Spherical Combustion Chamber

[Dave_G]

Here's a cute little motor that was recently given to me. It's never been run. It's very nicely constructed and the welds are beautiful. Quite an interesting little motor, and very simple construction.

[Dang911]

Was it a bong in a past life.....

[Dave_G]

Was it a bong in a past life.....

Ha Ha, I don't know...it's certainly a strange looking critter, though!

As long as the tailpipe is, I find it odd that they didn't give it a slight curve so that the thrust vectors from both inlet and exhaust were parallel. The longitudinal axis of the inlet is angled nearly 20 degrees with respect to the axis of the exhaust.

The entire thing is made out of 28 GA. Stainless, and the TIG welds are immaculate. That's no easy feat!

[Dave_G]

Here's a better view of the profile.

[Mark]

That looks like a fun engine, interesting to think about. Try holding up to your mouth as you drive down a busy street. It certainly would draw attention even sitting in your back seat if you were pulled over.
It reminds me of a book about the history of weapons that I was reading the other day. One was a tomahawk that was also a pipe, and apparently this was a common design long ago. Oh, those multi-purpose tools. ha
Mark
http://larrygotkin.com/knives/tomahawk-pipe.html

[Mr.B]

I got one of those years ago and its a great runner. Had it mountaid on a tracked vehicle (see pict) and on floater on water. Has 6 pounds of thrust although I never really measured. Yours probally was made by Desar Molnar (spelling?). I believe it runs around 240 Hz and creates a very strange and unpleasent stinging in the neck after being exposed to it for a couple of minutes, it screams.

[Mr.B]

I build a larger version of this design this summer and it kicks ass! I'm using an air valve for starting together with the spark and it instantly roars to life. Running a mere 40Hz (will upload sound file at some point)

[Dave_G]

Beautiful work, Mr. B!

Am I correct that on the Big Chamber version you built the Combustion chamber is about 250mm diameter?

Yes, please do post a sound (or better yet, video) file, I'd love to hear it running!

How much thrust do you get out of the large version?

Best regards,

Dave

[Mike Everman]

That is absolutely wild. Can't wait to hear it! I have to wonder if the center of the sphere becomes acoustically significant. I would expect so.

[Dave_G]

Hey Mr. B,

I just found your other thread here:

http://www.pulse-jets.com/phpbb2/viewto ... ght=#35963

So, 320 mm diameter, and not thrust-measured yet?

Maybe that Spezial Kommando has a fondness for doughnuts, or something? ;-)

[Dave_G]

That is absolutely wild. Can't wait to hear it! I have to wonder if the center of the sphere becomes acoustically significant. I would expect so.

Yeah Mike, it would be interesting to put a pressure tap directly in the center, wouldn't it? Or even map the pressure field across the entire section.

[Mike Everman]

Yeah. I've been designing a cooled probe stinger for my future data acquisition rig. Thinking of running it in and out with a linear stage so I can plot avg pressure vs. position pretty accurately.
I keep coming up with features for this mythical test stand. At some point I need to start putting it together, but it's looking like my retirement project!

[Dave_G]

Yeah. I've been designing a cooled probe stinger for my future data acquisition rig. Thinking of running it in and out with a linear stage so I can plot avg pressure vs. position pretty accurately.

Mike,

That's a great idea!

Use a ceramic tube like this one:
http://www.mcmaster.com/itm/find.ASP?ta ... ng=8746K11
And you won't even need to cool it.

I've used these for remote igniters - they work great and only 8 bucks.

Dave

[Mike Everman]

Too short, but I'll have to remember that one for other things. I want to map the entire length of the motor from up the tail, so need more than a metre. I'm thinking multi-walls and water or air cooling, but want to keep it small diameter. Hmmm, not super easy, to be sure.

[Eric]

Are you going to map the entire length, and incrementally move it to the wall and map the same way? The pressure and velocities are not uniform over the cross section of the pipe.