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dashdot · 01-31-2005, 06:22 PM

I've been lurking around here for quite some time, but haven't posted anything becuase I didn't have anything to say. Well, I made something I could talk about.

<a href="http://dotd.net/fire/flame.wmv">flamethrower!</a>

Note: I don't know how well my host can hold up. They're pretty pathetic at times.

The fuel tank is a 20lb tank, not 30 as the video says (typo, too lazy to correct it).

I've fueled and fired this thing 5 times so far. It is quite a sight to see in person. I usually fill the tank a little over halfway, to maintain pressure. With the compressor attached to it, it can maintain pressure for the full burn time. That video only shows the tank pressurized to about 90psi tops though. Maximum is 135psi.

The hose is a Buna-n hydraulic hose and all connections have gas-safe (as I was told, and as experiments in a bucket of gas have proven) threadlocker on them. Everything is rated for at least twice the pressure it is under.

The fuel tank has an air inlet and gas outlet at its top. A pipe internally extends down to the bottom of the tank to siphon the gas out.

The gun assembly is a pressure washer gun with about 12" of brass pipe that terminates in a check valve, then the nozzle (1/4" nozzle in this video). The gun was also left partially open in a bucket of gas for 24 hours and the seals did not degrade at all.

Since this thing is essentially a fuel air bomb, flashback is a huge concern. I haven't been able to find a flashback arrestor for use with a liquid like gasoline. Any suggestions on where to get one?

Total cost: Under $160.

Beyond that, any ideas for improvement?

Disclaimer: This is probably one of the most dangerous things you could ever make. Don't make one, don't try to make one, don't think about making one.

EXTRA DISCLAIMER!!

If ANYONE of you is stupid enough to try this, don't come crying back here.

This is probably one of the MOST dangerous things I've seen posted, because one simple mistake or screw up and you've made a full air bomb that can demolish a house or you've set yourself on [b]fire[b], which as I understand, is a particulary painful way to die (I hear that survivors actually wish they had died).

So please, don't make TFP the next example of "Guy does something stupid he read about on the internet, so lets censor the internet".

-lebell

EXTRA, EXTRA DISCLAIMER!

Original poster here. Once I saw the above disclaimer, I thought it prudent to add this bit extra:

If something went wrong with this device, it WOULD explode. And the above disclaimer's statement about a house being demolished is entirely true, and maybe even conservative about this thing's destructive power.

Taken from http://home.earthlink.net/~jimlux/energies.htm:

Gasoline has an combustion energy of about 47.4 MJ/kg, so a simple calculation will show that the cup (170g) will release about 8MJ when burned. When vaporized and mixed with air at the optimum ratio (stoichiometric), the mixture will occupy about 2100 liters, or a sphere some 0.80 m in radius. Assuming the mixture is ignited at the center of the sphere, it will take about 2.5 milliseconds for the flame front to propagate to the outer edge. This makes the assumptions that the flame front moves at the speed of sound (probably reasonable), and that the sphere of mixture doesn't expand appreciably due to the heating in the middle (probably very optimistic). So, 8 MJ in .0025 seconds is 3200 MW, or 3.2 GW

3.2 GIGAWATTS. That site states that a 3000lb car hitting a concrete wall is only 2.1 MEGAWATTS. This fuel tank exploding will incinerate you.

DO NOT DUPLICATE THIS PROJECT!!

01-31-2005, 06:22 PM	#1 (permalink)
dashdot Upright	Homemade Flamethrower I've been lurking around here for quite some time, but haven't posted anything becuase I didn't have anything to say. Well, I made something I could talk about. <a href="http://dotd.net/fire/flame.wmv">flamethrower!</a> Note: I don't know how well my host can hold up. They're pretty pathetic at times. The fuel tank is a 20lb tank, not 30 as the video says (typo, too lazy to correct it). I've fueled and fired this thing 5 times so far. It is quite a sight to see in person. I usually fill the tank a little over halfway, to maintain pressure. With the compressor attached to it, it can maintain pressure for the full burn time. That video only shows the tank pressurized to about 90psi tops though. Maximum is 135psi. The hose is a Buna-n hydraulic hose and all connections have gas-safe (as I was told, and as experiments in a bucket of gas have proven) threadlocker on them. Everything is rated for at least twice the pressure it is under. The fuel tank has an air inlet and gas outlet at its top. A pipe internally extends down to the bottom of the tank to siphon the gas out. The gun assembly is a pressure washer gun with about 12" of brass pipe that terminates in a check valve, then the nozzle (1/4" nozzle in this video). The gun was also left partially open in a bucket of gas for 24 hours and the seals did not degrade at all. Since this thing is essentially a fuel air bomb, flashback is a huge concern. I haven't been able to find a flashback arrestor for use with a liquid like gasoline. Any suggestions on where to get one? Total cost: Under $160. Beyond that, any ideas for improvement? Disclaimer: This is probably one of the most dangerous things you could ever make. Don't make one, don't try to make one, don't think about making one. EXTRA DISCLAIMER!! If ANYONE of you is stupid enough to try this, don't come crying back here. This is probably one of the MOST dangerous things I've seen posted, because one simple mistake or screw up and you've made a full air bomb that can demolish a house or you've set yourself on [b]fire[b], which as I understand, is a particulary painful way to die (I hear that survivors actually wish they had died). So please, don't make TFP the next example of "Guy does something stupid he read about on the internet, so lets censor the internet". -lebell EXTRA, EXTRA DISCLAIMER! Original poster here. Once I saw the above disclaimer, I thought it prudent to add this bit extra: If something went wrong with this device, it WOULD explode. And the above disclaimer's statement about a house being demolished is entirely true, and maybe even conservative about this thing's destructive power. Taken from http://home.earthlink.net/~jimlux/energies.htm: Gasoline has an combustion energy of about 47.4 MJ/kg, so a simple calculation will show that the cup (170g) will release about 8MJ when burned. When vaporized and mixed with air at the optimum ratio (stoichiometric), the mixture will occupy about 2100 liters, or a sphere some 0.80 m in radius. Assuming the mixture is ignited at the center of the sphere, it will take about 2.5 milliseconds for the flame front to propagate to the outer edge. This makes the assumptions that the flame front moves at the speed of sound (probably reasonable), and that the sphere of mixture doesn't expand appreciably due to the heating in the middle (probably very optimistic). So, 8 MJ in .0025 seconds is 3200 MW, or 3.2 GW 3.2 GIGAWATTS. That site states that a 3000lb car hitting a concrete wall is only 2.1 MEGAWATTS. This fuel tank exploding will incinerate you. DO NOT DUPLICATE THIS PROJECT!! Last edited by dashdot; 02-01-2005 at 07:06 PM..