Uniflow Engines

[Cyruscosmo]

Hey Fred

I am still not sure which direction I will go with boiler configuration, it depends on the tests I plan to do. This next weekend should see the start of actual projects “in” the shop and not the building “of” the shop.

What I had planned to do was build the engine, boiler, plumbing, pumps, reverse, forward gear box all mounted to a frame that can be lowered in place and bolted to the hull. As soon as I get the plans from Paul at Selway Fisher I will have a better idea just how big the frame will be.

By the time I finish the steam plant for the boat I will have finished a few other projects I have taking up floor space. At that point the shop will have plenty of floor space to build the hull and having the steam plant tested and ready to go will be a good motivator.

As far as the pump goes I was thinking a large diameter cylinder pump that has a large intake valve. The piston in the pump has two sizes to match the two sizes of the cylinder bore. When the pump cycles up water comes in through the large valve. When it cycles down the water goes through the piston to the other side which has a smaller chamber. Since the displacement of the chambers are different the pump moves water out the exit port during both the up and down stroke. With sufficient size I believe I can cycle the pump slowly to eliminate cavitation and still move the amount of water needed.

As far as the driver of the pump goes it will be pretty much setup as any steam driven feed pump. The only difference is that instead of being outside the boiler circuit envelope it will be inside. That way there are no external shaft seals to leak. I will be working on a prototype here sometime this summer to see if it is a possibility. If it works there will be two pumps mounted one on each side of the receiver tank. One works while the other is at standby. If one quits for some reason just shut the valves on one side and open the others. Bleed the steam into the condenser from the one non working pump and then open the flange and pull the whole pump out of the housing. Drop it overboard to cool and repair. We will see how it works out.

Yes I thought about the magnetic drive but eddy currents induced in the separation plate even if non magnetic posses a loss. The magnets would be very close to there upper max working temp. The hotter they get the less pump drive I would have. Once they reach that temp they become permanently non magnets. I am not exactly sure how well the setup would work as I do not know enough about it to speculate. The thoughts I did have would put the magnetic drive section in a small chamber connected by a shaft in a tube away from the impeller far enough so that the magnets would remain well below there max working temp. I do like the idea as this puts far fewer moving parts into the whole needing a water pump idea. That is why I asked about high temperature bearings. Even if the magnetic coupling was away from the heat the impeller would be right in the middle of it. And both bearings would be inside the boiler circuit with nothing but water for lube.

Cool filtered water could be fed into the magnetic drive section which would then move down the tube around the impeller shaft and out through the impeller bearings behind the impeller if heat was the only issue. But there again I don't know enough about bearings in that environment to speculate with much conviction.

A positive displacement plunger pump will displace X amount of water period. If the pump is moving then so is the water. The only bearings it has are the seals around the pistons which are already made to handle the heat. So you have a drive piston/plunger arrangement mounted on a common shaft so one moving part with two valves so add two more plus the valve arrangement. Not much to go wrong and pretty easy to fix.

The Mono tube has a pump as well that has to run or you get tube failure. Granted that pump has only the pressure of the system to deal with and not the heat as well but from what I have read the control systems are a lot harder to balance. You will also have a separator in the system which may as well be a holding tank like the LaMont. It's a good place to mount the site glass to keep the water level up in the system. Both need to keep the tubes full, both use pumps, both are smaller and lighter than there VTF counter parts, but the LaMont has a bit more leeway built in with the extra water in the system.

But there again I do not know enough about either a mono tube system or LaMont to settle on one or the other which will change while I experiment with pumps and these steam generators I have here.

Here are a couple pictures of the bigger heater unit. [img][IMG]http://i12.photobucket.com/albums/a222/ ... oe9zcc.jpg[/img][/img]
This is the coil out of the Landa burner. It has the same specs as the other smaller one save it will heat up to 10 GPM. With the adition of a super heater coil and an outter economizer this one would make a good monotube boiler I think. It will serve for the tests I will do to get a better idea of what exactly I do need.

On a side note can anyone tell me why I should not use an already made crankshaft like from a car or truck? I was thinking of starting with a 100mm stroked VW crank.

Cyruscosmo

[Lopez Mike]

I dunno. This all sounds like building the Space Shuttle before having built the Wright Flyer. So many things to design and sort out before you can go steaming.

I wish you luck. You will alway be welcome to hitch rides with any of the rest of us. We won't make too many comments (grin).

[Cyruscosmo]

Hey Mike

You live close enough to me that when I test my new "Space Shuttle" you can be right here with a beer in one hand and pizza in the other saying I told you so. At any rate I enjoy building things so it's all good.

What I am proposing is not too far out. The pumps of which I speak have been used for barrel transfer and paint pumps for decades. I am just using parts from proven designs to do a different job.

And Mike, I intend to take you up on that ride... soon.

Cyruscosmo

[fredrosse]

"The Mono tube has a pump as well that has to run or you get tube failure. Granted that pump has only the pressure of the system to deal with and not the heat as well but from what I have read the control systems are a lot harder to balance."

A monotube steam generator that generates steam, then superheats the steam within the same coil has control difficulties and potential burnout problems.

For a monotube steam generator that produces only saturated steam, in my experience these controls are very easy:

The monotube simply has a single main feed pump which pumps, say 200% of steam generation rate. Issue from the coils into the separator tank is about 50% steam, 50% saturated water. Steam is released from the top of the separator tank. Continuous letdown of this saturated water keeps the separator tank from flooding. For discussion purposes, say the steam generation rate is 100 PPH (Pounds per Hour), and the feed pump puts out 200 PPH.

The letdown saturated (hot) water then enters a small counterflow heat exchanger, preheating the cold feedwater which comes from the feed pump, before finally dumping into the cold feed tank (the cold feed tank is what we often name the "hotwell"). This counterflow heat exchanger recovers the great majority of available heat that was provided in the steam generating coils, so the scheme is energy efficient.
As a result you have a saturated steam generator that uses only one pump (the main feed pump), vs a Lamont style that uses the main feed pump plus the very hot saturated water circulating pump.
The letdown flow is controlled by a simple orifice, or manual needle valve, and will operate over a wide range of steam generation rates with no control adjustments, set it and forget it! This is because critical flow thru an orifice is very much a function of the entering fluid condition. For example, an orifice with saturated water entering at 100 PSI will pass 200 PPH, but when 100 PSI saturated steam enters the orifice, mass flow will only be 20 PPH. This fundamental property results in automatic level control in the separator tank, with no adjustments or changing controls. If the tank level is high, the orifice (located at the tank level you wish to maintain) will pass 200PPH, and tank level will go down to the connection elevation. If the tank level is low, then only steam enters the orifice, and thus only 20 PPH steam escapes, so level tends to increase.

If the fire is such that it generates say 25PPH, or 50PPH, or 100PPH, or 150PPH steam, then this fixed orifice is maintaining the proper level in the separator tank, and the coils are always flooded with steam/water. The water in the coils positively prohibits coil burnout. With steam generation rates from 25PPH all the way up to 100PPH, The design basis in this example), there is no moving control actions, the coils are always flooded with liquid water, separator level is always maintained. For this example, 200% firing would be the point where overheating the coils might begin, but even overfiring by large margins will not cause burnout in this example.

After the saturated steam is generated, then there can be another coil that superheats the steam, generally located after the steam generating coils, where flue gas has cooled down enough to avoid burnout. This arrangement would be the same for the saturated monotube or the saturated Lamont style boilers.

[fredrosse]

"On a side note can anyone tell me why I should not use an already made crankshaft like from a car or truck? I was thinking of starting with a 100mm stroked VW crank."

Two main reasons I can think of:

1. Using an existing IC engine crank, you do not have the pleasure of many machining hours, it is almost too simple.

2. An automotive or truck crank almost always has 4 or more crank journals, vs the common single journal crank from an industrial engine, easier to directly use a crank from an industrial single, twin, or triple cylinder engine, depending on how many cylinders you are planning for steam service.

[Cyruscosmo]

Hey Fred

Yeah it would be sorta cheeting to use an existing crank and Bart pointed something out to me that I had not thought of and that is oil slinging. So I will be going the "build my own crank" rout and as a bonus I can use sealed bearings as well.

WOW... Ok I understand a few more things now. I can see the merits of the Monotube over the LaMont but am still a bit fuzzy on the method of water level control. Can you point me in the direction of a working drawing that shows the Monotube circuit parts? I have found a few drawings but non of them mention a needle valve or orifice to control water level.

So what do you think a ball park figure in PPH should be to feed a 3x3x4 uniflow with good variable cutoff valve system, in front of a 20x20 to 25 pitch prop?

The last pictures I linked in the previous post shows the larger coils from the bigger burner we use here where I work. I plan to set that whole unit right on top a burner like Bart has, then fire it off with waste oil. I can add preheater coils and/or super heat coils as needed.

At least I can see what I can get out of that boiler arrangement while I build a crank...

Cyruscosmo