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Learning from the mistakes I made in my first attempts I researched Valves with no moving parts and found two.
1. The Tesla Valvular Conduite, uses the coanda effect to restrict the flow of liquid down a conduit in one direction. This is perfect but too complex to manufacture.
2. The Thrust Augmenter. Technology usually found in Pulse Jets, this can also increase the thrust of the engine.
1. The Tesla Valvular Conduite, uses the coanda effect to restrict the flow of liquid down a conduit in one direction. This is perfect but too complex to manufacture.
2. The Thrust Augmenter. Technology usually found in Pulse Jets, this can also increase the thrust of the engine.
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Signing UpStep 1How a Thrust Augmentor Works
A Thrust augmentor is placed a short distance after the exhaust directly inline with the opening. It has a converging intake followed by a diverging section.
As the fluid is forced out of the exhaust it enters the opening to the thrust augmentor draging in surrounding fluid from the local environment as it does so. This increased mass of fluid then accelerates out as the augmentor diverges.
At this point the pulse jet sucks in and this creates toroidal vortices in the augmentors diverging section which expand to the walls of the augmentor and travel along as fluid pistons, pushing fresh fluid infront and pulling in fresh fluid behind. Such a ‘piston’ is a more effective than a simple flat pressure front because it stays together over a much longer distance before degrading. In addition, its swirl also appears to act as a rotary pump, drawing even more fluid with it. All this air adds to the reaction mass and greatly increases thrust.
This means the fluid traveling down the augmentor has significant inertia capable of resisting the sucking action of the engine thus the intake fluid must come from else where. The shape and possition of the thrust augmentor mean that the intake comes from the front of the boat and in effect, sucks it forwards.
This means that all of the work done by the engine should be used to move the boat forwards ultimately increasing overall thrust and hence the boats velocity.
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As described by the first law of thermodynamics energy cannot be created or destroyed, only transformed. The device utilises energy that would otherwise slow the boat down to make it go faster:
Numerically, one cycle of the engine is split into two motions; Suck and blow. Lets say the total energy per cycle is ten units.
The blow power represents around 50% of the total cycle energy. It is likely to be slightly higher than this due to the energy put in by the heat source. When the engine blows most of the energy goes into pushing the vessel forwards so lets round that to 50% and so five units of energy pushes the boat forwards.
When the boat sucks in new water this represents the remaining 50% of the energy per cycle. This is done from 180 degrees though so only a proportion of it sucks the boat backwards. lets say 50% of the suck power which gives 2.5 units of backward energy per cycle.
Summing these we find that the 5 forward units minus the 2.5 backward units gives a total forward energy of 2.5 units.
This device redirects the energy that usually slows the boat down into pushing/pulling it forwards, so the vast majority of the energy that comes out of the engine is used to move it forwards. So when the engine blows, 5 units push it forwards. When the boat sucks 5 units suck it forwards, though less efficiently than the blow action as it sucks at an angle so not all the energy goes into sucking forwards, some is still wasted in turbulence and lateral water movement. Thus the vast majority of the energy goes into forward motion giving just under 10 units forward motion. Four times more than before, Though in practice this would be unlikely to reach double the original due to losses in the system.
NB- these numbers are for illustrative purposes and have no experimental measurement or mathematically modelled backing though the general principle still applies.
LBO
Ah yes; The Putt Putts! I got a Job at Jaguar on Thursday so the next month is going to be crazy until I move to my new house that I haven't started looking for yet in a new city that hasn't been decided yet. I will make time to do these tests for you though as I said I would and I am a man of my word.
Right. I have some 3/8" copper pipe to make my engine from though I'm at home now so I have no TIG or brazing facilities. On your recommendation I will make a new engine with no diaphragm. I only made one thrust augmenter so It will have to be a single intake/exhaust engine so I propose a coil boat with one intake/exhaust cut off at the coil and crimped closed. I also propose a simple foam hull to keep weight down and make build time shorter. Do you happen to know any tried and tested dimensions for a single tube coil boat engine or any good geometries as this will be new territory for me and I'm short on development time?
Having only one augmenter is a limiting factor. The problems with the engine you propose to build are that it will be very low power and a type that is difficult to run at consistent power. This will make testing results hard to measure with accuracy. Single tube engines are also very hard to fill though injecting the water through a small tube that can reach the closed end of the engine or using a bleeder valve will work.
I don't know what would be easier for you to build, another augmenter and something like my Easy Engine Build that requires no brazing or your plan when a reasonable test result is the main objective.
Regarding coil engine design these two links could help. I have done little work on coil engines.
Guss Flogels page at science toymaker http://www.sciencetoymaker.org/boat/g_e_flogel.htm
Jean-Yves pages at eclecticspace - Coil Engine Performance http://www.eclecticspace.net/index2.php?rub=poppop
Some reading is required to get to the parts you want. It's usually at the end isn't it? When the pipe leaves the coil it seems advantages to have it go up a bit first before down to the water. Length of the pipe from it's highest point to the outlet is usually best at about 62 x pipe ID. and the angle of rise from the outlet to the high point between 10 and 15 dgrees.
If I can make it work I will add a photo of a typical engine side view. This has a boiler rather than a coil but that does not affect the layout.
When testing remember to have them both the same weight.
Good luck.
That is a very good point about the weight of the boat. I hadn't considered that. Though the boat without the augmenter is lighter so you would expect it to be faster though the shuttle more prominent which explains the reduced shuttling with the augmenter and the increased mass.
If I where to use the 62xID relation you suggest my boat would be half a meter long. This seems a little excessive. my precious engine was around 15-20cm long and operated effectively. I am also considering whether the standard horizontal coil would be best or a vertical coil which could be made more longitudinally symmetrical Though apart from weight distribution I can't see how an asymmetrical boiler would affect performance.
Any thoughts?
"I would have to develop a new fabrication method and make two so that they are identical. For now I will keep it simple with one pipe." --------A quick and easy fabrication method is what is stopping me from doing a test.
"That is a very good point about the weight of the boat. I hadn't considered that. Though the boat without the augmenter is lighter so you would expect it to be faster though the shuttle more prominent which explains the reduced shuttling with the augmenter and the increased mass" -------Correct. Just put the augmenter on board when it is not attached to get the same weight.
"If I where to use the 62xID relation you suggest my boat would be half a meter long. This seems a little excessive. my precious engine was around 15-20cm long and operated effectively."-------- For example 1/4 ID pipe length would be .25 x 62=15.5".for the unheated (see photo) part of the pipe. Some of this can extend past the transom. Shorter can work on some engines but if you get steam bursts or burnout go longer. " I am also considering whether the standard horizontal coil would be best or a vertical coil which could be made more longitudinally symmetrical." ------Should be no difference. In this case I would use vertical as it better accommodates the rise of the pipe before tuning down to the water.-----"Though apart from weight distribution I can't see how an asymmetrical boiler would affect performance."-------It should not in this case. When I mentioned symmetry before I was referring to multi pipe engines where the pipe bends, lengths and ID's etc. need to be the same.
An engine need not have either a boiler or a coil to operate. A pipe closed at one end will work. However the larger the volume of the "heated part" be it coil or boiler makes the engine more friendly.
I will commence fabrication shortly and upload the results soon there after.
I think Jean-Yves found horizontal better than vertical but that was with two tubes and I don't think a large difference. A bent a piece of wire showing a compromise. I have built many engines where the tube doubles back and it did not hurt performance. The advantage is a shorter OA engine.
3 to 4 coils supposed to be best.
Stopping a moving boat, backing it up or generally messing with it can affect it's power for several seconds. It takes a few feet to build up it's speed and power because forward motion affects the balance between the power and intake strokes. A long straight run is best for speed testing but requires a guide wire to keep it on track. I test in a 8', diameter circular pond tethered to a center point. An average of ten laps or roughly 100 meters seems to give honest results though I guess the turning scrubs of a bit of speed.
Good luck.
To which section are you refering? I found the section on 'Proof of propulsive dissymmetry' and the one on 'Working principle
of a pulsed waterjet' but neither say anything about the suck not being useful. In fact in the latter document there is a diagram that describes a little as to why the thrust augmenter works. I hope the original content owner doesn't mind but I'll upload that pic for illustrative purposes.
Are you aware of how a pulsejet works? If so are you aware of the thrust augmenters they use? This is real proven technology just given a different, very similar application. Here's a little pdf on the subject: http://cap.ee.imperial.ac.uk/~pdm97/powermems/2009/pdfs/papers/132_0208.pdf
Maybe re-read the section in my instructable on how a thrust augmenter works or do a google search on them for clarification. I'm not suggesting that the sucking gives significantly more power. I'm suggesting that the established retarding forces the intake entails can be minimised and re-directed to have less effect on the forward motion and, if done correctly, may even add to the propulsive forces. This is all explained by Newtons second and third laws of motion; force is equal to mass multiplied by its acceleration and every action has an equal and opposite reaction respectively. The majority of the extra thrust comes from the vortex piston. Not the redirection of the sucking.
I would not use any of Jean-Yves material without permission but have no doubt he will grant it. We are continually trying to make contact with people who are interested in putt putt engines and boats and creating a library of information that is available to all. The Unofficial Mamod and Other Steam Forum have created a sticky thread that we hope will serve that purpose. The link to that thread is below and I encourage you to join in. It will help others if this conversation we are having goes on record at the Mamod site.
http://modelsteam.myfreeforum.org/ftopic40752-0-asc-0.php&sid=7ffe5fe4e0ff6da14a1cc6915718d862
Another site is on Yahoo but it is mostly a talk forum. http://groups.yahoo.com/group/pop-pop-steamboats/
You may PM Jean-Yves via either of these forums.
I'm not a scientist or engineer so my creations are the result of much trial and error. The increases in force and speed that I have achieved have come from listening to Jean-Yves and others, applying their knowledge and maximizing the design of the basic solid boiler pop pop engine.
The best proof of your theory is to build two identical boats and engines and test them with and without the inclusion of your ideas. I sincerely hope you can discover a way to make gains.
Jean-Yves Full Member Posts: 215
pulling or pushing a boat?
« Reply #1 on: August 04, 2007, 12:38:02 PM »
Hi all,
I just finished a new test to demonstrate that sucking water has no effect to propell a boat. There is no pop-pop engine in this demo, but it means that during the sucking phase of the reciprocating cycle there is no negative effect. It also means that it would be useless to complicate pop-pop engines with check valves in order to suck ahead and deliver backward. (I must confess that I had this stupid idea 3 years ago).
See attached document.
Jean-Yves
--------------------------------------------------------------------------------
Proof of propulsive dissymmetry.doc (110.5 KB - downloaded 4 times.)
Experimental proof (one more !) of the dissymmetry of a propulsion by reciprocating waterjet.
Purpose of the experiment: to show that sucking water on the bow of a ship has a negligible impact; though a jet backward propels.Principle of the foresee assembly:
A symmetrical hull (according to transverse and longitudinal axis) to avoid endless discussions.
Electric pump located in the middle of a pipe of ID « d ».
Internal diameter of the cross-over equal to more than 2xd.
Thus, on one hand the pressure drops upstream and downstream will be nearly unchanged. And on the other hand, the speeds inside the cross-over will be very low and the resulting forces being opposed they will cancel each other.
Longitudinal sucking Longitudinal delivery
Measurement of the boat velocity in both cases.Practical results:
Test conditions are described in appendix.
Measurement of the boat velocity when propelled by jet. Result: 72mm/s.
Measurement of the boat velocity during sucking. Result not measurable. Velocity lower than 1mm/min.
Knowing that the thrust evolves as the square of the velocity, one can calculate the ratio between pushing and pulling forces. ; i.e. the pulling force (when
sucking) is roughly 20 millions times weaker than the pushing one.
Conclusion : this experiment confirms the theory. Sucking ahead has a negligible effect, and the related assumptions used in other documents are justified.
Photo of the (so-called) ship.
Measurement of the pump flow. Result: one little in 64 seconds.
Wetted surface of the hull: 591cm2
Internal diameter of the pipe: 4.4mm
Internal diameter of the cross-over: 10mm
The measurement of the propulsion velocity took place outside on a bench that is 4m long. The first meter was used for initial acceleration, and the last one for stopping. The real measurement was done on the central 2 meters. To eliminate some eventual wind influence, tests were run in both ways.
The first sucking measurement took place on the same bench. The velocity was seen low, but influenced by the wind. The boat was going ahead or astern by some centimeters. New test were run indoor with a shorter and wider bench. Transversally the hull was kept at the centre of the tank by means of two slides (with a play of some millimeters). When the pump was energized, the vibrations got rid of the light permanent friction forces.
Vortex at the suction side.
Test conditions and lighting allowed us to observe the water surface and the movement of some particles just above the suction side.
I'm currently building a single seat racing car that is due to race at Silverstone in just over a week so I'm rather busy. As soon as I'm finished I'll rebuild two identical engines and hulls and get some experimental results for you. You sound enthusiastic and knowledgeable in the field of pop-pop boats so I'd like to bounce a few ideas off you and see if you've heard of any previous experiments. One thought I just had while reading that paper is the asymmetry of most pop pop engines and if one could be designed asymmetrical purposefully to suck from the front and blow out the back. I agree with the paper you quoted but I believe that noticeable gains can be made in performance from solving this fundamental issue with this engine. It's physics, we're wasting energy...
If you are going to build one or two engines to test your theories, (and I hope you do) I suggest starting with a proven design that should provide consistent performance with few idiosyncrasies so that test results will have reasonable validity that others could attempt to confirm by duplication. Two of my designs are available online.
The first is on a thread at the Mamod site. It requires to be assembled with silver brazing. Silver solder or glue will not do. The link is....
2 tube engine build.....http://modelsteam.myfreeforum.org/about29385.html
A better choice is described in one of my youtube videos. Easy build. No high temperature brazing required and can be built to be noisy or silent. Silent is better for testing because it is more powerful, more consistent and the noise won't drive you crazy if testing is prolonged. To make it silent use a rigid material for the diaphragm. Brass, aluminum, copper or steel (rusts) in .015 to .020" thickness will do. The link is......
Part 13-Easy engine build. http://www.youtube.com/user/PuttPutt4video?feature=mhsn#p/u
So far symmetry has proved to be important to getting good results so I will be interested to here your thoughts on how asymmetry might be an advantage and what you mean by the engines being asymmetrical now.
I have passed on your comments re a thrust augmenter to Jean-Yves and another clever fellow who's interest is mainly in rocketry. We will see if they can reach agreement on the potential merits. I would like to try it if there seems to be a potential for gains in force.
I'm happy to discuss any subject with you though I would rather do it on the Mamod site where you gain the advantage of other valuable input.
Good luck at Silverstone. My racing days are long gone.
With Epoxy resin it is easier to apply, seal, requires little skill and no extra tools such as a blow torch or soldering iron . When the flame laps over the edge and hits the join it just scorches the adhesive and the unit remains sealed as the rest of the glue maintains it's integrity.
Solder is the proper way of doing it but when the flame laps around the edge and catches the solder it has a tendency to melt a corner then for the molten part to melt all the solder it's attached to. So when the solder fails it blows the whole seal. It also takes more skill to seal. It's easy if your proficient at soldering but if your not a technical person it can be quite the challenge and this instructable is aimed at people of any skill level.
Experiment for yourself. Both methods work, I prefer soldering but Epoxy does the job and is much easier. I'd suggest you invest in some high grade Epoxy, if your buying it from Walmart or home depo the chances are it isn't going to work. No rapid or clear, you want the grey opaque stuff that comes in two half kilogram paint tins that takes 48 hours to set. Surface preparation is more important than when soldering; The surface should be keyed with some emery paper and cleaned with a solvent that doesn't leave a residue such as electrical contact cleaner. Your Epoxy should be weighed when you measure it out to ensure you get equal amounts of each and should be mixed until it is of a consistent colour. While setting it should not me disturbed.
On Pulse Jets they are rolled out of sheet metal and welded. Due to the size of the device I decided against that method as my engineering department doesn't have a roller small enough to my knowledge and welding would have been tricky with the thin metal and dodgy angles.