Steam rocket project

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Johansson
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Steam rocket project

Post by Johansson » Sat Sep 26, 2009 4:12 pm

A friend and I have been talking about building a medium sized steam rocket to learn more about these marvelous contraptions, we found an aprox. 100cm high oxygen bottle that will be used as the water tank. Heating the bottle will be done by external means so we won´t fit any heating elements or so in the bottle since it feels very unsafe to modify the bottle in any way.

Is it possible (by amateur means) to calculate the expansion nozzle or it trial-and-error the easiest approach since the exhaust jet will be a mixture of steam and boiling water?

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Re: Steam rocket project

Post by hinote » Sun Sep 27, 2009 12:10 am

Johansson wrote: Is it possible (by amateur means) to calculate the expansion nozzle or it trial-and-error the easiest approach since the exhaust jet will be a mixture of steam and boiling water?
HI:

I haven't posted on this Forum for quite a while. OTOH the steam rocket has been interesting to me from my first discovery of its existence.

One of the details I've pondered about this design is how the H20 (liquid) under pressure is forced into the nozzle and the expansion into a gas (steam) appears to take place here, complicating the pressure/velocity issue--and possibly compromising its efficiency.

My theory is that it may be appropriate to feed the nozzle from the "front" of the pressure vessel, and the resultant gas (steam) can be addressed in a conventional manner at the nozzle. This would be a simple mod to create.

I would like to hear from the "more knowledgable" about this subject, whether my proposed mod might improve the breed.

Best to all,

Bill H.

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Re: Steam rocket project

Post by Johansson » Sun Sep 27, 2009 9:46 am

Interesting idea Bill, from what I´ve figured out from the few sites I´ve found about steam rockets the nozzle feeds on water from the rear of the tank.

As you say the problem with this is to know how fast the water turns into steam once it enters the nozzle, if the steam hasn´t expanded enough inside the nozzle the efficiency would be low and lots of water goes to waste.

The oxygen bottle we are going to use is usually filled to 200bar and safety tested to even higher pressures, so it feels safe to do some test runs at 100bar which would mean a bottle temp slightly above 300C. We will have to do a couple of test runs to find out the total impulse and try different nozzles and throat areas to find the best balance between thrust and "burn" lenght.

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Re: Steam rocket project

Post by Viv » Sun Sep 27, 2009 3:06 pm

Hi Johansson

Nice to see you are taking account of the metal the bottle is constructed from and de-rating the maximum safe pressure to allow for weakening of the metal due to temperature effects ;-) that is normally one of the problems in steam rocket design, getting a pressure vessel material that will retain its strength at elevated temperatures.

For your nozzle design there are some nice nozzle design programs available for the rocker modelers, I have a nice PC one that works with a number of gasses but I cant remember if it had steam as an option, I will have a look for you when I get time.

And yes your right your nozzle performance is every thing to your project ;-) the one nice thing for you is that you are traveling horizontally (I hope) so the ambient pressure the expansion cone will see is constant.

Viv
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Re: Steam rocket project

Post by hinote » Sun Sep 27, 2009 11:24 pm

Johansson wrote:Interesting idea Bill, from what I´ve figured out from the few sites I´ve found about steam rockets the nozzle feeds on water from the rear of the tank.
Sounds like you've got a handle on what I'm trying to convey. Thanks for participating here!

Here's a youtube link to a dragster vehicle with a steam rocket:

http://www.youtube.com/watch?v=CDDI5h8J ... PL&index=2

I can only conjecture--but it seems that the exhaust (effluent) is far wetter than it should be if it was steam (gaseous) being expanded through the rocket nozzle.

Again, the question becomes--does the "water" (liquid) waste the available energy stored in the tank, or does it somehow supercharge the rocket? I don't have a clue, I admit.

Bill H.

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Re: Steam rocket project

Post by Viv » Sun Sep 27, 2009 11:35 pm

Found a link maybe its useful if you have not seen it before

http://www.aerorocket.com/
http://www.aerorocket.com/Nozzle/Nozzle.html
http://www.tecaeromex.com/ingles/vapori.html bit thin on the information but maybe interesting

Viv
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Re: Steam rocket project

Post by Johansson » Mon Sep 28, 2009 5:23 am

The question is how the water behaves inside the tank, I find it likely that it is all over the place once the pressure drop occurs since the water then suddenly starts to boil.

Viv, the mexican guy has built some interesting engines for sure. As you say he could have written in more detail about steam rockets, how is the release valve made for example in such a large engine? On the small engine I am attempting to build I will use a pressure rated ball valve but that would not be practical on a larger engine.
dim.gif
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Re: Steam rocket project

Post by Viv » Mon Sep 28, 2009 1:47 pm

Hi Johansson

In the past I always thought the pressure release was done by a burst plate but some one shot me down in an old post saying that was not a sensible idea ;-) I cant remember the post name but maybe worth doing a quick search on the forum as it has been discussed in the past.

How the pressure vessel contents behave is an interesting question but don't forget that what ever happens on the other side of the throat area in the nozzle cannot be seen by the pressure vessel due to the supersonic flow conditions there, the contents will not suddenly drop to ambient pressure when the ball valve is opened and start to boil, the water in the nozzle throat would be affected as the conditions of pressure and flow are rapidly changing with the nozzle geometry hence temperature is also affected, remember your comment about water in the exhaust?

Viv
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Re: Steam rocket project

Post by Johansson » Tue Sep 29, 2009 5:28 am

Yes, this is somewhat more complicated than punching a hole in a bottle I am afraid... :mrgreen:

The link you posted Viv with the Nozzle calc. program was interesting, too bad they didn´t accept Paypal since I don´t like sending my card number to people I don´t know. I have also searched for books on the subject but most titles with the word rocket are either a 700 page long analyze of gas flow behavour around a rivet in the rocket´s nozzle or a child bedtime story...

The trial-and-error method is another approach that might prove to be quite fun, but I still need to find a nozzle shape that is in the ball park first.

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Re: Steam rocket project

Post by PyroJoe » Tue Sep 29, 2009 3:33 pm

Mr B. posted some of his work:

viewtopic.php?f=9&t=2903

Maybe ballparkish.

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Re: Steam rocket project

Post by Johansson » Tue Sep 29, 2009 8:14 pm

Wow, I didn´t know about that thread. Thanks!
steam nozlle.jpg
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There I have a rough guideline at least, on the swissrocketman homepage there is also some info about a crude steam powered gocart with exactly the same size of tank as we are going to use. It gave the cart a decent push down the track.

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Re: Steam rocket project

Post by PyroJoe » Tue Sep 29, 2009 9:12 pm

1st run found here:
viewtopic.php?f=13&t=4542

Enjoy, and many thanks to Mr.B for sharing.

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Re: Steam rocket project

Post by Johansson » Wed Sep 30, 2009 5:24 pm

Regarding the bottle valve, can I use a ball valve as the throat section of the nozzle or am I messing up the function of the convergent/divergent nozzle that way?

Looking at Mr.B´s engine he has some sort of prechamber after the ball valve and before the nozzle throat, is that something that actually works or is it there just for the looks? That way the steam is expanded and then compressed again before the expansion in the divergent section of the nozzle, or am I not thinking correctly?

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Re: Steam rocket project

Post by marksteamnz » Thu Oct 01, 2009 4:39 am

From a/the previous thread

"Looks like a lot of fun.
I'm curious about the plumbing after the valves. If the valves on each tank are smaller bore than the piping chamber and nozzle after them then even when fully open the chamber isn't doing anything. Have you considered an individual expansion cone after each valve thus reducing the flow drag thru the piping, chamber etc?
Are you going to fit some baffles round the tanks so the heating is more even and efficient?
Cheers
Mark Stacey"

Answering my own question
The narrowest point in the plumbing is the "neck" of the expansion nozzle and if that's your ball valve that's it, plumbing, three into one, pipes, chambers nozzles etc before and after just reduce the flow and performance.

I will provide the link once again that is in the sticky at the top of this section that no one reads or remembers. Not that I'm bitter or old and cranky, no, no, ignore me, see if I care, to late now, I'm off to cry in the corner. So there!

http://www.canosoarus.com/17Misc/Products.htm
THE book on steam rockets which is also it's title and they take Paypal
Cheers
Mark Stacey
www.cncprototyping.co.nz

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Re: Steam rocket project

Post by Johansson » Thu Oct 01, 2009 5:01 am

Book ordered and point taken.

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