Hi we Operated Rotax 912 ULS engine with Indian Mogas (12-15% ethanol) for approximately 3 hours. During this period we didn’t find any abnormalities and the performance was fine.

Since it’s not permitted to use more than 10% ethanol fuel, we wish to proceed to use 100LL. 

Is there any procedure to follow for change of fuel in this case.

Thanks in advance 



  • Re: Clarification on fuel usage

    by » 5 weeks ago

    Hi Franklin,

    So long as your fuel tank is okay with your ethanol concentration the engine will be just fine. Hose now days should be just fine with your ethanol. There are places in the world that are higher than what you're using. The 10% is all Rotax tested. Even in the USA winter ethanol blend in some states is 15%. I personally would rather use the ethanol fuel over the leading of 100LL. If you do use 100LL use Decalin to help reduce the lead deposits. 

    Bottom line it's your choice. 

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

  • Re: Clarification on fuel usage

    by » 5 weeks ago

    Hi Franklin

    Just switch over to the Avgas, no special things to worry about.  I was involved with the tests on ethanol in Rotax 9 series many years ago.  it actually was a long term field test done in Brazil with 25% and the aircraft had automotive lines and filters with metal fuel tank.  The engine did just fine however there are many other concerns.  First, your engine has a carburetor and the fuel air ratio as you increase the amount of ethanol changes in the fuel.  Emissions, like NOx, climb very fast due to this.  Given this and other considerations the only approval that Rotax would issue was for 10%.  

    If you have access to products like Decalin, a fuel treatment that helps purge the lead while running Avgas, as Roger stated it is a good idea.  For sure follow the recommendations in the maintenance manual line on oil and spark plug change intervals being lower.  

    Just as a note there is some discussion currently at some high levels to test higher concentrations of ethanol.  The big problem is emissions and also fuel air ratio adjustments for higher concentrations.  We do not have a full on computer like a car that can adjust by knock sensors and O2 sensors for the correct burn.  At some point we need to recognise the limitations of a carburator system.


    Thank you said by: Jonas Andersson

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