915iS Fuel

That is a good question and Bill has raised some very good points that I will add to.

There is nothing wrong with <=10% ethanol in the fuel. (As long as it's acceptable in the airframe, the engine can handle up to 10%)

When dealing with a turbo engine, the higher the Octane rating the better. (This is 100% true and is why Rotax makes the recommendation for higher octane to help prevent detonation on higher compression or turbocharged engines)

93-E10 will pretty much guarantee that you won't see any water condense in the sump. (This is also true, however, ethanol suspends the water and Ethanol also draws moisture from the environment. This can lead to water contamination in the fuel, so it’s important to have the fuel stored in a controlled environment, changed/used frequently, and monitored for quality)

The 93-E10 is much more likely to have the pump tanks refilled a few times a week at a busy station.  Something to consider. (This is also true and a very good point! It’s also important to note the seasonal adjustment of fuel by manufacturers for high summer temperatures and low winter temperatures may affect the fuel vaporization rates. This can have consequences when using winter-grade fuel in hot summer months. Always use seasonally correct fuel)

Here are some things to consider:

-          Always use the recommended fuel as stated in the Rotax operators manual. If the manual states a minimum of 91 octane, this is the minimum octane rated fuel you need to use.

-          Fuel with 10% Ethanol is acceptable, however, you need to establish proper fuel quality control procedures to make sure the fuel is stored correctly and used frequently (always used fresh fuel!)

-          The engine can also run on 100LL fuel and this is the most stable and most controlled (quality) of all the fuels and can be stored the longest. However, the lead in the fuel requires more frequent maintenance (oil and spark) and this can bring up the cost. Using Declan or TCP fuel additive has shown amazing results and really does help scavenge the lead build-up from the engine. We have seen some really good things following an engine examination and were amazed at how little lead build up there was with the use of the fuel additives. Av-Gas has no seasonal adjustments, is less likely to be contaminated at the pump, and doesn’t vapor lock as easily.

-          93-E10 – (With proper fuel quality control procedures) – GOOD!

-          100LL (With TCP or Declan fuel additive) – GOOD!

-          90-E0 – Not the recommended octane value – Not Good

"  90-E0 – Not the recommended octane value – Not Good"

Well, now that I look at the manual again, it says "Min. RON 95." The "Ocatane rating" on the pumps in the US is not RON, it's (MON+RON)/2. Wikipedia shows an (R+M)/2 value of 90 is equivalent to RON 95. https://en.wikipedia.org/wiki/Octane_rating

Another thing, it was mentioned that E10 might be more likely to be refilled at the station more frequently. That's true, but E10 gas has a shelf life of about a month, whereas E0 has a shelf life of 3-4 months. 

So, if you were using E10 and you weren't going to fly for a month, would you use some sort of fuel stabilizer?

Please review the latest Rotax SI that was just released regarding suitable operating fluid https://lm.rotaxowner.com/mo/20201210/mo.html?fbclid=IwAR3a3Prx2hc9oa1Upd1PO1wZm23etHDiMUagZgZnlauIwxK0ESP_TKJgjm8

-          915 iSc/iS A - 915 iSc B - Min. RON 95 ( 91 AKI) 

95 RON plus an 87 MON averages to a 91 AKI, which is the octane rating you would see displayed on a U.S. retail fuel site dispenser

One should note that EN 228 Super, which is an approved fuel, has min RON and MON of 95 and 85, respectively.  This has, by definition, an AKI of 90.

Tyler Hathaway wrote:

One should note that EN 228 Super, which is an approved fuel, has min RON and MON of 95 and 85, respectively.  This has, by definition, an AKI of 90.

Interesting. That would seem to mean 90-E0 would be OK.  

I still have the question: if you were using E10 and you weren't going to fly for a month, would you use some sort of fuel stabilizer?