Steam Thruster?

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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DetroiTug
Full Steam Ahead
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Posts: 1863
Joined: Fri Nov 27, 2009 5:56 pm
Boat Name: Iron Chief
Location: Northwest Detroit

Re: Steam Thruster?

Post by DetroiTug » Wed Mar 14, 2018 1:41 pm

Quote: "Red flag does ring a bell"

There is no argument for this :)

-Ron
flashtwo
Just Starting Out
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Joined: Tue Feb 28, 2012 10:30 am
Boat Name: Vital Byte

Re: Steam Thruster?

Post by flashtwo » Mon Oct 01, 2018 10:02 pm

Hi,
I built a steam jet engine a number of years ago and mounted it on a model boat (see YouTube https://www.youtube.com/watch?v=gJvpVYJY_cs ).

Unfortunately, one of the lads in waders at the model boating event pushed the boat under water because he thought it was "on fire"! The video shows the boat with its rather waterlogged boiler insulation and low in the water.

The "rudder" was a pair of cylinders which, by using the Coanda effect, bent the jet stream to change thrust direction.

The jet exhaust managed to blow over a 6ft model destroyer at a distance of 10ft!

The exhaust contained lots of energy 1/2mv2 (as experienced by the destroyer), but little thrust. Any jet engine is very inefficient at low aircraft velocities, but the thrust efficiency increases as the aircraft speeds up; that is why full throttle is used on take off and engines are throttled back once the aircraft gains high velocity. If the boat could be brought up to a goodly speed, then the engine would have performed well.

If I held a metal plate a couple of feet away from the exhaust, I could feel a force of several pounds. This was because the energy was converted to a force on hitting the plate and the plate was outside the engine's frame of reference. If the metal plate was mounted on the model boat then no thrust would be experienced because no work was being done, Work = force x distance.

Shortly after WW2, the British mounted four Derwent jet engines on an old Victorian Paddle steamer supposable to study hull design. Even under full power it only went 1 knot faster than when it had paddles. See
https://www.flickr.com/photos/scottishm ... 4834159902 and http://www.douglas-self.com/MUSEUM/TRAN ... cyasht.htm.

I tried many configurations and, as has been mentioned earlier, any attempt to inject steam into a pipe containing water, will quickly result in condensation. Other configurations resulted in the steam bouncing off of the water and not imparting any momentum.

The conclusion that I came to was to direct the exhaust from the steam jet engine into a turbine which would be geared down to a conventional prop. Alternatively, one could inject water into the exhaust, which runs at 800degC (1472degF), to increase the mass flow and thrust. I'm in the process of converting the engine to run on kerosene instead of camping gas (its cheaper!)

Ian.
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