroleum). Comments?

    11. [...] previously wrote about using ethanol as an aviation fuel. After noticing that the national average for aviation fuel is now around $4.60/gallon, and E85 is [...]

    12. I am currently taking classes trhough Embry Riddle to gt my Air Frame /Powerplant license. I liked what was mentioned about getting the alcohal from other bio waste suh as wood chips, stalks from corn along with other things. It seems to me that there must be a big spin comming from the oil companies disguised as everday folks that think this process is too costly. The resources are there. So anyway.. How his the ethanol working? Maybe someday they can develope bio type fuels for turbine engines. B-52 and C-17s have flown on synthetic fuels.


    13. Hi Lee,
      It has been a little over three years since you made this blog post. These days it is not possible to buy autofuel without 10% ethanol in Maine (and most of New England).

      I am interested in using autofuel with 10% ethanol in a high wing experimental aircraft (Glastar) that has a 150hp Lycoming O-320-E2D in it. I’m pretty sure that the rubberized components in the fuel system, carb, etc should be fine with the 10% ethanol, and the engine will run fine with it as well. My primary concern is water, and phase separation from the ethanol at an inconvenient time.

      My question is, do you think that the gascolator in the fuel system will capture the water so that it will not make its way into the carb? Could you imagine enough water phasing out as to completely fill the gascolator then allowing it to continue to the carb?

      There is also a possible concern with the water separating from the ethanol, and then freezing during the winter months, but it would seem the likelihood of this happening is pretty slim.

      Do you know of anyone successfully using autofuel w/ 10% ethanol in their aircraft?



    14. Hi DJ, There is a lot of FUD floating around about ethanol in fuel. I can’t address it all, but the issue of material compatibility is pretty much over. Virtually all fuel components like hoses, seals, and fittings now are tested for ethanol compatibility. No one is using any materials that are vulnerable to ethanol.

      If you are worried about water getting in your fuel, please be aware that alcohol is often used to remove water from gas. Dry gas (which is usually made of methanol) is miscible with water and will make any of the water that’s collected in your tank a combination of water and ethanol. That reduces the water’s freezing point to a lower temperature while at the same time, making the combination of water and alcohol flammable, thereby reducing its harmful effects.

      If I were you, I’d experiment with one tank of auto fuel and one tank of AV gas until you were confident in the autofuel performs to your expectations. If you survive this experiment, you’d be best off not to tell anyone, because they will try to convince you that it is impossible and that anyone who ever flew with ethanol-based fuel died in the process :-).

    15. Hi Lee,
      I’ve been doing a bunch of research since I posted yesterday. Found a very interesting study that you can access at

      Essentially, you’d have to get more than a cup of water in a typical aircraft fuel tank before it would phase separate. IMHO if you have that much water getting into your fuel system, you are going to have problems no matter what fuel you are using (unless you can burn water, of course… :-) Water being absorbed via the fuel vent is essentially a non-issue as it would take several months at 100% humidity to get enough into the fuel to worry about.

      Also, read interesting discussions at these links:



      Short version is that I think it is reasonable to use E10 in an experimental aircraft. There is still an unknown in my mind whether you need fuel injection versus a carb, and there seems to be some concern about the diaphragm used in the mechanical Lycoming fuel pump, so I still have some additional research to do.

      However, so far it looks very possible.


    16. Using the 100 octane rating of Avgas and auto fuel numbers is incorrect. Auto fuel ratings are arrived at by adding motor method and research method rating and dividing by two. An approximate rating can had by adding six points to the pump value. I have successfully run high compression Continental and Lycoming engines on premium auto gas. In hot weather, run your boost pump for takeoff and climb.

    17. Hi Lee
      Glad to see that others are interested in flying with ethanol. Generally if you mention ethanol in a group of pilots you get rolled eyes and sneers. I am considering e85 ethanol for my O235 long ez. However, hi compression pistons will be required for optimum performance. This engine would be almost identical to the Cessna 152 powerplant that Professor Shauck at Baylor http://www.afdc.energy.gov/afdc/pdfs/2896.pdf
      had type certified. For a fiberglass aircraft the biggest job may be re-engineering the fuel tanks and strakes. I have seen complaints in EZ forums about pump gas with ethanol attacking the resin. Even small amount of softened epoxy will plug a fuel screen! Have you tested any coatings that would prevent the epoxy failure?

    18. Hi LRP, Before using alcohol in my tank, I’d test coupons made up of the material the tank is sealed with. In my Cozy, I used EZpoxy with 87 hardener which has the best reputation for fuel resistance of the commonly used epoxies. The rest of the airframe is built with MGS, but it has no history as far as fuel compatibility, so I didn’t want to chance it. I know that guys have run mogas with the standard 10% alcohol concentrations, but don’t know anyone who has run E85 in a fiberglass tank. Other coatings that are known for fuel resistance are Pro-seal and equivalent sealants that have been around for decades and are based on a MIL spec S-8802. It’s sold in various consistencies and by several companies. Here is a good article describing it. The Vanguard squadron have RVs, and those guys seal their tanks with this type of sealant and I’ve heard of no problems with tank leaks and they’ve been running pure ethanol (with 5% mogas for denaturing) for decades.

    19. Frank W. K. Hall

      Regarding you comments on how alcohol may be denatured: Ethyl alcohol, or ethanol, will only be lawfully denatured when made according to a specific formula that has been approved by the Treasury Department. Some formulas are published for public use. Application can be made to use a “proprietary formula”, but approval must be obtained before using any proprietary formula. For tax purposes denatured alcohol is classified as either “Specailly Denatured” or “Completely Denatured”. Specailly denatured alcohol (SDA) uses less obnoxious denaturantes as it is used in products that come into contact with the human body, such as mouthwash, skin or hair treatments, and room deoderant sprays. The use of SDA is regulated and can only be used for approved purposes. Completely Denatured Alcohol (CDA) is made to be poisonous and is not fit to be ingested by or come into contact with, the human body. There are very few standard formulas for CDA, but gasoline or benzine is an approved denaturant for CDA. Ethanol imported in bulk for use in blending with gasoline is ordinarily already denatured with gasoline. A CDA denatured with gasoline would seem to be particularly suitable for the use you propose in aviation fuel. regards, F. W. K. Hall

    20. Aviation fuel is a specialized type of petroleum-based fuel used to power aircraft. It is generally of a higher quality than fuels used in less critical applications, such as heating or road transport, and often contains additives to reduce the risk of icing or explosion due to high temperature, among other properties.

      Thanks for the post

    21. Being born and raised in Brazil, I got used to ethanol as a motor fuel not just for aircraft. But anyway, in the last 60 years the general aviation piston-powered engines didn’t seem to have evolved as much as car engines in the same timeframe, and it does make harder to enjoy the advantages of ethanol, either pure or blended with gasoline. Liquid-cooled engines tend to tolerate higher compressions better than the ancient air-cooled Lycoming and Continental ones that are still prevalent on the market, while a FADEC could provide a single-lever operation of the engine comparable to a Diesel or a turboprop and finally getting rid of carburettors that are more likely to an ice build-up and fixed-point ignition systems not so suitable to the needs of a flexfuel engine able to burn either the AvGas while it’s still there, MoGas as a more affordable alternative, or ethanol wherever it’s available, and any blend of those fuels at any proportion.

    22. I’m all for ethanol. I run E85 in my heavily modified Subaru WRX. The only downfall I see for use as an aviation fuel is range. In order to get the same range out of a plane you would have to carry more fuel making you heavier and reducing payload. Everything else is purely based off of myths or sheer lack of understanding as to how the fuel actually works, mostly moisture in the fuel. The only thing incompatible about some vehicles and E85 is the size of their fuel system. With a large fuel system every vehicle or motor can run on E85.

    Leave a reply

    CommentLuv badge