MichaelGibbs(at)cox.net
Guest
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 Posted: Wed Aug 16, 2006 7:23 am Post subject: Ethanol and wing tanksEthanol and wing tanks |
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Bob sez:
| Quote: | There are many ways to calculate "octane", but if you do it the same
way autogas and 100LL are done, Ethanol is over 100 octane.
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Autogas and avgas octanes are not calculated the same way. Avgas
octane is measured using the "MON" method, while auto fuels (in the
U.S. anyway) are typically measured using the (R+M/2) method (see
below). Since octane rating represents a ratio, it cannot exceed
100. Values for octane over 100 are really what are called
"performance ratings".
Paul sez:
| Quote: | An alky engine properly designed will have more horsepower that an
optimally tuned gas engine due to higher octane.
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There may be some rules of thumb for common fuels, but technically,
octane rating has no direct correlation with engine power or
efficiency.
"Octane" is a measure of the fuel's resistance to pre-ignition and
knocking. The Research Octane Number (RON) is determined by running
the fuel through a specific test engine with a variable compression
ratio under controlled conditions, and comparing these results with
those for mixtures of isooctane and n-heptane.
The Motor Octane Number (MON) or the aviation lean octane rating, is
a better measure of how the fuel behaves when under load. MON testing
uses a similar test engine to that used in RON testing, but with a
preheated fuel mixture, a 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 gasoline will be
about 8 to 10 points lower than the RON. Normally fuel specifications
require both a minimum RON and a minimum MON.
In most countries (including all of Europe and Australia) the
"headline" octane that would be shown on the pump is the RON, but in
the United States and some other countries the headline number is the
average of the RON and the MON, sometimes called the Anti-Knock Index
(AKI), Road Octane Number (RdON), Pump Octane Number (PON), or
(R+M)/2. Because of the 10 point difference noted above, this means
that the octane in the United States will be about 4 to 5 points
lower than the same fuel elsewhere: 87 octane fuel, the "regular"
gasoline in the US and Canada, would be 91-95 (regular) in Europe.
To learn more than you ever wanted to know about aviation fuel
octane, check out
<http://www.chevron.com/products/prodserv/fuels/bulletin/aviationfuel/9_ag_specsandtest.shtm>
or <http://www.prime-mover.org/Engines/GArticles/octane.html>.
Mike G.
N728KF
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