Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Steam => Topic started by: flashtwo on June 04, 2010, 03:34:43 pm
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Hi all,
Last weekend at the Wicksteed 2010 event, my Steam Jet powered experimental boat had its maiden voyage (see Wicksteed 2010 page 10 for description - http://www.modelboatmayhem.co.uk/forum/index.php?topic=21652.msg238462#msg238462 ).
Having developed a flash boiler for the Vital Byte experimental boat, I thought the light boiler could be used as the basis of a steam jet engine and last year tried out a couple of unsuccessful ideas and soon discovered that the steam condensed in the air before producing a force.
Last February, I had the idea of expanding the steam through a nozzle into the very hot combustion gases of the boiler much in the same way as an exhauster on a steam loco which uses the cylinder exhaust steam to draw the fire in the furnace.
A prototype engine (boiler? - I call it a Bengine) was built and gave an encouraging performance - the jet exhaust actually set alight a piece of wood! The "Bengine" was about 1200mm long though, quite impractical for a model boat. Then, as I was winding a flash boiler coil on a piece of 22mm copper pipe as a former, I had the bright idea of keeping the copper former as the exhaust pipe through which the steam jet would be aimed through.
This exhaust pipe not only supported the boiler coil, but also passed back through the furnace and eventually was used as part of the butane/propane gas pre-heater. Using this arrangement the length was reduced to 350mm and also the construction was simplified.
I built a “swinging” test rig to test the thrust produced by the Bengine and was confused by how little the swing moved horizontally compared with force exerted against a sheet of aluminium held in the jet exhaust stream. The swing indicated a thrust of less than 1 Newton (1kg held in the hand exerts a downward force of approximately 10 Newtons) – this equated to about 3 ounces of force in old money.
The force on the aluminium sheet was telling me a different story. At a very rough estimate, it was about 0.7 kg , which was about 7 Newtons. Well, according to Newton’s Third Law every action has an equal and opposite reaction – so what was happening here.
I also rigged up a simple Pitot Tube (the thing aircraft use for measuring their air-speed) to measure the exhaust velocity of the Bengine – astonishingly it was calculated to be in excess of 250mph (400km/hr for our Antipodean friends). I used this figure to calculated the mass flows, momentum and kinetic energy of the exhaust and, sure it enough, it confirmed the small amount of thrust being developed, but didn’t explain the force on the aluminium plate.
So, being a Mayhemer, I thought let’s build a boat and get some real world experience to confirm or contradict the theory. Having built the boat in record time off I set for Wicksteed 2010 ( the home test tank being too small for a proper test).
One little side feature was the addition of a jet vectoring device in place of the usual rudder. This device was based on the Coanda effect where a fluid flow follows a curved surface.
The maiden voyage confirmed the lack of thrust being developed, confirmed that the vector thrust steering was practical and, as chance would have it, the equivalent of the aluminium plate sailed by the exhaust in the form a metre long model of a destroyer. The model destroyer was heavily blown over to port by the Bengine exhaust blast – the steam jet boat was no friend to other users on the pond.
There was the dichotomy – the jet could knock over another boat, but could hardly move the boat it was suppose to be propelling.
What was going on with Newton’s Third law????
Ian
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Is it simply the fact that the exhaust needs something to react against? Maybe the energy is simply dissipated too quickly against normal atmospheric pressure as the steam expands on leaving the nozzle. Think about a hovercraft which only lifts a few inches off the surface, if you increaased the power it wouldn't rise much further as all the excess air would simply escape and provide no extra lift. I supspect something similar is going on here. What would happen if the jet was directed to emerge under water I wonder?
Colin
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... photos AND video to follow! O0
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You need smaller nozzle with a higher velocity jet. Think about a nozzle on a hosepipe.
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I'm thinking it's more volume of steam needed....
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boat mass times velocity = jet mass times velocity
too much mass and you run out of steam, so it has to be big velocity.
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Where is Dodgy Geezer when we need him? %)
Colin
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Interesting results.
I think you need to physically treat the device as a rocket. It doesn't "need" to push against a plate or the air or anything else: the thrust is generated purely from flinging reaction mass out the back.
What you might be finding is that the instant expansion of the steam when it reaches atmospheric pressure, is occurring in a hemispherical volume from your nozzle. This may well be accelerating ambient air generally backwards, thereby producing the effects you see on your aluminium plate and passing destroyers, but represents a net loss of useful thrust to the boat.
Look into rocket nozzles (http://en.wikipedia.org/wiki/Rocket_engine_nozzle) - they are there for a purpose, and the perfect one is shaped so that, in your case, it'll end with a length and diameter to allow your expanding steam to reach one atmosphere at the lip of the bell. (The steam'll still has substantial velocity at this point, of course, and this is now directed directly aft.)
Can you post some figures for pressure and steam rate, please? That'd give a good guide to developing the perfect plenum.
Andy
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That makes a lot of sense Andy. This is an interesting subject.
Colin
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http://www.youtube.com/watch?v=gJvpVYJY_cs
(http://www.youtube.com/watch?v=gJvpVYJY_cs)
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Together with a correctly designed "jet" nozzle as previously suggested, I was also wondering if an augmenter tube would be beneficial ??
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A jet engine works by sucking air in and expelling it - a propellor in air is doing the same thing more or less. A rocket engine does none of that but expells a huge amount of energy. A steam jet is a de-facto rocket engine but it would not be possible to create enough energy due to the small size of the nozzle (a larger nozzle cannot get enough steam), hence the lack of thrust. The augmenter tube might work because it would draw air in by venturi effect and thus increase the volume on exhaust.
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if you put a engine on the end of the steam pipe with a fan , it may go quicker. {-) {-)
Peter
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Thanks for all your interesting comments..
I wasn't the first to try a jet propelled boat, see this site....
http://www.dself.dsl.pipex.com/MUSEUM/TRANSPORT/lucyasht/lucyasht.htm
Apparently, from what I can gather from other sites, the jet powered version (remember a twin Derwent Meteor aircraft could exceed 600mph) was no faster than when it was powered by its Victorian reciprocating steam plant.
Another unusual application for a Derwent engine was to dry out a power station boiler after a major fire - I was the instrument engineer on the project and one concern was bending the boiler drum with uneven heating by the jet exhaust. Not many, I can tell you, stood too close when the engine was sitting there at 10,000rpm!
Colin, I think you are correct to say that the exhaust needs something to react against in the sense that it needs to accelerate more ambient air or the pond water. I've tried putting the jet under the water, but only get a large amount of bubbling.
Ian.
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Could your lack of thrust problems possibly be caused by the very use of steam itself. This is ejected from the nozzle with apparent great velocity but it is rapidly contracting as a gas/vapour the moment it leaves the nozzle. There is lack of mass being ejected and what is ejected is diminishing as it mixes with the cold atmosphere. A rocket ejects an expanding gas, a jet passes hugh masses of hot gas at high velocity so it would appear the steam powered 'rocket' boat would be rather innefficient and a poor use of the fuels energy.
I would be inclined to attach your steam generator to a well designed turbine where the energy and gas/vapour velocity will impinge directly onto blades which will absorb this energy much more efficiently.
Power stations use steam turbines to good effect, I've often considered playing with such a power plant but there is little to beat pistons and cylinders at our scale really.
It's great to experiment however and perhaps you could keep us posted from time to time on any firm findings you make.
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If you ran the steam through a venture with a pipe with water in the center to inject water into the stream would it work. Sort of like a Boiler injector? I remember something about fire hoses that worked like that.
Regards,
Gerald.
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Thats a ruddy good idea Gerald, why didn't I think of that.... must be getting old! It would use the inertia of the steam to throw a greater mass of material but I reckon it will still need a larger nozzle and possibly a bigger burner so could still be quite wasteful on energy.
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Thanks again for your comments,
The part of the problem that I couldn't understand was the Newton's Third Law bit. On my test pond I filled a large ice cream tub with gravel and placed it in the path of the jet exhaust and again the ice cream tub moved away much quicker than the boat could move. I could feel a good force on the tub but hardly a thing on the boat - there were no equal and opposite forces present.
The experiments that were unsuccessful last year were the ones which the steam was in direct contact with the cold water or just expanded in the relatively cold ambient air - the initially invisible steam just condensed in the water causing lots of visible vapour and bubbles or condensed in the air thus loosing its energy.
The video of the boat at Wicksteed was taken after its dunking (see the Wicksteed thread for details) and all of the boiler insulation was soaking wet. Normally with the Bengine up to temperature the 250mph exhaust jet is invisible for all its length indicating that the steam has not cooled and condensed. On startup I can see that the steam vapour doesn't expand and disperse sideways very much, but stays in a fairly confined jet.
As you can See ts the Third Law bit which is the problem.
Keep the ideas coming in, I think we will all benefit.
Ian
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It's all about thrust ( If in doubt watch "Chicken Run"... :-) ) Nothing to do with impact velocity, expansion of gasses or vapours... It's about thrust & the ability of a steam boiler to deliver such. As an example, a small Maccsteam boiler delivers 300 cu ins/min (4916ml/min) of steam at 50psi with 65/35 mix gas. In pounds per minute ( thrust) that is quite small... 0.026 lbs/min to my calculations, someone peease check as steam calculations weren't my forte'...
http://science.howstuffworks.com/rocket2.htm (http://science.howstuffworks.com/rocket2.htm)
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http://cgi.ebay.co.uk/JETEX-MODEL-PLANE-ENGINES-augmenter-tube-/190402270927 (http://cgi.ebay.co.uk/JETEX-MODEL-PLANE-ENGINES-augmenter-tube-/190402270927)
An augmenter tube may possibly increase the mass of ejecta, I would look at a nozzle design that maximises exit velocity of the steam. Guessing, I would make sure no ( or little) expansion occurs within the tube as that may nullify the effect.
Good luck & have fun... :-))
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Hi Ben,
I've tried trying to augment the exhaust flow by using a blown-edge aerofoil much like the Buccaneer aircraft used for low speed flight.
The exhaust flow was directed up through a slit nozzle around the curved leading edge of the aerofoil and then, using the Coanda effect, bent through 90 degrees to direct the thrust astern. The flow was boxed in at the top and air was sucked through to augment the exhaust flow.
It certainling sucked in air from the front and chucked it astern and the thrust may have been better but no greatly so.
With regard to your suggestions about thrust and the website example, what happens if I throw a cricket ball astern at 20mph and I'm already moving forward at 20mph - do I get any thrust?
Here's a couple of pics of the augmentor aerofoil.
Ian.
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With regard to your suggestions about thrust and the website example, what happens if I throw a cricket ball astern at 20mph and I'm already moving forward at 20mph - do I get any thrust? Ian.
It's all relative.... ok2 Never mind the velocity part of the equation ( for now).... you also have to have the mass per unit time to throw.. May I give a crude example. Stand on roller skates & throw a marble as fast as you can. Now throw a cannon ball & compare the distance you have moved. You have imparted the same amount of energy but you have moved further with the greater mass...
Looking at the pics it looks like you have been having fun with this... :-))
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If that doesn't work, you could try "Dempster Turb-O-Prop" :o
http://jetex.org/motors/motors-accessories.html
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If that doesn't work, you could try "Dempster Turb-O-Prop" :o
http://jetex.org/motors/motors-accessories.html
Cathrine wheel comes to mind... :-)
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Right,
I think I have an understanding of how propulsion works, be it conventional prop, gas turbine or bengine.
The steam / combustion gas emitted from the boats exhaust at high velocity has two components;-
1) The momentum = mass x velocity
2) The Kinetic energy = (mass x velocity^2)/2
Notice that the kinetic energy will always be much larger because the velocity is squared.
If the boat is stationary, or moving very slow compared with the exhaust velocity, then practically all of the energy is in the form of kinetic.
Now, here's the rub, the because kinetic energy is totally "frame referenced" the boat cannot "see" that form of energy, it can only feel the force caused by the momentum.
Only an observer can "see" the kinetic energy (strains of Einstein's Relativity creeping in here would you believe!). Hence, in the example on the pond above, the "observer" was the model destroyer which was hit by the kinetic energy which exerted a force on the model causing it to keel heavily to port.
So, there is no Newton's Third Law associated with the kinetic energy from the jet boat's point of reference!
All we need to build now is a "frame reference" eliminator!
What do you think?
Ian.
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PDX technology injects steam into a water flow and relies on the shock wave produced by the sudden condensation of the steam to accelerate the water in the tube... Of course the underwater unit in itself would generate drag, therefore an inboard unit similar to jet boat drive may be more efficient...
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Hi Ben,
(The following comments are my own opinion and may not reflect the true state of PDX's engine - (legal note!))
I had a friend who invested £5000 in PDX's underwater jet engine! I explained to him that a similar method was used by Savery over three hundred years ago and it was called the atmospheric pump.
I think, although I may be corrected, PDX said the engine still worked at 50% output with the input blocked, which seem to imply that the engine wasn't working as described.
If you read PDX's patent application (New Zealand NZ522762, US US2008310970) ,you'll see that little basic physics is explained and it all appears wishfull thinking; they themselves don't quite seem to understand the effect that pumping air into the intake has.
My thinking is that the heat energy in the steam warms up the water before it can do any useful work. Condensing steam to create a vacuum to do work is very inefficient, it is better to release the heat energy in the steam, or any other gas, by expansion in a cylinder (creating pressure) or through a nozzle (creating velocity).
I've not heard of anymore developement of the PDX system as a propulsion device.
This morning I'm fitting an internal brass tube in the boat to act as the "frame reference" eliminator. It involves major layout mods, but I hope to have it finished for testing next week.
Thanks for your interest.
Ian.
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Await your results with great interest... :-))
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it is better to release the heat energy in the steam, or any other gas, by expansion in a cylinder (creating pressure) or through a nozzle (creating velocity).
Americans used this to effect by gaining exrta thrust on take off of "Loaded" B52s by injecting water into the jet engines.
Regards Ian.
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Hmmmm.
Bear in mind that:
momentum = chalk
while
kinetic energy = cheese
%)
Kinetic energy is measured in joules, the unit of cheese energy, while momentum is measured in kg*m/s (or Newton seconds). A different kettle of fish.
The joules you're burning boils water, and the resulting pressurised steam has kinetic energy (on a molecular level, think of all those hot H2O molecules bouncing about inside the boiler. Temperature is just a measure of speed). Once released, the steam's kinetic energy is (hopefully) all sent aft. The momentum of the steam is the steam's mass times its velocity, as you say.
To maintain a steady-state of thrust (while acknowledging a slow net loss of water and propane over time) the amount of steam leaving the boiler (i.e. a mass of steam being accelerated from 0 to "v" m/s in the boat's reference frame) must not exceed the energy the burner's putting into the boiler (minus a bit, due to natural inefficiencies) else you'll run out of pressure. So we've obviously got a KE limit.
Maximising the momentum for a limited KE will produce more thrust. As you say, both momentum and KE are dependent on mass and velocity, and maximum momentum from a given KE suggests a low velocity and a large mass is best. This probably explains why pure steam-rocketry is inefficient: you can't boil water quickly enough for a respectable mass-loss, and the velocity of a released steam jet is automatically high. (This also answers why "chucking a cannon ball" is better than "chucking a marble".)
So, if we've a high-velocity/low-mass jet and would be better with a low-velocity/high-mass jet, I think the answer for more thrust/better efficiency comes down to:
1/ Utilising ambient air or water to increase the mass of the thrust stream (and thereby lower its velocity).
2/ Using a burner big enough to generate lots of steam, then lowering the temperature of this steam (= lowering its velocity) before it goes overboard by using a nozzle to allow the steam to expand down to 1atm.
3/ Both the above.
Andy
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Hi Andy,
Thankyou for your much appreciated input.
The physics that I couldn't understand was the ability of the exhaust to knock over the model destroyer with a force far in excess of that available to push the jet boat, which seem to contradict Newton's Third law.
I agree with you that the units of measurement are chalk and cheese, but according to my measurements of gas exhaust velocity (250mph) and mass flow (kg/s) there would be the equivalent of 120 Watts (mechanical not heat) in the exhaust, which was just disappearing into the ether and was not contributing in accelerating the jet boat.
There was a chap who fitted one of the those Wren type gas turbines to a model boat and was greatly disappointed with the performance. The typical exhaust velocity for those engines is about 1000mph, which, for a relatively stationary boat, resulted in most of the energy being kinetic and having zero effect.
As you can see earlier in the post, I did try and increase the mass flow by using an air augmentor, as you have suggested, but it didn't offer any great gain. On the other hand the use of your ambient water is to be tried. I'm currently installing a water tube in the bottom of the boat, through which (I hope!) the kinetic energy will be transfered between the high velocity gases and the water resulting in greater ejected mass at a lower velocity. This should reduce the kinetic energy component that is otherwise wasted to the environment.
The alternative is to use a turbine as the "observer" of the kinetic energy and gear it down to a prop drive, but that defeats the object of the project of using the power of a flash boiler without melting an engine.
Thanks for contributing to the discussion of the fundamental physics behind the problem - I'm pleased that I've learnt something new.
Ian
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Would this work.... ???? I'm not sure...but with superheated steam contacting cold (lake) water, it's bound to get interesting... :-)
(http://i18.photobucket.com/albums/b136/benjaml1/Cavalla.jpg)
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Aha - great minds!
That is very similar to what I'm trying to achieve, but without the venturi.
I've cut an enormous elongated hole in the bottom of the hull for a 38mm brass pipe (aluminium might melt!) to enter at an angle and another hole in the transom for the exhaust. I would prefer it to be glass fibre, but I will take some temperature measurements with the prototype first.
The design of the Bengine ensures that the exhaust is not primarily steam, but mainly the combustion gases at high velocity, the advantage being that there is far less condensible volume.
As you say, its bound to get interesting!
Ian.
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Other way round might work better- just like a boiler injector- you increases the velocity of the steam at detriment to pressure, this picks up water extremely well, but instead of having a combining cone that reduces velovity and increases the pressure back to boiler pressure, a further venturi would increase velocity and lower pressure even further.
In theory!
Greg
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Hi Ian
...according to my measurements of gas exhaust velocity (250mph) and mass flow (kg/s) there would be the equivalent of 120 Watts (mechanical not heat) in the exhaust, which was just disappearing into the ether and was not contributing in accelerating the jet boat.
I've been reading about Tesla turbines recently. Would there be (has there been?) any model application for high-speed steam using that technology?
Andy
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Hi,
Just to let you know that the Steam Jet Bengine boat "Vital Thrust" will be on display at the Guildford Model Engineering Society steam rally this weekend 10th & 11th July, 2010.
See http://www.gmes.org.uk/find.htm for the location of the society, it is from 11am - 5pm each day.
V.T. has been modified with a brass duct, similar to a conventional water jet boat, where the exhaust is directed into the the duct to induce a water flow, as was suggested by members recent posts.
The current problem is the separation of the gas and water in the pipe caused by the gas rising to the top and not sufficiently coupling with the water. Current plans are to fit thin brass horizontal plates in the duct to reduce the gas/water separation (any other suggestions?), but this will have to wait until after the rally.
Due to its current stage of modification V.T. will not be demonstrated, but, hopefully, the display will be a good topic of discussion.
Ian.
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The current problem is the separation of the gas and water in the pipe caused by the gas rising to the top and not sufficiently coupling with the water. Current plans are to fit thin brass horizontal plates in the duct to reduce the gas/water separation (any other suggestions?),
If vanes dont work I would try multi nozzles. I'm still a believer in the venturi/eductor principal though....
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Another thought... If you are familiar with the noise reducing upgrades on Boing 707's which was a petal shaped exhaust nozzle. This allowed ambient air to enter into the jet stream, reducing the noise causing eddys made by the shear... The next noise abatement evolution was the high bypass ratio turbo fan. Little did they know they would hit on improved efficiencies... However, I digress...
Maybe you should design /manufacture your nozzle as such ??
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Ah, the 707, one of my favourite airliners.... :-)
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Thanks guys,
I hope you're not suggesting that I join an aero-modellers club - wash your mouths out!
The by-pass idea is not a digression Benjamin, but a very good idea! One thought I had earlier on, was to allow ambient air into the plenum chamber, where normally the steam jet induces the combustion gas flow. The extra ambient air could increase the mass flow without pulling too much air into the combustion chamber, which, because of the boiler coil, has flow resistance.
I would imagine a kind of wide gate valve on top of the plenum chamber, whose opening could be adjusted as required, very much like the gate valve on top of the old Avon jets (not my favourite engine) used to bleed excess compressor air flow.
Perhaps I'll end up fitting a power turbine - what a hybrid machine that would be!
Ian.
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Have fun.... :-))
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Hi,
The jet boat "Vital Thrust" is part of the way through its conversion for transfering the gas exhaust kinetic energy into the water flow. The Bengine has been revrsed and the gases are now directed into a brass duct which allows water to enter in the keel and out through the transome.
The brass guide plates to stop the gas separating out from the water before energy transfer are to be fitted soon.
Ian
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Here's the other photo.
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Fantastic, I can't wait to see this work- could you expalin why the inlet and outlet are the same diameter- I would have thought that making the exhaust smaller than the inlet would allow more energy to combine and speed up the exit?
Greg
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Hi Greg,
I'm actually trying to do the opposite - slow the exit down by interacting the gas with the water.
Any kinetic energy present in the exhaust is totally lost and provides no propulsion to the boat, therefore the exhaust has to be at the slowest velocity (relative to the boat) - hence minimum kinetic energy.
I discussed this with many visitors to the Guildford Steam Rally, one of whom nodded at all the right points. I said that he seemed to understand what I was saying and he replied that he was the proverbial rocket scientist (with Qinetiq)!
Ian.
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Ah, I see- then as there will be more water by volume after the gas enters should the exhuast not then actually be larger?
Greg
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Oh you so have to bring it to Blackheath on Sunday Ian :-))
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Oh you so have to bring it to Blackheath on Sunday Ian :-))
what is happening at Blackheath?
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Hello again,
I didn't see you at Guildford this year.
The Blackheath Club have a regatta today at the pond on the south side of the heath. I think there will straight runners and tethered hydros there. I will be there with "Vital Byte".
Hope to see you and the familly.
Ian.
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Hi Ian,
I went to the Toy Boat Regatta at Colney Heath today, I wish could have been in two places at once!
did you take any photos at Blackheath today? also, where do i find out about Regattas at Blackheath?
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Oh..its a great stuff...and Sir is that engine in to Pratt & Whitney JT3D or JT8D-219 ...? thanks for the detaled photograph...
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Hi,
Being in facitious mode - some would say it has less to do with the Whitney part of the company! {-)
It has more in common with the Rolls Royce Trent 900 in that it lacks any lubrication oil ! {-)
Ian.
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Hi all Mayhemers,
Just a quick note to say that "Vital Thrust", with its experimental steam jet engine, will be on its first outing to the Ally Pally London Model Engineering Exhibition this coming Friday, Saturday and Sunday.
It will be on the Blackheath Club stand at the kind invitation of SteamboatPhil.
Hope to see some of you there.
Ian.
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And what exactly happened at the debut of the JET ????
I hope that photos were taken...as this has been an interesting topic to find!
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Hi Mojogear,
Vital Thrust was shown a lot of interest at the exhibition, particularly by professional engineers whose attention was caught by the title of the exhibit being "Rankine Cycle Jet Engine", the Rankine being the heat engine cycle employed by power stations as opposed to the Brayton cycle of gas turbine jet engines.
One combined cycle (gas turbine plus steam turbine) power plant engineer wondered if the steam jet engine could be scaled up to replace a gas turbine, one advantage being the elimination of the gas turbine compressor losses (30%?).
Another engineer appreciated the lack of high tolerance machined parts (apart from the water feed pump), unlike a gas turbine that has to be carefully constructed, and also no balancing requirement, since the engine wasn't rotating.
A marine engineer pointed out that the engine had zero torque (something that I had not appreciated), because of its lack of rotating parts, which might be an advantage in marine propulsion.
There was a trio of professional boiler engineers, who normally worked on major supercritcal boilers; they were fascinated by the novalty of the engine and you could "hear" their brains ticking over as to the industrial applications that the design might hold.
I had a long discussion with an industrial chemist about the difficulty of transfering the high velocity energy of the gas flow into the slower moving water flow. This is the major problem in applying the engine to boat propulsion, without using a power turbine and a propeller.
Thanks for your interest
Ian
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Hi Mayhemers,
Just a note to say that I've not given up on "Vital Thrust" and its steam jet engine.
I've recently managed to source some 3/8th inch stainless tube in "small" quantities, so that a higher temperature boiler can be constructed and also a stainless tube welder that can do the couple of joints that I need. The original copper boilers were always on the verge of failing with the extreme steam conditions of 720degC and 20Bar.
As you can see from the Flash steam plant control thread, I been concentrating on getting the new vertical monotube boiler working. Now that job is nearly finished I shall be back on the jet engine project.
Ian.
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Hi Mayhemers,
At last things are moving again (literally) with “Vital Thrust” (VT).
I have heeded the advice of benjaml1 and gondolier88, and have tried directing a pure steam jet through the water, although, to be honest, I did expect the steam to condense before any energy transfer took place – not so as it turned out.
The new flash boiler has been built out of stainless steel tube (2x 3 metres 3/16th inch) for the hottest parts and copper (1x 6 metres 3/16th inch) for the cooler. The new boiler weighs in at 1.4kg which somewhat less the 2.6kg of the original.
Welding has been avoided by ensuring the silver soldered joint between the lengths are at the boiler rear and are shielded against the direct flame of the burner.
The outlet is a threaded collar with 15 turns per connecting pipe, again to avoid welding and to enable the steam nozzle connecting pipe to be removed.
The steam nozzle (again threaded) is replaceable to enable different sizes to be experimented with – 1 and 2mm currently.
I’ve strapped an augmentor tube to the underside of VT (after extensive rebuilding of the hull) and directed the steam jet through it.
Using stainless, I’ve been able to run the boiler with very low feed flow from the electric pump without worrying about melting the pipe.
The boiler contains 500mm of copper pipe through which the butane/propane liquid fuel is vapourised before passing through an external gas cooler and then on to the gas control valve.
I’ve managed to get a very good water flow through the external tube, the velocity of which will always be relative to the boat – the faster the boat, the faster the water will enter the tube and be accelerated. In theory, with the steam jet velocity at hundreds of MPH, the water should still be accelerated even if the boat is travelling fast.
Obviously hull drag will be a speed limiting factor, but it will be interesting to see the performance on open water rather than in my test tank.
Tomorrow I shall fit a small rudder in the water jet flow and then down to Herne Bay model boat pond for a fun test run.
The attached photographs show the original boiler with its flow tube; the new boiler with its steam outlet going through a flanged collar; a close up of the steam jet nozzle: the general arrangement in “Vital Thrust” and the last photograph shows the external gas cooler.
Ian.
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Hi,
"Vital Byte" and "Vital Thrust" will be exhibited at the annual London Model Engineering Exhibtion 20th to the 22nd January, Ally Pally. They will be on Stand S, "A Team Boatyard" alongside the 14ft HMS Daring and other large "items".
Looking forward to having a good old chin-wag.
Ian.
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Have you tested it on the pond yet? I'd be interested to hear about how it performs. A video would be great.
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Fascinating thread by Flashtwo, but regretably no report of results in the boat. Have the results been posted somewhere else on the forum?
Thanks!
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Hi,
Martin took a video in 2010 at Wickstead and posted it on You-Tube under "Steam Jet boat".
I'm afraid there was an incident on its very first run when the electric water pump blew its fuse and the boat had to be rescued by a certain person in waders, who unfortunately interpreted the boiler burner flame as indicating that the boat had caught fire. Subsequently, he pushed the boat under water to douse the flames and in doing so saturated all the boiler lagging.
I managed to dry out all the electronics and put the boat back on the water (see video), but the saturated boiler lagging made the boat very heavy and absorbed a lot of the burner heat.
I have subsequently made many modifications to the system to try out various ideas and have come to the following conclusions:-
1). As a pure jet, the combined steam/combustion gas exhaust (at 240mph) contains mostly kinetic energy and little momentum. It is the momentum derived force that accelerates the boat.
2). The kinetic energy only becomes a force when it impinges on something not rigidly connected to the boat, e.g. another model boat on the pond, or a turbine on the boat.
3). The engine "stalls" if its exhaust is restricted by too much water, i.e. exhausting under water.
4). If a pure steam jet is used against the surrounding water most of the energy is lost by condensation, i.e. little kinetic or momentum is exchanged between the steam and the pond water.
Any pure jet propulsion system becomes more efficient the faster the vessel travels, because the relative speed between the vessel and exhaust velocity decreases and less energy is expelled in the kinetic form and more as momentum. This is why jet aircraft require full throttle on take-off and throttle back when upto speed where they are more efficient. For passenger aircraft the momentum is increased by using fan engines (contained props), which accelerate a large mass of air by-passing the engine core. Fighters still use a pure jet engine for high speed.
The only way to extract the energy, for the boat, is to gradually extract the kinetic energy without stalling the engine. One could put the gas exhaust through a highly geared turbine driving a conventional prop or, alternatively, gradually introduce water droplets that could pickup the kinetic energy. This way, the engine shouldn't stall and the kinetic energy will be recovered.
In the video, you may notice the unconventional "rudder". This is of my own devising and vectors the force by using the "Coanda" effect. The "Coanda" effect was discovered during the development of the first jet aircraft in 1910. The rudder was successful and doesn't restrict the exhaust, especially when going straight ahead.
The steam jet engine has extreme steam conditions of 710degC and 20bar, and the back end of the boiler runs at temperatures in excess of 910degC (the melting point of brass). Silver soldered joints do not survive!
I still want to develope the concept, but I must finish my monotube boiler boat first (see "Edwardian Steam Boat "thread). The monotube boiler has been successfully developed and is to transferred from my experimental boat "Vital Byte" to the new launch.
Thanks for your interest.
Ian
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Ian, thank you very much for following up and explaining more about how it works, both in practice and theory. I've noticed the same kind of thing, back few years ago when I built pulse jets. Well I should say similar kind of thing, not the same.
It is very stimulating to think about still, and I'm grateful for all of the detail you've posted, as well as your thoughts about it..
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Ian can you email me at hydragon@hotmail.nl,I want to ask you a couple of questions regarding the jet boat,thanks.
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Hi Mayhemers,
Nothing is new......!
Just been looking through the Birmingham Library's Bolton and Watt Collection and have found this concept of a marine jet engine;_
MS 3147/3/553 STEAM BOAT MEMORANDA WILLIAM CREIGHTON’S MEMORANDA AND SKETCHES 1815—1822
‘Envelope C – Propulsion; Dimensions’
29. Sketches. Patent Scheme. Not dated. Three sketches of boats propelled by air being blown out into the water at the stern. The first scheme features “farting out wind behind, the bubbles rising up an inclined plane to make the boat go forwards!!!”
This document is with others dated 1815 to 1817.
I love the technical description "farting out wind behind" - I wonder if Frank Whittle would have described his jet engine as such (or perhaps not!)
Ian
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Last time I heard of anything like that some Japanese guys were driving them at American battleships!
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Crikey, what with Geoff and his smoke generator system, various members experimenting with Computer based systems and your work on making a steam jet enegine, I reckon that we Model boat enthusiasts must be the most cerebral bunch in the historical/creative modelling hobby as a whole.
I hope you can upload some more footage of the VT family for us to see them in action.
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Await your results with great interest... :-))
Hello, I'm new user of tis thread.
The PDX engine works in different manner.
We are talking od HBE=HYDROGEN BOND ENERGY.
HBE IS THE NEW SOURCE OF ENERGY.
HBE is very simple to understand and simple is build an working device similar PDX that use the thrust for run an hydroturbine for produce the electricity directly. We are talking of new type of chemistry that we can call Mechanical Chemistry. To the end HBE no need combustion but is released from water droplets when lost the electrons for impact. You can use steam or compressed wet air as kinetic energy necessary for produce the HBE.
There are some example of HBE:
Henri Giffard - Steam Injector (very similar to PDX device)
Lord Armstrong/Michael Faraday - Hydro-Electric Machine
Peter Graneau - Arc explosion
Stan Meyer - Thermal Explosive Energy
Pistol Shrinp Effect
PDX device
All of these is made from HBE.. and I suggest to read papers made by Tucker Leavitt and Peter Graneau for open the mind to HBE. When you know how HBE is made you can build all device you want without limitations.
If you want watch an working HBE italian experiment https://www.youtube.com/watch?v=86ihwyJ63MU (https://www.youtube.com/watch?v=86ihwyJ63MU)
Because HBE don't appear only for mechanical impact but also if water droplets are submitted to the infrared radiation
Infrared radiation from sun or thermal spark removes the bonding electrons from water droplets and are absorbed from air like an sponge..
Also the Stan Meyer Injector works in this manner!!
Cheers
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What is your video supposed to show? It is completely dark, one can't recognize anything going on.
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About 2.3 mins you get some form of light production, presumably the infra red that Tutanka refers to.
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If I were someone wishing to invest in this technology (like BMW who amongst others are now investing in electrolytics and hydrogas generation) I would be profoundly dissapointed in the dark and grainy footage. Get it properly lit with a description of how it works and then you will get lots of inerest and maybe investment. Most people watching such videos have neither the technical ability or accumen to build their own system so your friend is not at risk of loosing any patents pending/ IP rights.
It looks intriguing, but could look and sound so much more so :-))
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Mechanical impact or infrared rays released the electrons from water droplets..
inside PDX the steam condense inside the water and the water is anelastic like an wall.
The steam impacting with the water release the electrons that are absorbed from air like an sponge and HBE pushes the water under pressure.. In this condition HBE is released and you can obtain the thrust.
in my HV reactor I use infrared rays released from arc voltage..
When my breath sended inside the reactor comes into contact with the high voltage arc, it is released HBE generating light and heat..
Different ways same result
I hope that these words open your eyes.
Regards