Fuel octane question

[yfin]

Simple question but maybe not such a simple answer!

If I put 50 litres of 91 octane unleaded fuel in my empty fuel tank and then add 10 litres of 98 octane premium unleaded fuel...

What is the approximate octane of the mixed fuel?

Thanks

[dsp26]

not sure if your question is serious, but mathematically i'd say:

~92 :p

[Limbo]

its hard to say, i rem that certain chemicals do not give exactly the equal amount of octane equivalent to other chemicals, so depending on what mixture your original fuel was made up of and then what fuel you put in it will effect your final octane rating. Look at the different 98 octane fuels and you'll note that they are made up of different chemicals to reach the final 98 octane rating

Its not as simple a add and divide

Even if you did give us the exact info we would need an expert to work it out for us. Dunno if anyone has an octane reading tool? that would be easiest

[yfin]

Yes, it is a serious question.

I am trying to work out the cheapest way to get my octane up to at least 95...

Long story - in short my work pays for unleaded fuel but not premium. I just tried some Nulon Pro Strength octane booster to 91 ron and the car was a lot better to drive (the ECU has a separate map for premium fuel). It was so much better I can't go back to 91 ron....! The only problem with the booster is that it is expensive. Trying to work out whether a mix of 98 would work - and if so how many litres would be required to a 73 litre tank.

[dsp26]

i've read (note not mine own experience) that those octane increasing tablets work only until 95oct regardless of how much you put in... so one of those every fill?

[Limbo]

I rem that they use toulene and xylene to mix with fuel to get the higher RON figures in race fuels. Your gonna have to play with the amounts as i don't know how much you need to make 98RON. I only know what chemicals they use.

Use the following at your own risk, i've never tired it but had look at making some a while back. Also have a look at this site
http://members.rennlist.com/951_racerx/RocketFuelFAQ.html

Homebrew Gasoline Octane Boosters

--------------------------------------------------------------------------------
Editor's note: I would NOT suggest that a person use the following fuel mixtures without considering the detrimental effects on your engine, vital engine components (O2 sensor, etc), and other potential damage. That said, the information is interesting.
Original published in:

GS-Xtra
1213 Gornto Road
Valdosta, GA 31602
(912) 244-0577

Editor: Richard Lasetter, president Gran Sport Club of America (GSCA)

Formula #1 - Toluene
R+M/2.........114
Cost...........$2.50/gal
Mixtures with 92 Octane Premium
10%...........94.2 Octane
20%...........96.4 Octane
30%...........98.6 Octane
Notes: Common ingredient in Octane Boosters in a can. 12-16 ounces will only raise octane 2-3 *points*, i.e. from 92 to 92.3. Often costs $3-5 for 12-16 ounces, when it can be purchased for less than $3/gal at chemical supply houses or paint stores.

Formula #2 - Xylene
R+M/2.........117
Cost...........$2.75/gal
Mixtures with 92 Octane Premium
10%...........94.5 Octane
20%...........97.0 Octane
30%...........99.5 Octane
Notes: Similar to Toluene. 12-16 ounces will only raise octane 2-3 *points*, i.e. from 92 to 92.3. Usually mixed with Toluene and advertised as *race formula*.

Formula #3 - Methyl-tertiary-butyl-ether (MTBE)
R+M/2.........118
Cost...........$3.50/gal
Mixtures with 92 Octane Premium
10%...........94.6 Octane
20%...........97.2 Octane
30%...........99.8 Octane
Notes: Oxygenate. Very common in octane booster products. Has lower BTU content than toluene or xylene, but oxygenate effect makes the gasoline burn better and produce more energy.

Formula #4 - Methanol or Ethanol
R+M/2.........101
Cost...........$0.60 - $1.75/gal
Mixtures with 92 Octane Premium
10%...........94.3 Octane (Methanol)
10%...........94.7 Octane (Ethanol)
20%...........Not Recommended
Notes: Methanol is wood alcohol. Ethanol is grain alcohol and found in Gasohol in 10% ratios. Both alcohols are mildly corrosive and will eat gas tank linings, rubber and aluminum if used in excessive ratios. Main ingredient in "Gas Dryers", combine with water.

Formula #5 - Isopropyl Alcohol and Tertiary Butyl Alcohol
R+M/2.........101
Cost...........$0.60-$1.50/gal
Mixtures with 92 Octane Premium
10%...........94.5 Octane
20%...........Not Recommended
30%...........Not Recommended

Notes: Similar to Methanol/Ethanol. Isopropyl Alcohol is simply rubbing alcohol.

Sample Mixture
To make your own octane booster, it is easiest to make up a large batch, and then bottle it up in "dosage-size" uses.
Below is the basic formula of one of the popular octane booster products. To make eight 16 ounce bottles (128 oz = 1 gal):

100 oz of toluene for octane boost
25 oz of mineral spirits (cleaning agent)
3 oz of transmission fluid (lubricating agent)
This product is advertised as "octane booster with cleaning agent *and* lubricating agent!". Diesel fuel or kerosene can be substituted for mineral spirits and light turbine oil can be substituted for transmission fluid. Color can be added with petroleum dyes.

[aaronng]

Toulene, xylene and MTBE are pretty nasty. If you were doing homebrew, using ethanol or propanol would be safer.

Why not use United's 95 octane 10% ethanol fuel?

[dsp26]

^^^yep toluene is cancerous and is NOT AVAILABLE for purchase here unless you own a licensed performance workshop... but good info Limbo!!

[Limbo]

hehe
like i said its at your own risk.
I just happened to come across the mixture one time when i was looking for more power.
The above is apparently proven stuff from the US where some of the chemicals are easily available

[JohnL]

hehe
like i said its at your own risk.
I just happened to come across the mixture one time when i was looking for more power.
The above is apparently proven stuff from the US where some of the chemicals are easily available

Yes, so are guns, and look what that's done for the USA. Just because an uninformed Yank 'sticks his head in the oven' would you do it to?

Seriously, these chemicals are not something you want to play with lightly and without stringent precautions. You might say 'well they sell this stuff to us in petrol, how bad can it be?'. The answer is 'very bad', most of these 'zenes' etc are Grade A carcinogens (and those that aren't are probably Grade B). They used to spray DDT around children's playgrounds, how bad was that?

If you expose yourself to these chemicals in any but minute quantities they may not kill you tomorrow, but you run a much greater cancer risk later in life. It's just as well servos are self serve these days, or in a few years there'd probably be an epidemic of cancer in pump jockeys (who would be exposed a lot).

Never get unleaded fuel on your skin (zenes are absorbed readily through the skin), and wash it off if you do, don't breathe the fumes more than you can possibly avoid. Unleaded has much more of this shit in it than leaded fuel, and is much more dangerous, but on the bright side you won't die of lead poisoning. It won't be suprising if in a few years (X critical years after the widespread introduction of unleaded fuel) if there isn't a significant rise in cancer that could be attributed to the chemicals in unleaded petrol.

[JohnL]

Toulene, xylene and MTBE are pretty nasty. If you were doing homebrew, using ethanol or propanol would be safer.

Why not use United's 95 octane 10% ethanol fuel?

Before I start, I'm no expert on the following, it's just my current understanding from what I've read:

Because alcohol has a lower calorific value than petrol has, i.e. less BTUs by volume. This means that to get the same amount of power out of alcohol (methanol or ethanol) you need to inject about twice as much of it, but even so in an otherwise unmodified engine you're unlikely to get the same power from it as you will with petrol.

(Racing engines running methanol will typically produce a bit more power than an equivalent engine running petrol, but not directly because of the fuel being alcohol, rather because alcohol fuel allows the use of very much higher compression ratios because it has such a high octane rating, and it's this that gives more power, but at the expense of using about twice as much alcohol as the equivalent petrol engine will use petrol)

Alcohol has approximately half the calorific value of petrol, so if you dilute (adulterate?) the fuel with 10% alcohol you will in theory have about 5% less BTUs in the petrol / alcohol blend than in a non alcohol / petrol blend (all petrol based fuels are blends of some description). From a power perspective this might be OK if your ECU knew what was in the tank and knew to inject a richer mixture to make up for it, but it doesn't (even if it did, it would have issues for economy). There will be real issues for economy too because if the engine is producing X% less power at Y throttle opening, you'll end up using Y+ throttle to make up for the deficit. Car fuel injection systems (and carburettors) are calibrated to run on 'petrol', not a hybrid petrol / alcohol blend with a significantly different chemical make up and an inferior calorific value.

This may be somewhat simplistic, because the alcohol is an octane booster and will mean that some of the aromatic hydrocarbons (the zenes et al) normally used as octane enhancers will still be present but in lesser quantity, and there may actually be more actual 'petrol' (i.e. heavier hydrocarbons) in the blend also displacing some of the aromatics. The light aromatics also have a lesser calorific value than the heavier hydrocarbons that make up the actual 'petrol' content of the blend (one reason why lower octane fuel will typically produce more power in low compression engines than higher octane fuel does), but not so low as alcohol. This might mean the 5% figure I stated above could be pessimistic, i.e. it may not be quite that bad.

All this talk of special home brews etc, just use 'premium' high octane pump fuel with no alcohol, don't think you can do better than the highly trained proffessional chemists at the refineries.

[EuroAccord13]

Why not just mix half and half.. I'm sure you'll get the 95 mix....