Originally Posted by leiboshi
Thanks. New info for me. Can you explain what means research octane and motor octane?
There are two separate tests for Research Octane Number (RON) and Motor Octane Number(MON). Wikipedia has a great explanation (note: iso-octane has a 100 RON, n-heptane has a 0 RON):
The most common type of octane rating worldwide is the Research Octane Number
). RON is determined by running the fuel in a test engine
with a variable compression ratio
under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
There is another type of octane rating, called Motor Octane Number
) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing
to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.
In most countries (including all of Europe
) the "headline" octane rating, shown on the pump, is the RON, but in the United States
and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index
), Road Octane Number
), Pump Octane Number
), or (R+M)/2
. Because of the 8 to 10 point difference noted above, the octane rating shown in the United States is 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US
, is 9192 in Europe. However most European pumps deliver 95 (RON) as "unleaded", equivalent to 9091 US (R+M)/2, and some even deliver 98 (RON), 100 (RON), or 102 (RON).