Instructables

Can you check this design?

On Aug 26 I posted an ask about a design of a new type of motor.  I received some good advices.

Redesigned 02/10/12

The previous design had a major flaw, that went unnoticed at first but it became clear as I went into the construction of the prototype: the thermal barrier would be totally useless, because the steam produced in the boiler necessarily have to go through liquid water to make its way into the compression chamber. This would have two disabling consequences: 1) the vapor would cool quickly, 2) the water would heat up quickly, too. Since any heat engine operation is based on temperature differences, this failure is vital.

The new design does not have that problem. The water falls directly into the hot boiler, a small amount at a time, with the piston in the upper dead point, or below (note that my drawing is reversed with respect to what would be a conventional combustion engine). The water is kept cold by being stored in a separate reservoir, attached to the motor body only by the inlet and outlet pipes.

Water injection is performed by momentarily opening a valve at the appropriate time. Since the interior of the water reservoir accumulates pressure as the engine works, this pressure would be in principle the responsible to force the output water through the tap. If that's not enough, I could add a little manual compression pump to initially load the reservoir with compressed air. So once the Primus heaters worked, which were extremely useful for decades. The exact moment, quantity and duration of water injection should be adjustable during operation of the engine, to find the optimum point for these parameters. These mechanisms have not thought of yet, but they can not be too complicated.

As regards the boiler, it is likely that one heated surface be insufficient to rapidly vaporize the water, since in these conditions it usually adopt a globular shape that greatly retards heat transfer (Leidenfrost effect, http://resnickscity.wordpress .com/2011/01/page/3 /, http://es.wikipedia.org/wiki/Efecto_Leidenfrost, http://en.wikipedia.org/wiki/Leidenfrost_effect). I think that could be solved relatively easily by a double bottom to the boiler, in order to "force" the water into laminar contact with the hot surface. If this is insufficient, it would still be possible to inject the water by pressure between two heated surfaces. I have to also investigate the possibility of to make "super hydrophilic" the surface of the boiler.

Regarding the compression chamber, this design makes it much longer, thus establishing a better differentiation between the bottom hot and top cold. But the main novelty is that the displacer stops acting on a small amount of water to turn acting, as in the Stirling engine, on the entire volume of the steam in the compression chamber. By forcing the steam to move towards the cold zone it produces its condensation, thereby changing the pressure by decompression, and so completing the cycle of the engine. The condensation water adheres to the cold walls of the chamber, then it slides down by gravity, and is intercepted midway by the retaining ring, which leads it back to the water reservoir through a single action valve, spring driven. I guess that to pass the water to the reservoir will be enough the vapor pressure that occurs in each cycle.


The accompanying drawings are quite precarious, but only pretend to give a general idea of the design. Please ask me if you want more details

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Nuevo diseño 02/10/12

El diseño anterior tenía una falla importante, que me pasó desapercibida al principio pero se hizo evidente a medida que avanzaba en la construcción del prototipo: la barrera térmica iba a resultar totalmente inútil, dado que el vapor producido dentro de la calderita tendría que atravesar forzosamente el agua líquida para abrirse camino hacia la cámara de compresión. Esto tendría dos consecuencias inhabilitantes: 1) el vapor se enfriaría rápidamente; 2) el agua se calentaría también rápidamente. Dado que el funcionamiento de cualquier máquina térmica se basa en las diferencias de temperatura, esta falla resultaba vital.

El nuevo diseño no tiene ese problema. El agua cae directamente dentro de la caldera caliente, una pequeña cantidad por vez, estando el pistón en el punto muerto superior, o sea abajo (ojo, que mi dibujo está al revés respecto de lo que sería el de un motor a explosión convencional). El agua se mantiene fría, por estar guardada en un reservorio separado del motor, unido a él solo por los caños de entrada y salida.

La inyección de agua se realiza mediante la apertura momentánea de un grifo en el momento oportuno. Dado que el interior del reservorio de agua acumula presión al funcionar el motor, esta presión sería en principio la encargada de impulsar la salida del agua a través del grifo. Si esto no fuera suficiente, habría que agregar una pequeña bomba manual de compresión para cargar inicialmente de aire comprimido el reservorio. Así funcionaban antiguamente los calentadores Primus, que fueron sumamente útiles durante décadas. El momento exacto, la cantidad y la duración de la inyección de agua deben ser regulables durante el funcionamiento del motor, para hallar el punto óptimo de esos parámetros. Esos mecanismos no lo he pensado todavía, pero no pueden ser demasiado complicados.

Respecto de la caldera, es muy probable que una sola superficie recalentada sea insuficiente para vaporizar rápidamente el agua, dado que en esas condiciones esta suele adoptar una forma globular que retarda mucho la transferencia de calor (efecto Leidenfrost, http://resnickscity.wordpress.com/2011/01/page/3/, http://es.wikipedia.org/wiki/Efecto_Leidenfrost, http://en.wikipedia.org/wiki/Leidenfrost_effect). Creo que eso podría solucionarse con relativa facilidad haciendo un doble fondo a la caldera, de manera de "obligar" al agua a establecer contacto laminar con la superficie caliente. Si esto fuera insuficiente, siempre quedaría la posibilidad de inyectar el agua a presión entre ambas superficies recalentadas. Tengo que investigar también la posibilidad de hacer "súper hidrófila" la superficie de la caldera.

Respecto a la cámara de compresión, este diseño la hace mucho más larga, estableciendo así una mejor diferenciación entre la zona inferior, caliente, y la superior, fría. Pero la principal novedad es que el desplazador deja de actuar sobre una pequeña cantidad de agua para pasar a hacerlo, como en el motor de Stirling, sobre el volumen completo del vapor contenido en la cámara de compresión. Al obligar a este a desplazarse hacia la zona fría produce su condensación, cambiando así la presión por descompresión, y completando así el ciclo del motor. El agua de condensación se adhiere a las paredes frías de la cámara, resbala luego por gravedad hacia abajo, y es interceptada a mitad de camino por el anillo de retención, que la conduce nuevamente hacia el reservorio de agua a través de una válvula de simple acción, a resorte. Supongo que para hacer pasar el agua al reservorio será suficiente con la presión de vapor que se produce en cada ciclo.

Los dibujos adjuntos son algo precarios, pero no pretenden más que dar una idea general del diseño. Por favor, pregúntenme si quieren más detalles.

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Bill WW2 years ago

Rickharris dijo: "La fase es de 90 grados hacia fuera. El piston debe estar en la parte superior cuando el desplazador esta en la parte inferior, asi como el aire enfria por las aletas del piston es hacia abajo."
Sí, estoy de acuerdo, pero tu diagrama muestra exactamente eso, cierto? El diagrama muesra el piston en la parte superior, el desplazadoren en la parte inferior . Ademas, muestran la condensacion de vapor tirando el piston hacia abajo.

Tal vez no entiendo, todavía no he leido el texto.

En mis motores Stirling, yo no estaba seguro de la fase correcta. Por lo tanto, hice una conexion ajustable en el eje del volante. Vea las fotos.

Más tarde.


Rickharris said: "your phasing is 90 deg out though. The piston should be at TDC when the displacer is at the bottom so as the air cools by the fins the piston is drawn down.

Yes, I agree, but your diagram shows exactly that, correct? Your diagram shows piston at top, displacer at bottom. Also, you show the condensation of vapor pulling the piston down.

I have not yet read your text.

On my Stirling engines, I was unsure of correct phase. Therefore, I made an adjustable crank connection to flywheel shaft. See photos.

More later.
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rimar2000 (author)  Bill WW2 years ago
Thanks Bill for your concern. Yes, I have thought add a crank too, in order to have more possibilities of adjusting. The exact moment, amount, speed and duration of the water injection into the boiler is critical. In my drawings I left out deliberately those details to not complicate the entire thing.

I have to learn to differentiate some key concepts of engineering, such as torque and power, for example, but my knowledge base is a bit meager.

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Gracias Bill por tu preocupación. Sí, he pensado en añadir un cigüeñal también, con el fin de tener más posibilidades de ajuste. El momento exacto, la cantidad, la velocidad y la duración de la inyección de agua en la caldera es crítica. En mis dibujos he dejado de lado deliberadamente esos detalles para no complicar la cosa entera.

Tengo que aprender a diferenciar algunos conceptos claves de la ingeniería, tales como torque y potencia, por ejemplo, pero mi base de conocimientos es un poco escasa.
¿Cuál es el tamano de tu prototipo? Se que es temprano en el diseno. Es posible que yo tenga algunas ideas para los componentes.

Senor Harris tambien tiene ideas buenas.

Mi esposa y yo estamos en nuestro pequeno bote durante tres dias. He impreso tu diseno y lo estudiaremos. Prehaps mientras disfruta de una copa de vino.

Buena suerte con tu presidente.

Bill

What is the size of your prototype? I know it is early in design. I may have some ideas for components.

RickHarris also has good ideas.

Wife and I are on our small boat for three days. I have printed your design and will study it. Prehaps while enjoying a glass of wine.

Good luck with your president.

Bill
rimar2000 (author)  Bill WW2 years ago
Thanks Bill.

My prototype uses the cylinder head of a wasted chainsaw, the inner diameter is 3.3 cm, the length 5.2 cm. I will elongate the cylinder maybe 6 or 7 cm with iron tube. The boiler is stainless steel 0.5 mm thickness, conical beaker shape, with a circular lip to attach it with screws.

I go slowly, I must do many other things daily. That allows me to think improvements or flaws in the project.

Hope you enjoy your 3 days vacation trip!

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Gracias Bill.

Mi prototipo usa la cabeza de cilindro gastada de una motosierra, el diámetro interior es de 3,3 cm, la longitud de 5,2 cm. Voy a alargar el cilindros quizás 6 o 7 cm con tubo de hierro. La caldera es de acero inoxidable de 0,5 mm de espesor, forma cónica de vaso, con un labio circular para sujetarlo con tornillos.

Voy poco a poco, tengo que hacer muchas otras cosas todos los días. Eso me permite pensar en mejoras o defectos en el proyecto.

Espero que disfrutes de tu viaje de vacaciones de 3 días!
:-) Your right Bill it was late when I posted (my excuse)

The phasing is right so no need to cool the inside of the cylinder.

Cooling the outside of the finned end WILL improve performance though.
rickharris2 years ago
As James Watt identified cooling the cylinder has bad side effects and his main improvement to the steam engine of the time was to develop the external condenser.

This is a sort of Stirling engine, It shouldn't need any other cooling beyond the finned section of the displacer cylinder.

your phasing is 90 deg out though. The piston should be at TDC when the displacer is at the bottom so as the air cools by the fins the piston is drawn down.

http://www.animatedengines.com/vstirling.html
rimar2000 (author)  rickharris2 years ago
Thanks Rick for your concern. I have some doubts about the design, it is obvious. But basically I think this outline should work.

As you said, it is a stirling machine, but with the aggregate of steam, which empower it enough to turn it in a useful motor. There are many variables involved to play with them in order to get the contraption working.
I am sorry to sound negative bout it but Newcomen in the 1700's designed the first useful steam engine but it was very inefficient because he cooled the cylinder to allow atmospheric pressure drive the piston down thus loosing a lot of energy.

James Watt saw this and designed the external condenser to avoid this problem and much improve the system.

The stirling engine (Robert Stirling 1800's) was at the time a big improvement on the steam engine as it did not use the high pressure boiler with all it's danger.

Many Stirling engines were built, mainly as farm engines to drive machinery and they were very successful.

If it had not been for the gasoline engine they would still be around.

Modern research into Stirling engine design has focused on the use of various gasses to improve the thermal efficiency other than that the systems remains the same as when designed in the 1800's.

Your steam isn't needed in your design as the rapped air in the system will be very effective in making it work, expanding when heated and cooling when in the upper chamber. To make it more efficient you can cool the upper part more effectively - in fact the system works fine if you leave the bottom at room temperature and make the top end VERY cold.

All it needs is the temperature differential.

I have done some work to develop a water based stirling using water as the piston and driving it out the rear as a jet to power boats. The idea works but needs more time. A combination of stirling and ram jet ideas.

Good luck with your development. take care high pressure steam is deadly!

rimar2000 (author)  rickharris2 years ago
Thanks Rick for your comment.

An English doubt: when you said "rapped", did you want to say "trapped"? Google does not translate the term.

I didn't know these attempts of steam Stirling machines, good info. I think my design is not dangerous, because it uses a very little boiler, and a very little volume of water each time. My doubt (one of them) is if the steam will condense really, at the desired speen, because could be difficult to cool the head of the chamber.

I understand by your description that Newcomen cooled and heated alternatively the cylinder, this is not the case in my design. I've read about liquid displacer Stirling machines, Seems interesting.
My idea for a water ram jet
jet.jpg
rimar2000 (author)  rickharris2 years ago
Your ram jet project is akin to pop-pop motor, but with the aggregate of frontal valves panel. Have you done some attempt to build it? It does not seems very difficult, except the valves. Consider the possibility of leave aside them, they are problematic. Nikola Tesla designed a "solid state" valve for fluids.

I think pop-pop motor is not scalable, but I'm not sure. Please tell me if you do something with this project, it is very interesting.
I have built many pop pop boats :-) i agree in principle this is a similar idea.

Yes I have built a small version of this some time ago - it works - in a tank anyway - You need forward motion to ensure it doesn't pop pop pulling water in at the back as well as the front

- The addition of the front valve increases the thrust to something that I think will scale up to provide useful power. -

one day I will return to it and go bigger so I can build a boat and test it .

I also looked at a more stirling version which heated the air above the water pressing the water down - but for this I envisage a mechanically driven displacer so that the water can act as cooler and the heat can be above the boat to make things easy.


heat expands the air forcing water out the jet

The displacer is mechanically raised and lowered by a small electric motor and crank allowing the lake water to cool the air drawing in more water to repeat the cycle.

He construido muchos barcos pop pop :-) Estoy de acuerdo, en principio, se trata de una idea similar.

Sí, he construido una pequeña versión de esta hace un tiempo - que funciona - en un tanque de todos modos - Es necesario el movimiento hacia adelante para asegurarse de que no pop pop tirando agua en la parte posterior, así como frente a la

- La adición de la válvula aumenta el empuje frente a algo que creo que va a ampliar para proporcionar energía útil. -

un día voy a volver a ella e ir más grande para que pueda construir un barco y probarlo.

También busqué a una versión más stirling que calienta el aire sobre el agua pulsando el agua hacia abajo - pero para ello tengo previsto un desplazador accionado mecánicamente para que el agua puede actuar como más frío y el calor pueden estar por encima del barco para hacer las cosas fáciles.


calor expande el aire expulsando agua del chorro

El desplazador está mecánicamente levantado y bajado por un pequeño motor eléctrico y la manivela permitiendo que el agua del lago para enfriar el aire en el dibujo más agua para repetir el ciclo.
rimar2000 (author)  rickharris2 years ago
Interesante combinación el agregado del motor eléctrico. Espero que me comentes los cambios que se vayan produciendo.

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Interesting combination, the electric motor aggregate. I hope you comment me the changes that are occurring.
So far this Stirling has never been built - maybe one day.

I don't see what it wont work though and it avoids the issues of water cooling the heat source.

For my under water ram jet in a full size I think that like a train boiler the heat source would need to run through tubes to make the surface area larger and effectively become a flash boiler

En lo que va Stirling nunca se ha construido - tal vez un día.

No veo por qué no lo puedo trabajar bien y evita los problemas de agua de refrigeración de la fuente de calor.

Por mi bajo chorro de agua ram en un tamaño completo Creo que al igual que una caldera de tren de la fuente de calor se debe ejecutar a través de tubos para hacer la superficie más grande y convertido de hecho en una caldera de flash
rimar2000 (author)  rickharris2 years ago
I agree with you, but a train boiler would be expensive, difficult to install and too heavy. Maybe something intermediate.
Sorry I forgot the picture
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rimar2000 (author)  rimar20002 years ago
speen ---> speed

Yes ,sorry - trapped -