BP ultimate!

[iaint]

Originally posted by clive
My point is that it could be that RON here may well be more potent that we think.

The key comparison would really be between Japanese RON and UK as most of our cars are tuned for the JAP 100 RON fuel.  

Whilst it\'d be great if we found out out 97 RON was equivalent to 100 RON in Japan I seriously doubt it.  It\'s usually the americans who use a different scale to the rest of the world.  I\'m sure we\'d have heard something to do with this before aswell.  Plus: there\'s no way we\'d have something better over here, htat\'s just sods law!

Iain

[weasley]

Let me explain further, given that this is my area of profession (well, related).

RON is Research Octane Number.  It is measured by running a fuel on a special engine with variable compression ratio.  You increase the compression until the engine starts pinking, then you see what the compression is.  You then test mixtures of reference fuels with known amounts of iso-octane in them.  The reference fuel which gives the same result as the test fuel determines the result - ie if the reference fuel had 95.5% iso-octane in it then the matching test fuel would have a RON of 95.5 (probably rounded to 96).  Does that make sense??

Another common test is for MON, that being Motor Octane Number.  This uses the same basic test as the RON test but has fixed ignition timing (compared to the variable ignition timing of the RON test).  Therefore it is more severe, causes earlier pinking and therefore gives lower results, so a fuel\'s MON is always less than its RON.

The MON is thought to be more realistic for road use, so in America what they do is take the average of the RON and MON and call it the "Anti-knock Index" or AKI.  You may also see it written as the R+M/2 octane.

Therefore American pump octane numbers are lower than the equivalent in the UK (and most of the world).  However, RON is RON wherever it is used, so Japanese RON is the same as UK RON.  Japanese 100 RON fuel is indeed more \'potent\' than our 97/98 and goes some way to explaining why JDM cars often offer higher power engines than their European equivalents since the engines are mapped and tested on the 100 RON fuel.

Why octane?  Iso-octane as a chemical is highly resistant to pre-ignition, so the more the better.  A 95 RON fuel doesn\'t actually have 95% iso-octane in it but it has an equivalent level of knock-protection.  You can get >100 RON by the use of additives which improve the knock resistance to be better than a 100% iso-octane fuel.