single acting enclosed crankcase

A special section just for steam engines and boilers, as without these you may as well fit a sail.
lostintime
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single acting enclosed crankcase

Post by lostintime » Thu Nov 09, 2017 2:44 am

Provided that a steam to oil heat exchanger (regulated to a few pounds,just enough heat to keep the oil above condensing temperature) was used, are there any other major problems associated with them?
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barts
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Re: single acting enclosed crankcase

Post by barts » Thu Nov 09, 2017 3:53 am

I've done this - it works to get the water out. However, over time it tends to force oil out during the exhaust stroke.

I would put a separate double acting cylinder above the existing one w/ a distance piece like a ship's generator.

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Re: single acting enclosed crankcase

Post by Lionel Connell » Thu Nov 09, 2017 6:55 am

This setup can be made to work well if you exhaust though the head as per a normal 4 stroke IC engine, but with a 2 stroke cam. Don't pressurize the sump, make a new piston and add as many extra oil rings as you can. Some ventilation of the sump is an advantage and use an oil mist collector to reuse the oil. Going for a dry sump setup is the best, heat the external oil tank to remove any water, alternately a partial vacuum can be drawn in the reserve oil tank to remove water. If you modify the crank to reduce the stroke, it will enable you to extend the piston and make room for more oil rings. There are some heat energy losses associated with inlet and outlet passing through the same head, BUT, if you build a smaller engine and run it at higher RPM to achieve the same power, these losses are greatly reduced. This is because the total internal surface area of the engine that is exposed to steam is reduced, and thus the transfer of energy via conduction is greatly reduced. Big steam engines turning slowly was big engineering mistake where efficiency was concerned.
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Re: single acting enclosed crankcase

Post by barts » Thu Nov 09, 2017 6:58 pm

Note that the 'big engines turning slowly' is a bit of a red herring; large scale marine engines ran at higher
piston speeds than our small plants.

Many steamboaters like to overprop a larger engine (or like our Rainbow, use a step-up gear) so that
the engine runs at a slower speed than would normally be the case. If you look at full-size practice,
mean piston speeds were about 1000 ft/min on full power designs like Titanic or USN Texas. On our little
compounds w/ 4" stroke, this would be 1500 rpm - we usually see these engines running no faster than
400 rpm - perhaps 600 for the racing types.

Complicated engines are fun on the test bench - much less so 100 yards from a rocky shore in a stiff on-shore
breeze w/ adverse currents.

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Re: single acting enclosed crankcase

Post by lostintime » Thu Nov 09, 2017 11:30 pm

Its actually reliability that im concerned about, I have free use of a three axis mill to make a set of heads, but no lathe. I would have to farm all turning out, and with the price of well balance compressor assemblies rated at 1500 rpm I think I can tune close to optimum piston speeds. I attached an image of what I basically want to scale down and run in reverse. Its its one of four 150hp single acting compressors with coalescing oil recovery (oil drops into float chamber and is returned), the white cylinder in the background is a fully flooded 163 tube vertical "fire tube" with main chamber and "steam dome" to the right. This compressor runs at 3500 rpm and is rebuilt every 20,000 hrs as a pm. But the working fluid is ammonia. I believe it will be easier for me to overcome the oil carry over issues than it would be for me to find a competent shop to machine a full balance rotating assembly, though I may be wrong. Steam is new to me.
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barts
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Re: single acting enclosed crankcase

Post by barts » Fri Nov 10, 2017 12:12 am

Here's a link to a web page about the first engine I had in Otter, which I made from
a refrigeration compressor of 2" bore x 2" stroke.

http://www.smaalders.net/bart/engine.html

I ran this engine for almost 20 years, until the bearings wore out due to lubrication issues
(it had served as a air compressor in a friend's business for 5 years or so prior to this).

It would still be running well if I'd set up some distance pieces and put double acting
cylinders on top... note that this was standard construction for ship's generating plants.

http://www.douglas-self.com/MUSEUM/POWE ... ss1927.jpg

The one I examined internally used a completely enclosed governor in the crankcase,
pressure lubrication, etc. and was still in great shape after decades of service.

An industrial air-compressor conversion would be relatively simple in terms of machine work
and you'd have an engine that would work quite well.

Note that high piston speeds don't necessarily make the steam plant more efficient - that's
really more to do with valving design, number of expansions, jacketing, etc. A higher speed
plant _is_ more efficient in terms of space, weight, etc... but not necessarily in terms of
lbs/ihp-hr of steam consumption.

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Re: single acting enclosed crankcase

Post by lostintime » Fri Nov 10, 2017 1:57 am

Industrial air compressor is exactly what I was thinking, mill a a head with as close to the same head spacing of the final head as possible but with a port for a fast acting pressure transducer tied to a data logger. Then use proxy sensors to fire selinoid valves to establish a data log before machining the proper monkey works mechanical system. Changing simple sheet metal flags on the flywheel and a two axis adjustment of the proxys with real time readout should recover more time from the math than it will take to do it. (Optimizing for one speed constant load)
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Re: single acting enclosed crankcase

Post by Lionel Connell » Fri Nov 10, 2017 3:38 am

I have to disagree, a smaller higher speed plant of similar design type is definitely more efficient than an unnecessarily large one, so long as it is not taken to the extremes. Less internal surface area means less energy absorbed into the material and transferred back into the exhaust or lost to the atmosphere by larger external surface area, the steam being in the cylinder for less time means exactly the same thing. A small engine has less reciprocating mass, less friction, and is less weight to be carried by the boat thus a more efficient hull can be used, and less fuel needs to be carried. All the same reasons that the V8 IC engine cannot compete with a V6 or turbo V4. If life cycle being measured in tens of thousands of hours as a consideration then the design criteria starts to lean back toward a larger engine, but a hobby boat engine is unlikely to ever see two thousand hours. If the engine is to be fully enclosed then slow revolutions for aesthetic reasons is not a consideration. There is of course a point where a smaller higher speed engine will require gearing down the drive in order to retain a large efficient propeller, but look at modern boats and you will see that a smaller engine with reduction drive and large propeller is by far the preferred method.
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Re: single acting enclosed crankcase

Post by barts » Fri Nov 10, 2017 4:18 am

I'd much rather ride in a boat where the engine is turning at 300 rpm than one where the engine is turning at 1500. Keep in mind that every time the RPM doubles, the inertia forces go up by a factor of 4... so that 1500 rpm job will need to be balanced 25 times better to achieve the same smoothness. Keep in mind that a normal marine steam engine operates at much lower BMEP than a diesel or gas engine... and so cylinders, etc. will be larger. Yes, one can build something that uses 1000 psi steam at 1000 F, but then I really don't want to share the boat w/ it.

I go steamboating to relax, and talk w/ friends while we're exploring the marine environment. Less noise and clatter is a good thing here... I was just talking w/ a friend who fired their 40' steamer on wood for the first time; he commented on how quiet it was w/o the noise from the oil burner.

I try to make my steam plants efficient at low rpm; that keeps things pleasant in the engine 'room'.

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Re: single acting enclosed crankcase

Post by lostintime » Fri Nov 10, 2017 4:41 am

I did not mean to start a debate on efficiency, diesels won, I believe different applications warrant different approaches, my goal is a sail auxiliary that uses it's ballast weight as lead acid batteries for ports and dull drums, and a recharge system that can run on about anything that burns. An efficient (relatively speaking) power unit to "recharge" if I cant regenerate from the prop. I'd love to have a big slow turner to pass the free days, but then id be too busy boating to build a boat...
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