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Thread: Autogas

  1. #21
    Senior Member jrevens's Avatar
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    Default Re: Autogas

    Hi Josh,

    On your post #15 of this thread, the attached image refering to minimum octane for the 912is shows just a little bit of a statement at the bottom that starts out saying that “AVGAS 100LL places greater stress on the valve seats due to its...”

    What is the rest of that statement?

    Thanks.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  2. #22
    Senior Member Esser's Avatar
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    Default Re: Autogas

    AVGAS 100LL places greater stress on the valve seats due to its high lead content and forms increased deposits in the combustion chamber and lead sediments in the oil system
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  3. #23

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    Default Re: Autogas

    My 912 has water cooled heads. My ford v6 was water cooled...including the heads. After 100 hrs the ford had damaging lead deposits in the exhaust chamber of the heads. I was using 100 LL. The machinist, an A&P, removed the deposits and suggested I use non-alcohol auto fuel since the water cooled heads did not reach temperatures high enough to purge the lead. Spark plugs gave a clear indication of the lead buildup. 300 hrs later plugs did not show lead. Cost is less than 100 LL or at least similar. Incidentally, it stores well also in my mower and pressure washer. But, on cross countries use of 100LL cannot be avoided. A 23 hr flight from AZ to FL did not seem to be a problem. My view of this question is to use auto fuel as much as possible at least in water cooled engines.
    Bud
    IV Speedster
    912 UL
    IVO ground adjustable

  4. #24
    Senior Member Flybyjim's Avatar
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    Default Re: Autogas

    I will look for the receipt from Swift, but I believe it worked out to $4.65 gal.

  5. #25

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    Default Re: Autogas

    Hi Esser, I stand corrected. 91 octane is correct. My supplier buys fuel at a local refinery and blends it themselves to 92 and no ethanol so I guess I always have 92 lurking in my brain.

  6. #26
    Senior Member Dave S's Avatar
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    Default Re: Autogas

    After reviewing Josh's post and others on the octane rating for gasoline; figured I better update my post (#2 on this thread) because the references I was using for the acronyms we commonly used in antiquity - (like the 1970's) where I mentioned the octane rating of 91 for the rotax requirement is an average of two methods for determining octane i.e. R + M /2 which you normally find labeled on the fuel pump.


    Josh's post referencing the Rotax octane requirements indicates 95 Octane RON also indicates that is equivalent to 91 Octane AKI.

    Apparently "AKI", "RON" and "MON" are the more commonly used acronyms in some places

    so: AKI = Anti Knock Index = R+M/2 or RON (Research Octane Number) + MON (Motor Octane Number) divided by 2

    "R" or "RON is an octane rating determined via analysis of the fuel; while "M" or "MON" is an octane rating determined by actually running he fuel in a standard engine to determine when it starts to knock.

    Sheesh!....almost as bad as the alphabet soup of acronyms the FAA puts on us

    AKI, RON, M, R, MON, R+M/2, RON+MON/2

    What can be really confusing is seeing two numbers in the Rotax book 91 and 95, and without associating the units, or how the units are determined, pretty difficult to recognize that 95 and 91 are the same number.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  7. #27
    Senior Member Esser's Avatar
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    Default Re: Autogas

    And I think only the US and Canada use AKI. Of course we couldn’t use something the rest of the world uses
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  8. #28

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    Default Re: Autogas wiht 10% AVGAS 100

    I worked on a 160hp SUperCub in Alaska that belonged to an outlaw trapper guy. He never got annuals, no pilot license and he has over 11,000 flying in a Alaska. He insisted on using unleade car gas in his 160 high compression engine so I had a fuel blender at a local refinery help me and we determined that you only have to add 10% 100 LL to unleaded car gas and it raises the anti know index over 100. Before we did that , the trapper burned a couple of pistons in the summer on a hot day (80) low level full throttle....after we came up with the mix , no more problems.... TEL was used because it only takes a very small amount to raise the anti know indext right up there... So I am guessing in a Rotax little 100 LL wont hurt and will likely help prevent detonation or pings....The problem with a full diet of 100 LL is it will coat the inside of the combustion chamber and raise the effective compression ratio. Then if you put some cheap car gas in the same engine later, you might get into detonation area,especially at low altitude and full throttle on a hot day..
    Car gas has butane and other aeromatic fuels added to raise the antiknow index but it these things that cause problems with rubber hoses and gaskets.
    Alcohol is a another problem but pure alcohol has an antiknok index of 100 so it helps raise the antiknow index number.
    exthane, methane, propane , butane , pentane, ?,?,iso octane.... Iso octane has a knock index of 100 and that is what was historically used in a test engine and then the ratio was compared to regular car gas as to what pressure it could take before pinging.....Alkand parafin series of hydrocarbons are what is in the fuel...
    SO in summary, adding 10% avgas 100 will raise the anti knock index and provide some protection against detonation. Avgas is stable and will store for several years. I have used some gas that it over 5 yrs old....The real problem is the EPA was sued by friend of the earth and so there is a deadline to remove the lead from the fuel....so far, there have been limited results. The test engine is the Lycoming TSIO 540 J2BD engine with is turbo supercharged and makes 350 hp at 41" MAP so the thinking is if an unleaded avgas can be made to run in this engine, it will run in the rest because this engine has a fairly narrow detonation threshold.I was lucky to have a petroleum engineer who designed and built the refinery at North Pole, Alaska and another flyer who was a fuel blender at the refinery so they taught me a lot about fuels. The petroleum companies will tell you nothing because of potential liability...

  9. #29

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    Default Re: Autogas

    List of straight-chain alkanes

    The members of the series (in terms of number of carbon atoms) are named as follows:
    methane, CH4 – one carbon and four hydrogen
    ethane, C2H6 – two carbon and six hydrogen
    propane, C3H8 – three carbon and 8 hydrogen
    butane, C4H10 – four carbon and 10 hydrogen
    pentane, C5H12 – five carbon and 12 hydrogen
    hexane, C6H14 – six carbon and 14 hydrogen
    heptane, C7H16; octane, C8H18;
    There are more but iso octane has an antiknock index of 100 and that is what gasolines are compared to. If octane pings at 100, 91 car gas pings at 91% fo the pressure required to make octane ping...

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