Half a croissant, on a plate, with a sign in front of it saying '50c'
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marine steam jet engine

Go faster in water
  (+7, -1)
(+7, -1)
  [vote for,

like a jet engine, but replace:

compressor -> liquid water pump; combustor -> boiler; turbine -> steam turbine; nozzle -> differently shaped nozzle, and will be outside the water (since pressure in air < water)

working with water will be a lot more efficient, since power absorbed by the water pump will be far less than that absorbed by an air compressor.

the boiler, of course, wont be converting all the water to steam (which would leave residues); it will have a high pressure brine outlet as well.

it will be even more eficient if the nozzle can make the water condense as well, turning the latent heat as well into kinetic energy; This might be possible if we mix some air (a low mass fraction) with the steam, so we have a hybrid steam/gas turbine engine.

something like that is actually used on the harrier jump jet (water injected behind the combustor), but in the air, water would run out pretty fast. it is ideal for marine applications though.

arvin, Aug 25 2006

Diagram http://aravindet.go...es.com/Graphic1.jpg
A rough diagram of the engine [arvin, Aug 25 2006]

Steam Rockets http://www.tecaerom.../ingles/vapori.html
Steam rockets used on cars [jmvw, Aug 25 2006]

Injector, an alternative nozzle http://en.wikipedia.org/wiki/Injector
Save the poached fish for the galley! [Skrewloose, Mar 20 2009]

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       A +, though I'm not sure how you can turn latent heat into kinetic energy.
ldischler, Aug 25 2006

       Would this be better then a steam rocket?
jmvw, Aug 25 2006

       I like the idea, but I'm not sure about the brine ejection being effective... Seawater is nasty stuff. Maybe freshwater lakes?
James Newton, Aug 25 2006

       yes, [jmvw], since the propellent (water) is being sourced from the environment, it does not have to be accelerated.   

       i shud think boilers for salty water would have been invented by now... maybe some inert coatings on the metal?   

       of course, freshwater lakes would be more benign... but the ship would sit lower, and drag will be more...
arvin, Aug 25 2006

       //but the ship would sit lower, and drag will be more//
ldischler, Aug 25 2006

       [arvin], I have to admit I don't know much, but please help me to understand your system.   

       Your system picks up water as it travels, which seems handy for a system that uses steam. This could also be done with a steam rocket, yes?   

       It seems you are powering a turbine with steam. Is this correct? Why are you choosing a turbine with fast rotating parts rather then a much simpler rocket, Is it more efficient? Is it better suited for lower speeds?   

       Is there a purpose for the rotating part in your turbine? Does it drive something? The water pump?
jmvw, Aug 26 2006

       //but the ship would sit lower, and drag will be more//   

       I think the difference in displacement of a boat in salt or fresh water is very small in displacement mode and nonexistent when planing, but If you're going to power a boat with a turbine, can I suggest a hydrofoil or WIG setup?
jmvw, Aug 26 2006

       hey [jmvw], we are in halfbakery here! none of us know anything - ok, at least not enough to try and make these things!   

       the rotating parts are supposed to be a part of a standard gas turbine. it serves 4 purposes:   

       1. provides heat for boiling the water (through the bleed air)   

       2. provides mechanical power for pumping the water.   

       3. provides electrical power for running other ship systems (you can't have this without rotating parts somewhere)   

       4. i wanted to mix air and steam before passing it through the nozzle... i might be doing something wrong here, but here is my reasoning: some of the steam might condense during the expansion in the nozzle. if it is all steam, this sudden decrease in volume will cause a collapse in pressure, and perhaps flow separation from the nozzle walls and a reverse flow of air from outside. better to have air mixed in, which can take the volume, and absorb the latent heat, of steam that condenses. i have no theoretical knowledge of what i'm talking about here... its just a hunch.
arvin, Aug 26 2006

       Planning to cook the fish, are we?
loopquanta137, Aug 27 2006

       the jets will be above the water, where they work better.   

       it may cook low-flying seabirds that dont watch where they go, and leaping fish possessed with an urge to leap just after a massive ship barrels past and narrowly misses them.
arvin, Aug 27 2006

       So, you ARE keeping the compressor and the other parts? I thought you were getting rid of that. It's a regular gas turbine engine that also produces steam to give it some extra kick, is that it?   

       Maybe you can just use venturi effect to draw water spray in before the combustion, so it's heated and boiled in the combustion process.   

       BTW, anyone know how airplanes produce electricity? They don't just have a belt with an alternator on one of the turbines?
jmvw, Aug 27 2006

       i think i'll keep the gas turbine (basically for the mixing of air and steam thing) but we can do away with the boiler and directly spray water into the exhaust and let it boil there. (this is looking more and more like a regular jet engine now :(   

       and yeah, jet engines have some mechanical coupling between the shaft and an alternator outside... i think they use some nifty gears and not belts though!   

       (we have an ancient soviet mig-17 engine in a lab... it has a couple of narrow driveshafts that come out at the bottom, and rotate when someone whirls the compressor blades. probably for the alternator.)
arvin, Aug 27 2006

       /probably for the alternator/ Yup. Or close enough. Modern gas turbines, at least, have a power take off for fuel pumps, oil pumps and generators.
david_scothern, Aug 28 2006

       You may have something here. Injecting water after the compressor could work as an intercooler increasing power and it could reduce the combustion temperature and thus reduce NOx emmissions. I could be wrong.
jmvw, Aug 28 2006

       just to clear a few things up. any turbine engine will have at least one accesory drive(gear box) that will run a variety of accesories (funny that) which include such things as pumps (fuel,oil,hyd) governors, starter turbines , propeller control units and alternators just to name a few. they dont run of belts they are always direct drives. Also it is not unknown for a turbine to have water injection to increase power during high demand such as take off. Not related to the subject at the top but may answer a few questions.
djthearn, Aug 28 2006

       Am I right in thinking the original idea was to run a traditional steam power plant cycle, but with the majority of the energy in the steam being used for thrust in an exhaust, rather than being extracted by the turbine (which would produce the boat's power and run the intake pump etc)? This would also mean that the turbine wouldn't have to worry about damage from droplets condensing as well, as the exhaust steam wouldn't be fully expanding.   

       For thrust, you may be able to exhaust into the water using an 'injector' (see link), thus using the pressure of the steam, and the cooling effect (and density) of the surrounding water.
Skrewloose, Mar 20 2009


       I must be missing something. Combustion releases energy. Boiling requires energy...
Smurfsahoy, Mar 24 2009

       This cannot be new. I went through a similar design process in the early 1970's, so someone must have made it/proved it cannot work in the mean time?
eight_nine_tortoise, Mar 24 2009


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