Designing a new engine for a big(ger) boat...

[fredrosse]

There is certainly much interest in this new project!

I have some information that might be of interest here, having run a uniflow engine for a few thousand hours on a domestic Heat-Power Project. Also be sure to check out the Whitecliffs Project, a high pressure uniflow engine using (I think) GM 53 series cylinder sleeves.

The attached sketch is for a GM-71 Series Uniflow Engine conversion, double acting.


And a PV diagram for a 2 cyl double acting uniflow 23HP @ 450 RPM

[barts]

Here's a very preliminary cylinder cross section... some things my OpenOffice sketch doesn't make clear:

http://smaalders.net/barts/engine1.pdf


* exhaust belt is a weldment, machined after welding and sealed to cylinder exterior with viton o-rings and seal plates. Engine cylinder is mounted via the the exhaust belt.
* piston is built up hollow for weight savings
* poppet valves are actuated by pulling rather than pushing.
* drawing is not to scale

- Bart

[fredrosse]

Looks like your basic layout will be a workable engine. Lots of additional details to be worked up, but basically just alignment grooves to keep everything in line, and seals for those areas. Attached sketch is a unitized Popet Valve with "Pull up" motion, suitable for high pressures.

[fredrosse]

Bart, have you started on the hull design, or are you going to hunt up something already existing for conversion?

A page fron some powering software might be close to what you are planning, except it is somewhat more displacement than your 10,000 pounds.

[barts]

Excellent - thanks for all the info, Fred. Lots to reply to here!

I'd thought about modeling release; I've not done that yet in my calculations and need to add that in. [I use a small python program to do all the calculations; it makes varying parameters much easier]. I note fairly high exhaust back pressure (10 PSIA) in the two cylinder marine engine; most of the boats I'm seeing are running about 2 PSIA (26 inches hg), which definitely makes a difference when looking to use shorter cut-offs and when calculating BMEP.

The poppet valve is simple and clever; I assume this design is for a single acting engine?

The 23 CID single acting engine is relatively simple. I'm somewhat hesitant to put a spring in the high temperature steam, though. The use of clamps to retain the valve assemblies is worth remembering. There seems to be limited space for sealing the high pressure valve stem; how was this done?

I've been mulling over sealing the various bolted together surfaces. In the exhaust portion of the engine viton o-rings will work nicely; I need to use o-rings there since the clamping force is orthogonal to the sealing surfaces. In the cylinder heads, I'm inclined to machine a small indentation and use high temperature automotive RTV sealant; this works fine at 600F. The cylinder end components are indeed aligned with alignment recesses on both sides of the cylinder head and the underside of the steam chest cap.

My brother designs boats (along with other things); his website is http://smaalders.net/yacht_design/. He's doing the design for the hull; here's an initial proposed sketch of the lines, including a box keel to facilitate beaching (nice to be able to do in the San Juans):

Sea Lion draft lines_Dec 2012.jpg (18.67 KiB) Viewed 10102 times

. I've got copies of Skene's Elements of Yacht Design and David Gerr's Propeller Handbook here, so running the basic numbers is not difficult. We're going to emphasize efficient performance at 6 - 7 knots; burning two or three times the fuel to go 8 or 9 is fun at a steamboat meet, but for longer distances quite impractical. I want to take this boat all over the Northwest via water, so living aboard in comfort is an important part of the design.

- Bart

[fredrosse]

Nice hull you have worked up, looks like a comfortable and seaworthy hull.

Packings for popet valve stems shown on the following sketch. The packing arrangement on the exhaust valve I have used with good success on the admission valve of my single cylinder uniflow engine, shown yesterday “Popet Valve, with sharp cutoff, and relief feature”, and of course it would work well in exhaust service.

The admission valve packing can be extended to a deep gland, as Abner always advocated, but in my recent experience with fancy packing materials available today, less of a gland depth is needed, provided alignment is good and the shaft or rod has a good hard chrome finish.

As to the spring in the HP steam space, that may pose a problem with temperatures that might occur. The design shown was for total temperature of 500F, but 600F, with excursions sometimes, may introduce material difficulties. Seems that the spring could be mounted exterior to the steam space, and an alternate packing tensioner could be used.

[Oilking]

Folks,
Hal Fuller, the last of Skinner Uniflow, at the end was working on a steam adaptation for a 6-71, so the buzz goes. What I understand from posts made by people tha claim to have talked to Fuller, is that the piston in the block was converted to a crosshead, and the steam cylinders replaced the heads. No one seams to know what became of any of Fullers drawing or if they even existed. If anyone knows more about this I'd like to hear?

That said, the following thoughts:
What about a 2-53 or 2-71 block with the steam cylinders on top? The enclosed pressure lubed crackcase could be a plus and the cam might be able to be modified to run the valve gear?

Dave

[barts]

Well, I ran some more numbers to get a better sense of what was happening. Correcting for release dropped power slightly; it's effectively like a slightly smaller engine. What was more interesting was examining compression pressures as a function of clearance. Here, the need for good condenser vacuum is obvious. What is not as obvious is that when maneuvering using the throttle, even if condenser vacuum is maintained via a steam eductor, the peak cylinder pressures due to inlet steam may be lower than the compression pressure - and then the engine may stall or fail to run. You really want a good vacuum with a uniflow - 26" hg is a good start. Recompression pressure is on the order of 180 psi for 2% clearance; this is great for steady state efficiency but will cause problems when throttled down.

The easiest way to deal with this is to provide additional clearance volume when maneuvering. I'm working out the details of a combined cylinder drain and added volume valve that would serve both needed functions. The simplest method of solving this is of course to just
provide more clearance volume, but this directly detrimental to efficiency, so some effort here is worthwhile.

- Bart

[barts]

Folks,
Hal Fuller, the last of Skinner Uniflow, at the end was working on a steam adaptation for a 6-71, so the buzz goes. What I understand from posts made by people tha claim to have talked to Fuller, is that the piston in the block was converted to a crosshead, and the steam cylinders replaced the heads. No one seams to know what became of any of Fullers drawing or if they even existed. If anyone knows more about this I'd like to hear?

That said, the following thoughts:
What about a 2-53 or 2-71 block with the steam cylinders on top? The enclosed pressure lubed crackcase could be a plus and the cam might be able to be modified to run the valve gear?

Dave

This could work, but these engines were _heavy_ - much heavier and stronger than we need. Just the block w/ crank & pistons is at least 500 lbs; the completed engine was close to 1000 lbs. Fine for stationary use, but somewhat excessive for marine use unless one is using +1000 psi steam. Besides, I'm hoping for something at least slightly better looking .

- Bart

[Oilking]

Bart,
I also have a copy of an old Navy pub, Naval Reciprocating Steam Engines, that I found in a book store in Tiawan. It has a wealth of steam engine info with the last chapter dedicated to the three cylinder marine Skinner Uniflow. It has details of the double cam variable valve timing, and manuvering valve to start and reverse the engine. I have recently found reprints of this pub on Ebay for ~$30.

The manuvering valve is engage to dump part of the recompressed steam to the exhaust trunk. I don't see why this can't be done with the drain valves if size right. The Skinner used the manuvering valves as the cylinder drains drains during warm-up.

Dave