How much 100LL to stabilize MoGas?

[timwinters]

So, one of the very few disadvantages of being based at a small rural field is that we have no fuel. This results in the ocasional drive up to H88, which has both 100LL and 93 octane MoGas, to get a batch of fuel, and store it in my barn/shop. I buy both, but hesitate to get over a one month to six week supply because of MoGas' instability, so I typically limit my trips to 60 gallons or so.

But, what if, instead of keeping them separate, I blended them? Say 2/1 MoGas to 100LL. Or 1 gal of 100LL in each 5 gallon can? Would these mixes be more stable and be able to be stored for longer periods?

I'd buy more fuel per trip (80 miles round trip) if I had the confidence that it could be stored for a few months without degrading. I think 119 gallons is the max that can be legally hauled in MO w/o a DOT approved trailer/apparatus and I'd easily burn 119 gallons in less than 3 months between March and November.

Any gas gurus here?

 

[N801BH]

I have been blending 75% mogas with 25% 100LL since the burned piston (issue).... The 100LL seems to stabilize the mogas's degradation... Not a hint of problems in 4 years..

 

[Geico266]

I have been blending 75% mogas with 25% 100LL since the burned piston (issue).... The 100LL seems to stabilize the mogas's degradation... Not a hint of problems in 4 years..

That is the ratio i use when storing planes for a period of time. Works for me too.

 

[Tom-D]

I use 5 gal. gas cans, I place 2 gallons of 100LL in each and then fill with 92UL, We've had no problems using it with in 3 months.

How long will it stay good ?? Don't know.

 

[Morgan3820]

Stupid question maybe, but is Stabil OK for aircraft use?

 

[kyleb]

I'm not sure mixing 100ll and mogas will result in the stabilization you seek. The most volatile fractions from the mogas are still going to evaporate faster than the rest, leaving you with a mystery fuel in the tanks.

 

[N801BH]

I'm not sure mixing 100ll and mogas will result in the stabilization you seek. The most volatile fractions from the mogas are still going to evaporate faster than the rest, leaving you with a mystery fuel in the tanks.

All my long term storage stuff like lawn mowers, weed eaters and other motors that go unused for 8 months during our "short" winters, I fill with straight 100LL..

I fly my plane almost daily so even my 75-25% cocktail does not sit in my planes tanks for more then 2-3 weeks so I cannot comment on the extended storage stability of 100LL / mogas mixtures... YMMV..

 

[O-200]

Stupid question maybe, but is Stabil OK for aircraft use?

Interesting question.
I would prefer fresh fuel of course, but an interesting question none the less.

George

 

[Silvaire]

You can mix it however you want and make up your own formula but the fact is that mogas is not regulated in any way, shape or form like avgas so regardless of what percentage you decide on you are still dealing with an unknown variable. In other words - you don't have a formula. To be honest, you'd seriously have to test every batch of mogas to ensure it has no ethanol because there is no regulation forcing them to tell you the truth about what's in there.

 

[Geico266]

You can mix it however you want and make up your own formula but the fact is that mogas is not regulated in any way, shape or form like avgas so regardless of what percentage you decide on you are still dealing with an unknown variable. In other words - you don't have a formula. To be honest, you'd seriously have to test every batch of mogas to ensure it has no ethanol because there is no regulation forcing them to tell you the truth about what's in there.

That takes all of 5 mins, I test every other tank full. Each tank I haul in saves me $ 200 min. It's worth it.

 

[JHW]

You can mix it however you want and make up your own formula but the fact is that mogas is not regulated in any way, shape or form like avgas so regardless of what percentage you decide on you are still dealing with an unknown variable. In other words - you don't have a formula. To be honest, you'd seriously have to test every batch of mogas to ensure it has no ethanol because there is no regulation forcing them to tell you the truth about what's in there.

On the contrary, Mogas is regulated in myriad ways. So many ways in fact, that if you live in an area without a botique formulation, you are seeing that batch-batch variability because you are getting fuel formulated by his regulation this day, another regulation another day.

 

[Geico266]

You can mix it however you want and make up your own formula but the fact is that mogas is not regulated in any way, shape or form like avgas so regardless of what percentage you decide on you are still dealing with an unknown variable. In other words - you don't have a formula. To be honest, you'd seriously have to test every batch of mogas to ensure it has no ethanol because there is no regulation forcing them to tell you the truth about what's in there.

Where are the dozens, thousands of cars disabled by bad fuel? No regulation standards for gasoline? Really?

 

[RV10flyer]

I was talking to one of my customers that works at a local refinery a few weeks ago. He said auto fuel may be pumped through a pipeline into a storage tank with diesel or something else right behind it. He said they just switch the valves at the proper time but said that there is still alot of mixing goes on. 100LL is completely different.

 

[JHW]

I was talking to one of my customers that works at a local refinery a few weeks ago. He said auto fuel may be pumped through a pipeline into a storage tank with diesel or something else right behind it. He said they just switch the valves at the proper time but said that there is still alot of mixing goes on. 100LL is completely different.

That's true. How much do you think that 5 gal out of millions in the tank matters ? Do you think it might be insignificant compared to the already present diesel constituents in gas and vice versa? Do you think anyone ever thought about this before you ?

 

[Capt. Geoffrey Thorpe]

That's true. How much do you think that 5 gal out of millions in the tank matters ? Do you think it might be insignificant compared to the already present diesel constituents in gas and vice versa? Do you think anyone ever thought about this before you ?

Where I worked, we had an "off spec" tank that would get whatever was coming down the pipeline until the right stuff showed up. Typically, there would be a "flag" of something with a significantly different density than what we wanted to make it obvious when to switch. The offspec stuff got burned to heat the reactors.

But, that plant has since been shut down. http://articles.chicagotribune.com/...energy-crisis-natural-gas-peoples-energy-corp

 

[Skylane81E]

That's true. How much do you think that 5 gal out of millions in the tank matters ? Do you think it might be insignificant compared to the already present diesel constituents in gas and vice versa? Do you think anyone ever thought about this before you ?

Considering many fuel injector cleaners contain kerosene (or even "jet fuel!") according to the labels.

 

[Silvaire]

Where are the dozens, thousands of cars disabled by bad fuel? No regulation standards for gasoline? Really?

Let me ask you this: when winter comes do you just leave that mogas in your lawn mower, weed whacker and chainsaw until next season? And you've had no troubles doing that?

I'm simply pointing out that it is not as stable as avgas, not by a long shot. That was the original question in this thread.

 

[docmirror]

Chevron and Shell basically say that mogas will last for about a year in an automotive fuel system. Of course, they don't operate on vented fuel systems, so I would say that would shorten the time significantly. Non-Ethanol gas like we would use would tend to have a longer shelf life.

I've used mogas(no blend) that sat in the airplane tank for 4 months without any issues. Sumped it well, checked the color and flew it off. If it had been dark, or smelled like turpentine, I would have defueled and put in new, but it smelled like gas, and had the yellow tint I usually see with mogas. YMMV

 

[az350x]

I have been blending 75% mogas with 25% 100LL since the burned piston (issue).... The 100LL seems to stabilize the mogas's degradation... Not a hint of problems in 4 years..

Was the hole a result of running straight Mogas, and that's why you switched to the 75/25 blend?

 

[az350x]

Sort of on-topic questions here- I'm a long-time pilot, but new to dealing with auto gas STC, and am looking to join the ranks of experimental aircraft owners. The idea of using SOME Mogas mixed with 100LL to cut the cost down is very inviting, and I have a 90-gallon tank I could use for transport and dispensing the Mogas into the plane. I would always be running a mix, btw, and flying fairly regularly commuting long distance with the plane. Overall, probably 90% of the fuel run through the plane will be avgas.

So, my questions-
1- I know certified aircraft require auto gas STC- anything required for experimental?
2- are there physical changes required to be made to the fuel system to run some Mogas?
3- does induction method matter? (Carbureted vs. fuel injection- both normally-aspirated)
4- does operating altitude play much of a role in this?

Also, for clarification, I'm looking at Lycoming 320 or 360-powered models for this.

Thanks for the info!

 

[Capt. Geoffrey Thorpe]

Sort of on-topic questions here- I'm a long-time pilot, but new to dealing with auto gas STC, and am looking to join the ranks of experimental aircraft owners. The idea of using SOME Mogas mixed with 100LL to cut the cost down is very inviting, and I have a 90-gallon tank I could use for transport and dispensing the Mogas into the plane. I would always be running a mix, btw, and flying fairly regularly commuting long distance with the plane. Overall, probably 90% of the fuel run through the plane will be avgas.

So, my questions-
1- I know certified aircraft require auto gas STC- anything required for experimental?

Nope

2- are there physical changes required to be made to the fuel system to run some Mogas?

Depends.

3- does induction method matter? (Carbureted vs. fuel injection- both normally-aspirated)

Nope

4- does operating altitude play much of a role in this?

Some

Also, for clarification, I'm looking at Lycoming 320 or 360-powered models for this.

Thanks for the info!

Anything else?



You have to assume that the auto gas will have a higher vapor pressure so you want to minimize trying to pull the fuel from wings to higher up in the engine compartment and letting the fuel lines in between get hot. At higher altitudes, you have less ambient pressure in the tanks so it easier to form vapors in the fuel lines.

Gravity feed is typically good, in tank pumps are a good thing.

If you want to run E-10 then you will have to use SAE grade hoses and not aircraft stuff, and you will likely have to make changes to the "rubber" parts in the engine fuel pump and carburetor.

Check around to see if others have had some experience running auto fuel in the same aircraft design.

 

[Skylane81E]

If you are going to run fuel containing ethanol be sure your fuel system is comparable, from gas cap to tail pipe. It isn't unheard of for a place filled with corn juice to develop massive leaks in short order.

 

[Capt. Geoffrey Thorpe]

If you are going to run fuel containing ethanol be sure your fuel system is comparable, from gas cap to tail pipe. It isn't unheard of for a place filled with corn juice to develop massive leaks in short order.

Leaks are less likely to be problem than the fuel lines swelling shut and having the engine shut down on takeoff.

I know someone who had that happen.

 

[Skylane81E]

Leaks are less likely to be problem than the fuel lines swelling shut and having the engine shut down on takeoff.

I know someone who had that happen.

We have a Lancair on the field that only holds gas in one wing now

 

[docmirror]

So, my questions-
1- I know certified aircraft require auto gas STC- anything required for experimental?
2- are there physical changes required to be made to the fuel system to run some Mogas?
3- does induction method matter? (Carbureted vs. fuel injection- both normally-aspirated)
4- does operating altitude play much of a role in this?

Also, for clarification, I'm looking at Lycoming 320 or 360-powered models for this.

Thanks for the info!

I am working on the same basic set of criteria as you. Looking at running mogas(92 octane) in a O-320. The issues I'm coming up with boil down to two basic safety issues.

First is vapor pressure. I'm in TX and it gets hot here. My plan is to remove any/all 90deg fittings and go with curved pipe. Put the fuel pump right at the outlet of the tank so that there is always good head pressure behind the pump which will be the lowest pressure point of the fuel system. Run my lines directly to the mechanical pump and insulate any lines that are inside the engine bay, even if behind the baffle plate to protect them from heat. I'm considering running a circulating return line with a pressure regulator to keep a continuous flow of fuel going and return it to the tank.

Next is detonation margin. The O-320 comes in three basic comp ratios; 7:1, 8.5:1, and 9:1. The difference is in the pin to crown distance. I have the 8.5:1 pistons and the spec for those is 91/96 octane. I figure I'm within the limits of the detonation margin if I use pure 92 octane mogas, or a mix of 50:50 mogas and 100LL. To mitigate any problems I'll have my carb set so that full rich mixture is avail through all settings. I'm going to install a knock detector kit on the crankcase and one on the hottest head.(http://tunertools.com/gizzmo-electronics!!!-k!!lite-engine-knock-monitoring-alert-light.html) I'm considering an electronic ignition like the TEC3 http://www.electromotivestore.com/ setup with automatic retard in the event of detonation. If you have a lower C/R, pure mogas would be no problem.

<edit: I am not considering ANYTHING with Ethanol in it. The issues are just too great>

 

[Capt. Geoffrey Thorpe]

We have a Lancair on the field that only holds gas in one wing now

What is the fuel tank made of?

edit

OK, answered my own question...

The fuel tanks in the Lancair appear to be molded into the wing and use the fiberglass / resin wing skin as the fuel tank itself. Some resins do not survive E-10. I suspect that a Lancair that is leaking as a result of the E-10 has serious structural problems...

And, apparently, even E-0 auto fuel can be a problem with plastic tanks: http://www.usjabiru.com/uploads/JSA-006_Auto_Fuel_Bulletin.pdf

 

[Clark1961]

I'm not sure mixing 100ll and mogas will result in the stabilization you seek. The most volatile fractions from the mogas are still going to evaporate faster than the rest, leaving you with a mystery fuel in the tanks.

I tried to let this go, I really did...but this is at best a misleading statement. The addition of a lower vapor pressure mixture will reduce the quantity of lighter fractions that vaporize.That's just the way hydrocarbon mixtures work.

 

[denverpilot]

I tried to let this go, I really did...but this is at best a misleading statement. The addition of a lower vapor pressure mixture will reduce the quantity of lighter fractions that vaporize.That's just the way hydrocarbon mixtures work.

Heh. Sucks being a hydrocarbon engineer reading Internet stuff doesn't it?

 

[Clark1961]

Heh. Sucks being a hydrocarbon engineer reading Internet stuff doesn't it?

prolly as much as when you read IT or radio stuff...

 

[Skylane81E]

What is the fuel tank made of?

edit

OK, answered my own question...

The fuel tanks in the Lancair appear to be molded into the wing and use the fiberglass / resin wing skin as the fuel tank itself. Some resins do not survive E-10. I suspect that a Lancair that is leaking as a result of the E-10 has serious structural problems...

And, apparently, even E-0 auto fuel can be a problem with plastic tanks: http://www.usjabiru.com/uploads/JSA-006_Auto_Fuel_Bulletin.pdf

Yep, realistically needs a new wing to get back in the air

 

[bullwinkle]

I'm really happy my CTSW is approved for mogas with ethanol up to 15%. It's a bit of a PITA to haul in gas to fill it, but the savings are substantial. When I bought it it had full tanks of 100LL, and I have noticed no change in performance since switching to 93 ocatane mogas.

BTW, mogas is the preferred fuel for the Rotax 912, the ethanol is not an issue for it and the lead in 100LL causes deposits on the valves and gearbox.

 

[N801BH]

Was the hole a result of running straight Mogas, and that's why you switched to the 75/25 blend?

I am 99% sure the labeled 91 octane was 85 octane..... or less....


This is a VERY experimental / prototype motor and I do run it VERY hard trying to get it to fail..... The first 300 hours I ran it at 1725f egt and it performed very well in those 60,000 miles traveled, including trips to OSH and various other airshows, fly in's etc..... On that flight I keep leaning it till it hit 1775f.. I am sure the elevated temps didn't help and the plane itself is so noisy inside it is impossible to hear it detonating.... I have since backed off on my maximum egt temps , down to 1650 or so and I installed a air /fuel mixture gauge to monitor the incoming charge... It is a "must have" gauge for experimental engine development project and works surprisingly well...

http://www.aemelectronics.com/wideband-air-fuel-systems-15/digital-wideband-air-fuel-gauge-25/

 

[Geico266]

I'm really happy my CTSW is approved for mogas with ethanol up to 15%. It's a bit of a PITA to haul in gas to fill it, but the savings are substantial. When I bought it it had full tanks of 100LL, and I have noticed no change in performance since switching to 93 ocatane mogas.

BTW, mogas is the preferred fuel for the Rotax 912, the ethanol is not an issue for it and the lead in 100LL causes deposits on the valves and gearbox.

The lead in a Rotax usually causes problems as it makes a pastey sludge gumming up the rings, and spraq clutch keeper springs. You are wise to run mogas in it. Run seafoam in the oil ( on the ground) for 30 mins, 10 mins at a time with a half hour cool down in between. It will help flush the lead out. Change oil every 25 hours for the next 3-4 oil changes.

 

[Henning]

Where are the dozens, thousands of cars disabled by bad fuel? No regulation standards for gasoline? Really?

It happens on a DAILY basis, modern cars you don't really notice it because they have knock sensors which will automatically retard the timing to prevent detonation, but in old junkers like I drive, we notice it all the time. There is a Vallero station by the house I won't buy fuel from because it's so bad. My room mate with a newer car bought some there and she thought her car was dying because suddenly it had no power and was running hot. Got fresh gas from Racetrack and back to good.

 

[az350x]

Nope


Depends.


Nope



Some



Anything else?



You have to assume that the auto gas will have a higher vapor pressure so you want to minimize trying to pull the fuel from wings to higher up in the engine compartment and letting the fuel lines in between get hot. At higher altitudes, you have less ambient pressure in the tanks so it easier to form vapors in the fuel lines.

Gravity feed is typically good, in tank pumps are a good thing.

If you want to run E-10 then you will have to use SAE grade hoses and not aircraft stuff, and you will likely have to make changes to the "rubber" parts in the engine fuel pump and carburetor.

Check around to see if others have had some experience running auto fuel in the same aircraft design.

I'd never (knowingly) run ethanol. I'm thinking Lancair 320/360 or Glasair I for an aircraft. I doubt if I'd ever even run straight Mogas- most likely adding it (topping off) 1/2ish full tanks at home before a couple of 100LL fill-ups on my trips.

Thanks again for the feedback.

 

[Capt. Geoffrey Thorpe]

I'd never (knowingly) run ethanol. I'm thinking Lancair 320/360 or Glasair I for an aircraft. I doubt if I'd ever even run straight Mogas- most likely adding it (topping off) 1/2ish full tanks at home before a couple of 100LL fill-ups on my trips.

Thanks again for the feedback.

See the Jabiru service bulletin I linked above before you put auto gas in a fiberglass / resin tank.

 

[az350x]

See the Jabiru service bulletin I linked above before you put auto gas in a fiberglass / resin tank.

Yikes. And then at the end they say you can use non-ethanol 91+ octane Mogas. Seems to be contrary to the message of the whole SB prior to that point, doesn't it?

 

[kyleb]

I tried to let this go, I really did...but this is at best a misleading statement. The addition of a lower vapor pressure mixture will reduce the quantity of lighter fractions that vaporize.That's just the way hydrocarbon mixtures work.

Help me with this. My point was that the lighter fractions will still evaporate faster than the balance of the mix, leaving you with a mystery fuel. Not true? I figured Boyle's law pretty much assured that. But I'm not a petro guy, so I defer to expertise...

 

[SoloEqs]

mogas is not regulated in any way, shape or form like avgas

Not true.

From Petersen (http://www.autofuelstc.com/stc_specs.phtml):

"The following states require compliance with D-4814 in whole or in part or require critical specifications values per ASTM D-4814: Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Minnesota, Mississippi, Montana, Nevada, New Mexico, North Carolina, North Dakota, Oklahoma, Rhode Island, South Carolina, South Dakota, Tennessee, Utah, Virginia, Wisconsin, and Wyoming. Only eight states require compliance with the aviation fuel spec D-910. There is no federal requirement for aviation fuel to meet the spec. Therefore control of auto fuel is tighter than it is for avgas."

 

[RJM62]

Yikes. And then at the end they say you can use non-ethanol 91+ octane Mogas. Seems to be contrary to the message of the whole SB prior to that point, doesn't it?

I was scratching my beard over that myself, considering the information Jabiru presented regarding other harmful solvents being present in non-ethanol Mogas.

I know that in the 103 world, Mogas (both ethanol and non-ethanol) is routinely used with no apparent ill effects. But a lot of the fuel system components in ultralights are in fact designed for cars. Also, the tanks on ultralights are usually exposed, making any degradation of seams (if the tanks even have seams) more easily apparent and less harmful to anything except the tanks themselves and the grass beneath them. That's not true in more conventional aircraft.

-Rich