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Metal rocket prototyping.  RSS feed

 
Steve Farmer
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I've knocked up a couple of small rocket stoves from scrap box section steel just to try out some dimensions and with limited success.
I'm intending to build something more useful with a steel core, but I accept the limitations.

Some bulletpoints in mitigation.

The core will be "disposable" tho I will still want to do what I can to lengthen its life.
The core will be as small as possible while still being useful so shouldn't get as hot as full size burners (at the possible cost of an incomplete burn?).
I'll be putting an exhaust gas temperature (EGT) gauge in for my own curiosity.
I'm very low on experience in this field so when I've learned more I'll probably move onto a design without metal. Metal is cheap and convenient for prototyping.
Turbo diesel engines run exhausts that get pretty close to the temp needed for complete combustion in a rocket burner (In fact they sometimes run hotter but not for sustained periods).

I'm interested in knowing the best place to put the EGT gauge. I'll experiment but any ideas to get started on where in the burn tunnel/riser the hottest point can be found?

I wouldn't argue with anything in this thread about the problems of using metal, but I think with a bit of experimentation and careful measurement we might find metal cores have a place in the right circumstances. I'm prepared for my own experiments to prove me wrong on this.
 
Satamax Antone
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Steve, my position is; you will waste your time with metal. Why in the world would you accept tradeoffs in combustion efficiency, just for the convenience of using metal? In the exhaust of a diesel, it's far from complete combustion. What do you get in deisels? 600C° or thereabouts at max. Far from complete combustion. I just try to help people stop wasting their time with metal builds. As i know they don't work.

Here's an exerpt from another thread.

You see this thing? It's hydraulic tubing About 6.5 or 7mm thick.

By the end of the 32 hours burns, it was like puff pastry in the elbow. The metal was about 1 inch thick inside, because of the spalling, and the cyclonic rocket was unusable. The gas bottle started sagging under it's own weight. That's metal heated to the white. You obviously see the spalling. That's not on the oxygen rich side, which creates the spalling usualy. If you don't trust me. Carry on. But please, don't tell me afterwards that your contraption works wonders and such. I know that if you reach the proper temps for a rocket stove of any kind to work properly, steel won't hold.


I can even tell you that i'm killing refractories too. I've had the bricks and refractory tubing in another stove, glowing orange. That's more than 900C°, yep celcius, not farenheit. How long do you think steel could survive at that kind of temp. Seemingly, a rocket can reach 1200C° on a regular basis.

I should have cut that elbow on the cyclonic rocket, to show the world what a rocket can do to metal. But i threw it in the skip before thinking about it.






 
Steve Farmer
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Satamax Antone wrote:Steve, you will waste your time with metal. Why in the world would you accept tradeoffs in combustion efficiency, just for the convenience of using metal?


I'm figuring that I won't be getting a complete burn anyway, due to the necessity of small size/low weight/portability.
I'll reiterate that I'm using metal in a prototyping phase. I might use a build once before redesigning.
The metal is so cheap that it's free and the J-tube is cut and welded in well under an hour.
I'm expecting a design issue in getting it to work as efficiently as possible while being as small as possible - that will make the metal issue irrelevant.

I accept that a metal chamber/riser has no place in a final unit, especially one sized to heat a living space.
 
Steve Farmer
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Satamax Antone wrote:What do you get in deisels? 600C° or thereabouts at max.


pushing double that at max for short bursts and 900C can be reached towing or climbing. Around and above 900C EGTs you are going to destroy your engine, but it's going to be the pistons melting or the head cracking, not the exhaust manifold failing, as the diesel is combusting at upto 4000C for 1/18th of the time and that's where the damage is done.
 
Steve Farmer
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This thread was split out from another thread. The first post was originally a response to the very sensible comments about metal chambers and risers being a bad idea in rockets.

When I'm ready to continue with my prototyping I'll start a new thread so that the details are set in context of my aims and limitations for the specific intended use scenarios in outdoor, non permanent, prototyping situations. So I won't be posting further in this thread and will now mark it as resolved.
 
Satamax Antone
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Steve, for prototyping, metal can be OK. But there is other options. For the heat riser, and the end of the burn tunnel, you could use vermiculite board. It cups and bends sometimes with the heat. But nowhere near as bad as with metal. Andfor lightness, it's better than metal. Tho, you can't realy use that for the feed tube and begining of the burn tunnel. So refractory bricks would be in order. But they're not light. If you want light for prototyping, use insulating firebricks. To me, that's the best material you can use for a rocket stove. Exept for wear.

But a insulating refractory brick core, and vermiculite board heat riser is a good way to start. That could hold two or three years. Instead of hours. Which would happen is the metal is well insulated. It's light too. Peter has done some fair bit of research here, with some of thoses materials.

It's worth reading the whole thread.

http://donkey32.proboards.com/thread/355/small-scale-development

The general consensus is, anything bellow 4 inch diameter, is not realy worth anything. Besides for cooking. There's one 3 inch batch iirc. But i never saw much results about it.

As you seem to understand about cars, anything below 4", has problems due to drag, because of the boundary layer. Usualy good mixing, but with realy bad draft.

I get back to metal and prototyping. Aluminized steel and rockwool make good temp heat risers. The alumina forming a barrier to protect the steel. Tho, it doesn't last!

Hth.

Max.
 
Satamax Antone
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Steve, sorry for the inconvenience.
 
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