Pulse Jet

[Bluepete]

In light of Blue's jet parachutist, I remembered a bit of physics and made myself a pulse jet engine! These are the type of engine used to power the "Buzz Bombs" of WW2. This one, however, won't do much more than scare the neighbours. It is WAY louder than the video portrays :D :D

All it is is a jar with a 10mm hole in the lid. You can just see me adding three teaspoons of Nitro fuel (the stuff in Blue's RC car) and then lighting it with a small gas torch.

http://i157.photobucket.com/albums/t48/conker51/th_PulseJet.jpg (http://s157.photobucket.com/albums/t48/conker51/?action=view&current=PulseJet.flv)

The odd sound at the end is me chuckleing like a kid on Christmas morning!

[Wideboy]

THAT IS SERIOUS COOLNESS :cool:

[aarond]

thanks that is so cool! Now i have something to do tomorrow!!!!

[husky03]

cool man.

[yorkie_chris]

If any of you lot have welding kit, then stop looking NOW before you get out of hand. :-P

[600+]

u are obviously still off work :d

[El Saxo]

Wow, that's ace! Can you make an SV do that? :lol:

[rpwoodman]

What's the physics behind it?
I don't understand how a bit of fuel in a jar with a hole in the lid can behave like that?

[wyrdness]

What's the physics behind it?
I don't understand how a bit of fuel in a jar with a hole in the lid can behave like that?

I'd guess that the fuel burning uses up the oxygen in the jar, which almost stops combustion. More air is then sucked back into the jar which starts combustion again.

There used to be a really good website on pulse jets, made by a guy in New Zealand. He made the mistake of attaching a sat-nav to one and calling it a 'home-made cruise missile' which attracted the attention of the NZ government, which shut him down. He should probably have called it something like 'sat-nav controlled model plane'.

Edit: Here's the website: http://www.interestingprojects.com/

[rpwoodman]

I'd guess that the fuel burning uses up the oxygen in the jar, which almost stops combustion. More air is then sucked back into the jar which starts combustion again.

For that to happen, I'd have expected it to be a lot more exact than BP suggested in his original post. The shape of the jar would come into play, as would the size of the hole, the placement of the hole, and the ambient temperature. Maybe I'm over complicating things - I'll have a look at the web site you cite.

Thanks!

[ThEGr33k]

COOL! Didnt know you could make one that way tbh.

Here is the next project for you pete :p

http://www.youtube.com/watch?v=G20shVGrjlQ

Then the one after :p (I wanted to make one of these... just never got around to it.)

http://www.youtube.com/watch?v=BZoymnZRBVc

Thats ultra cool.

[yorkie_chris]

For that to happen, I'd have expected it to be a lot more exact than BP suggested in his original post. The shape of the jar would come into play, as would the size of the hole, the placement of the hole, and the ambient temperature. Maybe I'm over complicating things - I'll have a look at the web site you cite.

Thanks!

You're producing a resonating system, basically the gas burns, pressure increases, pushing gas out, combustion then slows, and due to the low pressure created by the momentum of the gas leaving, a fresh gulp of air is sucked in, reigniting with the fuel and beginning the process again.

Any volume of gas in a chamber has a resonant frequency, so everything does come in to play, it's quite precise if you want to extract useful thrust from one, but pretty much anything can sustain and make a lot of noise :-D

[rpwoodman]

You're producing a resonating system, basically the gas burns, pressure increases, pushing gas out, combustion then slows, and due to the low pressure created by the momentum of the gas leaving, a fresh gulp of air is sucked in, reigniting with the fuel and beginning the process again.

Any volume of gas in a chamber has a resonant frequency, so everything does come in to play, it's quite precise if you want to extract useful thrust from one, but pretty much anything can sustain and make a lot of noise :-D

Thanks for the info - 'ppreciate it. Something for me to dwell on.