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Simple Pulsejet / Reynst combustor

Unread postPosted: Tue Jul 08, 2008 1:53 am
Author: Insomniac
I have seen many videos on youtube of the 'jam-jar pulsejet', and after trying it myself, I decided to try making one that would last a bit longer.

The best result so far has been from a tin can I drilled a hole into. It runs, but after about 10 seconds it goes out. Not exactly sure why, as plenty of fuel is left, but I suspect the immense heat generated causes way too much fuel to vapourise, making it too rich to run. It is a pain to light, as I have to get LOTS of fresh air in with a small pump with a hose attached, light, and hope for the best. Somtimes it works, somtimes it doesn't.

[youtube]http://www.youtube.com/watch?v=aiEin1SyOEI[/youtube]

If any of you have a little free time, try making one out of whatever you can find. If it lights, goes brrrp then stops, the hole is a tiny bit too small. If it just goes whoosh, it is probably too big. See if you can make one run longer than mine... then tell me how you did it lol.

Later tonight I might make another vid so you can see the flames shoot out of it.

Unread postPosted: Tue Jul 08, 2008 2:18 am
Author: Tom
I like the simplicity of the "Jam Jar Jet" , but when you made a working one will it give you (enough) trust? Anyway I'm going to try it myself, what is the fuel your using?
G's from the Dutch, Tom

Unread postPosted: Tue Jul 08, 2008 2:55 am
Author: Insomniac
I never really intended this to power anything, so thrust really isn't that much of an issue. (although if I manage to get any thrust from one reliably I might mount it to a small car or boat) Also, these seem very depended on how much fuel vapourises. I have yet to make one run on it's side, probably due to the higher surface area the fuel has. Perhaps a 45* angle would be a good compromise????

Anyway, I made another out of an identical tin, but with a slightly smaller hole. It is louder and goes out quicker. I decided to try running it in some water to cool the fuel a bit, so I sat it in a bowl with a few cm of cold water in it (any more and it will float). It was fantastic. Although it didn't quite manage to burn all the fuel, it easily burned for 3 or 4 times as long as the one in the vid, and the bottom half of the tin glowed a dull red.

I am using Methylated spirits as fuel. I think it is also known as denatured alcohol outside of Australia.

Unread postPosted: Tue Jul 08, 2008 4:15 am
Author: Insomniac
Ran it again tonight. It was one of the longest runs yet, at about 40 sec. The water does a pretty good job of keeping it lit. It didn't get red hot this time though.

[youtube]http://www.youtube.com/watch?v=BJ8QTXzB1XA[/youtube]

Unread postPosted: Tue Jul 08, 2008 4:29 am
Author: Carlman
[youtube]http://www.youtube.com/watch?v=FZmjBAY-UrA[/youtube]

how about that?

EDIT: not mine

Unread postPosted: Tue Jul 08, 2008 5:00 am
Author: Insomniac
Yeah I've seen that vid before, its a really good engine. Unfortunately I don't have access to a welder so my tin cans will have to do. I might have to try weighing down mine so I can submerge it a bit deeper. Howefully it will run a bit longer that way.

Unread postPosted: Tue Jul 08, 2008 7:46 am
Author: Sticky_Tape
could you make a small toy car run on that?

Unread postPosted: Tue Jul 08, 2008 9:17 am
Author: starman
Sticky_Tape wrote:could you make a small toy car run on that?


Not really that practical, wouldn't you think Sticky? Fun to play around with though.

Unread postPosted: Tue Jul 08, 2008 10:01 am
Author: rp181
try a pipe hammered rect on one side, on the other, have a cut (from hacksaw) about a inch up. Hold propane torch (lit) about a inch from the opening, the torch goes out, but the end of the pipe ignites and goes out really fast.

Unread postPosted: Tue Jul 08, 2008 2:08 pm
Author: jimmy101
Insomniac
Do you have any good strong magnets? Perhaps use'm to hold the can down in the water by placing them below the pan.

I wonder if it'll work with water in the chamber along with the methanol? It may well slow down the methanol evaporation rate too much but it might be worth a try. The water will also help to keep the temperature from rising too much.

I wonder if you could weight the can with water inside and use gasoline as the fuel, the gasoline is lighter than water and will float on top.

Adding water would also let you fiddle around the the volume in the can without having to build a new chamber for each test.

Unread postPosted: Tue Jul 08, 2008 5:14 pm
Author: rp181
one guy made a valveless pulsejet with propane feed ou of copper (its easy, hardest part is getting pipe size right), but it could only be run for about 30 sec before solder started melting.

Unread postPosted: Tue Jul 08, 2008 5:32 pm
Author: SpudFarm
the perfect farting machine :D

Unread postPosted: Tue Jul 08, 2008 7:12 pm
Author: Insomniac
jimmy101 wrote:Insomniac
Do you have any good strong magnets? Perhaps use'm to hold the can down in the water by placing them below the pan.


You are a freaking genius! I have quite a few ultra strong, flat magnets I have salvaged from old hard drives. I'll have to try it when I get the chance, but I'm going to be away from home for a few days so I won't be able to do it straight away. Really good idea though.

As for placing water in the can, I think I'll leave it as it is. I got a 40 second run out of it so my main issue is heat causing it to be too fuel rich, the actual proportions of the engine seem to be fine.