Making Flamethrowers

I came across the below entry in the London UK newspaper, the Guardian, and it reminded me of the time I built a flamethrower.

From the Monday January 2, 2006
edition of The Guardian:

The Freedom of Information Act, hailed by Lord Falconer, the constitutional
affairs secretary, as "a giant step forward" in sweeping away official secrecy, is one year old today.

Over the past 12 months, it has led to the release of much information formerly kept from public view. Here, the Guardian gives a taste of what has been disclosed so far: from serious matters to lighter ones; from the top of Whitehall to the outer reaches of government.

Here is one entry of the information released under the act:

"More than 300 weapons were seized from Scottish school pupils last year, including air pistols, claw hammers, knuckle dusters, knives, swords, and an improvised flamethrower."

Now, I know US public schools are tough, probably tougher than British schools. Still, it makes me wonder about a student who would bring a sword to school. It seems impractical as well as imprudent.

As far as the improvised flamethrower goes, I built one once for my warrior robot, Tosca. Tosca wasn't much of a fighter, but for a short while, it had a flamethrower. Although Battlebots dissallowed flamethrowers, other tournaments allowed them.

The knowledge regarding flamethrower building is arcane to say the least. How does one build one from scratch? A robot builder I met, named Jon, spent some time experimenting with flamethrowers and he got pretty good at it. I'll skip the mechanical details, but here's some interesting chemistry tidbits regarding flamethrowers from Jon:

. . . there is a direct relationship between flash point of the fuel and length of the flame. Low flash point fuels like toluene burn up before the fuel is projected more than one or two feet. In fact, a very low flash point fuel like ether can vaporize within the system and back up into the tank, so the pump is trying to move gas instead of fluid and produces limited amounts of fire. High flash point fuels, say, xylene, will stay together longer and so project farther. But very high flash point fuels, for example kerosene, do not burn completely, so it’s messy because unspent fuel is winds up spewing everywhere.”

Eventually, I wound up simply using propane because it was the easiest to project. Using the vapor pressure inside the cylinder of propane we could get a six to eight foot flame. It never did much damage to the other bots, but the flamethrower was mostly for pleasing the crowd, anyway. I remind all that, for the vast majority of people, building your own flamethrower is a very, very bad idea.

But if you have built one in the past (and remember, I don't advocate that you do) I'd like to hear about it.

The photo above is that of mechanical artist Christian Ristow's Subjugator -- it's a great flamethrower/ robot.