Sea Lion Engine build

[barts]

Bart,

Curious as to the intended starting procedure. Seems in a single cylinder Uniflow that with the compression or re-compression stroke that starting could be difficult. Some sort of conventional exhaust poppet valve for starting? That can then be left closed once flywheel inertia is sufficient?

-Ron

I'm thinking the following:

This engine will have steam jackets for the head and cylinders, so getting the engine close to operating temperature involves rotating the engine to mid-stroke upstroke (intake valves closed) and cracking the throttle (which puts steam into the heads) and admitting steam to the cylinder jackets. I'll use a steam ejector/eductor to pull a vacuum on the condenser. Each cylinder drain has two valves in series, one close by the cylinder and another further away; the space between is additional clearance volume for starting. Once the cylinder/heads are hot, with the timing completely retarded (opening perhaps 5 degrees after TDC - for starting) and the first drain valve on top and bottom open and the second closed, I'll bring the engine a bit past TDC and use a small starting lever to open the top poppet valve until the engine rotates enough for the cam to keep the valve open.

The bottom half of the cylinder will have the exhaust port open and be at vacuum. The piston will come down quickly and should provide plenty of power to accelerate the flywheels sufficient to compress whatever air remains in the bottom cylinder, esp. since we're running w/ additional clearance volume and the cylinder was at full vacuum. Once the engine is running (remember, the Kitchen rudder's neutral position allows us to do this w/o the boat moving) the drains can be closed.

Note that the poppet valves will act as relief valves into the heads if we get condensation in the cylinders. As with any larger engine,
warm up will take some time.

If both cylinder drains are open to vacuum, the engine should go to TDC due to different areas on piston top and bottom.

The engine will stay running in the same direction until we're finished with engines; the Kitchen rudder will provide fwd/rev and neutral.

That's the theory, anyway; we'll see how it works when I get this built.

- Bart

[Ironman]

Bart, thanks for this thread and for posting good pictures and spec. I am watching this thread closely.

[barts]

Bart, thanks for this thread and for posting good pictures and spec. I am watching this thread closely.

I've not posted an update in a bit; I'm welding up the base (so the crank can come off my workbench ) and needed to accurately bore the holes for the columns, which are in a 10" x 11" rectangle. Since the completed base weighs about 100 lbs, doing the layout work on the granite table as I would usually do seemed dubious at best. As a result, I'm finally replacing the DRO on my mill; the factory DRO was broken when I bought the well-used mill. This turned out to be a more fiddly job that I expected, so engine updates are lagging.

- Bart

[fredrosse]

Bart, you are putting on the lagging already? Quick work indeed!

[barts]

Bart, you are putting on the lagging already? Quick work indeed!

I'm not nearly that quick.... but I have given some thought to the cylinder lagging, since the cylinders are steam jacketed so will be at 350-400F. This makes a big difference for uniflow engines using saturated steam, according to Prof. Stumpf.

Superheated engines only need to jacket the heads, apparently; this is automatic for me since the steam chest for each cylinder is above the cylinder head. I'm wrapping the heads and cylinders in fiberglass, and over that a spun metal head cover and a simple round jacket over the cylinder itself. With the green paint, I'll be prob. making the covers from brass for extra engine sparkle.

- Bart

[Ironman]

Bart, thanks for this thread and for posting good pictures and spec. I am watching this thread closely.

I've not posted an update in a bit; I'm welding up the base (so the crank can come off my workbench ) and needed to accurately bore the holes for the columns, which are in a 10" x 11" rectangle. Since the completed base weighs about 100 lbs, doing the layout work on the granite table as I would usually do seemed dubious at best. As a result, I'm finally replacing the DRO on my mill; the factory DRO was broken when I bought the well-used mill. This turned out to be a more fiddly job that I expected, so engine updates are lagging.

- Bart

I hope there are pictures of this I am saving all the info in this thread.
I have a pile of AmishCad drawings in my desk and some things you are doing are similar to my ideas. Such as the steam jacket, which I planned to vent exhaust into to heat the cylinders.
I have made a cheap DRO for my mill that uses a Bluetooth transmitter and the readout is on a cheap tablet. So far I have the quill and table on scales.

[SL Ethel]

You might want to think twice about 212 degree exhaust steam as a cylinder jacket as opposed to 300+ for boiler pressure steam- it will likely do more harm than good. Have a look at Prof. Stumpf's book (available free on google books) - it gives a very thorough thermodynamic overview of what's going on in a uniflow.

Cheers,
Scott

[Ironman]

You might want to think twice about 212 degree exhaust steam as a cylinder jacket as opposed to 300+ for boiler pressure steam- it will likely do more harm than good. Have a look at Prof. Stumpf's book (available free on google books) - it gives a very thorough thermodynamic overview of what's going on in a uniflow.

Cheers,
Scott

Thanks Scott,
It seemed like a good idea at the time.... I suppose the guy that cut cooling fins on his Youtube steam engine thought that too.
For what it's worth, everyone seems to quote Google books as a Stumpf second edition source. When I looked at that, it is a book, and I wanted to have a document such as PDF because books don't fare well in my shop environment.
This link is from Cornell I believe and lists a bunch of different download formats.
https://archive.org/details/cu31924015551702

[Ironman]

Hey Bart,
In a previous thread you discussed cams and timing in your Sea Lion engine:

With a fixed valve duration of about 30 degrees, short cut-off is achieved by advancing the valve timing to 11 degrees before TDC; this is about 2% of the stroke. The remaining 19 degrees is all admission time, yielding 5.5% cut-off. If we shift the valve timing to opening at TDC, the result is cut-off at 14.5%, using 3 x the steam. In addition, since we're driving a prop, the speed of the engine will go up, increasing power output still further.

And also you mentioned the need for lightness of the valve train, which has been the quest of every IC engine builder since the flathead days. If as you mentioned, you are planning to use a cam and follower, the valve train weight is important.

So here is my first dumb question on this forum....
I have always admired the simplicity and effectiveness of the valve eccentrics of steam engines for some reason, as I guess they remind me of the desmodromic valve system of the Moto-Guzzi.
I am wondering if you were to put two eccentrics on the crank, one set to peak at 12 degrees BTC, and the second one to peak at 19 degrees after TDC (I may have my degree numbers out a bit here) then by using a Stephenson linkage you could shift valve timing and thus rpm at will. The output of the linkage could be used as a cam lobe to lift and drop the valves.
But because the eccentric would control the motion in both directions, you would have removed most of the loading on the valve springs.
This would not provide instant valve closure but according to what I read, that becomes more important further down the power stroke.

Does any of this make sense?

[barts]

Hey Bart,
In a previous thread you discussed cams and timing in your Sea Lion engine:

With a fixed valve duration of about 30 degrees, short cut-off is achieved by advancing the valve timing to 11 degrees before TDC; this is about 2% of the stroke. The remaining 19 degrees is all admission time, yielding 5.5% cut-off. If we shift the valve timing to opening at TDC, the result is cut-off at 14.5%, using 3 x the steam. In addition, since we're driving a prop, the speed of the engine will go up, increasing power output still further.

And also you mentioned the need for lightness of the valve train, which has been the quest of every IC engine builder since the flathead days. If as you mentioned, you are planning to use a cam and follower, the valve train weight is important.

So here is my first dumb question on this forum....
I have always admired the simplicity and effectiveness of the valve eccentrics of steam engines for some reason, as I guess they remind me of the desmodromic valve system of the Moto-Guzzi.
I am wondering if you were to put two eccentrics on the crank, one set to peak at 12 degrees BTC, and the second one to peak at 19 degrees after TDC (I may have my degree numbers out a bit here) then by using a Stephenson linkage you could shift valve timing and thus rpm at will. The output of the linkage could be used as a cam lobe to lift and drop the valves.
But because the eccentric would control the motion in both directions, you would have removed most of the loading on the valve springs.
This would not provide instant valve closure but according to what I read, that becomes more important further down the power stroke.

Does any of this make sense?

I'm not sure I understand your idea exactly, but I think this would work for an engine w/ a larger cut-off. A Stephenson linkage basically sums two sine waves, and the result is, of course, another sine wave (there's a trig identity for that). Let's say we use +/- 15 degrees on the either size of valve maximum travel, and say we want 1/4" valve opening. So the equation is such that

1/4" = eccentric_swing * (1 - cos(15 degrees))

cos(15) = .966, so .25/(1-.966) = 7.35" !

Even if we use a eccentric to actuate the valve, I think getting 30 degrees of dwell on the valve opening is going to be quite difficult. I think the only way to get a eccentric linkage to give this short a cut-off is to use a riding cut-off w/ a slide valve or piston valve w/ a separate cut-off sleeve. The Lenz valves use a lever w/ a cam follower to solve the same problem; the Corliss valves used a rocking valve w/ a detaching linkage and dashpot on a constant rpm engine.

I considered using a small high pressure cylinder with a piston valve and regular eccentric linkage of some sort, exhausting to the uniflow low pressure cylinder; this was also a popular setup in Europe on stationary engines and on some British marine engines. However, this makes either for a much taller engine or one has to go to multiple single acting cylinders; this adds significant complication and space requirements to the engine.

I've further simplified the design to run the camshaft vertically up the front of the engine with two cams, each driving its valve directly, getting rid of the rockers and actuating arms; the only additional weight in the valve train will be the roller follower and some portion of the valve spring.

I'll adjust the valve timing by using a sliding sleeve engaging two helically milled slots; this can easily provide the desired
level of phase adjustment.

Out to the shop to work on the mill DRO so I can bore the column mounting holes in the right place.

- Bart