In WWII, aromatics were mostly Benzene and Benzene derivatives, used mainly to increase the Octane number. After an Octane rating of 100 (101 - 150), the term is "performance number." In WWII, we had gasoline with two ratings, the lean rating (cruise condition, leaned out), and the rich rating (full power, full rich). We started the war running 80 / 100 fuels (generally) and ended with fuels called 115 / 145, sometimes mistakenly called grade 150 fuel. Nobody makes 115 / 145 fuel anymore except by special order.
The US
started the war using fuel with octane ratings from around 65 to 100, in 1939-40 there was no "rich rating".
Grades may have included 65, 73, 80, 87, 90/91 and 100. The lower grades were used in light aircraft and trainers.
see:
http://rgl.faa.gov/Regulatory_and_G...86f3a8c564f1a8525670c00523a93/$FILE/E-216.pdf
For the inline 6 cylinder Ranger which was available to use 4 different grades of fuel. Each engine used a different compression ratio (but no supercharger).
Large commercial and military aircraft used 87 pretty much as a minimum although a few planes using P & W Wasp Juniors had a small tank of 87 octane and several larger tanks filled with 80 octane. The 87 octane was used for take-off and then the plane cruised on the cheaper 80 octane. This was one of them.
There may have been some very short lived grades of fuel between 91 and 100 at this time. 91/96 did show up as a standard later.
Post war things get real confusing as were four grades of Military fuel (80, 91/96, 100/130, 115/145) and five grades of commercial fuel (80/87, 91/98, 100/130, 108/134 and 115/145) in 1951. Please note there were a few differences between military fuel and commercial. Commercial fuel had slightly lower evaporation temperatures, more allowable gum residue and precipitate, but lower allowable lead content in the mid grades.
Please note that during WW II there sometimes more than one specification per year for a given grade of fuel. 100/130 went through 3 if not 4 specifications (maybe more) and that does
NOT include either the pre war American 100 octane, the British pre war/early war 100 octane, or the 100/125PN fuel.
First 100/130 only allowed 3.0 CC of lead per US gallon, the 2nd allowed 4.0 CC of lead and the 3rd allowed 4.6 CC of lead. Please note that just because 4.6 CC could be used doesn't mean it was used in all batches.
Benzine was not well liked by early WW II despite being a "go to" additive in the 1920s and early 30s. It had a few problems for aircraft use if you weren't record breaking at sea level. One was that if froze at 42 degrees F. That is 42 degrees above zero, not below. Another was that it good for about 17,300btus per pound of heat value compared to the desired 18,700 Btus per gallon of av gas. While it's anti knock rating running richis very, very good it's anti-knock ability when running lean is not so great. Adding lead to Benzine does just about nothing.
C-3 was also found to 40% aromatics (!), which is about twice that of British fuels. US fuels were less than 5% aromatics, and British fuel gave early P-38s fits when they got to the UK because the engines were set up for U.S. fuels. I have little doubt that the BMW 801 in the test was not very comfortable on U.S. fuel.
Early British fuel was sometimes 40% aromatics. Early American fuel was under 2%, this was lifted to 5% for a short period to help increase production but little of this may have been actually made. The short lived 100/125 fuel was allowed to use 20% aromatics although not spelled out in specifications. The upper limit was more a by product of heat energy content specification.
Please see, "Development of Aviation Fuels" by S. D. Heron.
