Fuel Question

Gasoline produces more bang (power) per molicule that Methane and Nitro Methane, right?

the other way round i think.

I thought I read a post here that said that Gasoline produced more power than the other fuels mentioned.

nope, thats y dragsters etc. use either high octane fuel or methane etc.

Dragsters use methane or high octane fuel becasue it resists detonation better than gasoline but that still doesnt' tell me if it produces more power than gasoline. I'm gonna keep looking.

they do have more power because they are more volatile. which means they are more likely to combust, and when they do they combust with a higher force. thats chemistry more than mechanics working

Dragsters use those fuels because they resist detonation better than gasoline. That still doesnt' tell me if they produce more power though, I'm gonna keep looking.

when they combust with a higher force----------basically means they combust with a higher power. force and power are almost the same thing

like alcohol, that burns way more than gasoline does, and the top fuel dragsters use alcohol because of this. it burns more, and i think it also combusts at a lower pressure than gasoline, so the pistons dont have to compress the fuel so much, which puts less pressure on the engine

Penzoil, I pretty much posted the same thing twice casue the link the to thread was not updated. I see what you are saying now, thanks.

Whitebread,

You get more heat produced per molecule for gasoline than for methane because there is more carbon and hydrogen per molecule. This assumes that both get the right amount of oxygen to burn completely.

Nitromethane actually burns cool and slow if a small puddle is lit with a match. It acts quite differently when compressed though. Then it gets explosive. The reason it gives a lot of energy, I suppose, is because of the extra oxygen it brings into the combustion chamber. Like nitrous oxide supplies extra oxygen.

Pennzoil,

You said "...they do have more power because they are more volatile. which means they are more likely to combust, and when they do they combust with a higher force..."

Volatile means that something evaporates easily. I'm pretty sure that gasoline evaporates more easily than alcohol (ethanol), that's why it can be harder to start a car with a lot of alcohol in the tank. Just because something is volatile that doesn't mean it's going to burn well. Freon is very volatile, but it does not burn.

Also, alcohol burns with a relatively cool flame and it burns more slowly than gasoline. Alcohol has an octane rating of about 100, so it resists detonation better than gasoline but, since it delivers less power than gas, mixtures like "gasohol" give you fewer mpg than pure gas. (Remember, high octane rating does not equal high power output, only that a higher compression ratio can be used.)

Later you say "like alcohol, that burns way more than gasoline does, and the top fuel dragsters use alcohol because of this. it burns more, and i think it also combusts at a lower pressure than gasoline, so the pistons dont have to compress the fuel so much, which puts less pressure on the engine"

Alcohol is less flammable than gasoline, and with its higher octane rating, alcohol can withstand higher pressure than gasoline before it detonates. Because of this the pistons can compress it more and this is where you get your power from - the high compression ratio used. There are probably more reasons why dragsters use methanol than gasoline that I don't know about, like maybe the large percentage of oxygen it brings with it compared to the total weight of the molecule.

Sciguyjim, that is exactly what I thougth I just needed someone to comferm it. Thank you very much.

sciguy, I feel compelled to point out that having an extra "O" in a fuel molecule usually results in less power when it burns. An easy way to think about it: when you burn CH4, the C and each of the Hs combine with O to make CO2 and H2O (if it all burns to completion). If one of the Hs already has an O stuck to it (as in CH3OH), then there is less energy that will be released when the reaction goes to completion (because it's starting out partly oxidized)... details schmeeetails.

Ivymike, I see what you're saying. I was thinking more along the lines of the oxygen in the alcohol being removed completely from the molecule and combining with something else in the case where there wasn't sufficient oxygen supplied from the air.

here are some numbers that ought to add to the confusion:

From Engineering Fundamentals of the Internal Combustion Engine, Willard W. Pulkrabek, 1997
Heating values of various hydrocarbon fuels (HHV, LHV), in kJ/kg, molecular mass, in kg/kmol, stoichiometric AF ratio, octane numbers (MON, RON):

Gasoline (similar to C8H15), 111, 47300, 43000, ~14.6, 80-91, 92-99
Methane (CH4), 16, 55260, 49770, 17.2, 120, 120
Methanol (CH3OH), 32, 22540, 20050, 6.5, 92, 106
NitroMethane (CH3NO2), 61, 12000, 10920, 1.7, -, -

So if you look at the energy released by the fuels (w/o regard to the engine), it would seem that Methane has the most bang per unit mass. If you look at the energy released per kmol of the fuel, you get the following (HHV only):
Gasoline: 5.250E+6 kJ/kmol
Methane: 0.884E+6 kJ/kmol
Methanol: 0.721E+6 kJ/kmol
NitroMethane: 0.732E+6 kJ/kmol

Gasoline comes out on top in the "bang per molecule" category, with a six-fold advantage over the smaller molecules.

But wait, there's more:

If we look at the amount of energy released for a given mass of air (more like what you'll have in an engine, but still ignoring compression ratio and the air displaced by the fuel, again HHV only):

Gasoline: 3240 kJ/(kg air)
Methane: 3213 kJ/(kg air)
Methanol: 3468 kJ/(kg air)
NitroMethane: 7059 kJ/(kg air)

If you take into account the higher compression ratio alowed by Methane or Methanol (not sure about N.M.), they begin to have an advantage over gasoline (excluding the effects of the fuel displacing air).

So anyway... it was a tricky question. My answer is that nitromethane releases the most energy per kilogram of air, while methane releases the most energy per kilogram of fuel, and gasoline releases the most energy per molecule. Nitromethane releases the most energy in a given engine, and I suppose that's all that matters here.

Good analysis! Thanks for looking up all those stats. I tried to look up some but couldn't find what I wanted.