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aviation fuel mix with gasoline?

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I had a little bit of a positive contribution tucked in there :redface:. Guess I just countered with too much poking-of-fun. Hint taken, my apologies.

 

 

Anywho...

That is an interesting read about the specifics of the differences between countries and fuel rating systems. Didn't know that much went into the octane rating.

 

I've been told stories by a friend that owns a shell station, and always wondered how wal-mart style budget fuel stations can get away with selling lower quality gas. Based on that, I guess it makes sense to a degree since the octane rating is an average of two rating systems, and some preferential adjustment might be introduced to save costs.

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Aviation gasoline

1 gal = 112,500 Btu

 

Gasoline:

1 Gal Gasoline (mid grade) = 125,000 Btu's

 

 

Yes I copy/pasted the above. and after the little bit of actual research I did to back up my first post, mid grade gasoline is commonly assumed to carry the above listed energy, in british thermal units. Make up your own mind.

 

In response to the original question, the answer IMO, is no, your stock engine, in stock tune will NOT make more power by simply filling up with 100 octane AVgas at the local airport. Nuff said outta me.

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Higher octane fuel contains less BTU/gallon than lower octane fuel. plain and simple.

 

It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn.

 

What you should be looking at is Btu/lb, not Btu/gallon. A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content by volume (per litre or per gallon). This is because ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl group for a H hydrogen which transforms the gas ethane (C2H6) into ethanol. To a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

 

 

 

Aviation gasoline

1 gal = 112,500 Btu

 

Gasoline:

1 Gal Gasoline (mid grade) = 125,000 Btu's

 

 

Yes I copy/pasted the above. and after the little bit of actual research I did to back up my first post, mid grade gasoline is commonly assumed to carry the above listed energy, in british thermal units. Make up your own mind.

 

 

Well, if your talking about a gallon of fuel, perhaps but that's not a correct analogy and that is the flaw in your statement, it's the stoichiometric ratio of fuel to oxygen as it's mixed in the engine that matters! So, if your going to make a point then we have to do it correctly. If gasoline is run at its preferred maximum power air/fuel mixture of 12.5:1, it will release approximately 20 MJ (about 19,000 BTU) of energy, where ethanol run at its preferred maximum power mixture of 6.5:1 will liberate approximately 25.7 MJ (24,400 BTU), and methanol at a 4.5:1 AFR liberates about 29.1 MJ (27,650 BTU), that is why oxygenated fuels make more power and VP and others are making oxygenated race fuels. It gets even better when you run Nitro!

 

I think that about covers it for this topic

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the stoichiometric ratio of fuel to oxygen as it's mixed in the engine that matters! So, if your going to make a point then we have to do it correctly. If gasoline is run at its preferred maximum power air/fuel mixture of 12.5:1, it will release approximately 20 MJ (about 19,000 BTU) of energy, where ethanol run at its preferred maximum power mixture of 6.5:1 will liberate approximately 25.7 MJ (24,400 BTU), and methanol at a 4.5:1 AFR liberates about 29.1 MJ (27,650 BTU), that is why oxygenated fuels make more power and VP and others are making oxygenated race fuels. It gets even better when you run Nitro!

 

 

I think you you also sould point out the fact that methanol has only about 40% the energy density of gasoline. 19,800BTU/lb for gasoline and ~8500-9000BTU/lb for methonal, as i recall. Then ethanol is around 14,000BTU/lb.

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I'm going to summarize this one more time. Then I'm closing this thread.

 

Gasoline is what most of our cars came setup so it's usually what we stick with. Gasoline is a mixture of hydrocarbons. The petroleum distillate fraction termed "gasoline" contains mostly saturated hydrocarbons usually with a chemical formula of C8H18. The air fuel ratio, A/F Ratio, for complete combustion is 14.7:1, stoichiometric. The A/F ratio for maximum power is approximately 12.5:1 - 12.8:1. This means that a theoretcial engine at max power, 12.8:1, consumes 12.8 pounds of air for 1 pound of fuel. Gasoline has approximately 18,400 BTU/lb . Using the air flow calculator with the default inputs we will use a 355 SBC, so it consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and consumes 2.89 pounds of fuel. Therefore if we are using gasoline our engine is producing 53,176 BTU's of energy at 6500 rpm.

 

 

Alcohol is usually used in the form of Methyl alcohol or methanol. CH3OH is the chemical formula. Methanol burns at a much richer mixture than gasoline does, between 5.0:1 - 6.0:1. That's 5 lbs of air to one pound of fuel. Methanol has approximately 9,500 BTU/lb. Using our 355, example above, SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and now at 6.0:1 ratio for Methanol is 7.11 pounds of fuel. Therefore if we are using Methanol fuel our engine is producing 67,545 BTU's of energy at 6500 rpm.

 

 

Nitromethane is a fuel that is used mostly in specialized drag racing classes, "nitro funny cars" and "top fuel". Nitromethane's chemical formula is CH3NO2. The oxygen in nitromethane's molecular structure means that nitromethane does not need as much atmospheric oxygen to burn, part of the oxygen needed to burn nitromethane is carried in the fuel itself. Typical A/F ratio for nitromethane is 1.7:1 and nitromethane has an energy content of 5,000 BTU/lb. Using our 355, example above, SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and now at 1.7:1 ratio for nitromethane is 25.08 pounds of fuel. Therefore if we are using Nitromethane fuel our engine is producing 125,412 BTU's of energy at 6500 rpm.

 

Clearly Nitro is the winner here. Methanol makes about 20% more power in the same engine than gas does. Hence the saying, Gas is for washing parts, alcohol is for drinking and nitro is for racing!

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