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Thread: Piper Completes Flight Tests of Archer Fueled by 93 Octane

  1. #11

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    Interesting reading, very informative.
    I have a 300 gal tank in my hanger which a bulk dealer fills for me, I use high octane and test for ethanol each time. So far nothing has appeared. I also fire sleeved all my fuel lines and have never had a problem. I live in the north where we seldom get above 80f so I don't believe vapor lock is an issue.
    What I take from what I have read is that auto gas has higher volatility, it evaporates quicker which would make it "better" fuel as only gasoline vapors burn so the easier it evaporates the easier it will burn?

  2. #12
    Aaron Novak's Avatar
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    Quote Originally Posted by raytoews View Post
    Interesting reading, very informative.
    I have a 300 gal tank in my hanger which a bulk dealer fills for me, I use high octane and test for ethanol each time. So far nothing has appeared. I also fire sleeved all my fuel lines and have never had a problem. I live in the north where we seldom get above 80f so I don't believe vapor lock is an issue.
    What I take from what I have read is that auto gas has higher volatility, it evaporates quicker which would make it "better" fuel as only gasoline vapors burn so the easier it evaporates the easier it will burn?
    Incorrect,
    Engines dont run on "vapor", they run on atomized liquid droplets for the most part. There are "light ends" in the fuel that will vaporize, and this is to help cold ignition. With auto fuel the vapor pressure varies with the season, meaning that in winter the fuel has more light ends to help cold start, in the summer less to avoid vapor issues. Here lies much of he issue, the ever changing chemistry and the random addition of various light solvents like toluene. Part of it changes in the pipeline, part of it is up to the individual station. From a design standpoint, trying to design and calibrate an engine for auto-fuel is like hitting a moving target in the dark. From the outside to people that dont know engine design, it does not seem like a big deal though, and I think this is where a lot of arguments come from. Either you understand it, and know what will be required to deal with it, or you dont understand it and think everything will work just fine all the time.

  3. #13
    Quote Originally Posted by I_FLY_LOW View Post
    My Lyc O-320, per the manual, said to use 87 octane, unleaded.
    What manual is that, I Fly? Are you referring to the Lycoming Service Instruction on acceptable fuels, and specifically 87 AKI mogas?

    Octane numbers without a frame of reference can be misleading... 87 AKI mogas is comparable to 82 motor octane avgas... for instance, as you probably know...

    Piper's ethanol-free 93 PUL (premium unleaded) demonstration isn't a very universal solution, given that west of the Great Plains, 91 octane alcohol-containing premium is more the norm...

    I used to visit Gonzales quite frequently... we have a styrene plant in Donaldsonville...

    Paul

  4. #14

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    What were you saying about AKI, OICU812, C3-PO and all that?
    Notice the lower portion of the second pic... "Approved by F.A.A".
    Also notice the limitation of lead content in the third pic.

    This is a repro, and when I run across it, I'll post the original.





  5. #15
    Aaron Novak's Avatar
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    Quote Originally Posted by I_FLY_LOW View Post
    What were you saying about AKI, OICU812, C3-PO and all that?
    Notice the lower portion of the second pic... "Approved by F.A.A".
    Also notice the limitation of lead content in the third pic.

    This is a repro, and when I run across it, I'll post the original.




    Ok I must not see what you are seeing. In none of the pages above does it mention unleaded Mo-gas. It is calling for 80/87 AKI "aviation grade fuel". It also most certainly does not specify 87 (r+m)/2 octage automotive fuel. I could see where you might be confused though since the av and automotive world both use the word "octane", though measured differently.

  6. #16

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    Quote Originally Posted by Aaron Novak View Post
    Ok I must not see what you are seeing. In none of the pages above does it mention unleaded Mo-gas. It is calling for 80/87 AKI "aviation grade fuel". It also most certainly does not specify 87 (r+m)/2 octage automotive fuel. I could see where you might be confused though since the av and automotive world both use the word "octane", though measured differently.
    AvGas vs Auto Fuel:
    http://en.wikipedia.org/wiki/Avgas#Grades

    Octane rating:
    http://en.wikipedia.org/wiki/Researc...rement_methods

    AKI:
    Anti-Knock Index (AKI)[edit source | edit]

    In most countries, including Australia and all of those in Europe, the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Pump Octane Number (PON).

    So, what's wrong with running auto gas in the lower compression O-320's if Auto fuel has the correct anti knock ratings?

  7. #17
    Aaron Novak's Avatar
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    Quote Originally Posted by I_FLY_LOW View Post
    AvGas vs Auto Fuel:
    http://en.wikipedia.org/wiki/Avgas#Grades

    Octane rating:
    http://en.wikipedia.org/wiki/Researc...rement_methods

    AKI:
    Anti-Knock Index (AKI)[edit source | edit]

    In most countries, including Australia and all of those in Europe, the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Pump Octane Number (PON).

    So, what's wrong with running auto gas in the lower compression O-320's if Auto fuel has the correct anti knock ratings?
    Here in the US a auto fuel can have a higher Ron, and lower Mon ( or the other way around ) and still be a legal 87 ( or other ) octane. Yet they can act completely differently in an engine. This is a hard thing for people outside the engine industry to understand. Literally I can go buy 2 batches of auto fuel that have the same pump (r+M)/2 rating, and they can have significantly different knock margins ( degrees of spark timing to knock ) on a higher output engine. Thats why in the auto and powersports engine world, we are spending huge ammounts of effort on knock control systems, and it is nowhere near easy. Aviation fuel is rated on a different research engine, and does not vary due to the nature of the testing. 100 octane aviation fuel will be the same from batch to batch, year to year. The auto fuel industry has a lot of ability to blend in whatever stock are cheap today, dope it up to just meet the sloppy standards and call it a day. Thats why you end up running 93 (ish) auto fuel in your 80/87 rated engine, as the worst cast auto 93 will probably have knock margins close enough to 80/87 to be safe for the most part.

  8. #18

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    Along with that, I'm surprised 100LL has lasted as long as it has, with all the removal of lead in everything else.
    http://www.flyingmag.com/blogs/fly-wire/avgas-pain-pump

  9. #19
    Aaron Novak's Avatar
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    Quote Originally Posted by I_FLY_LOW View Post
    Along with that, I'm surprised 100LL has lasted as long as it has, with all the removal of lead in everything else.
    http://www.flyingmag.com/blogs/fly-wire/avgas-pain-pump
    Im not. It has lasted as long as it has, because auto fuel as we know it, is not a direct replacement in many ways. The issue with replacing 100LL has less to do with the lead, and more to do with the chemical make up of the fuel itself that affects everything from fuel system materials to long term corrosion to vapor lock to who knows what else. Some engines may need to have their valve and seat materials adjusted for longer life. Sure some higer output engines need the extra knock margin the lead gives, but most do not. The best alternative I see, is a 94UL aviation specific fuel, with engines that have had their materials adjusted accordingly. Anything else is like rolling the dice.

  10. #20

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    You're not?
    They sure had no problem shoving 10%, and now 15% ethenol down our throats.
    Older engines and even gast stations are being affected by it.

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