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Octane additives

  • Jeff Fleming
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1 month 21 hours ago #17278 by Jeff Fleming
Jeff Fleming created the topic: Octane additives
The manual on the 9th 14 calls for 95 octane. The only thing in my area that I can find is 91. Is it safe to use an octane additive?

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1 month 18 hours ago #17279 by Roger Lee
Roger Lee replied the topic: Octane additives
Your 91 Octane is fine.
Read this:

Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

Motor Octane Number (MON)

Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.[citation needed]

Anti-Knock Index (AKI) or (R+M)/2

In most countries, including Australia, New Zealand and all of those in Europe,[citation needed] the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).
Difference between RON, MON, and AKI

Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system.
See the table in the following section for a comparison.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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1 month 18 hours ago - 1 month 18 hours ago #17280 by Roger Lee
Roger Lee replied the topic: Octane additives
Actual octane rating table

EURO RON MON US: (R+M)/2 (AKI)
90 83 86.5
92 85 88.5
95 87 91
96 88 92
98 90 94
100 91.5 95.75
105 95 100

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 1 month 18 hours ago by Roger Lee.

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1 month 2 minutes ago #17285 by Glenn Martin
Glenn Martin replied the topic: Octane additives
As Roger says...
Depends on where you live and what they version of octane rating they are quoting. In NZ we quote RON and therefore "91" would NOT be suitable we have to use "95" for 912ULS.
Where do you live ?

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4 weeks 2 days ago - 4 weeks 2 days ago #17289 by Roger Lee
Roger Lee replied the topic: Octane additives
Jeff lives in Arizona. Our 91 Oct. (AKI rated fuel) also has pump advertised 10% ethanol. That said I have friends that test every single batch of fuel they get over the last 12 years. It is usually
6-7% and they have only seen 8% a couple of times.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 4 weeks 2 days ago by Roger Lee.

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4 weeks 2 days ago #17294 by Glenn Martin
Glenn Martin replied the topic: Octane additives
Thanks Roger,
As you say the "91 AKI" will be fine. Our CAA (Equivalent of your FAA) issued a warning here about Rotax and Ethanol fuels but I believe that was for a 15% blend. Rotax does have a limit which I am sure you know off the top of your head.

I have a Sting S4 composite aircraft and there is a guy in California whom had all sorts of trouble with his composite fuel tank and Ethanol fuel (Richard De Haven Sting flight) so not a Rotax issue but one to be careful of....

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4 weeks 2 days ago #17304 by Roger Lee
Roger Lee replied the topic: Octane additives
Rotax publishes 10% ethanol use. That's what they tested. There are places in the world that are over double this. Fuel tanks can be the issue especially if they are fiberglass. Call your aircraft Mfg to make sure about ethanol use and their tanks. Hose and engine aren't usually the issue. Fuel tanks can be sloshed with protectants to ensure ethanol isn't an issue. Flight Design sloshes all their tanks and you can put anything in them.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
The following user(s) said Thank You: Glenn Martin

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