Effects Of Mixing Octane Rated Fuels.

[Scuderia_Russ]

We were head scratching at work yesterday....
Can anyone tell me what will happen to the octane rating of a fuel if for example I mix one part 95RON with one part 102RON for example? Is it simply a case of the overall rating 'averaging' out?

Thanks.

[timbo]

My initial instinct says that if you have purely alcane hydrocarbons mixtures given that rating it would be simple averaging. However if you have doped fuels effects may be non-linear.

[ISLAMATRON]

That is actually how they make mid grade gas... they mix the high test with the low test to make mid grade

[Flummo]

You may get an average, but you may also get "problems" caused by the lowest octane stuff "overriding" the other ingredients, resulting in lower mixed octane rating than average. Basically a case of junk remaining junk, no matter what it is mixed with. It may go the other way too...

Diffrent chemicals work in diffrent ways, as far as I know there is no sure way to know how any specific mix works except to test it.

[flynfrog]

Can anyone tell me what will happen to the octane rating of a fuel if for example I mix one part 95RON with one part 102RON for example?

[The FOZ]

Basically a case of junk remaining junk, no matter what it is mixed with. It may go the other way too...

I'd tend to agree with this reasoning.

Someone who should know what he's talking about, once told me that in areas where refineries only have a single pipeline to move product to distribution centers, they alternate between pumping gasoline in it's various grades, diesel, etc., all through the same pipe. The stuff that lives between one fuel type and the next is called the "plug" and gets dumped in with the low-grade gasoline.

But in a completely theoretical model, I expect that mixing two different octane grades will result in an averaging, by volume. This is the principle behind octane boosters. A bit of very high octane in a tank of lower octane will result in a slight raise in octane rating.

I think.

[ISLAMATRON]

That is how it is done in most of north america, most places get 1 pipeline for all the refined fuels... to seperate the fuels they insert a plug, that also cleans out the pipeline and makes a high pitched squeal as it does, so they call it a squealing pig.

Another interesting thing is that all the gas for all the different chains of gas stations goes thru the same pipe, it is only after the gas is pulled out of the pipeline is when the additives from each different chain are put into the gas.

[Scuderia_Russ]

Ok, thanks for the replies.

[casper]

The webpage , http://www.turborick.com/gsxr1127/gasoline.html, has a very good explanation on gasoline's properties. In Section 6.15 It states that :

6.15 Can I mix different octane fuel grades?

Yes, however attempts to blend in your fuel tank should be carefully planned. You should not allow the tank to become empty, and then add 50% of lower octane, followed by 50% of higher octane. The fuels may not completely mix immediately, especially if there is a density difference. You may get a slug of low octane that causes severe knock. You should refill when your tank is half full. In general the octane response will be linear for most hydrocarbon and oxygenated fuels eg 50:50 of 87 and 91 will give 89.

Attempts to mix leaded high octane to unleaded high octane to obtain higher octane are useless. The lead response of the unleaded fuel does not overcome the dilution effect, thus 50:50 of 96 leaded and 91 unleaded will give 94. Some blends of oxygenated fuels with ordinary gasoline can result in undesirable increases in volatility due to volatile azeotropes, and that some oxygenates can have negative lead responses. Also note that the octane requirement of some engines is determined by the need to avoid run-on, not to avoid knock.

[Ian P.]

Hay....don't knock it.
My buddy RON Ricardo mixes fuel and his Motor (3L Turbo MTBE) goes pretty good. At least half the time. Well it used to.
There is a method to his madness.
But here I am running on again. If someone will inter-ject it would all stop.