Finding Airports that sell 91 Octane Mogas?

Discussion in 'Hangar Talk' started by Jamaica Scott, Aug 9, 2020.

  1. John Melchert

    John Melchert Filing Flight Plan

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    MOGAS used to be a spec, and you could rely on the Octane being at least 91 AKI, non-ethanol. But most often these days, the term is used for fields that obtain and sell auto fuel that does not meet the original MOGAS spec, but is nevertheless fine for use in aircraft with auto fuel STC's, or prefer the unleaded fuel such as Rotax and other newer engines. But you need to check with the supplier if your engine requires a specific min Octane level. There are pumps that state 93, but this may (likely) is not the case, or the 93 refers to a different rating than AKI (like straight RON). High-compression Rotax engines, such as the 912ULS or 912iS, or 915 require 91 AKI or higher. So one must be sure. Many facilities that advertise MOGAS supply 87 or 89 AKI fuel because many low-compression Lyc/Conn engines with STC's can use it. Most Rotax 4-cyls, other than the original 912 UL engine, can't. Also, regarding Ethanol, just say NO. Some "think" it's Ok, or not a problem, but there are LOTS of problems, even if the seals and rubber components in your plane are OK with it. That is just the start. The bigger issues include lower power-density, which means you get less bang per gallon (i.e. less power from your engine). This is no wives' tale, this is a fact. Another big issue is that alcohol absorbs moisture. This is why us northern folk used to put alcohol additive in our tanks in the winter (before they just added it to the fuel). It would absorb any melted snow that fell in the tank, or condensation from the air that would fall to the bottom of the gas tank and freeze. But when this happens, it leaves your Octane level an UNKNOWN. The alcohol was added to boost the Octane level. When Ethanol absorbs moisture, it screws this up. And then there are the added GUMS, and the very short lifespan of Ethanol fuel, ...
     
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  2. BlueDream

    BlueDream Filing Flight Plan

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    G100UL is the answer to MOGAS powered planes. I have spoken with the company, and asked how this fuel would do in a rotax 912 is, and the answer was better than mogas. For various reasons. It's 100 octane, no lead, and no ethanol. And if the FAA ever pulls their heads out of their asses, it should be in almost all GA airports across the country within the next year. The FAA is holding it up like they hold everything up. Maybe if everybody starts shouting at them, they might wake up.
     
  3. Racerx

    Racerx Pattern Altitude

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    It may be the answer if it were available.
     
  4. John Melchert

    John Melchert Filing Flight Plan

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    Yep, totally agree. If we had G100UL we'd be done. It would be everywhere, and everything could use it safely. Some folks will still use auto fuel because they can and it will likely, most often, be less expensive. But with G100UL, ubiquitous, no ethanol issues, no old gas issues, etc. It's Oshkosh week next week. Maybe we'll hear something from Gammi or the FAA.
     
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  5. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    Welcome to PoA!

    Maybe AOPA could get G100UL or UL94 at KFDK...
     
    Last edited: Jul 23, 2022
  6. John Melchert

    John Melchert Filing Flight Plan

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    That's a great idea!! I'll be at Oshkosh this coming week; speaking again with Gami about G100UL fuel and listing locations as they become available on flyunleaded.com. Now that it has been approved on an STC with an AML (Approved Model List) basis, it needs to be available, and I'm sure they have plans beyond the single CA county. Many experimental aircraft don't require an STC. But again, it needs to be available. Somewhat of a catch 22.
     
    Last edited: Jul 28, 2022
  7. Pinecone

    Pinecone Pre-takeoff checklist

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    Because technically, they are not "octane" ratings. They are Performance numbers.

    And US pump MOGAS is not labeled with "octane" ratings, they are labeled with the AKI (Anti Knock Index). Which is the average of two test methods that give MON (Motor Octane Number) and RON (Research Octane Number). The two methods differ in the test conditions of things like intake air temperature and cylinder head temperature. MON is lower than RON, as it is more harsh test conditions. They are tested in a special single cylinder engine with adjustable (while running) compression ratio. They raise the compression ratio until they see detonation. Then they without changing anything, they run the engine on pure iso-octane to start (octane 100), and then with mixes of less and less iso-octane and n-heptane (octane 0). When they reach the mix that causes detonation, that is the "octane number" of the fuel tested.

    There is no specific relationship between RON and MON or AKI. A 90 AKI could be 89 MON and 91 RON or 80 MON and 100 RON.

    A number of years ago, several German car manufacturers has detonation problems from autobahn high speed cruising even though the engines were fueled with the proper RON fuel. They found that the MON was too low. So they mandated that fuels used in those cars must have an MON no lower than 10 points below the RON. So Euro Premium 98 RON had to have an MON of no lower than 88, leading to an AKI of 93 (sound like a familiar AKI? ). So one can be pretty sure that any high quality US fuel has the same minimum MON to RON ratio.
     
  8. Dana

    Dana En-Route

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    If iso-octane is 100 octane, why couldn't it be used directly as a 100 octane fuel?
     
  9. John Melchert

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    And avgas isn't either MON or RON. It is a different method for aviation fuels. It is closer to RON in practical terms however, so 100LL is really more like 93 or 94 in AKI terms. This is another reason why mixing 100LL with lower octane Auto Fuel to supposedly get a higher (ostensibly calculated) octane level isn't a good idea. You really don't know what you're ending up with, putting your engine, and perhaps your life, at risk. That's not to say you can't mix these fuels; you surely can. Just be sure everything you put in your tank has at least the minimum octane your engine requires all by itself.
     
  10. dbonnar

    dbonnar Filing Flight Plan

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    I’d switch my Rotax to anything 92-100 without ethanol, but not sure I’ll find in Calif.
     
  11. John Melchert

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    Screenshot_20220724-185246_Chrome.jpg No MOGAS in CA, but several around Oakland, and one elsewhere that sell UL94 from Swift (from flyunleaded.com)
     
    Last edited: Jul 28, 2022
  12. Pinecone

    Pinecone Pre-takeoff checklist

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    Where was MOGAS a spec? And who's spec? AFAIK Mogas was a term used for any auto fuel used in aircraft as a counter point to Avgas. And there were use of auto fuels before the Rotax engines came into use.

    Actually most anti icing, like HEET used to be methanol, but that is not good for O2 sensors. So many products changed to isopropyl alcohol.

    Ethanol is not added to boost octane. It is added as an oxygenate. They used to use MBTE, but that was polluting ground water so it was pulled from use. MBTE was added to auto fuel in certain areas during winter to reduce pollution. If you tracked you gas mileage, you could see the change from winter to summer gas. When they switched to ethanol, they changed to everywhere and year round. Which shows it is NOT pollution related, but a gov subsidy.

    But I do agree with your just say NO to ethanol. I race SCCA in Spec Racer Ford. The Gen 2 cars ran an early 90s Ford Escort engine. It was rated for regular (87 AKI) fuel and we raced for many years without problem. All of a sudden, we were braking pistons. The piston for break above the first compression ring. Switching to premium did NOT fix the issue. The fix was to switch to race gas, which did not have any ethanol. No more borken pistons.
     
  13. John Melchert

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    Not wanting to enter some online debate here. There's way too much of that out there. Here's an article on Ethanol in fuel that explains what I was stating and more psu.edu. Ethanol, like (all?) other alcohols absorb moisture. Ethanol is used as an oxygenate (with adverse side effects no one talks about) AND boosts Octane. There is other information, as you stated, that doesn't really mean much in this context. Regarding MOGAS, yes, it is indeed used today as a reference for auto fuels in general, which was my point. Due to the numerous and many fuel specifications, you don't really know what you're getting anymore, not even at the different filling stations for your car. But, when it was first used as a term by our military, there was a specific specification for auto fuel. There are now many specifications, and different ones used by different refineries and different countries. It is no longer "reliable", which was my only point, and really the only thing that is important here.
     
  14. John Melchert

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    Regaridng GAMI and G100UL. I met up with Tim Roehl, president of GAMI, and we had a somewhat lengthy conversation regarding the state of G100UL. Or more accurately, I asked simple questions and Tim elaborated extensively on things. Bottom line, the FAA is seemingly, deliberately, holding things up. GAMI has jumped through all the necessary hoops. After that, GAMI jumped through numerous other hoops that the FAA has attempted to put in front of them, and then GAMI sailed through them with ease. GAMI has done everything required and then some, and then some more. The FAA just won't sign the approval. In essence, you need to follow the money here. And the money is in Phillips, the largest refinery of 100LL, and their Eagle brand. Eagle is not ready and for whatever reason ($$$$?) the FAA is holding back approval for GAMI until they are. Makes me quite upset. I've asked Tim to write this up and I'll post it all on flyunleaded.com. I know Swift ran into some of the same stuff. But GAMI is ready. The FAA is out of hoops for them to jump through. There has been tests completed on hundreds of engines and airframes, pretty much everything that exists in any numbers. GAMI has two STC's and extensive Approved Model Lists (AMLs), AND GAMI even had their testing process audited. All good. They are done. We could have it everywhere and ditch 100LL today if the FAA would stop with the pandering of Phillips. One wonders what is really going on there.
     
    Last edited: Jul 28, 2022
  15. Daleandee

    Daleandee En-Route

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    I really do appreciate the update here but in reality this is what we've known, or rather suspected, all along. You're certainly not the only one upset over this. The question really is, what can be done about it? Again, we find we have the government we deserve ...
     
  16. Dana

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    I thought the mogas STCs required mogas to a specific ASTM specification?
     
  17. John Melchert

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    Petersen's STC's for Auto Fuel are. Here is a snippet from there website "Auto fuel STCs were developed using fuel blended to ASTM specification D-439. D-439 has now been superseded by D-4814. The difference between the two specs is in the test methods outlined. D-4814 added test methods to be used at the refinery for oxygenates but does not require the addition of oxygenates. Studies have been done in Europe that show EN228 to be virtually the same as D-4814. Hence most European governments accept the STCs." This can be found near the bottom of the page at https://www.autofuelstc.com/stc_specs.phtml.
     
  18. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    It won't match the distillation curve that the FAA mandates for avgas that is based on the typical Hydrocarbon blend from the 1930s.
    Probably not great for cold starting either without some lighter HCs - but that is just speculation.

    because the farm lobbies pump mega dollars into the system. And because politicians can claim that they are reducing the dependency on foreign oil.

    Adding oxygenates to the fuel reduces emissions in your 1972 Chevy Malibu, but not so much in a modern automobile with more oxygen sensors (upstream and downstream of the catalyst) than you can shake a stick at.
     
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