RE: octane meathods

["Robert Myers" <rmyers@inetone.net>]

Good job, Bob.

Your question about how you get octane ratings above 100 is a good one and
the addition of tetra ethyl lead is one obvious answer.  "Isooctane"
(2,2,4-trimethylpentane) is a very knock resistant fuel due to its highly
branched structure.  It isn't, however, the *only* good fuel.  Using the
data obtained as you described one can draw a graph relating percent
isooctane and engine performance.  The ratings above 100 octane are simply
an extrapolation of the curve thus determined.  There are a number of
different fuels (methanol, nitromethane, etc. come ro mind) as well as
additives which will reduce the engine's tendency to knock and thus raise
its octane rating.  These would be effective even if the engine were
running pure, 100% isooctane.

At 11:00 PM 12/14/97 -0500, you wrote:
>Brett Dikeman said on Thursday, December 11, 1997 at  11:57 PM:
>>I would be interested in
>>seeing how the various methods are calculated/tested.
>
>This had me running for my copy of Taylor (1).  Basically, octane ratings
>compare the detonation tendency of the subject fuel to standards such
>as isooctane (less detonation tendency than average fuel) and normal 
>heptane (more detonation tendency than average).
>
>Basically, you take the fuel to be tested and run it through a test motor
>at standard conditions.  You set the compression ratio of the motor
>(obviously not your common street car motor, the CRF test motor is a
>special single cylinder rig with variable CR) so that the knock intensity
>matches the standard knock intensity as measured on the knock indicator.
>Then, using this set up, you run various mixtures of the above two fuels
>until you get a mixture that matches the knock intensity of the fuel under
>test.  The percentage of isooctane required for the match is the octane
>number.  The CFR (Cooperative Fuel Research) Committee motor method
>and research methods differ as follows:
>
>Factor                   Motor Method          Research Method
>------------------          --------------------
--------------------------
>Inlet temp.               300 deg. F                   125 deg. F
>Jacket temp.            212 deg. F                   212 deg. F
>Speed                     900 rpm                       600 rpm
>Humidity                0.0036-0.0072          0.0036-0.0072
>  (mass/mass dry air)
>
>(From Taylor, Vol. 2, p. 144)
>
>Taylor claims that since 1940, the research method numbers have shown 
>greater correlation with passenger car road-test octane numbers then the
>Motor method.
>
>Given the above, how does one get octane rating above 100?  Well, for fuels
>with less detonation tendency than isooctane, there are some test
>procedures involving either the addition of lead to isooctane or the use of
>performance numbers using the rich and lean mixtures and calculations using
>the imep of isootane and of the fuel under test.  For a detailed
discussion, I 
>refer you to Taylor.
>
>(1) Charles Fayette Taylor, "The Internal-Combustion Engine in Theory and
>     Practice, Volume 2: Combustion, Fuels, Materials, Design, Revised
>     Edition", The M.I.T. Press, Cambridge, Mass. and London, England,
>     1968 and 1985.
>
>
___
   Bob
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