Good times in science land! Make magazine did an article about jam jar jets -- basically a simple pulse jet in a jar (technically, a Reynst combustor). But, I don't have a copy of Make, so I did a little reading at pulse-jets.com and set out to build one from odds and ends in the recycling bin and a bottle of isopropyl alcohol.
The first few attempts were failures. I used empty aluminum cans, which are easy to work with (cut apart, join together, punch holes in, etc.), but apparently don't have enough internal volume or geometry to sustain a puttering reaction. Nevertheless, I scared the cats with a few good shrieks and bangs, and the good news about cans is that if you get a bang instead of a whoosh, there's no glass shrapnel.
If someone has built a pop can jet, I'm curious to see how it was done!
Anyhow, I didn't have a jam jar, but I did have a medium sized mason jar. Punching a one inch hole in the lid, and suspending a few inches of similarly sized pipe inside did the trick. I get about four seconds of "wuga-wuga-wuga" pulse jet action before it burns out. It sounds like a busted subwoofer, and it's pretty sweet to see the blue flames dancing around inside at night. I'm sure I'll get longer runs with a fuel that isn't watered down ... but it works well enough as a party trick!
In other news, high quality ping pong balls will burn enthusiastically without leaving ashes behind. Nitrocellulose, for the win.
Here's some videos of jam jar jets in action: