Steam rocket project

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Johansson
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Re: Steam rocket project

Post by Johansson » Thu Oct 08, 2009 7:11 pm

The book arrived today, guess that I won´t get much sleep tonight... :roll:
Rocket book.JPG

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Re: Steam rocket project

Post by Johansson » Sat Oct 10, 2009 5:22 am

I rebuilt the engine last night, a test stand was made so I won´t have to drag the welding bench around. The new nozzle has a 4mm throat and 15mm exit with a 28° cone angle, it will be interesting to see how it performs.

I moved the pressure gauge after Viv´s suggestion, it wouldn´t have lasted very long sitting directly on top of the engine. A new propane burner is also fitted.
Nozzle side.jpg
Nozzle mounted.JPG
Stand completed.jpg

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Re: Steam rocket project

Post by Johansson » Sat Oct 10, 2009 5:39 pm

More progress, tomorrow I will take it to the annual Day of the Blue Smoke Festival (smaller than it sounds) in a village nearby and show it.

I built a somewhat remote valve opener today so I won´t have to have my hand so close to the steam path, works like a charm.
Teststativet_klart.jpg
Ventilutlösare.jpg
Baksida.jpg

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Re: Steam rocket project

Post by Johansson » Sun Oct 11, 2009 3:29 pm

The new nozzle seems to be on the large side even though it has a 1mm smaller throat diameter than the old nozzle, it empties the tank in less than 2 seconds at 35 bar and I would like to have a burn time of 5 seconds to be able to get a grip on how it performs. I´ll make a new nozzle with a 2mm throat instead of 4mm as it is now.

I also brought home a new oxygen tank for the large rocket engine, 20 liter volume will be interesting to say the least.
Lilla och stora.jpg

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Re: Steam rocket project

Post by Viv » Sun Oct 11, 2009 3:47 pm

Hi Anders

What does the convergent section of your nozzle look like? the reason I ask is that you are altering only one design point by changing the throat dimension ;-)

Viv
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Re: Steam rocket project

Post by Johansson » Sun Oct 11, 2009 4:13 pm

This is the convergent section of the nozzle, if I had the right tools I would have made a true radius in the throat section but with these small nozzles I had to leave a 2mm straight throat section. It opens up to 13mm if I remember it correctly. I calculated it to 9mm but since the tube connecting the nozzle to the ball valve was 13mm ID it felt like a 2mm flat edge around the hole wound act as a choke. Please correct me if I am wrong.

When I make the smaller nozzle I will of course recalculate the entire nozzle and not only change the throat area.
Nozzle rear.jpg

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Re: Steam rocket project

Post by Johansson » Fri Oct 16, 2009 1:52 pm

Here is a video of a run with the new nozzle, I will try with an even smaller nozzle to get the burn time up to at least 4 seconds so I have time to study the steam jet and perhaps get a stable thrust reading from it.

http://www.youtube.com/watch?v=I25o44dMa7s

Most of the recent work is on the pulsejet engines so they are tuned in for the racing this winter, but when I find the time I will give the steam rocket some attention.

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Re: Steam rocket project

Post by Johansson » Sun Oct 25, 2009 9:39 am

After doing some more tests on the small engine I´ve found that a throat diameter of 2.5mm gave a burn time of 6 seconds, that seems to be a good compromise between thrust and time for a race vehicle. The large oxygen tank holds 36 times more water so if I did my calcs correctly the throat diameter of the large rocket nozzle should be 12mm to give the same burn time.

My friends came by yesterday with a ball valve built for hydraulic use, a pressure gauge and some couplings so all that I need to do is to make a pair of nozzles out of aluminum on my lathe before we can start the tests. A test bench with a thrust gauge has to be build first but my friends will take care of that.
Kulventil_stora raketen.JPG

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Re: Steam rocket project

Post by Johansson » Fri Oct 30, 2009 4:16 pm

The new nozzle is finished and we have only to finish the engine mounts before we can do the first test run, hopefully we can do that tomorrow.
Raketsparken 2.JPG
Raketsparken 5.JPG
Raketsparken 7.JPG

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Re: Steam rocket project

Post by Johansson » Sat Oct 31, 2009 10:06 pm

We finished the kick frame today and fired her up, a leaf blower provided air for the burner to shorten the heat-up time some.
Eldning 1.JPG
Eldning 4.JPG
The first run was very unstable because of the kick end bouncing up and down, we had put steel pipes under the kick to make it roll easier for thrust measurements and that combined with the towing rope fitted too low on the frame was not very good. Despite this we recorded an initial thrust of 90kg which held for a couple of seconds and then dropped to 50 kg after 10 seconds.

The second run was better since we put the kick directly on the ground to get rid of the bouncing, we couldn´t take any thrust readings because of this but since we ran the engine at 50 bar instead of the 40 bar in the first run it should have produced a peak reading around 100kg. Total burn time was 22 seconds not counting the 15 seconds of low thrust at the end of the run, this was with 12mm throat, 17 liters of water and 50 bar bottle pressure.

Here are three frames following each other from the video clip, it really gives quite a punch once the valve is opened.
Ruta 1.jpg
Ruta 2.jpg
Ruta 3.jpg
As soon as the lake freezes we will try to run it, it should prove to be an interesting ride...

http://www.youtube.com/watch?v=1qaJmlAhkD4

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Re: Steam rocket project

Post by Johansson » Sat Oct 31, 2009 10:32 pm

double post

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Re: Steam rocket project

Post by PyroJoe » Mon Nov 02, 2009 2:51 pm

WOW!
Freakin' awesome man!
Good job as always,
Joe

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Re: Steam rocket project

Post by Johansson » Mon Nov 02, 2009 3:54 pm

Thanks Joe!

Before the next run we will have to fit a safety valve just in case the pressure gauge breaks, ok if we hurt ourselves but at the race there will be spectators and other racers so the organisers won´t be too happy if we don´t have some sort of safety release valve. We aim to run the rocket at somewhere below 100bar so a 100bar safety valve should give a good safety margin since the normal bottle pressure with oxygen is 200-300bar.

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Re: Steam rocket project

Post by Viv » Mon Nov 02, 2009 4:02 pm

Hi Anders

Thats a pretty amazing result for your first go with the big bottle ;-) nice to see its green and running off wood too, your steam book seems to be paying off

Viv
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Re: Steam rocket project

Post by Johansson » Mon Nov 02, 2009 9:51 pm

Yes, I expected to spend some time tweaking the nozzle before it would work correctly so I am very satisfied. :D

Actually, the book wasn´t as informative as I would have hoped. It covered how his engine was built very well but there wasn´t very much about designing your own rocket, I should have bought both books instead of just one in case the other one was more into calculations.

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