Gasoline for combustion fuel?

[kjjohn]

How powerful would gasoline be if used as a combustion cannon fuel? Also, how would you vaporize it prior to injection into the chamber? Could it compare to the power of MAPP?

[jackssmirkingrevenge]

How powerful would gasoline be if used as a combustion cannon fuel? Also, how would you vaporize it prior to injection into the chamber? Could it compare to the power of MAPP?

[youtube][/youtube]

That should pretty much answer your questions

To illustrate the power of petrol, have a looks about 3 minutes into this video, comparing a teaspon of petrol to a teaspoon of black powder:

[youtube][/youtube]

[starman]

It's been done a few times. Here's a link to RCMAN's gasoline cannons.

The key is finding a way to consistently carburet or vaporize the gasoline. However, for all the trouble you won't be getting any more energetic shots than you would if you were using the much easier, safer, cheaper and ready to use propane or MAPP.

[MrCrowley]

With that blackpower/gasoline test, to be fair the powder wasn't even packed, it would pretty much be like flash powder going off.

[rp181]

people have had success with spray bottles.

[CpTn_lAw]

Conditions were not the same for gasoline fumes and BP. To deflagrate, black powder must be compressed, so, had it been a small packed container, that would have been fair. I don't know where i read it, but IIRC, 1 teaspoon of black powder stands for approx. 80 grains, 15 grains of powder give 270 cubic centimeters of gas when combusted, so 80 grains ==> 1440 cubic centimeters of gas.
If it's compressed, the pressure increase if much more fast, giving more acceleration; So, the comparison between gasoline and BP isn't accurate.

Still, BP has 3MJ/kg potential energy, where petrol has 46 MJ/kg....

[jimmy101]

Still, BP has 3MJ/kg potential energy, where petrol has 46 MJ/kg....

Mostly because the BP has to provide it's own oxidizer. Petrol does not.

In a constant sized chamber, filled with the maximum amount of fuel, the BP will release a heck of a lot more energy than will petrol. The chamber can be completely filled with BP, but can only have a few percent of the chamber volume in petrol.

[D_Hall]

To deflagrate, black powder must be compressed,

Not the case. Black powder's burn rate is largely unaffected by ambient pressure (ie, confinement). That's what makes it so ideal for use in pyrotechnics (it will go like a bat out of hell even without confinement). For a counter point, nitrocellulose's burn rate is highly dependent upon ambient pressure. That's part of what makes it so safe for use in firearms (because a loose NC charge doesn't burn worth a damn it makes NC storage facilities much safer places than BP storage facilities).

At the office, we deal with all sorts of exotic explosives on a daily basis...and yet we still consider BP to be the most dangerous thing we handle largely due to it's unconfined ignition/burn characteristics.

[Willdebeers]

Conditions were not the same for gasoline fumes and BP. To deflagrate, black powder must be compressed, so, had it been a small packed container, that would have been fair. I don't know where i read it, but IIRC, 1 teaspoon of black powder stands for approx. 80 grains, 15 grains of powder give 270 cubic centimeters of gas when combusted, so 80 grains ==> 1440 cubic centimeters of gas.
If it's compressed, the pressure increase if much more fast, giving more acceleration; So, the comparison between gasoline and BP isn't accurate.

Still, BP has 3MJ/kg potential energy, where petrol has 46 MJ/kg....

E=MC2 says that you can get a huge amount of energy from a small amount of mass. You have enough "potential energy" in your body to blow up half the world, if you could harness it. Perfect for birthday parties, or just making a really good point.

[psycix]

E=MC2 says that you can get a huge amount of energy from a small amount of mass.

Yeah only when going nuclear, where a small piece of the matter is transformed into energy. And when converting ALL the mass into energy you're talking antimatter...

Of course cptn_law is talking about chemical potential energy.

[SpudBlaster15]

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[jrrdw]

I see this thread going out of topic and not really getting back on topic. If PCGUY, any other moderator wants to open it back up so be it.

[sgort87]

Ehhh, ain't hurtin nobody. I find it amusing.

[D_Hall]

How exactly do you explain quickmatch then? Standard blackmatch made by soaking a cotton string in BP slurry will burn quite slowly, but if you add confinement (Thus pressurizing the reaction), the burn rate of the fuse increases by a factor of several tens.

Right off the bat, I see nothing to indicate a bulk burn rate increase. What I see is nothing more than a surface burn increase due to redirection of flame on the exterior of the string. In other words, the post-combustion gas expansion rate is faster than the bulk material burn rate. If one redirects that gas expansion to a new chunk of propellant (ie, further along the string), then one sees a "burn rate" that is really nothing more than a device to measure the gas expansion rate.

This is NOT the same thing as burn rates going up due to honest to gawd confinement. The simple paper tube shown in your link hardly qualifies as "confinement." Hell, most spud guns aren't capable of demonstrating the effects of honest to gawd confinement (hint: Those who study these things generally use pressures measured in thousands of psi.)

Confinement significantly increases the burn rate of most pyrotechnic compositions. However, I suspect it has more to do with a pressure differential in the casing forcing the flame front through the composition at a greater rate than a simple rise in ambient pressure.

D'oh! There I go typing before I've fully digested everything you've said. You even appear to agree with me. You're seeing a surface flame propogation effect, NOT a bulk burn rate effect.

Since you're more or less with me at this point....

I don't know numbers off the top of my head but I'll say this:

Burn rate of propellants is typically quantified something like....

Rate = A * P^x

Where...
A = a constant.
P = absolute pressure.
x = what's known as the burn rate coefficient.

The burn rate coefficient is the dominant driver where propellant behavior characterization at high AND low pressures is concerned. For black powder, the burn rate is very nearly zero. In other words, BP at 0 psi burns at roughly the same rate as BP at 10,000 psi. Good rocket propellants have a coefficient on the order of 0.8. That means that yes, they burn one HELL of a lot faster at 10,000 psi than they do at 0 psi. Guns? Sorry, off the top of my head I don't know, but I wouldn't be surprised to see coefficients on the order of 1.5.

Note that I am NOT talking about flame propogation effects from one chunk of powder to another. I'm talking about bulk single-piece combustion properties.

[SpudBlaster15]

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