Mixing LL100 with EN 228

by Dov Elyada in 912 / 914 Technical Questions 12 years ago

Rotax 912-series Operator's Manual (Nov. 2010, p. 2-9) implies that using LL100 avgas, though not recommended, is acceptable "when other types of gasoline are unavailable."

My question is, may I mix? Suppose some EN 228 Normal is left in my tanks but I need to fill them up in order to safely arrive at my destination. May I add LL100 on top of the EN 228?

Thanks for your advice
Dov Elyada

Re: Mixing LL100 with EN 228

by Roger Lee » 12 years ago

Roger Lee

125 5.12k 4.52k

Hi Dov,

Yes you can mix.
You didn't specify if you have a 912UL 80 hp or a 912ULS 100hp. If you have the 912UL you can use the equivalent of 87 Octane or higher and if you have the 912ULS then you have to use the equivalent of 91 octane or higher. If you have the 912ULS you can mix 87 octane with 50% 100LL, but no less 100LL (more 100LL than 87 oct. auto fuel)to get the octane level you need for the 912ULS.

from Wikipedia:

"Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are different conventions for expressing octane ratings, so a fuel may have several different octane ratings based on the measure used. Research octane number (RON) for commercially-available gasoline varies by country. In Finland, Sweden, and Norway, 95 RON is the standard for regular unleaded petrol and 98 RON is also available as a more expensive option. In the UK, ordinary regular unleaded petrol is 91 RON (not commonly available), premium unleaded petrol is always 95 RON, and super unleaded is usually 97-98 RON. However, both Shell and BP produce fuel at 102 RON for cars with high-performance engines, and the supermarket chain Tesco began in 2006 to sell super unleaded petrol rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 86 and 87 AKI (91-92 RON) for regular, through 89-90 AKI (94-95 RON) for mid-grade (European premium), up to 90-94 AKI (95-99 RON) for premium (European super).
The octane rating became important as the military sought higher output for aircraft engines in the late 1930s and the 1940s. A higher octane rating allows a higher compression ratio, and thus higher temperatures and pressures, which translate to higher power output. Some scientists even predicted that a nation with a good supply of high octane gasoline would have the advantage in air power.[2]"

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

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Re: Mixing LL100 with EN 228

by Dov Elyada » 12 years ago

Dov Elyada

3 5 0

Thanks, Roger

I didn't mention that I have a 100HP 912-ULS because the operator's handbook doesn't make a distinction in this respect. Anyway, I always use 95-octane unleaded (Israeli regular-unleaded), which everybody in this country uses for Rotax 912-series aviation motors.

I understand from you now that I can mix 95-octane with 100LL in any proportion, as in such mixing the octane level will always stay above the 91 minimum. Is that right?

Dov

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Re: Mixing LL100 with EN 228

by Roger Lee » 12 years ago

Roger Lee

125 5.12k 4.52k

Hi Dov,

You are correct. have a safe flight. :)

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

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Re: Mixing LL100 with EN 228

by Kevin Machniak » 12 years ago

Kevin Machniak

6 167 40

Is Decalin required in a mix ? .Do you add as per Decalin instructions for the 100LL ?

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Re: Mixing LL100 with EN 228

by Roger Lee » 12 years ago

Roger Lee

125 5.12k 4.52k

Hi Kevin,

If you are using 100LL then a lead scavenger should be used, but it isn't required. It will help keep the lead build up down, but won't make it all go away. Decalin is a good product that doesn't have the harsh chemicals in it like TCP so it can be kept in the cabin if need be and shouldn't hurt you plane. Decalin uses 1/2 oz. per 10 gal or 100LL. I haven't heard anything negative about Decalin and I use it myself when stuck using 100LL traveling.

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

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Mixing LL100 with EN 228

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