99 Ron

[DreXeL]

That\'s interestin drex,
So if 98ron Optimax is modified unleaded then what is 97ron super unleaded to have more energy?
Is it true to say the higher the octane rating the lower the calorific value? So Tesco 99 would be lower than Opti 98?  
Have you got any info on specific calorific values of opti, super, tesco?
Cheers

Super unleaded is produced at the refinery to 97ron (or 99ron), Optimax is \'modified\' 95ron.

Higher octane doesn\'t mean a lower calorific value, but Opti has a lower calorific value than super unleaded because it is made from normal unleaded.

Generally super unleaded has a higher calorific value than normal unleaded.  

I\'ve googled for specific values but I can\'t find any, I\'m basing what I\'m saying here after reading various Optimax threads on different forums, and the general consensus is that Optimax has a lower calorific value than most super unleaded fuels.

[D3S]

Thats interesting stuff, i mean i have noticed the difference then again the amount of time i spend with the car i should do lol.

Another thing i have noticed if this is possible, the fuel economy is better as well. Ok on long journeys it is. Around town it dont make sod all difference lol

Gavin

[fc3sPAT]

add to that too, Tesco in oxford by the BMW plant sell it at 95.9, tried it then really felt the difference, didnt use optimax again,

Pat

[Sy.]

Slough tesco\'s has it ....
Its great stuff .

[Trevrx]

The bit I dont get is, if a higher RON fuel burns cooler or slower thus reducing chances of knock/det, the calorific value should be less?  If it also has a high calorific value that means it burns releasing a higher energy/heat. It can\'t be both?
More heat = more risk hence the use of high RON fuel.
Any chemists here lol?

[Rich Cheung]

Are there any Tesco garages selling this 99 ron stuff for us northern monkies ??  

[feelio]

Just thought I\'d add to the list.........Barhill Tesco\'s off the A14 (Near Cambridge)

[Mark Ide]

can this list be made sticky and updated at the front of the thread (if you know what I mean?)
Please

[fraser]

The bit I dont get is, if a higher RON fuel burns cooler or slower thus reducing chances of knock/det, the calorific value should be less?  If it also has a high calorific value that means it burns releasing a higher energy/heat. It can\'t be both?
More heat = more risk hence the use of high RON fuel.
Any chemists here lol?

I\'m not a chemist, but I am a development engineer, so lets see if I can explain this.....
The RON figure relates to the flame front speed of a combustible. The simple explanation of why a reason higher RON figure reduces knock is, the flame front moves faster than the fuel can pre-ignite (knock/det).  The higher the pressure in the cylinder (boost level), the earlier that pre-ignition is likely to occur and therefore the higher the flame front speed that is needed to prevent pre-ignition.
As you rightly say the calorific value relates to the amount of energy that can be released when the fuel is oxidised, but this does not equate to the speed at which the fuel burns. Therefore a fuel can have a very high RON number but contain very little energy, and vice versa.
In hydrocarbon fuels such as petrol RON is primarily dictated by chain length of the molecules and this can be altered in several ways at the refinery.  But conversely over time the RON of fuel tends to reduce which along with water ingress is why an old tank of fuel can cause problems if a car has been left to stand.
This is not my area of specialisation and I have tried to keep it relatively simple so please correct me if I have made any glaring mistakes.

[Trevrx]

Thnx for that Fraser,  are you sure about higher RON igniting faster?
I thought higher ron ignited slower thus pushing the stroke further after TDC and reducing the risk of trying to force the piston/rotor backwards.
I know knock/det occurs after the spark has ignited the fuel correctly at somewhere near TDC (to allow for the flame front to give max power somewhere around 10\' after TDC) but in a milisecond the flame goes to pot and ignites uncontrolably, back to front, too quick.

I thought high ron also gave lower combustion temps because of this (igniting slower).

The thing I still dont get is, although ron and C/V are unrelated, a higher C/V has to burn hotter hence surely raising the ron rating?

[andrewrx7]

I started reading through this, but to be honest, couldn\'t be bothered finish it!

A serious explanation follows:

Prepare To Fall Asleep...zzzzzzzz

Onlyif you\'re really  interested!  :evillaugh

[antnicuk]

Harlow, Edinburgh Way sells it, 97p