Steam rocket project

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PyroJoe
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Re: Steam rocket project

Post by PyroJoe » Thu Oct 01, 2009 5:32 pm

Hi Mark,
The update was much appreciated and many thanks, would have posted thanks that day, but was hoping a bigger hitter would give a hat tip.

Would be working more with rockets if there wasn't a military station nearby, running a radar system.

Sending up fast moving guided craft with extra small wings, tends to concern the officials for some reason.

Thanks again,
Joe

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Re: Steam rocket project

Post by Johansson » Sat Oct 03, 2009 8:29 am

I´ve started to build a test engine from a small oxygen bottle just to get some "run time" without having to heat 20 liters of water for each test, it will be heated by propane from the tube burner that I have yet to weld to the frame. After some test runs I can fit a siphon tube to the conical bottle fitting so it picks up the steam from the far end of the tank to try Hinote´s idea, but my guess is that I will need a different CD nozzle when I go from water to steam.
IMG_1799.JPG
IMG_1800.JPG
I will use my IR-termometer to check the bottle temp so I won´t have to fit a pressure gauge, I figure that the less couplings and gauges before the ball valve the less risk of anything springing a leak.

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Re: Steam rocket project

Post by hinote » Sat Oct 03, 2009 3:05 pm

Johansson wrote: After some test runs I can fit a siphon tube to the conical bottle fitting so it picks up the steam from the far end of the tank to try Hinote´s idea, but my guess is that I will need a different CD nozzle when I go from water to steam.
Anders:

Don't forget that the static mode and the dynamic (under acceleration) may need different pickup locations. It's quite possible that a straight tube will do the job for a dragster (and certainly for a rocket) but you'll need to access the gas space at the "top" of the interior.

Still TBD is whether the turbulence in there will make this refinement unneccessary.

I've attached a simple graphic (2 versions) of what I'm trying to convey.

BTW nice work there, so far!

Bill
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feed tube 2 versions.JPG

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Re: Steam rocket project

Post by Johansson » Sun Oct 04, 2009 6:55 pm

I finished the small steam rocket today and gave it a go, since I only had my IR hand held termometer to rely on I decided to play safe and only run it slightly above 100°C bottle temp. The bottle volume is 600ml so I filled it to 500ml to have enough air left in there.
IMG_1806.JPG
The nozzle is made from PTFE plastic and has a 5mm throat and 13mm exit diameter with a bell form internally, I used a grinding tool to shape it in my lathe and it turned out really well. Before that I made a steel cone with a 20° angle and tried to form a copper tube into a cone in the lathe but the cones always split before I got the right diameter at the end.
IMG_1805.JPG
IMG_1807.JPG
The first run was made with 120°C bottle temp and it produced a nice steam jet but little or no thrust, the second time I ran it my friend video taped it and I decided to give it some more heat. At aprox. 150°C I opened the steam valve and the result can be seen in the Youtube clip below. After building a better test bench than the chair I used now and with a pressure gauge fitted I will increase the temp further until I reach 50 bar bottle pressure, the bottle is used to store oxygen so I won´t be anywhere near the rated pressure.
IMG_1808.JPG
http://www.youtube.com/watch?v=W4wwxPW8ldo

I can´t wait until we start building the real engine, imagine 30 times more water and 100 bar bottle pressure! :twisted:
Last edited by Johansson on Sun Oct 04, 2009 7:57 pm, edited 1 time in total.

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Re: Steam rocket project

Post by hinote » Sun Oct 04, 2009 7:44 pm

Johansson wrote:After building a better test bench than the chair I used now and with a pressure gauge fitted I will increase the temp further until I reach 50 bar bottle pressure, the bottle is used to store oxygen so I won´t be anywhere near the rated pressure.
Cool!

I have 3 things for you to consider:

1. I checked a steam table for "dry saturated steam" (probably optimistic) and the temp corresponding to 50 bar is 313C. You should probably consider something more temp resistant (and stronger!) for your nozzle than PTFE for those conditions.

2. You may want to consider using a remote valve actuation (string pull?) and some shielding for yourself, as you increase the pressure and temp. I imagine you've heard the usual stories about oxygen tanks flying around after being knocked over and breaking off the valve. Oxygen at pressure doesn't begin to create the energy of water/steam heated to the same pressure.

3. Tie the test stand down, real good! You're going to be amazed at the power increase as you crank up the press/temp.

Have fun, be safe!

Bill

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Re: Steam rocket project

Post by Johansson » Sun Oct 04, 2009 8:08 pm

Correction, it isn´t PTFE but Delrin. I made the nozzle out of this because I was out of brass, if it breaks I will make a new one in a better material.

I did not expect the significant rise in thrust just from a 30-40°C rise in water temp, otherwise I would have strapped the engine down better and opened the valve from a distance. Next time I run it I will bolt it down to the welding bench. One thing I noticed when the steam jet hit me flat in the face was that the pressure drop cools the steam down very fast, it couldn´t have been more than piss warm 50 cm after the nozzle.

To me it looks like the nozzle is under-expanded, perhaps I should try to open it up to 15mm for the next run?
Steam jet.jpg
Steam jet.jpg (78.62 KiB) Viewed 5286 times

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Re: Steam rocket project

Post by hinote » Mon Oct 05, 2009 12:19 am

Johansson wrote: I did not expect the significant rise in thrust just from a 30-40°C rise in water temp, otherwise I would have strapped the engine down better and opened the valve from a distance. Next time I run it I will bolt it down to the welding bench. One thing I noticed when the steam jet hit me flat in the face was that the pressure drop cools the steam down very fast, it couldn´t have been more than piss warm 50 cm after the nozzle.
Hi Anders:

You are obviously entraining a LOT of liquid water here; that means it's grabbing the heat from what's left in the steam to try to evaporate (Google for "heat of vaporization"). You're very fortunate this time--but maybe this is an event to warn you about more serious consequences when you crank up the temps/pressures.

There are numerous stories from the US Navy about guys who had legs and arms summarily cut off by superheated steam leaks; this is probably more extreme than the conditions you're utilizing--but it's certainly worth respecting IMO.

BTW the most obvious failing of the Rankine cycle (that's steam engines) is the heat of vaporization that has to be included in the entry of the cycle, and the same which has to be removed at the end (condensation). The result is, the only practical application of the Rankine cycle includes substantial regeneration--and that is the only thing that is saving the modern electric power generation plants that utilize steam as their method of thermodynamic conversion to mechanical energy (to drive AC generators). Efficiencies of greater than 90% are being realized as a result of regeneration. Truly amazing IMO.

Bill

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Re: Steam rocket project

Post by Johansson » Mon Oct 05, 2009 5:29 am

Fortunately I decided not to use a siphon tube, if it had been pure steam instead of water I would not be the same handsome man that I was yesterday morning... :mrgreen:

How much do the steam expansion change with different water temperatures? Is it possible to make an efficient nozzle that works for different temps/pressures or do I have to decide exactly what running conditions it will see before I can design the nozzle?

These questions will of course be answered once I get my book, but I am eager to find out.

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Re: Steam rocket project

Post by Johansson » Mon Oct 05, 2009 7:42 pm

I ran the engine again today after I had fitted a 100 bar pressure gauge and opened up the nozzle somewhat, first I took it up to 25 bar where it didn´t do much good but during the second run at 35 bar it packed much more punch until the nozzle blew off. I have some video footage but it is not interesting enough to upload to Youtube.
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IMG_1826.JPG
I found that the IR-termometer is not a reliable method to estimate the steam pressure, when my reference point directly below the pressure gauge was at 80°C the tank pressure was close to 10 bar so I´ll stick to taking pressure readings from now on.

Some modifications has to be done before I can run it again, the ball valve has developed a small leak so I will have to get a better one and I have to make a brass nozzle since the Delrin nozzle as started to show signs of heat damage in the throat area. I might have opened the nozzle up a little to much, the exit/throat ratio is 4:1 now.

Some way of measuring thrust is also needed if my goal with this is more than filling the workshop with steam, a standing thrust rig with a reflector plate at the bottom would be nice.

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Re: Steam rocket project

Post by Johansson » Mon Oct 05, 2009 7:57 pm

Some captured pics from the runs:

25 bar
25 bar.jpg
25 bar.jpg (70.57 KiB) Viewed 5239 times
35 bar
35 bar.jpg
35 bar.jpg (68.96 KiB) Viewed 5235 times
The aprox 100kg welding bench was pushed forward against the wheel blocks and the rocket test stand flexed aprox. 1 cm during the 35 bar run so there is plenty of thrust even at a relatively low bottle pressure. 8)

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Re: Steam rocket project

Post by Viv » Mon Oct 05, 2009 7:59 pm

Hi Anders

A small picky point but i cant imagine your pressure gauge is rated to operate accurately while directly attached some thing that hot ;-) normally what you do for steam fitting a gauge is to have it mounted to a short length of tube (6" to 12") thats been rolled up a few turns so its not sitting to far away.

http://www.spiraxsarco.com/resources/st ... eakers.asp

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Re: Steam rocket project

Post by hinote » Mon Oct 05, 2009 8:09 pm

Johansson wrote: it will be heated by propane from the tube burner that I have yet to weld to the frame.
BTW as long as I'm participating in this thread (as a non-expert, please!), I have an observation about your burner:

The burner efficiency is probably quite low, because you aren't premixing any air with the propane. A simple fix for this would be to open up the end of the burner tube where the propane tube is. If I were doing it I would rotate the angle so it's pointing down and then drill a series of holes around the propane fitting. Observing the fuel/air ratio for propane, it would be approximately correct to size the air holes to the same proportions as the F/A. Or, you could drill more holes than necessary and then weld some closed after initial testing.

The goal here would be to get a nice blue flame from the burner slots. I'll bet the flame temp would be hotter by at least 25% (a guess).

Bill

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Re: Steam rocket project

Post by Johansson » Mon Oct 05, 2009 8:50 pm

Viv wrote:A small picky point but i cant imagine your pressure gauge is rated to operate accurately while directly attached some thing that hot
You are right about that, but since I don´t have any tools to cone hydraulic tubes I figured that I rather wear out a pressure gauge than risk a coupling coming loose under pressure. I will try to get a coil made for me when I am rebuilding it.
hinote wrote:The burner efficiency is probably quite low, because you aren't premixing any air with the propane.
Good input, I got a little bit nervous when I was heating the tube for the 35 bar run and saw wave patterns on the underside of the tank. After I fired it I found that it was thick soot deposits rather than deformations to the tube which I first believed. Compared to the amounts of propane wasted during the Thunderchine tests the small farts I am using to heat this engine is almost negligible, but it would be nice to get rid of the sooting. Will try some modifications to the burner later.

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Re: Steam rocket project

Post by Ves » Wed Oct 07, 2009 7:42 am


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Re: Steam rocket project

Post by Johansson » Wed Oct 07, 2009 7:22 pm

Ves wrote:A successful steam rocket: http://www.aquarius-aerospace.de/index-e.html
Nice link, to bad there is very little information on the homepage. The video clips would have been interesting if they were clickable.

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