Small Ramjet - no welding, no glue, slip fit - $6.

[Pete Doyle]

I put together a small ramjet - or what I hoped would be a ramjet - from two auto exhaust adapters. A fellow near me makes them to order. I had two made so that one would just slip inside the other - two inches at that point. The ends were made 1/4" different from each other in diameter. What would be the inlet is 1.75" and the exhaust is 1.5". I used a simple injector made from some 1/8" brass tube and cut a flame holder from a piece of scrap steel.
It works marvelously well - I think.
Attached are two pics of the piece in parts and a short video. Air is from an electric leaf blower. The jet running with the blower on low speed and then switched to high.
Pete

[Pete Doyle]

FWIW - This is a follow-up to the first post about this little ramjet. I have finally been able to edit a more complete (still only 20secs) version of the video. This slightly longer version includes the blowtorch start. I used the torch as the simplest method of stating this "test of concept" design. It was necessary to light the entire tube and feed in propane before turning on the air. The change, once the air is on, is dramatic. The focused cone of the jet is clearly visible.
Pete

SlipFit Ramjet video4.mov

(1.98 MiB) Downloaded 248 times

[larry cottrill]

Pete -

A few comments after looking at this a few times:

I think what you have is a reasonably good low-speed ramjet. Like the original Maggie Muggs, the diffuser is not ideal, but probably OK. I think your only real problem is air supply. You're not really running her hard enough, at least in the video. You do get good, stable combustion, but I doubt that the net effect is much better than a thrustless burner. After startup, I would try moving the air supply MUCH closer to the intake; naturally, that will force you to use a LOT more fuel to maintain combustion.

When you have it right, the sound of the blower will be completely drowned out by the jet, because the internal pressure will be significant (a couple of pounds per square inch, at least). If you can get it to the point where the flame looks good and the noise starts to scare you, you've got it. Of course, I'm not sure that a weldless design can stay together for that! Again, it ought to look like Steve's video when it's really running well.

Good luck!

L Cottrill

[Pete Doyle]

Larry: I much appreciate the advice. I did what you suggested with the original two ramjets and the difference was amazing. They both look, at least, like the jet in the suggested video.
I will take your advice here also. The blower is about two feet away from the jet at present. I'll try moving it closer and feeding in more fuel
Pete