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Old 05-06-2011, 10:10 AM
Location: Houston, Tx
3,644 posts, read 5,444,569 times
Reputation: 1614


Originally Posted by NJGOAT View Post
All of the different octane levels are based on petroleum. When the refinery "cracks" the crude oil they end up with different hydrocarbon chains. These chains are then separated into their composite groups and that is where different fuels come from. You end up with the following:

Methane - single carbon atom.
Propane - three atoms.
Butane - 4 atoms.
Pentane - 5 atoms.
Hexane - 6 atoms.
Heptane - 7 atoms.
Octane - 8 atoms.

In WW2 they discovered that they could add TEL (tetraethyl lead) and boost the compression resistance of fuel. Using "leaded" fuel allowed refiners to take the lower quality material and use more of it in their mix, so they may have used a mix of 60% octane, 20% heptane, 20% pentane, added in TEL and got the equivalent of "87". Of course, lead is bad for the environment and it's use was eventually banned.
Thank you for the informative essay on octate. I already know some of it but learned a lot more. One thing I can add. Lead was banned for automobile gas but is still used in the production of aviation gass, which requires a 100 octane rating. It is called 100LL, which stands for 'low lead'. Also, you don't even want to know what that stuff costs per gallon.
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Old 05-06-2011, 10:38 AM
Location: Northern MN
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100ll is 4.50 to 6.50 a gal


In February 2010 General Aviation Modifications announced that they were in the process of developing a 100LL replacement to be called G100UL, indicating "unleaded". The new fuel is made by blending existing refinery products and produces detonation margins comparable to 100LL. The new fuel is slightly more dense than 100LL, but has a 3.5% higher thermodynamic output. G100UL is compatible with 100LL and can be mixed with it in aircraft tanks for use. The production economics of this new fuel have not been confirmed but it is anticipated that it will cost at least as much as 100LL
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