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Thread: Mogas/Compression

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    D.A.'s Avatar
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    Mogas/Compression

    I did a search and apparently the use of non-ethanol auto fuel is an even bigger topic than before. That being said, I couldn't find the comfortable compression level for Mogas use stated as before. I remember threads from years ago and I THINK 8:5-1 was considered doable reliably, has that changed with more years of experience now? Also, I thought I saw a post somewhere that suggested Lycoming Angle Valve engines couldn't take as much compression with Mogas as parallel valve engines, is that correct?Thanks

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    cubdriver2's Avatar
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    I'm 8.6 and burned it for years. JimC who is more knowledgeable said 9.0 was about the limit on 91oct

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    The combustion chambers and crude ignition systems are the biggest problem with aircraft. A flat open dish with no turbulence inducing squish bands is the biggest problem. These engine might run better with a single spark plug and a well programed timing curve. Well two good timing curves.
    Recently with the introduction of an advance curve with modern ignitions the engines will burn Mogas safely.
    The O360 parallel valve meets low low compression needs since it is an 80 Oct certified engine.

    Compression ratio itself has nothing to do with octane requirement. I drive a 50yo carbureted car with 10:1 compression on 91Oct non eth. But cars have had technological improvements since pre WW2. Few airplane engines have had any. If anything with modern metallurgical changes they are worse. By today's standards that is low compression. How many here drive turbocharged engines, there equivalent compression ratios exceed 16:1 today.
    I still would love to know where that design study done by Continental with Honda engineers went. All I can guess is the engineers committed suicide due to the dark ages restrictions they were held to.
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    I want to add to this, I was one of the earliest onboard for this STC back in 1983 for the C150 I had. The fuel specified by the STC and limitations imposed when related to the fuel available today have little relevance to the original restrictions from back in the early 80s.
    The gasoline produced back then was crude compared to the rocket juice made today to meet the engineering demands of our highly technical road vehicles.

    To me, stating 40YO engineering restrictions is not a plausible limitation. Granted other than the few who have installed modern ignitions on there aircraft nothing else has changed with our planes. By regulation the FAA prohibits change with our getting near 100YO engines that have not seen any improvement in over 60 years.
    Look back at a 60YO Ford or Chevy motor, What are your daily drivers today.
    Look at Europe's aircraft engines now, many based on modern automotive engines.

    Maybe, just maybe someone will take a new Ford 3.5 Truck engine and put a gearbox on it for aircraft use. Keep it free from 80YO regulations and let it fly.
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    frequent_flyer's Avatar
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    Quote Originally Posted by CharlieN View Post
    The O360 parallel valve meets low low compression needs since it is an 80 Oct certified engine.
    There are many variants of the O-360 parallel valve engine with different compression ratios. According to Lycoming documentation only the O-360-B and O-360-D series engines are approved for 80/87 fuel (format lost by copy/paste but should still be understandable):

    FUEL AND OIL –
    *Aviation Grade Fuel
    Model Series Minimum Grade
    O-360-B, -D 80/87
    O-360-A1P, -C1F, -C4F; HO-360-C1A 91/96
    O-360-C, -F; HO-360-A, -B; IO-360-B, -E; HIO-360-B 91/96 or 100/130
    O-360-J2A 91/96 or 100/100LL
    IO-360-L2A, -M1A, -M1B 91/96 or 100LL
    HIO-360-G1A 91/96 or 100LL
    O-360-A, -C1G, -C4P, -A1H6; TIO-360-C1A6D 100/100LL
    IO-360-B1G6, -C1G6, -J, -K2A, -A1D6D, -A3B6, -A3D6D;
    HIO-360-A1B 100/100LL
    AIO-360-A, -B; IO-360-A, -C, -D, -F 100/130
    HIO-360-A, -C, -D, -E, -F 100/130
    TIO-360-A 100/130

    Note the 7.2:1 compression ratio of the -B and -D engines:


    O-360-B, -D Series
    FAA Type Certificate .................................................. .................................................. ................................286
    Rated horsepower........................................ .................................................. .................................................1 68
    Rated speed, RPM............................................... .................................................. .......................................2700
    Bore, inches............................................ .................................................. .................................................. .5.125
    Stroke, inches............................................ .................................................. ................................................4. 375
    Displacement, cubic inches............................................ .................................................. ...........................361.0
    Compression ratio .................................................. .................................................. ................................... 7.2:1
    Firing order .................................................. .................................................. ......................................... 1-3-2-4
    Spark occurs, degrees BTC............................................... .................................................. .............................25
    Valve rocker clearance (hydraulic tappets collapsed) .................................................. ....................... .028-.080
    Propeller drive ratio .................................................. .................................................. ................................... 1:1
    Propeller driven rotation (viewed from rear) .................................................. ....................................Clockwise

    Ref: https://www.lycoming.com/content/ope...O-360-60297-12
    or search for "Lycoming Part No. 60297-12"

    I don't know at what 100LL price I'd be tempted to run my CC 363i on auto gas but with $5.14/gal at my base airport were are not there yet.
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    [QUOTE=
    I don't know at what 100LL price I'd be tempted to run my CC 363i on auto gas but with $5.14/gal at my base airport were are not there yet.[/QUOTE]

    I think for many today it is more a question of availability of 100LL rather than price. It is in my case. I'm looking at options for a new engine and am leaning towards 8.5:1 or less so that e-free high octane car gas can be used.
    "Fast is fine, but accuracy is everything." Wyatt Earp
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    Not sure how long out lead free avgas is but will soon be here.
    California and Massachusetts have residents sewing the state and airports over the "lead falling in my yard and garden" I did not know Beverly Mass had many household gardens, but they have rich lairs.

    The UL fuel is readily available and suitable for use in C-402 and such.

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    D.A.'s Avatar
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    Wow, as usual, you guys are all way over my head - LOL. I just asked because an after market company that I stumbled onto offered 8:5-1 pistons for a parallel valve engine I was thinking of overhauling. Good info, thanks!
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    Bill Rusk's Avatar
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    My understanding is that 8.5 to 1 is a no brainer for 87 oct auto gas. I am pretty sure Ken at Lycon told me 9 to 1 was safe for auto gas but I would personally try to get 89oct or above with that. My next engine will be 9 to 1. I feel that is safe with auto gas.

    Bill
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  10. #10
    D.A.'s Avatar
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    Quote Originally Posted by Bill Rusk View Post
    My understanding is that 8.5 to 1 is a no brainer for 87 oct auto gas...
    Awesome! I'm running with that.

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    Gordon Misch's Avatar
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    I'm using the Peterson STC for MOGAS with 8.5 compression O-320. The STC specifies 91 octane. I have no idea whether lower octane would be prudent - that's just what the STC says, as an FYI.
    Gordon

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    D.A.'s Avatar
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    Quote Originally Posted by Gordon Misch View Post
    I'm using...MOGAS with 8.5 compression O-320...91 octane...
    Exactly what I wanted to hear! Thanks

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    I just had a O-360 angle valve 195hp engine built for me that is set up for 91UL. I’m not really a gear head so don’t know the compression ratio, but I could ask if you need to know.

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    I am not sure how to link to is but this mornings FAAST Blast is,

    Today, the FAA and our industry partners announced a safe path toward an unleaded general aviation future. You probably have many questions on what this means for your aircraft, what the timing is, and how the FAA will support the diverse group of piston engines operating today.

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    I had a call from AOPA yesterday about putting an R&D ticket on an airplane for them to run testing with unleaded fuels. Not entirely sure where they are going with it, but sounded interesting.
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    Our engines are designed to develop peak cylinder pressure at 15-16° after TC. Engine manufacturers establish timing advance in different engines to achieve max pressure at the proper crank angle in high power configuration. Most Lycomings are timed at 25° before TC. My 390 uses 20° before. Increasing compression ratio, like reducing octane, warrants retarding the timing to compensate for faster fuel burn, or we risk developing max pressure closer to TC, which is dangerous. Having max pressure later than 15° after will give up a little torque but won’t harm the engine. Lower octane fuels, higher compression ratios, and especially the combination of the two will require adjusted timing curves in many engines.

    For you others with EI, here’s a little Pmag info. Pmags are set for 25° advance and don’t shift timing until MAP drops below 25”. Max advance occurs at 22”. The A curve max shift is 9°. So 34° advance at 22” MAP. For fixed pitch airplanes that don’t develop high MAP this explains why some guys see uncomfortable CHTs and why Pmag instructions suggest retarding the timing to improve temps. The “danger” will be what happens in economy cruise when the timing is advanced using lower octane or higher compression than the engine was designed for or tuned for. I’ve been advised to use the A curve AND to retard 5° to get the 20° the engine requires. That with 100LL. How to adapt to lower octane will be interesting, and ethanol may be the answer to maintaining high compression without detuning.
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    Timing vs compression ratio vs fuel octane....
    Retarding the timing to run lower octane fuel with a higher compression engine is one "solution",
    but the resulting loss in power kind of negates the reason for the higher compression.
    Depending on where you operate, getting e-zero mogas can be kind of a crap shoot--
    let alone a particular octane blend.
    My 470 has only 7:1 CR, so it'll burn just about anything.
    I'm curious just how much of a bump in horsepower could *realistically* be expected
    by going up to say 8.5:1 (assuming suitable octane fuel).
    There is 91 octane available locally, but my source for 87 octane is a lot closer & less hassle,
    so I'm not sure if bumping it up would be worth the trouble.
    Cessna Skywagon-- accept no substitute!

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    180Marty's Avatar
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    I'm curious just how much of a bump in horsepower could *realistically* be expected
    by going up to say 8.5:1
    I think that describes a Texas Skyways O470UTS that is 252 hp at 2600 rpm so up 22 hp.

  19. #19
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    A friend was running junky mogas in Africa through his 180 hp 172. The CHTs were super high with the stock 8.5:1 pistons. Switching to the lower compression (7.2:1?168 hp?) pistons solved the problem.

    Sent from my SM-G965U1 using SuperCub.Org mobile app
    Last edited by DJ; 02-24-2022 at 11:13 AM.
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    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    I had a call from AOPA yesterday about putting an R&D ticket on an airplane for them to run testing with unleaded fuels. Not entirely sure where they are going with it, but sounded interesting.
    What engine is in this airplane?
    N1PA
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    skywagon8a's Avatar
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    Quote Originally Posted by CharlieN View Post
    I am not sure how to link to is but this mornings FAAST Blast is,

    Today, the FAA and our industry partners announced a safe path toward an unleaded general aviation future. You probably have many questions on what this means for your aircraft, what the timing is, and how the FAA will support the diverse group of piston engines operating today.
    ​The rest of the FAAST Blast.
    We want you to hear it first and directly from us. Here are the facts:

    WHAT WAS ANNOUNCED
    A new initiative that outlines how the FAA and our aviation stakeholders can safely eliminate the use of leaded aviation fuel by the end of 2030 without adversely affecting the existing piston-engine fleet. This isn’t a mandate. It’s a way that we can safely make this transition.

    HOW WE WILL ACHIEVE THIS
    There are four pillars to this partnership between government and industry:

    • Develop Unleaded Fuels Infrastructure and Assess Commercial Viability: Industry stakeholders will coordinate the production of commercially viable unleaded fuels and create the necessary infrastructure and distribution channels to support widespread usage of these fuels.
    • Support Research & Development and Technology Innovations: The FAA and industry stakeholders will support research and testing of piston engine modifications and/or engine retrofits that may be necessary for unleaded fuel operations.
    • Continue to Evaluate and Authorize Safe Unleaded Fuels: The FAA will address fleet-wide authorization of unleaded aviation fuels of different octane levels. The Piston Aviation Fuel Initiative will continue to evaluate, test and qualify high-octane aviation unleaded fuels with the objective to ultimately transition the fleet to unleaded aviation fuel. Learn more at faa.gov/sustainability.
    • Establish Any Necessary Policies: The EPA is evaluating whether emissions from piston-engine aircraft operating with leaded fuel contribute to air pollution that endangers public health. The EPA plans to issue a proposal for public review and comment in 2022 and take final action in 2023, which can lead to EPA regulation of lead emissions from piston-engine aircraft. The FAA will subsequently publish regulations that certify piston engine modifications, new piston engines that do not require leaded aviation fuel, and regulate fuel components for aviation fuels.


    WHAT HAPPENS NEXT
    As our work progresses, we will keep you and your pilot associations informed about key issues such as unleaded fuel evaluations, infrastructure development, decisions about engine modifications and retrofits, and changes in regulations. We will work on getting every member of the GA community involved so that the transition away from leaded fuel will keep you flying safely.

    If you have comments, you can email the FAA at EAGLE@FAA.gov.
    Eliminate Aviation Gasoline Lead Emissions (EAGLE) Initiative

    Sincerely,
    The FAA
    N1PA

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    BC12D-4-85's Avatar
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    2030? EPA? Hope they can reach a consensus before they retire (sarcasm)

    Gary
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  23. #23
    skywagon8a's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    2030? EPA? Hope they can reach a consensus before they retire (sarcasm)

    Gary
    This get rid of the lead issue has been on the docket since all of the current employees of the FAA and EPA were in high school. No hurry.
    N1PA
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  24. #24
    BC12D-4-85's Avatar
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    Who has the biggest stick? FAA or EPA - excluding Washington DC's elected officials-representatives? If all three get involved with hearings and meetings we may outlive the result. Let's enjoy the moment and go fly while we can. Various States can do what they will assuredly.

    Above it was asked in #17 about the effect of a 7:1 vs 8.5:1 on HP. I expect that's been answered for example for several engines like the O-320's and O-360's providing other parameters remain the same. Maybe there's a 6-7% increase when they're a normally aspirated/non-altitude engine?

    Gary
    Last edited by BC12D-4-85; 02-24-2022 at 08:50 PM.

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    The AOPA interpreted the fourth "pillar" as maintaining 100LL availability until they figure things out.
    Anybody believe GAMI (not GAMA) when they say they already have a fleet-wide solution? (G100UL).
    What's a go-around?

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    Quote Originally Posted by Skywalker View Post
    Anybody believe GAMI (not GAMA) when they say they already have a fleet-wide solution? (G100UL).
    YES, the technology has been here for decades, I made comments earlier in this thread that no one cared to read or comment on but the fuels are there.
    AOPA and members of our government make major money for this change to be delayed as long as possible.
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  27. #27
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    Fuel replacment won’t happen overnight. Production, transportation, storage, and dispensing will require new equipment as aviation transitions from 100LL to a different fuel. The cost of a redundant distribution, storage, and dispensing infrastructure will be mind boggling. Who’ll pay for that?

    The fuel itself is the easy part. Getting it into our planes will be the hard (and expensive) part.
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    Quote Originally Posted by stewartb View Post
    The cost of a redundant distribution, storage, and dispensing infrastructure will be mind boggling.
    Not trying to be difficult, but I do have experience in this. I ran a small Av Fuel retailer back in the 90's for a few years.

    Redundant distribution is not necessary. The same trucks are used for almost all gas type products. They are not quarantine tanks. There isn't even any difference to the driver - except the placard number. It's as simple as dispatching a load of "new " fuel rather than "Fuel Classic." (sorry Coca Cola) Last I heard Av fuels are not sent through pipelines anywhere, so that should not be a consideration.

    Storage is similar. As it will be a direct replacement product, it can be stored in the same vessels that had stored the fuel it is replacing. At worst, the storing facility will have to empty the tank prior to refilling with the new. Believe me this happens a lot anyway.

    Dispensing is equally simple. Assuming similar flash points and outgassing coefficients, the equipment should likely not need recalibration. The only change should be price point on the dispensing machinery.

    I suspect that with the reason for change and likely very similar nature of the new product, it will be acceptable to mix with the old, therefor making storage and the changeover a very simple process. My suspicion is most places will wind up receiving their first load of "new" on top of the dregs of old into their usual storage device - and just keep rolling on.

    The most likely problem I see with the changeover is changeover of process at the refinery. Not knowing what processes may be different, or what additives needed, changing the "production line" could be a time consuming process. That could tax standing reserves while distribution is supplied. Since its such a small piece of the overall market, the effort likely won't receive prioritization, and so the lag in time could be challenging for front line supply.


    I agree that figuring out the new formulation should be (relatively) easy. Of course now that the government's getting involved, it won't be fast.

    ( no hate allowed on that last comment. I'm a recovering former Federal employee myself. )
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  29. #29

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    Quote Originally Posted by RedOwlAirfield View Post
    Last I heard Av fuels are not sent through pipelines anywhere, so that should not be a consideration.
    Are you referring to Fuel as Gas or Jet fuel. I question this since most Jet fuel is shipped by Pipeline.

  30. #30
    stewartb's Avatar
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    I made my comments after having a conversation with the fuels manager for the company that imports all 100LL into Alaska. He thinks this transition will never happen. He made a pretty good case for why. Ultimately I'll just go with the flow whichever way it works out. I can adapt.
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  31. #31
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    I’ll be saving $134.75 (based on current prices this week) per 55 gallon (full tanks) fill up

    MoGas is a no brainer for me

    I can live with the 5hp loss for my engine being built for MoGas

    Edited to add: The above is for 91UL non-ethonal
    Last edited by Utah-Jay; 03-02-2022 at 11:20 AM.
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    That's about the same per-gallon savings I see,
    buying locally-available 87 octane e-zero mogas vs 100LL at my home airport.
    Cessna Skywagon-- accept no substitute!

  33. #33

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    Quote Originally Posted by CharlieN View Post
    Are you referring to Fuel as Gas or Jet fuel. I question this since most Jet fuel is shipped by Pipeline.
    I was referring to Av Gas - and I apologize for the incorrect nomenclature. The jet world is so far from my aviation experience that my mind doesn't even consider it.

    Regarding Jet Fuel going via Pipeline, that must be a new thing or regional. I know in the 90's none of the pipelines coming into the Atlanta ( Doraville) area carried Jet Fuel. It was really quite a big issue too, as the current truck driver shortage began of course in the "Suicide Wagon" industry. Suicide Wagon is what we drivers used to call gas tankers. The job paid terribly, usually required deliveries in places God never intended a truck to go and bad working hours. Oh, and it was high risk. Many times I couldn't get Av Gas until the airlines got all theirs delivered. I understood it, but it was a scheduling consideration.

    I'd be interested in details of jet fuel pipeline practice. Back in the day they were told since it had to be trucked from the line head to the airport anyway, there was no value to dedicating a line for it. Additionally at the time, Mo Gas demand was incredible and growing. So where is the line head there in the Northeast? Or have lines been constructed direct to Airports?

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    Quote Originally Posted by stewartb View Post
    I made my comments after having a conversation with the fuels manager for the company that imports all 100LL into Alaska. He thinks this transition will never happen. He made a pretty good case for why. Ultimately I'll just go with the flow whichever way it works out. I can adapt.

    If the EPA weren't involved and the political climate were different, I might agree with him. These days though, because our fuel has the word "lead" associated with it, the fear and paranoia machine that is current society WILL have it done away with. I only see two options and I don't think most folks care which one happens. One is we get new "friendly" fuel to use - price be damned. The other option is we don't and we can't fly. I truly believe that the American public couldn't care less - unless they hate us for being rich. The only real option for us is a new fuel. Being an optimist I'll continue to function with that assumption until proven wrong.

  35. #35

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    Quote Originally Posted by RedOwlAirfield View Post
    So where is the line head there in the Northeast? Or have lines been constructed direct to Airports?
    Direct to airport. Airport has enough storage just a temper the flow. Gasoline is piped to depots, trucks transport to stations. Around here all brands pull their gas from the same depot. Ethanol is loaded on the truck last as it is leaving for it's route. If I am correct the truck blends the fuel at the station as it delivers.
    For our electric power generation stations, their LNG is piped directly to them as well as to the depots for distribution to home & industry. Same with heavy oil. Many regions such as around cities the homes get their utility gas direct from the main feed.

    Maps of all the pipelines can or used to be found online, it is almost frightening how many underground lines are hidden under the dirt.

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    So just how hard would it be to put a knock sensor on a lycoming cylinder? DENNY

  37. #37

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    I expect there would be an awful lot of mechanical noise to program circuitry to filter out.

  38. #38
    BC12D-4-85's Avatar
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    https://resources.savvyaviation.com/...-pre-ignition/

    Says watch the individual cylinder's CHT (rise) and EGT (drop) as potential signs of detonation. Can be high intake air temps - fuel grade - timing - compression - hot spots. No guarantees of course.

    Gary

  39. #39

    Join Date
    Jan 2021
    Location
    Nevada
    Posts
    85
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    Quote Originally Posted by CharlieN View Post
    Direct to airport.

    Makes Sense. Glad they finally got that done.


    [/QUOTE]Around here all brands pull their gas from the same depot. [/QUOTE]

    Same as back in the day. Everybody in the region was selling the same gas regardless of the brand. [/QUOTE]

    [/QUOTE]If I am correct the truck blends the fuel at the station as it delivers.[/QUOTE]

    We never used to, but we've already established that my experience is out of date. I'm not willing to take that job again just to find out how it's done now.

    Thanks for the information.

  40. #40

    Join Date
    Aug 2015
    Location
    AK, ME - what time of year is it?
    Posts
    730
    Post Thanks / Like
    Denny's comment about a knock sensor made me laugh out loud because as I was reading through all this my thoughts were to those of us who have to use staged/stored gas that can sit for months. Long term stable storage of lower octane fuels is going to be a real issue for folks in the boonies. Lowering octane also lowers the length of time gasoline stays stable (forming gums, varnishes, and lower octane hydrocarbons). 87 octane gasoline starts to degrade after about three months; 93 closer to nine months. Our Beavers ran fine on 100ll that had been stored in full, tight 55g drums for 3-4 years.

    Octane numbers can be thought of as "anti-knock indexes," where the higher the number the more heat and pressure can be put on the fuel before it spontaneously combusts. I suppose we can start adding MMT and stabilizers to our lower octane fuel to compensate. Proper storage helps a lot: Race Fuel Storage - Sunoco Race Fuels

    I'm putting 7.8:1 pistons in my IO360 build to head off problems before they develop.

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