Originally Posted by
megan
As I said, for ratings above 100 the community has adopted the word "Octane", but technically it's not correct. Octane rating of a fuel is one that has the same knock characteristics of a particular mixture of iso-octane and heptane. 90% iso-octane and 10% heptane has an octane rating of 90. Pure iso-octane ie 100%, has a rating of 100 octane. With a fuel that has better knock characteristics than 100% iso-octane they obviously had to come up with a means of quantifying the knock rating, hence the "Performance Number". As you can see from the chart both lean and rich ratings are given as PN ("Performance Number") because both are above 100, though they seem to have transposed the rich and lean numbers. Once again, technically 100 is as high as an octane rating can go. I must emphasise the word technically ie the petroleum industry, not community common usage.
Not so..
Perhaps I wasn't clear enough in my previous post.
The 100/ 130 bit in Avgas 100/ 130 for example refers to 2 different test results using 2 different engine types.
The 100 number is an Octane number in this case a MON (Motor Octane Number) obtained by testing the fuel on a MON engine, method ASTM D 2700.
The 130 number is a PN (Performance Number) determined on a F4 Supercharged engine, method ASTM D 909. The 2 engines are quite different, the methods are very different as are the results. One is an Octane number, one is a Performance Number.
When running a MON test on an Avgas sample the result is always over 100 because the 100/130 bit refers to a minimum spec of 100. The reference fuels over 100 required for the test are prepared by adding TEL (tetra ethyl lead) to isooctane.
There is an error in that Shell info sheet. The method is ASTM D 909, not 910..