In article ,
(Hildegrin) writes:
Cub Driver wrote in message . ..
British based Spitfire IX squadrons had converted to 150 octane
(actually 100/150 octane, for lean/rich rating) by, or during, May 44.

Is this the same as 100 octane, then? As used for example in the
Curtiss P-40?


The common 100 octane fuel had an octane rating of 100/130, which
means 100 in lean mixture, 130 in rich mixture. 150 octane was
actually 100/150. I suppose that means no difference in lean mixture,
but in rich it had a tremendous effect. The Merlin went from 67" to
82", for example (although the USAAF rated them more conservatively,
at 72" iirc)

100/150 wasn't in use until the spring of 1944, although it was being
tested in 1943.

The Lean Mixture/Rich Mixture rating system didn't get adopted until
late 1942 or early 1943. (For those who don't know, the first number
is the Lean Mixture rating, the second is the Rich Mixture.
Before then, ratings were rather arbitrary, and true antiknock
performance depended on various characteristics of the individual
blend. Since Gasoline isn't a specific chemical, but a blend of
various hydrocarbons, performacne at one particular test point didn't
necessarily mean the same performance across the full range of
conditions. The Lean/Rich rating system, standardized testing using
calibrated sensors to detect knock, and the definition of
characteristics that were seen to be important (Antiknock, Vapor
Pressure, viscosity, Specific Gravity, & a whole slew of other stuff)
was an important bit of standardization by the U.S. and U.K.

Hildegren, have you checked out the N.A.C.A. Technical Reports Server?
(It's also mirrored at Cranwell) Among the thousands of reports is a
whole series on Aviation Fuel development, and the development of
testing methods.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster