Resources/Information for Crank Lubrication?

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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gondolier88
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Re: Resources/Information for Crank Lubrication?

Post by gondolier88 » Sat Mar 17, 2018 9:12 pm

Triangletom,

I haven't bothered to do swept volume calcs on your cylinder sizes- but just glancing at your dimensions leads me to think that you may be compromising yourself somewhat by your design;

1- your point about it being a small engine and a large engine on a common crank is very valid- however you would actually be asking a very small engine to power a very large vacuum pump and a lot of heavy metal until all is at working temperature- steam jacket-ting would go some way to remedying that- but that in itself brings big challenges in terms of machining or patternmaking/foundry work depending on what direction you go.

2- The amount of steam that would go into the HP cylinder would be a tiny fraction of what would be required to run the 2 x 5LP cylinders- not even enough to register on a pressure gauge I wouldn't wonder! This means that both the HP and 1IP cylinders would be required to run non-expansively- essentially becoming over complicated piston valves for the last three cylinders, and totally eradicating the point of the engine in terms of efficiency.

Unless running for very long periods (6hrs or more) non stop at a cruising speed then the most efficient multi-cylinder engine we can hope to use in a small launch is a triple at best- these also have the inherent advantage of being very balanced, something the majority of compounds, even good ones, can only hope to be. But in reality a small HP twin is all the engine most launches need, can run all day at pressures that wouldn't budge a compound and don't require energy loss into an air pump.

Just my thoughts on what is a fascinating suggestion for an engine design!

Greg
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marinesteam
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Re: Resources/Information for Crank Lubrication?

Post by marinesteam » Sat Mar 17, 2018 9:22 pm

In a similar vain to Greg's point.

I've always wondered if compound engines of our size (smaller than ship's engines) suffer from more losses in operation of the valve gear than they gain from the efficiency of compounding and if the losses get greater with the addition of more stages of compounding.

Ken
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Re: Resources/Information for Crank Lubrication?

Post by DetroiTug » Sat Mar 17, 2018 9:59 pm

Greg and Ken, agree with both of your assessments and suspicions.

Another issue with all those cylinders (iron mass), is thermal loss. Just as we discussed in the "steam thruster" thread, anything cooler than the steam is killing it. A quadruple expansion engine in our sizes ( low internal cylinder volume in relation to internal surface area (( Mouse and elephant as Mike mentioned)) would need to be ran at very high steam pressures and pull a vacuum on the LP.

-Ron
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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Sat Mar 17, 2018 11:35 pm

To put things in perspective, bearings like this are used in things like the rear axles of giant american pickups and they generally are still in there rolling away when the truck is worn out and scrapped. Plan on a hundred years in a steam engine.
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Re: Resources/Information for Crank Lubrication?

Post by cyberbadger » Sat Mar 17, 2018 11:51 pm

Lopez Mike wrote:Plan on a hundred years in a steam engine.
Oh shoot! Was that the service interval I didn't realize! ;)

My Toledo is 16 years late for a service interval. :-P :o :lol:

-CB
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Re: Resources/Information for Crank Lubrication?

Post by Lionel Connell » Sun Mar 18, 2018 4:28 am

I think that if commercial users of marine steam engines back in the day were prepared to pay double or triple the amount of money to purchase a compound or triple over what they would have paid for a simple engine, and for them to be prepared to accept double or triple on maintenance cost for the engine, that the fuel savings must indeed have been worth it. It is quite obvious that the major manufacturers had all developed compounds, triples and quads, and the market would not have gone in that direction if there was little or no benefit in doing so. The engines were used in a very competitive market and I am sure that boat and ship builders/operators would have done their homework before dishing out sizable amounts of cash for engines. Operating cost over the initial investment would have been foremost in their decision making. It would appear that with small launches the compound was the engine of choice toward the end, and would have been so for a reason.

In any case, if a guy in the steam boat hobby wishes to build a complex engine, he is doing it for the love of building and owning the engine. He will spend 100 times more hours building the engine than he will spend steaming the boat, and probably spend 100 times more money building the engine, boat and boiler than he will ever spend on fuel. For a builder, the journey is in the workshop, and the celebration is on the water.

There is plenty of historical information that provides a pretty good idea of what cylinder volumes were found to be best across a triple or quad. With the triple it seems that the HP is usually about 1/3 the diameter of the LP with the stroke usually a little larger than the diameter of the intermediate cylinder.

Lionel
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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Sun Mar 18, 2018 4:56 am

There is no question that multiple expansions are very much more efficient than a single expansion. But I'm not convinced that the advantage scales well. At some point, I think around the size of our engines, the optimum combination converges to a two stage design. And I think that when you get down to the size of a Stuart Yacht Compound v.s. their Yacht Twin (single expansion) it would be very hard to choose. Heat loss and friction are just killing you.

In my case, there are so many changes that I need to make to improve fuel consumption without compounding that I will probably enjoy the simplicity of my single. No vacuum pump for one thing.

As to the ratio of building to steaming, my new hull is watertight, the hull and deck are painted and it's on the trailer. Later this year I'll be swapping in the machinery from my old boat and finishing up the interior. I'm 150 hours into it. That's equal to a month of all day steaming. Grrr.

I love to see sophisticated engines being built and, hopefully, running. But my personal list of things I do precludes living in my shop while I scratch build an engine even though I am equipped for it all the way from foundry facilities to a paint spraying rig. I have a 3/4 completed 1/5 scale locomotive, a 36 foot sailboat, a full schedule of cross country motorcycle races in Baja and a partner who is an absolute master of the 'Honey Do' list. "Ah yes, that unfinished utility room!" "Are we going kayaking next week?"

And, a significant reality check, I'm 74. Creak! Groan!

So please take me for a ride when you get it steaming.
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Re: Resources/Information for Crank Lubrication?

Post by TriangleTom » Sun Mar 18, 2018 5:13 am

gondolier88 wrote: Triangletom,

2- The amount of steam that would go into the HP cylinder would be a tiny fraction of what would be required to run the 2 x 5LP cylinders- not even enough to register on a pressure gauge I wouldn't wonder! This means that both the HP and 1IP cylinders would be required to run non-expansively- essentially becoming over complicated piston valves for the last three cylinders, and totally eradicating the point of the engine in terms of efficiency.

Just my thoughts on what is a fascinating suggestion for an engine design!

Greg
You would be absolutely right if this were like a normal compound, in which the steam stays in the engine for the entirety of its expansion. However, what differs here is that the steam exiting the HIP cylinder (which will be essentially saturated at 120 PSI) will go back to be superheated again up to about 475 F at constant pressure. This results in a much greater volume of steam for the same pressure, necessitating much larger cylinders.

Ron-

Yeah, there's definitely going to be a lot of thermal loss, especially at first. I'm planning on running at 250 PSI if that makes a difference.

Honestly, in addition to possible efficiency improvements I'm planning on doing a quad because it it complicated and challenging and that's what's fun for me. Also, I'm really not familiar with any applications of steam reheat on reciprocating steam engines, so that should be interesting because as far as I can tell it really isn't seen much.
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Re: Resources/Information for Crank Lubrication?

Post by gondolier88 » Sun Mar 18, 2018 5:55 pm

Lionel Connell wrote:I think that if commercial users of marine steam engines back in the day were prepared to pay double or triple the amount of money to purchase a compound or triple over what they would have paid for a simple engine, and for them to be prepared to accept double or triple on maintenance cost for the engine, that the fuel savings must indeed have been worth it. It is quite obvious that the major manufacturers had all developed compounds, triples and quads, and the market would not have gone in that direction if there was little or no benefit in doing so. The engines were used in a very competitive market and I am sure that boat and ship builders/operators would have done their homework before dishing out sizable amounts of cash for engines. Operating cost over the initial investment would have been foremost in their decision making. It would appear that with small launches the compound was the engine of choice toward the end, and would have been so for a reason.


Lionel
Whilst true, there is a caveat that almost all builders of steam launches seem to miss these days- we're not commercial users!

Historically, builders of steam machinery of renown such as DesVignes and Simpson Strickland were big advocates of high pressure machinery 'where a plentiful supply of fresh water exists and a ready supply of fuel' were available it was the machinery of choice for discerning launch owners- it was easy to use, very powerful, smooth running and very quiet in comparison to an equivalent size compound (note size is equivalent in terms of space required, not engine output)

The reason for compounds and triples being the engine of choice for launches at the end was absolutely nothing to do with efficiency for the most part- the majority of compounds and triples running on freshwater didn't condense for example. It was a fashionable thing to able to say that your launch had a big triple 'just like Titanic!' the fact that the Titanic had huge condensers and ran an exhaust steam turbine to power the centre shaft was, of course, quietly passed over for the wow factor of having apparently cutting edge steam machinery in your launch.

Having driven dozens of marine engines of high pressure, compound and triple designs I can absolutely guarantee that at launch sizes of 50ft or less running on fresh water the energy required to supply steam to a compound in an environment where non-stop cruising speed is hardly ever achieved, reliable reversing and manoeuvring capability required at all times to avoid other boats, stopping at jetties etc etc is not justified in terms of fuel savings. It always makes me smile when seeing an advocate of compound machinery spend a lot of time raising boiler pressure to blowing off point in order to warm the engine through, with steam blower going to keep a draught through the fire, spend another considerable amount of time waiting for a lot of water in the engine to pour out of the drains before becoming steam, then run with the 'simpling' valve open for 10mins while manoeuvring away from the berth, then wait another few mins for the vacuum to build and then say they're running compound for efficiency reasons.

Meanwhile, a HP twin owner has got the boiler upto around 50psi, opened the throttle and has manouvered away from the berth safely with reliable forward and astern motion available, drains shut shortly after the first few revs of the engine with exhaust drawing the fire through the boiler with pressure rising steadily and has made 30mins of steaming fun on the water before Mr. Compound is thinking about opening the throttle! Oh, and he's in total silence while sipping a G&T in elegant steam style!

As I build/restore and maintain steam launches on behalf of customers as well as look after historic steam launches in voluntary/trustee capacity I can absolutely say that as a builder I will recommend the best machinery for the job in terms of return- fact is that for 99% of all steam launches, this means not compound/multiple expansion!

In terms of steam usage- the most efficient way to run a HP twin is a boiler WP of around 120-150psi, with throttle cracked open to allow 25-35psi of chest pressure- which usually results in a cruising speed of around 70-80% of hull speed and a measurable amount of real throttle superheating. Compare that to a compound engine on the same boiler- throttle wide open with valve gear 'notched up' to give best expansive working, but poor balancing and a lot of wear on the valve gear with accompanying wear and noise and the argument of steam efficiency in terms of pounds of steam used doesn't stand up if looking for the exact equivalent power output for the same hull performance, and the boat and machinery will be a step up in terms of weight which also restricts acceleration- and as HP twins rev a lot better than compounds, they can be loaded higher too.

Don't misunderstand me, I love to see a well made compound or triple in a launch, they're beautiful engines to watch and run, but they shouldn't be seen as being a fuel-saving option in launch sizes.

Greg
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Re: Resources/Information for Crank Lubrication?

Post by DetroiTug » Sun Mar 18, 2018 7:47 pm

Greg, Great post!

After being around many operating steam launches at meets and elsewhere, my observations concur with what you have written above.

I think the biggest issue with a compound in a small boat where the load is varying wildly, is having a fixed cutoff on the LP. On large ships, I read and heard that every time a compound powered steam ship left port to make a long distance trip, the engineer would pull an indicator card on the LP and balance the cutoff to the load and speed for highest efficiency. I've heard reports of engines equipped with a pressure gauge on the receiver, that 0 psi was observed underway at certain speeds.

I like what you wrote about running the twin throttled slightly, that is how mine runs the best.

-Ron
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