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On 15 Jul 99, at 8:52, Michael Geurink wrote: > With my aircooled aircraft mechanics hat on I fully concur with Jim. Take > the octane number on the pump as directly related to flashpoint. The lower > the number, eg 87, the lower the temperature and/or pressure the fuel will > spontaneously ignite. That's why we flyguys use 100/130 & occasionally 140 > octane fuel. It is my understanding that avgas uses a completely different rating system for octane, so you cannot compare the octane numbers. I have NO idea why this is so. > Actually it's usually not even the octane content that is > referred to with the number. It used to be but it's more efficiently done > by other chemicals now. Pumps by us here in no-VW-show-country (Indiana) > declare the number on the pump to be an anti-knock rating rather than the > popular octane nomenclature. Under the automotive system the octane rating is measured by comparing the resistance to knock of a particular fuel to that of pure Octane (straight chain 8 carbons, 18 hydrogens.) If they are the same then the fuel is given an octane rating of 100. It turns out that there are 2 popular ways to make this comparison and they end up giving different numbers. The 2 are called the RON (Research Octane Number) and the MON (Motor Octane Number.) The number that is usually put on the pump in the US is the average of the 2 = (RON + MON)/2, but the number that VW specifies as required is the smaller of the 2, so this explains why we can almost always "get away with" a couple of % less than what VW seems to ask for. Jim - ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* -----------------‹Xá------------------------------------------ Search old messages on the Web! Visit http://www.vwtype3.org/list/