Stephenson's Link Hookup Question

[DetroiTug]

Mike,

I'm in full agreement with you. Based on my limited experience though, not sure if that is much an endorsement .

I've been hanging around with some very experienced steam folks (some have been steamboating since the 70's), and what they keep reiterating is that the power comes from the boiler. The engine is just a means of transforming the boiler's power in to real work. One can drive a large engine slow on the volume of steam created or drive a small engine fast, the net horsepower will be the same. The efficiency of the plant is the ability to generate the steam in the vessel and maintain it's same temperature/pressure all the way to the engine's cylinder(s) for expansion. Any place the steam can cool even a few degrees is lost power.

I seen a Naptha launch at Henry Ford museum a number of years ago, the cylinder for that engine was up inside the burner of the boiler which was a ring. I thought they did that to save space and it seemed very odd. Now it makes a little more sense. The original Locomobile cars, the steam line is very short, the steam line comes out of the boiler and goes immediately to the engine.

Seems like shortening the cut-off or "stroke" as some refer to it is essentially decreasing the size of the engine, hence decreasing it's torque output. We ran "shorter stroke" on the tug last year, but it was at the expense of power. In other words we were compensating for two things: 1. A boiler that was not generating enough steam. And/or 2. Lack of insulation and heat loss, condensing the steam on the way to the engine.

Not sure how accurate this is, but this is the tack I'm going to take going forward.

-Ron

[SteamGuy]

Mike-

I have to agree with you, I have seen too many small steam engines that look like water pumps, they just gush water out of everywhere, expecially the exhaust.

From what I have read though, the norm for many/most steam engines is that the valve gear tends to be either poorly designed, or the valve not adjusted correctly, and so often a steam engine runs at a fraction of its designed horsepower.

I think of it sort of like the old automobiles. If you did not set the dwell and then use a timing light, your engine would still run, but you was not performing as designed. For my race car buddies, timing and advance was everything for the igition and valve system. I guess at a minimum I want to get to the point where I can have a good idea if any given steam engine is performing close to its designed output.

[SteamGuy]

I read a good steam book on efficiency (can't remember which one), but I did jot down some notes, which are as follows:

Can't vouch for their accuracy, but this is what I noted.

Steam engine losses:
Losses in a steam engine include:
a) Rejection loss.
b) Thermal loss.
c) Mechanical loss.

Steam engine efficiency:
Steam engines were often designed for maximum efficiency at full load.

High speed operation of steam engines decreases condensation, but increases wire drawing. High speed steam engine valves are generally made larger than slow speed engine valves.

A higher boiler pressure is generally used for multi-expansion steam engines.

The efficiency of a steam engine is a measure of how much energy is transmitted from the steam to the movement of the flywheel of the engine. By cutting off the steam supplied to the cylinder before the piston reaches bottom-dead-center (BDC), energy can be extracted from the expansive nature of the steam, thus increasing the efficiency of the steam engine.
The best ratio of expansion gives the lowest consumption of steam per horsepower.

Efficiency can be gained by using waste heat to preheat the water that is fed into the boiler (feedwater).

Small steam engines are less efficient than large ones.
Low speed steam engines are more efficient than high speed steam engines.
(It is unknow if this statement is valid for the steam engines designed in the early 1900's.
It is assumed that any reciprocating engine can operate more efficiently as slower speeds if the required power can be produced at a reduced speed, since energy is lost every time the reciprocating parts have to be stopped and reversed in direction. In a given range, more engine speed equals more power produced, since the number of power strokes per revolution increases with speed. Above a certain speed, power begins to reduce with increased speed.)

Some energy is wasted by the process of expelling the steam exhaust from the cylinder of the engine.

Cylinder condensation reduces work produced by a steam engine. Superheating was often used to reduce or eliminate cylinder condensation.

There is some flow of heat in a steam engine due to conduction.

Methods to decrease rejection losses are as follows:
1. Increase steam pressure.
2. Use superheated steam.
3. Use a compound engine design.
4. Improve flow with multiple valves and uniflow design.
5. Vary speed.
6. Decrease clearance and increase the ratio of expansion.
7. Use cylinder jacketing to reduce condenstation.
(Some designs used the waste stack flow to heat the cylinder)
8. Decrease valve and piston leakage.

Higher speed steam engines need more compression for efficiency than slow speed engines.

Mechanical losses:
Methods to reduce mechanical losses are as follows:
1. Mimimize (by design) pressures on bearing surfaces.
2. Use proper lubrication of all load bearing surfaces.
3. A vertical engine has less friction than a horizontal design.
4. Look at the effects of running the engine "over" or "under".
(Large stationary engines generally run over due to the ease of maintenance)
5. Friction losses increase with the power of an engine.

Friction losses:
Friction points include:
1. Bearing friction.
2. Valve friction.
3. Gland friction.
(Some steam engines used metal-faced packing or metal inserts, with forced oil lubrication on the glands)

The oil is supplied to the bearing surfaces of an engine with the intent of producing a thin film of oil that separates the two wearing surfaces. Bearing surfaces often had grooves cut into their surfaces in various configurations and angles to help distribute the oil across the face of the bearing. The leading edge of the grooves was rounded, and the trailing edge of the groove was sharp. The sharp edge helped to return oil
to a reservoir after it had traveled across the face of the bearing surface, thus allowing the oil to be recirculated.

[gondolier88]

The oil is supplied to the bearing surfaces of an engine with the intent of producing a thin film of oil that separates the two wearing surfaces. Bearing surfaces often had grooves cut into their surfaces in various configurations and angles to help distribute the oil across the face of the bearing. The leading edge of the grooves was rounded, and the trailing edge of the groove was sharp. The sharp edge helped to return oil
to a reservoir after it had traveled across the face of the bearing surface, thus allowing the oil to be recirculated.

Hi Pat,

Under no circumstances should the leading edge be round- if in the event of miniscule fragments of grit etc entering the oil they would be ensconced into the wedge shaped void given by the oil groove being round. Every one I've seen on the upmarket launch engines in the Windermere Steamboat Museum has razor sharp edges.

I would hesitate to inject oil under pressure into a metallic bound gland packing- if there is enough room for oil under pressure to lubricate the gland then there is enough room for steam under pressure to leak past too. Graphite based and soft metal packings are more than enough for the pressures and temperatures that are found in the typical steam launch. I can see how oil could be seen to reduce friction- but in the case of a reciprocating rod such as a valve rod the friction given by oil under pressure would still be quite considerable as the rod would act like a pump ram. Graphite is well known for it's self lubricating qualities in the harshest of environments, and if packed properly will last for years without trouble.

Greg

[Lopez Mike]

Misunderstanding as to what he meant as the leading edge I believe.

That said, we run our bearings both ways (reversing engines) so both edges should be sharp so as to have them work as crud scrapers.

I have ball bearings on my crank shaft (heresy!) so no problemo.

[SteamGuy]

Greg-

As I recall, the from the book, rounding the leading edge of the oil groove on the old engines was quite common, but it also seemed like this was in reference to very large engines, with journals perhaps 12"-18" wide.

The idea was to build up a dam of oil and oil pressure such that the crank actually floated on a thin film of oil without metal to metal contact.

If the crank is floating on a film of oil, then small particals of debris should pass through the gap. I guess if you are operating in an environment contaminated with grit, then you will have all sorts of problems no matter how you do it.

Typically, marine environments are not known to be high grit/dirt locations, as witnessed by the fact that air filters are not installed on outboard motor engines, since there is typically no airborn dirt at sea.

For a small engine, I am sure it would be difficult (but not necessarily impossible) to rouind a very small oil groove edge. For engines like an automobile engine with forced oil systems, your film of oil between metallic parts would be created by pressure by the oil pump, so no rounded leading edges would be required.

For a slow moving steam engine without a pressurized oil system, and expecially in a marine environment, I would think a rounded leading edge on the groove would make perfect sense. I have seen babbit bearings which operated in dirty environments, and sometimes they do get grooves in them from debris, but that would not negate the benefit of creating a film of oil ahead of the edge.

Perhaps not a critical issue to small launch engines, but most definitely a practice what was used in the past for steam engines.

I will try and remember where I saw that.
They had pictures, etc.

[gondolier88]

Hi Pat,

I can certainly see the sense if there is a proper filtered oil recirculation system in place, but as for a marine environment being non-gritty, I would go an any coal fired launch before assuming that fact, no matter how clean the owner keeps the boat, as soon as a new bag of coal is put on there are piles of grit in the most unlikely places, usually at foot level, the same as the main bearing caps...

However grit doesn't always come from external sources, white metalled bearings have been known on many an occasion to flake small pieces off- if one of thes got trapped in the 'wedge' of oil going into the leading edge then it would make an awful mess of the rest of the rest of the white metal in the bearing.

The engines to which I reference having razor edged grooves are not what you would consider small engines as far as launches go- W.Sissons 100nhp Triple expansion from Thames passenger boat Majestic for example.

It is certainly interesting to see how manufacturers policies and attitudes were different to certain aspects of engine design.

Greg

[wsmcycle]

steamguy

"need more compression " what can this possibly mean?

[SteamGuy]

Greg-

It is baffling the variety of methods and techniques used for the old engines.
I looked last night for the info on the rounded edge bearings, but no luck.
If I run across it, I will post the source.

I guess part of the fun of it is trying to separate fact from fiction.
Often the old steam engine books were written by academics who generally noted the differences in design techniques between similar engines, and then tried to arrive at some sort of concensus about the best design to use. It is obvious that the exact techniques used for steam engine design were closely guarded secrets. but we can get an idea of design intent by reverse engineering some of the old engines.

Very few engine designers wrote books about how they did it. Charles Porter is one example of a designer who wrote a book about his experiences (Porter was the father of the modern high-speed steam engine. He was told that no engine was capable of operating at 300 rpm under any circumstances, but he proved everyone wrong in very short order). Porter's design rendered the giant Corliss completely obsolete overnight, and reduced the size an engine required to produce a given horsepower by many orders of magnitude and complexity.

An amusing story that Porter tells concerns his first high-speed engine which he displayed at a British exposition in the mid 1800's. The chief of the exposition prohibited him from running his engine faster than 100 rpm, and when Porter first started his engine, he ran it at 150 rpm. The chief quickly appeared with watch in hand, and counted the rpm. After a few tense minutes, he finally stated "Mr. Porter, if your engine can run that smoothly at 150 rpm, you can run it any any speed you want".

As far as needing more compression, the valve closes the ports at around 90% of valve travel if I remember correctly, and it does this to allow pressure to build up on the far side of the piston, and cushion the reciprocating parts, which have to come to a rest before reversing direction.

So you could increase compression by changing the valve, such that the exhaust port closes earlier in the stroke, or you could increase compression by reducing the clearance between the cylinder head and the piston at TDC. Caution must be used since bearings wear, and the piston may contact the head in that case, ruining the engine. Also, too much compression with a D-valve will cause the valve to lift off the seat if the pressure exceeds that of the pressure in the steam chest, and the valve will chatter (not good for the valve or the seat).

Some books put great emphasis on minimizing clearance in steam engines, and others recommend generous clearance to allow for parts/bearings to wear.
I tend to err on the side of generous clearance, since a head crash would do tremendous damage.

[steamboatjack]

Gents,
The lube oil discussion should be a new subject, tagging stuff on makes life difficult when you have to look back.
Regards
Jack