Flying with ethanol in your mogas (petrol)

[Sam Rutherford]

I have a question about a, hopefully, theoretical only situation.

I am in Africa, my only way of getting out from where I am is to use car fuel (mogas). I then find that it has the 'normal' amount of ethanol blended in.

It's an 'emergency', can I still use this for a 3 hour flight to an avgas supplying airfield?

I know of the vapourisation problem at high temps, but is there any other immediate effect? Mostly what I read/heard about is with regard to longer term engine/hose damage.

Another factor is of course how much are you adding to the avgas already remaining (10%? 90%?).

For my example specifically, the aircraft is mogas approved (and not just a paper exercise, but with upgraded fuel lines, upgraded fuel pump and a fuel pump cooling air-scoop).

I know that you shouldn't - but I'd like to be aware of everything before finding myself in a position where options might be (extremely) limited.

Thanks in advance for your thoughts/ideas...

Sam.


PS I am aware that this would be an illegal flight - like I said, in an emergency...

[Pilot DAR]

In an emergency, Mogas which contains Ethanol, will work. Its negative characteristics are mostly long term affects, other than ice, which can happen fast in the correct conditions. If you have chosen to use an emergency fuel, which does not conform to the Mogas STC, and are accepting the risks of the several distinct problems you may be creating for yourself, You will be best if the emergency fuel is blended into approved fuel at the lowest practical concentration, and then the unburned fuel is removed from the system right after the flight. Even draining fuel from an aircraft in that amount has its serious risks for safety. When you exceed 10% of non gasoline in your fuel, your are into territory beyond the scope of this brief message - do not do it without aviation regulatory approval. Such an approval would be an STC.

Ethanol fuel itself is generally suitable for burning in an aircraft engine, its getting the fuel to the point in the engine where it is to be burned, and assuring that water does not accompany the fuel to that point, which are your challenges. I have about 20 hours flying an ethanol test Cessna 150, which was flown on pure ethanol for more than a year. With all of the proper controls and changed operating techniques, it worked perfectly fine. The aircraft was very modified, and there were demanding operating techniques, but it was safe, and did not harm the engine.

Enthanol is not an approved avaiation fuel additive for the following reasons:

It has a much lower energy density, so you have to burn a lot more to get the same power = more fuel flow, larger fuel lines, less range (in the order of half). All of the flight manual's performance information goes out the window.

It will hold water, which will separate out later, and either not burn when you want it too, freeze when you don't want it to, and/or corrode the expensive and hard to inspect insides of your fuel system.

It will attack the non-metallic elements of your fuel system. If your aircraft has bladder tanks or a wet wing, I would not even consider it - replacing rotten bladder tanks is expensive!

Proper planning prevents poor performance - plan to not need to use emergency fuel, you will stay safe, legal and insured, and won't have to worry about fouling up your fuel system.

Pilot DAR

[shortstripper]

Makes you wonder why they're so keen to see it used in car engines! To keep the garages active perhaps?

SS

[Pilot DAR]

I don't want it in my car engine either, so I drive a diesel!

[EchoMike]

I'd be quite interested in the exact modifications done to the 150 to run it on ethanol.

I'd also be interested in the new operating procedures, and in the results of flight testing.

I know about the water to ice problem, but I think the original poster is somewhere in Africa where ice isn't going to be a problem - and I'm in Florida, where ice is definitely not a problem.

I've got some aircraft O rings sitting in a jar of ethanol right now, they've been there a month, submerged, and show no changes, they don't even leave black stains on your fingers when you rub them.

The Autogas STCs from EAA and Peterson say "no alcohol" at all, so even 10% is illegal (although in practice, it appears to work just fine).

Purdue University STC'd a 152 for pure ethanol back in 1996, they found the engine made slightly more HP than stock and had to be derated a bit because a 5% increase means recertification. They had a gallon container of avgas on the firewall for easier starting, once the engine was running they switched to 100% ethanol. Range was decreased about 20%.

Someone else STCd a 150 for 100% ethanol also, I have the STC number, but no real information yet.

I'm interested in doing this on my 150 (which has the long range tanks) so the range isn't a problem for me. I'd be very interested in your comments and results of this experiment.

Best Regards,

Echo Mike

[Pilot DAR]

The modifications were mostly a major change to the fuel system and instrumentation. Larger fuel lines all the way around, long range tanks installed, a gasoline tank on the firewall ("football" tank out of a Cessna 185), with a filler just in front of the right side windshield. A valve to allow you to start on the gasoline tank supply. The carb was rejetted and had a metal float, and a fuel flow indicator added. I recall that the only change to the engine was the use of C90 high compression pistons.

The range difference was more like 60% of the gasoline range. Fuel flow during pure ethanol takeoff was more than 11GPH, where 6 or 7 would be standard on gasoline. Starting could be challenging, though it always worked. Running pure ethanol worked quite well, though the plane was about useless to carry more than fuel and the pilot. The way the W&B worked out, with full tanks, and by 180 pounds, I could carry a light passenger, and that was it. Not a thing in the back.

Operationally, the challenge came when you mixed ethanol and gasoline. The mixture worked well, but correct leaning was vital, and not easy during the takeoff roll. If you think its challenging setting power during the roll on a turbo, or turbine, you should try leaning during takeoff, when you have no idea what the optimum fuel flow should be. It also varied based upon how well the two fuels were mixed in the tank. When adding gasoline, you had to stir it up as much as possible, to even out the blend, otherwise the mixture could vary on its own. Frequent attention was needed.

This made range planning extremely crude. For this reason, the required performance charts were impossible to develop. That was on of the major show stoppers for STC approval. We also felt that the operational challenges would be too complicated to train the average pilot, and engine damage, or fuel exhaustion accidents could result. The other aspect was that this was ten years ago, so there was little demand to operate on ethanol, and it was hard to get and expensive. The need for the mod just was not there.

If the mod were to be done, and the aircraft never operated on gasoline, this would be approvable. ATSM published a very good book called Future Fuels for General Aviation, by Cesar Gonzalez (of Cessna at the time) and Kurt Strauss. I highly recommend it. The ASTM website is where to look for it. Staff at the university in WacoTexas are also very familiar and experienced with this fuel. One professor who I met a number of times flew transatlantic in a homebuilt on ethanol.

I hope that helps,

Good luck, approval will be a challenge,

Pilot DAR

[astir 8]

DAR's tale of running on "pure" ethanol is interesting but slightly off Sam's original question. Sam is dealing with a mogas/ethanol blend which will almost certainly be less than 10% because that is the threshold (a not entirely scientific one) which most major car manufacturers will accept as a standard fuel without it affecting performance, fuel consumption, warranty etc. so that is what most standard mogas blends peak at.

Brazil runs about 24% ethanol in its standard gasoline but Brazil builds its cars to suit.

Ethanol for blending with gasoline has to be "anhydrous" - e.g. over 99% pure. At blends of less than about 10% the extra oxygen available in the ethanol assists the combustion process. As an octane enhancer ethanol has been substituted for a (rather environmentally nasty) gasoline additive called MTBE in unleaded gasoline in many parts of the world for a number of years now. At those blend ratios, because of the oxygenation effect there is no loss of power resulting from ethanol containing less energy/litre than gasoline.

There were problems with older vehicles when ethanol blends were first introduced as the ethanol could attack flexible components in the fuel system but these days all vehicles are ethanol resistant. There were also problems that a lot of older cars contained build-ups of gums and other deposits in the tanks which were dislodged by the ethanol and bunged up downstrem items like carb jets. Again not applicable to modern cars as the crap hasn't built up.

However those two problems probably caused many of the urban myths concerning the evils of ethanol blends.

Now "pure" ethanol as operated by DAR would have been hydrated ethanol which contains about 4% water (it takes a lot of effort to turn hydrated into anhydrous ethanol). Pure ethanol contains much less intrinsic energy than gasoline (19.6 MJ/litre compared with 32 MJ/l for gasoline). Hence fuel consumption for the same power output has to be greater, hence more fuel has to be carried and DAR's problems with weight.

Engines dislike starting on pure ethanol, therfore DAR had to have his little tank of gasoline for start-up - just like the old tractors which ran on kerosine.

Where does all this get Sam? The chances are, his available mogas blend is somewhere between 5 and 10% anhydrous ethanol. Fuel icing would not be an issue because there isn't any water in anhydrous E. If his engine has been converted to mogas it would have been recently, so the chances are that his flexible bits are ethanol resistant.

However if his engine manufacturer says "no ethanol" there are either (a) good reasons or (b) like most suppliers they are leaning way way on the side of caution just in case. However, large chunks of the world's mogas supplies already contain some ethanol as an octane enhancer whether the fuel companies have publicised it or not.

Most likely his engine will be fine. Can't say more than that though!

P.S. "Flex fuel cars" use the engine management system to adjust the ignition & injection systems to run on anything from (almost) straight gasoline to (almost) straight ethanol and there are no engine management issues. We'll probably all be driving flex fuels in a few years because they'll be built as the standard unit.

[Mickey Kaye]

Why an earth aren't modern aircraft design to be able to run on mogas with an ethonal percentage? If cars can be made with ethonal resistant O rings, fuel tanks and fuel pipes etc why can't planes. And I am not conviced problems with icing and vapour locking in fuel pipes can't be overcome.

What about ROTAX engines that run best on MOGAS are they able to take MOGAS with an ethonal percentage?

AVGAS is price is sky high and it this case pretty hard to find. MOGAS maybe a way forward.

[Pilot DAR]

astir 8,

Thanks for that informative post, I can always learn more! While agreeing with everything that you have said in the context of today's world, most aircraft still require fuel conforming to yesterday's world. Therefore, the list of approved fuels for most aircraft, even those having a Mogas STC, will not include fuels containing more than deicing amounts of alcohols. As you can appreciate from my previous post, this is not because it won't work, but more because it won't work exactly as it did before. This makes operating and performance data (that which lawyers tend to introduce during the liability trial, following an aircraft running out of fuel) very hard to pin down. It simply ends up that nobody wants to stick their neck out and do such an approval for that reason. I reached that conclusion years ago, and did not do that approval. I stand by that decision today. When the time comes that I can no longer get pure Mogas, I will approve my plane to allow ethanol, but only because only I fly it.

When the legal and design approval systems as they apply to aircraft, catch up to the world of changing fuel, I will re-evaluate the decision to approve enthanol based fuel in aircraft. In the mean time, anyone can make application to their local authority for such an approval- but its a lot of work. Until then, the fuel used, must conform to that approved for use in that aircraft. If you can't get the fuel, you can't legally fly...

Pilot DAR

[Rod1]

“What about ROTAX engines that run best on MOGAS are they able to take MOGAS with an ethonal percentage?”

The following applies to the UK and may not be applicable else ware.

The Rotax manual for my 912s says it can cope with up to 5% ethanol. It is and probably will be possible for many years to buy Mogas with no ethanol content. Ethanol is only one way of producing biopetrol.

Ethanol usage in aircraft other than micros is not allowed. If you use Mogas (as I do), you have to carry out a simple test. It the Mogas passes then you can use it. The test is not sensitive and cannot detect 5% Ethanol content. Micros have no blanket restriction on using Ethanol.

Rod1

[Mariner9]

Quite a fair summation Astir, but a few minor corrections to some technical points you made, and one important caution:


Ethanol for blending with gasoline has to be "anhydrous" - e.g. over 99% pure.

Ethanol purity for biogasoline is typically specified at 99.5% min, with water content 3000ppm max (0.3%)


Now "pure" ethanol as operated by DAR would have been hydrated ethanol which contains about 4% water (it takes a lot of effort to turn hydrated into anhydrous ethanol).

I would think this is unlikely. A fairly simple dehydration process to produce ethanol suitable for fuel use is for treatment with Benzene.

Where does all this get Sam? The chances are, his available mogas blend is somewhere between 5 and 10% anhydrous ethanol.

From bitter experience, I can say that that's a dangerous assumption where African fuels are concerned :=

Sam, the best advice in your circumstances (ie for an emergency flight) would be to transfer all remaining Avgas into 1 tank for use in takeoff/landing, and find some min 95 octane Mogas (if you can) for the other. Start up on Avgas, but check your engine runs at or close to normal max static rpm on the Mogas before you depart

[Avtrician]

If running on Mogas is an alternative to copping an AK slug in the back, then as long as the engine will run, I'd go for it.:bored:

[tangovictor]

Rod, you mentioned the simple test, could you please run through it ( again )
some say buying mogas from Asda / Tesco is risky and its better to stick with Shell / BP etc ? is that correct ?
Cheers
TV

[aviate1138]

TV said....

"Rod, you mentioned the simple test, could you please run through it ( again )
some say buying mogas from Asda / Tesco is risky and its better to stick with Shell / BP etc ? is that correct ?"



Aviate asks....
If you happen to be near a refinery, say Exxon at Fawley you will see tankers from Shell/BP/Sainsbury/Asda/Tesco all taking fuel from the same outlet. When does the change to branded fuels, Optimax etc happen? Do the tanker drivers include company additives during the refuelling stage? Or not in the case of Asda/Tesco etc?

Hmmmm.....

[Rod1]

The following text is from the CAA;

A simple method for determining the presence of alcohol in fuel is to thoroughly
shake a test cylinder containing 90 ml of the fuel to be tested and 10 ml of water.
If, after settling, the water volume has increased, then alcohol is probably present
in the fuel and the fuel is, therefore, unsuitable for aviation use.

Rod1

[Sam Rutherford]

Thank you to everyone for that - highly informative. The question was with regard to getting out of an 'uncertain situation', I think I have my answer.

Thanks again, Sam.

[Mariner9]

If you happen to be near a refinery, say Exxon at Fawley you will see tankers from Shell/BP/Sainsbury/Asda/Tesco all taking fuel from the same outlet. When does the change to branded fuels, Optimax etc happen? Do the tanker drivers include company additives during the refuelling stage? Or not in the case of Asda/Tesco etc?

No simple answer to this, it very much depends on where you live and where your local fuel is sourced from. If you live near a refinery, the chances are that they have tanks dedicated to certain grades, or add differing "multifunctional additive packages" when filling to the tanker.

Away from the refineries, the fuel will be sourced from distribution depots that may be oil company owned or independant. No common methodologies adopted in these terminals - some have different tanks for different grades, others dont.

Currently, good advice to avoid ethanol in the UK would be to stick to oil major filling stations and avoid supermarkets.

[tangovictor]

thank you Rod for the fuel testing tip

Mariner 9 are you saying that Aviate 1138's advise is not correct ?

( If you happen to be near a refinery, say Exxon at Fawley you will see tankers from Shell/BP/Sainsbury/Asda/Tesco all taking fuel from the same outlet. When does the change to branded fuels, Optimax etc happen? Do the tanker drivers include company additives during the refuelling stage? Or not in the case of Asda/Tesco etc? )

[Lurking123]

The picture gets rather grey when you start looking at aircraft designed for MOGAS. For example, many Type Certificate Data Sheets for CS-VLAs which have a Rotax up front prescribe "Minimum 95 Grade Unleaded Automotive Gasoline or AVGAS 100 LL if other fuel is not available". The CAA then put additional restrictions on this of the aircraft certification. I think Rod has it about right, check for Ethanol and that's it. As far as all the aircraft and engine log book entries are concerned...........:rolleyes:

[Mariner9]

Mariner 9 are you saying that Aviate 1138's advise is not correct ?

( If you happen to be near a refinery, say Exxon at Fawley you will see tankers from Shell/BP/Sainsbury/Asda/Tesco all taking fuel from the same outlet. When does the change to branded fuels, Optimax etc happen? Do the tanker drivers include company additives during the refuelling stage? Or not in the case of Asda/Tesco etc? )

Nope, Aviate was asking a fair question and I answered it. The tankers often do load from common outlets, but refineries and larger distribution terminals have multiple loading gantries so can cater for differing formulations.

Regarding the ethanol test - and speaking as a so-called fuels expert and owner of a Rotax-powered aircraft, I comply with the legislation by doing the test but mainly ensure ethanol avoidance by sticking to one particular oil-major fuel. (PM if you want to know which one - I can't endorse any particular fuel on a public forum)

[dwj]

Here in Canada the only mogas that is guaranteed to be ethanol free is Shell V-Power (their highest octane grade), which is what I use in my 172 without any problems. I think Shell V-Power is also guaranteed to be ethanol free in other countries, but you should check with Shell if you are unsure. Sometimes it says on the petrol pumps what the % of ethanol is, but most times it does not.

Dave