enginehistory.org

[jjuutinen]

Any information on what would the octane/PN rating of current 98E automobile fuel if rated with avgas method?

[szielinski]

Recently there has been some consternation about ethanol content in petrol here in Australia. Lately when I have been filling up at the local there has been a print on the counter of the analysis of that week's/load's fuel. One thing I did notice was that there was a "scientific rating" that seemed to be about the same increase in PN as you would expect from the rating of the fuel mentioned.
I'll grab a copy and post it if I can.

[szielinski]

I haven't forgotten, just left the bit of paper on the kitchen bench.
Something I found out in the interim, though, the only petrol I know of here (Australia) that has a rating of 98 is from Shell, and is called "Optimax". The data I have left at home is about "Vortex" (sold by Caltex) which is a fuel rated at ~95.
From memory the lead replacement petrol was higher anyway at 96.9. This is the RON - Research Octane Number (the MON - Motor Octane Number is lower at about 85).
Which suggests something similar to the two number PN ratings.
How different that is to the "avgas" method I don't know, but I will still see if I can find out for you. Again apologies for the delay.

[szielinski]

Ok, here goes...
for the "Vortex" fuel, RON 95.2, MON 84.8, volatiles 28.5%
for LRP, RON 96.2, MON 84.3, volatiles 31.1%
(I'll keep an eye for similar results at the Shell outlets).
Dividing 96.2 by 84.3 gives around 114%, which is NOT the same result as 130/100 (130%); so I would guess that the RON is not calculated the same way as for aviation ratings since there is such a big difference in maximum octane rating.
Maybe you could get onto one of the oil company web-sites and ask them (particularly if they make avgas). Also, ask the guy who wrote the 100LL fuel article in TM.