Steam fires underwater jet engine

New Scientist.com ^ | 29 January 03 | Ben Crystall

[aculeus]

A revolutionary new steam engine, described by its inventors as "an underwater jet engine", may soon be powering dinghies and speedboats more efficiently, cleanly and safely than a conventional outboard motor.

The Pursuit Marine Drive produces thrust by using the energy from high-pressure steam to draw in water through an intake at the front and expel it at high speed through the rear. The steam emerges at high speed from a rearward-facing ring-shaped nozzle into a cone-shaped chamber, where it mixes with the water (see graphic). Shock waves created as the steam condenses are focused by the chamber to blast water out of the back.

The drive was invented by Australian engineer Alan Burns and developed in Britain by engineers at Pursuit Dynamics in Royston, Hertfordshire. Last week, New Scientist witnessed a version just 20 centimetres long develop around 30 horsepower (22 kilowatts) in a test tank, enough to power a speedboat. But the company says it can be scaled up to about 300 horsepower.

A crucial element of the design is that water flowing into the engine draws in air through a vent ahead of the steam jet. The air bubbles change the way the steam mixes with the water, and this significantly increases the engine's efficiency.

Heat scavenger

Computer simulations have shown how this works, but Pursuit Dynamics is keeping the details secret. "We know the answer," says Mike Todman, the company's chief technical officer, who was previously chief engineer with the marine engine division of Rolls-Royce. But he says it will not be revealed until patents are granted.

Steam for the drive is generated in a small boiler burning diesel or petrol. If the drive is being used to assist propulsion in a ship, the boiler can scavenge waste heat from conventional engines. It can be fed by seawater if necessary.

The boiler may be built from corrosion-proof materials, and if the steam flows fast enough it will blast out any other deposits. With no moving internal parts, and no propeller, the engine should be cheap to manufacture. It is also robust, and can easily cope if seaweed or rope are drawn into the inlet.

Water emerging from the engine is no more than 3 or 4 °C warmer than the water it draws in, so there is no danger of scalding. And as it does not leak oil like conventional outboards, and has no propeller that could injure large sea creatures, it should be less damaging to the environment.

The steam drive can also function as an extremely robust pump. It can shift water, sewage or oil, and in a demonstration for New Scientist, Todman shoved large quantities of lard and cardboard into the inlet without the pump suffering any ill effects. It could even mix materials used by the food industry. "It doesn't simply mix -- it macerates," says Todman.

Pursuit Dynamics itself does not plan to manufacture the engine. Instead, the company hopes by the end of the year to have licensed other manufacturers to make it.

[aculeus]

[Pyro7480]

Very cool!!! I wonder how much these engines will cost. However, I won't be completely impressed until they develop (or perfect) a magnetohydrodynamic (catepillar) drive. (Hunt for Red October fans will know what I am talking about)

[Mr. K]

kewl...!

[spokeshave]

perhaps shrillary can use it to clean old crusty....

[IronJack]

Any engine that runs on steam has a problem with response; it takes a while to "rev" up or down. I don't see any jackrabbit throttle response with this design, but it could work for larger vessels.

I still don't quite get the "shock wave" idea. Steam condensing in an air/water mix causes shock waves? How? Why? Is it the latent heat of condensation that is being given up into the stream? Unless it's pretty high-pressure steam, I can't imagine it has enough energy to cause a shock wave sufficient to provide much propulsion.

But it's been a long time since college physics and phase dynamics.

[Fiddlstix]

Bump

[spokeshave]

Sounds like another cold fusion fiasco

[aculeus]

I goofed and didn't fill in the "source" box.

This is from New Scientist.com and I would be grateful if you executed a "fix".

Many thanks.

[Ronaldus Magnus]

Pursuit Dynamics itself does not plan to manufacture the engine. Instead, the company hopes...

...to take the company public, sell out, and flee to Tahiti before any one figures out that the design is limited to a theoretical hydromechanical efficiency of 0.005%. ;~)

[Dinsdale]

If the steam is superheated it might vaporize additional water. But I don't see how wet steam could create shock waves except some sort of reverse cavitation low pressure waves.

The boiler discription does'nt include a superheater so I'm assuming wet steam and scratching my head.

[Libertarianize the GOP]

http://www.freerepublic.com/perl/bump-list

[dozer7]

"Any engine that runs on steam has a problem with response; it takes a while to "rev" up or down. I don't see any jackrabbit
throttle response with this design, but it could work for larger vessels.

I still don't quite get the "shock wave" idea. Steam condensing in an air/water mix causes shock waves? How? Why? Is it the
latent heat of condensation that is being given up into the stream? Unless it's pretty high-pressure steam, I can't imagine it has
enough energy to cause a shock wave sufficient to provide much propulsion.

But it's been a long time since college physics and phase dynamics."

good point. pulled out my steam tables, been some years, and reviewed them. i had trouble following the concept. but then i am retired and senile could have missed something.

regards
the dozer

[Dead Dog]

Why would she do that, without parasites, she has no social life.

[John Jamieson]

Expect very low efficiency or our subs would already be using it.

We built these out of a candle and a copper tube 50 years ago.

[norraad]

Finally, someone invented a cardboard & lard pump!

[zebra 2]

Shock waves? It would have to be extremely high-pressure steam. Not the kind you'd find on a speedboat--unless its boiler's thermal efficiency is likewise extremely high, its fuel mighty potent, and its hardware HD. Besides, every steam-into-water system I've seen is extremely noisy.

[Weirdad]

Maybe there IS an element of cold fusion going on in this. Bubbles bursting in the right way can generate tempertures in the millions of degrees (though for a very limited mass of water), and some think that small, hard to measure amounts of fusion could be going on in certain types of turbulent bubble streams. Maybe they got the "mix" just right, and the energy output seems very efficient because they are actually getting a boost from small amounts of cold fusion.

( I know, I know, close my tags: </tin_foil_hat> )

[dark_lord]

Expect very low efficiency or our subs would already be using it.

Well, subs tend to use conservative technology. But in any case, quiet technology. This thing will be noisy as hell. It won't be used by subs.

[El Gato]

Depending on what speeds it's best at, it would make a heck of torpedo drive, assuming it works as advertized. Maybe it's a varient of the Russian "rocket" torpedo motor?

[Leo Carpathian]

>>...to take the company public, sell out, and flee to Tahiti before any one figures out that the design is limited to a theoretical hydromechanical efficiency of 0.005%. ;~) <<

Sounds about right.

What makes water go out back rather than both ways? Smart "shock waves"? Smells fishy, without fish sucked in :-)