Proposed design

Psignorian · Post by **Psignorian** » Mon Nov 24, 2003 5:29 pm

Upon glancing inside at the natural gas burners inside my furnace, I was fascinated to find that they appear to be ramjets. A nozzle for gaseous fuel is positioned in front of a tube about 3/4" inch in diameter, which has a flared front end and a flameholder cap at the end. I'm assuming there is an electric starter on the end as well. It appears to produce a tongue of flame at least an inch and a half in diameter and about six inches long.

My thought is that perhaps I could make a similar setup, using a bottle of propane. I'm going to assemble this on an arm with a pivot point at the center and a counterweight to balance on the other end. Any thoughts as to whether this will work, people?

Stephen H · Post by **Stephen H** » Tue Nov 25, 2003 12:03 am

from what i understand (which isnt much) no... it needs air moving though and past it at 200kph minimum!

Stephen

Psignorian · Post by **Psignorian** » Wed Nov 26, 2003 1:58 am

True, but could not a stream of pressurized fuel such as the flow from a propane bottle running full open create such a stream? I think the way the burner works is via venturi effect. They look like PJ thrust augmenters in a way, only they don't flare out. If I can, I'll try and take a picture and show it. That, or I'll just build the darn thing. :D Either way, should be great, no?

Viv · Post by **Viv** » Wed Nov 26, 2003 9:40 am

You should have a look at the pressure jet engines as this is part of the way that they work.

Have a read in the old forum in the pressure jets area and you will find some good write ups on how they work and what problems they have.

Viv

Psignorian · Post by **Psignorian** » Sun Nov 30, 2003 3:16 am

Okay, I've looked, and I do see the similarities. In my case, though, I'm not preheating the fuel, so it almost certainly wouldn't get up to supersonic speeds, unless I figured out a system to preheat the fuel to induce high in-line pressure. Hmmm. I do know that if I build the test bed the way I'm thinking of doing(essentially, think a rotor), it'll induce centripetal force on the fuel, pushing it out of the nozzle at a higher rate. If it got going fast enough, though, the concept for the ramjet would prolly take over, if it didn't start immediately. I'll just have to do the build and see how it works out, I s'pose.

Psignorian · Post by **Psignorian** » Tue Dec 02, 2003 3:24 am

Correction, centrifugal force. >.>;

Psignorian · Post by **Psignorian** » Thu Dec 04, 2003 7:42 pm

I was right the first time. Argh. Well, enough people make that mistake I s'pose.
Anyway, I've been running some static tests of burners I've made; I'm not sure if they're producing any level of useable thrust(though I'm getting a good roar out of a larger one), so I'm going to call them burners for now, and until I build a test stand. Also, I think I've figured out a low-cost alternative to building a complicated stand involving pneumatic or hydraulic controls, though I'm sure people've thought of it already. Those fish-weighing tools should do nicely(just the cheap spring-scale types, though maybe an electronic one would be cool too), as weight is really a measure of force being exerted.

John Werner · Post by **John Werner** » Tue Dec 23, 2003 2:46 pm

Psignorian wrote:I was right the first time. Argh. Well, enough people make that mistake I s'pose.
Anyway, I've been running some static tests of burners I've made; I'm not sure if they're producing any level of useable thrust(though I'm getting a good roar out of a larger one), so I'm going to call them burners for now, and until I build a test stand. Also, I think I've figured out a low-cost alternative to building a complicated stand involving pneumatic or hydraulic controls, though I'm sure people've thought of it already. Those fish-weighing tools should do nicely(just the cheap spring-scale types, though maybe an electronic one would be cool too), as weight is really a measure of force being exerted.

John Werner wrote:
What if you were to inject water? Would the steam add any thrust as it does in the Loud Mouth engine?

Psignorian · Post by **Psignorian** » Thu Jan 01, 2004 5:46 am

Mmmm...I dunno. Currently, the design is such that the flame isn't being held insde of the device...and *insert expletive*, I just realized the perfect place for the flame holder on my larger variant. :D Too bad I'm 900 odd miles from home right now, or I'd build it. =/

The small size burner is made from copper pipe that I flared at one end, and squeezed into a rough X at the other. Seems to work okay, makes a nice roar at a few turns of the dial on the torch I'm using as the fuel jet. The larger one is made of steel pipe, consisting of one 1"x7" pipe nipple, one 1"-3/4" reducer, a 3/4" nipple, and a 3/4"-1 1/4" reducer. It seems to be able to hold the flame better when I hold the propane jet in the 1" end, rather than through the 1 1/4" end, with the flame coming out of the reducer(which is more of an expander in this setup) in a big(6-7"x14-18") blue plume with a 1"x3" inner flame, which is more of a blue-green color. I suppose that it works better this way because the 3/4"-1 1/4" reducer...well, reduces the velocity of the air because of the drop in pressure it creates. I've yet to make the flame blow out with it, save when I accidentally moved the torch I have that I use as a fuel jet.

As far as water injection goes...well, I don't think that'd work, as it would interrupt the combustion, gas flow, whatever. Maybe not, though. I'll look into it once I get a better model going.

larry cottrill · Post by **larry cottrill** » Mon Mar 29, 2004 8:11 pm

Psignorian wrote:Mmmm...I dunno. Currently, the design is such that the flame isn't being held insde of the device...and *insert expletive*, I just realized the perfect place for the flame holder on my larger variant. :D Too bad I'm 900 odd miles from home right now, or I'd build it.

Psignorian -

If the combustion is unconfined, it's not a jet, it's a burner. If the combustion is partially confined so that a pressure rise is obtained, with a corresponding pressure drop across an exit nozzle, it's a jet. If the combustion is fully contained so that the pressure rise increases without limit, it's a bomb.

In some supersonic ramjets, there can be an adequate pressure rise to achieve thrust force without a restricting nozzle [the 'nozzle' zone can even be flared, like a deLaval cone], but this is only if the combustion gas itself is moving at transsonic speeds [at the local gas condition - VERY fast for superheated gases]. In most practical cases, the definitions I've stated above are good enough.

The term 'jet' always implies a pressure drop across some sort of nozzle, with a corresponding stream velocity boost, and in fact, it is the nozzle itself which forces the pressure rise due to combustion in the chamber [i.e. the so-called 'back pressure' of the nozzle at the exit velocity and density turns out to be the chamber pressure, if losses are small enough to be ignored].

L Cottrill