Sometimes you run into things that just cry out “elegant”. Some are so simple as to look like nothing at all, crude bits of nothing. Those are my favorites.
This one is a stellar example.
It has a boat ‘hull’. A Candle. And a bit of bent tubing. That’s it.
IMHO, it is best described as a “pulsating heat pipe” that is open ended with both ends under the water. A loop of pipe near the candle gets hot and when steam forms, shoots a load of fast water out the back. The steam cools in a cold section of pipe, and cold water is sucked back into the pipe, eventually hitting the hot part, that puffs it out again. High speed straight out, low speed diffuse origin in. Differential thrust / drag. The boat goes forward.
I have to wonder how large one of these could be made… It just cries out to be tried at the ‘full scale’ level. Perhaps with larger tubes it would need a feed pump to keep things more stable (or more quiet ;-) but in any case, a ‘steam jet powered boat’ would be a bit fun. Especially one that worked on any old fuel you had (even trash) and had no lubrication or maintenance (other than dumping the ash box…)
A kind of pulse jet for boats…
About 1/2 way down this page:
The same site has a ‘cannon’ made from film cans… ( I knew I was saving them for something ;-)
Someone has a great imagination, a sense of fun, and way too much time on their hands…
As much as it reduces the elegance, I have to wonder if a bit of differential drag in the two pipes would lead to better water pumping all the way into the hot part. Perhaps as simple as a small bend in one leg, or a slightly pinched exit from one of the pipes? For a large design, perhaps putting Tesla Valves in the pipes would lead to one way water in / steam out asymmetry? It would still have no moving parts, and be very very elegant, though lacking some of the ‘crude charm’ aspect… It would also allow for differential optimization of the steam nozzle vs water inlet configurations and orientations. Water scoop forward and small, steam nozzle rear facing and larger… Or perhaps that’s just putting a load of yellow paint on a lily…
I did find an online patent for one with one end of the tube completely sealed, but that seems to lack some desirable features, like having the mass flow always be from front to rear.
Frankly, IMHO, this just cries out for someone to make a full sized version. I’d like to see a State licensing authority try to figure out where the ‘engine’ was and what to classify it as.
It also looks like other folks have played with the idea as well. This video looks like ‘similar, but different’:
While this one is a twin engine model:
This Canadian is claiming the world speed record. It looks, from the tube count, like he has a multiple engine job. My count of the rear facing tubes would make it a 4 engine model. However, it also has a forward facing tube on the right side, so there may be some “special” design in use… AND… In this other video we see what is likely the same engine. It is described as a single engine, but with multiple tubes.
IF (and it is a very big if) the scale speed ‘scaled up’ with full size, that would be a respectable boat speed. Even if you only get 2 to 4 MPH out of it, it would still be fun on a lake.
The test of multiple hull designs and tests with variations in engines, engine shown clearly:
I’m left to wonder how I could have lived all these years an not known of these before…
This page claims they have been around for over 100 years:
Though it was forgotten by most until about 1982:
Basil Harley seems to have rediscovered the 1891 invention of the pop-pop boat about 1982, after having written several articles on pop-pops for Model Boats magazine during the 1970s. In a 1975 article, Harley mentions a similar boat seen in a French journal from 1880. The pop-pop boat as we know it originated in an 1891 British patent for water pulse engines by an inventor named Thomas Piot. The patented engine was of the coil type.
The popularity of the boats spread quickly, however, and they were soon being manufactured in many countries. In Toyshop Steam, Harley mentions a series of boats made in the first decade of the 20th century by the German toymakers Ernst Planck. In 1916 a US patent was granted to Charles McHugh for the diaphragm type engine. (See patent document.) The McHugh patent was specified for use in toys, while the Piot patent was apparently left more general. The addition of the diaphragm seems to have produced a toy with great appeal, as evidenced by the large number of advertisements found in magazines such as Popular Science and Boy’s Life (see illustration). The German name for the boat, toc-toc, originated as a product brand name for a diaphragm-boilered boat in the late 1920’s, while they have also been called put-put, phut-phut, and pouet-pouet boats elsewhere.
One passage implies that the Tesla valve version with inlet forward, jet rearward, would be a significant improvement (as would be some insulation on all those exposed hot surfaces …)
In The Flying Circus of Physics, Jearl Walker pinpoints the crucial quality that makes the pop-pop boiler function:
The candle converts some of the water in the boiler to steam, which then pushes the water column back through the tube to emerge behind the boat in a jet. Upon leaving the boiler, some of the steam condenses in the cooler tube and contracts, thereby pulling water back into the tube. However, the key feature is that the water entering the tube comes from a hemisphere of directions, not from a single direction. There is a net propulsion forward because of the asymmetry in the jet emission rearward and the inflow from all directions in the rear hemisphere.
This strongly implies that even more asymmetry would work even better. Alternatively, a nozzle designed to entrain water during the steam expulsion to increase the rearward mass (i.e. through a venturi and flare), while favoring water intake from the front during the ‘reload’ stage, could also work well.
My vision of it would have a small scoop pointed forward, pipe to the boiler area, a Tesla Valvular conduit to assure water only flowed in that way, the boiler, pipe toward the rear (no valve) ending inside a vented flare such that the steam jet would entrain water mass rearward (like the steam injector pumps in steam engines). Some water would still be able to reverse flow up the exhaust pipe (to help prevent vacuum collapse of the system, if nothing else ;-) but at speed, more would come from the front of the craft.
For those not familiar with it, the Tesla Valve has no moving parts, very fast response time, and acts as a fluid diode allowing substantially one way fluid flow only. The valve is shown in detail on the top, mounted on a turbine housing in the bottom:
More than you would ever want to know about it here:
Patent description (with the above image) here:
There is also a tease reference to someone having made full sized boats…
And then there is Peter R. Payne, whose interest in the engineering aspects of the water pulse-jet led him to some fascinating experimentation using them in full-sized boats. If you want to take your construction project to the leading edge of the technology, Payne’s work is the handbook for your efforts.
I found four of his papers here:
But the type and size means it will take me a while to slog through it and find if there is a mention of the full sized performance.
UPDATE: In reading one of them, it includes performance data and even a picture of the boat.
And this biography: http://www.brigidashwood.com/peter-r-payne sure sounds like an interesting fellow I’d have loved to know, but he, too, has met his end.
In it there is another tease talking about a 14 foot scale of boat powered by one of these engines.
At that point the trail goes muddy, and this post is getting a bit long. OK, perhaps someone else can put in the time to find an image or performance data on the larger scale boat.
It looks to me like there ought to be a fairly easy path to some improvements that would make this a very workable personal sized craft with near zero maintenance and very long life. The big question I see would be fuel costs (and perhaps sound levels). It would also make a good gimmick in an ‘alternate timeline’ story where folks in, oh, Egypt of the Pharaohs invent a steam boat from copper pipe and oil lamps… and dominate the world…
At any rate, now I have another toy I want and will likely never have ;-)