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I operate a Rotax 912ULS in a C42 Microlight, naturally as we have not been flying for almost 3 months I plan to replace the fuel tank contents ( approx 20L) incase of deterioration. I have always used MOGAS unleaded RON95 BS EN228 without any issues. I was contemplating upgrading with MOGAS super unleaded RON 97/98 and wondered what grade unleaded fuel people use in their rotax 912 uls aircraft. The ROTAX SI 912-016 R8 specifies using MOGAS Min Ron95 for the 912uls EN228 Super or EN228 Super plus. Would I be correct in assuming the EN228 Super is RON95 & the EN228 Super plus is 97/98 ??

Phil

  • Re: MOGAS Fuel

    by » 3 years ago


    Using fuel in an internal combustion engine with a higher Octane rating than is needed by the engine is of no benefit. This does not help the engine or improve performance. The only possible benefit is that a higher octane fuel will take longer to go stale as it has further to drop.

    Our club has 912ULS engines and we have always used RON 91 ASTM D2699 fuel here in NZ for over 7000 hr. When the engines reach 2100 hrs they are still in great condition, original compression and clean internally.

     

     


  • Re: MOGAS Fuel

    by » 3 years ago


    In EN228 terms regular used to be 91 octane, super was 95 and super plus was 98. This changed a few years ago so 95 officially became just unleaded (but commonly called premium in UK) and 98 became super. There is no super plus now. This change seems to have escaped Rotax.

    So unleaded (or premium) 95 should be OK for a ULS. However some brands of super have the advantage of 0% alcohol whereas 95 has to contain alcohol unless it is from a low volume supplier (this concession is UK only I think.) The pump still has to be labelled E5, this means up to 5%, including 0%.

    I only became aware of this confusing situation recently from someone with more specialist knowledge than me, I previously thought you had to use super (i.e. 98).


  • Re: MOGAS Fuel

    by » 3 years ago


    EN228 Super/ RON 95 with up to 10% Ethanol is all you need for the ULS engine.
    As Glenn stated, higher Octane fuel will not improve anything other than your Fuel supplier's profits.

    3 months is NOT a long time to hanger a plane.
    Drain a quarter Liter of fuel from your sump and smell it.
    If it smells like Gas and NOT Turpentine and is Not full of Water, it will be fine.
    The first portions of the gas to get lost are the light fractions that make starting easier.
    If your engine starts on this "Old" gas, it will Run fine.
    You have a 50-liter tank,  Add at least another 20 liters to the "Old" gas to "Freshen it Up" and go fly off the tank.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


    Thank you said by: Philip Meech

  • Re: MOGAS Fuel

    by » 3 years ago


    Phil.

    I changed from NZ   95 to a fairly new 100 mogas ( no ethanol) primarily for longevity of storage. Was told 6 months with almost nil drop in octane. However found serious swelling issues with the carb diaphragms. Think it was additive related.

    Pete

     

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    Thank you said by: Philip Meech

  • Re: MOGAS Fuel

    by » 3 years ago


    RON, road octane number, is not really a good way to specify aviation fuels.  (RON and ROZ are the same test) AVGAS is tested and specified by MON rating.  RON is generally used as a measure for lower RPM/lighter load uses.  MON generally predicts how fuel will react under higher RPM/heavier loads.  In the USA they average these (R+M)/2 method to give you AKI, anti-knock index.  That said if you are not yet having detonation issues with your fuel it suggests you have not reached the limits of detonation for that application.  A higher rating will control the onset of detonation so for that reason a higher grade could be considered a safety consideration.  Yes, it will not give you more power however it is better protection from detonation.  

    If you contact your fuel companies, you will see that they claim fuels will not change enough to worry about obtain values in a 6-month window.  There is a big caveat on that when we start to add ethanol, that drops the fuel useable window to 3 months.  If you live in a country or region where the blend fuels for temperature, like most of North America, you must be very careful not to use winter blend fuels in the summer months.  This primarily is due to the extreme changes within the fuel from the supplier to give you better fuel vaporization in cold temperatures.  For most of the USA that is mid-September to mid-April for winter fuels and in the summer months it changes.  The primary change is the RVP, Reid vapor pressure, of the fuel.  Avags generally is less that 7.8 to 9 PSI which will be consistent all year.  Auto fuels however can vary drastically on RVP, from summer of as little as 7.5 up to 9 and winter blends up to as high as 15 (yes above atmospheric pressure) 

    Ethanol can create some major changes.  Once ethanol is blended into fuel it becomes hydroscopic, absorbs water.  if there is enough moisture in the air this can start to drop out in a condition called phase separation.  Don’t worry too much that is not the worst of it.  If the ethanol drops out the real problem is the value of the octane can drop.  For a 10% ethanol blend that can be as much as 2 points of the total octane of the fuel.  (pure ethanol itself has an octane of 113 and is used to raise the octane of a poorer quality fuel) For this reason never store ethanol fuels longer than say 3 weeks.  My reasoning is we have no idea how long it was in transport or storage before we got it for the aircraft, so why take the risk.  

    Stuck?  Not sure what to use?  Not sure what is in your tank?  The good bit is you can top up with some Avgas 100LL (that is on the MON scale by the way) it will blend just fine and help increase your octane while your auto-fuel will cut the lead within the avgas volume.  

    So to answer the original question.  Use the higher-grade fuels, it is better protection from detonation.  


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