Gary Foster

I don't think lower octane fuel is more combustable. This is what I understand.

The octane rating is in fact a measurement of how controlled a burn a fuel will make on a reference internal combustion engine.

Without getting too technical, when the fuel air mixture burns, there can be 'hot spots' in the flame front. A lower octane fuel will have more hot spots at a greatly higher temperature than the rest of the flame. A higher octane fuel will have a less varied temperature difference across the flame front, thus a more 'controlled' burn.

I think you can probably guess why super high temparature hot spots are a bit of a problem in something made of aluminium.

Gary

carl

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by owbow:
<B>off topic as not "Super" i know, but noticed that Shell NUL=BS 7070, everywhere else's NUL=BS EN 228
[/quote]

BS7070:1985 [specification for unleaded petrol (gasoline) for motor vehicles] was revised into BS7070:1988. This appears to have now been superseded by BS EN 228:1993, BS EN 228:1995, BS EN 228:1999 and finally BS EN 228:2000 [Automotive fuels. Unleaded petrol. Requirements and test methods] which is listed as 'current'.

All available at

AndyMc

I agree with Walker

I regularly drive past shell Stanlow oil refinery and I know loads of people that work there,my dad worked on their main distillation plant for many years.

Stanlow supplies 1/4 of all the petrol sold in the UK and is the biggest refinery complex in Europe.A lot of the petrol leaves by road and I have seen the following tankers fill up there,these are the ones I can remember.

-Shell
-Texaco(loads)
-Esso(loads)
-BP
-Sainsburys
-Safeway
-Tescos
plus a whole host of private hauliers and unmarked tankers.

Each different company does not have its own gantries to load from,they use which ever one is free at the time.Each gantry only has a few pipes connected to it(that I can see)

Behind the gantries are the tanks where the petrol is stored, there are not that many tanks.

I think most people are agreed that the base petrol is the same and that the additives make the difference that people notice.

Imagine how many different combinations of petrol types and additives there are for that many different customers.

Whenever I ask the people that work there if there is a difference they normally smile and say something like "what do you think?".Non of them deny it but they also will not confirm it.It is a big secret and they are obviously under pressure not to tell.

My mate also told me there are only a few additive plants that supply the whole of Europe.

It seems unlikely to me that each company has its own additives added at Stanlow.

What is a fact is that people notice a difference between brands but there is no general concensus as to what is the best brand,some say ESSO some say Shell etc.If Esso always had Esso additives etc you would expect everybody to say the same thing.

I think this can be explained by which refinery made the petrol in that area.For example Esso petrol in the north west is more than likely made by Shell(with Shell additives) where as Shell petrol in the South is probably made by whoever owns(I forget) the big refinery by the Isle of White (using their additives))and so on.

Other things to bear in mind is that petrol ages over time and loses the higher boiling point fractions that help provide the knock resistance.I wonder how often SUL tanks are filled,I'm sure I'm the only one that uses SUL at my local station.

Also when a petrol station recieves a load they are supposed to let it settle for a while before it is put on line.Do you think they always do this?

Any of these thing could cause the differences people notice

My mate also told me that the recipe of petrol is changed between summer and winter to improve winter running etc.

I will try to get a more definitive answer than the guess work above

Andy