Current and Proposed New-Builds

Let us select the best of the ten ,well cared for, S3/B16 and make it more frugal.
Urie class S are more or less same mass and power and has two 22 times 28 cylinders.
Let us fabricate a 23 inch/26inch highpressure cylinder and place it 3 feet one inch from centerplane on starboard side on our selected B16/S3.
The centre crankthrow can then be driven by a 34 inch bore/26 inch stroke low pressure cylinder.
The uncluttered backboard side can be used for a balancing rod a la Nord of France 2-8-2 tank and we have balance as good as a SR WC/BB (almost).
The best french fourcylinder compound used 11.2lbs of steam to make one indicated horsepower (Stannier 4-6-2 used 14.3)
Our B16 /4 can be considered as one side of the SNCF 141P and have bigger cylinders.
11.1lbs or less is realistic.
I accept credit cards for deposits

 

This description (at least, of the engine) is correct. However a compound is a bit more efficient than a simple expansion machine. As the steam expands in the cylinders the temperature falls, and it carries heat away from the cylinder, and this heat has to be replaced by the next charge of steam. In a compound, the expansion in each cylinder is less (compounds run at longer cut-off), so there is less heat to be replaced. I've probably not explained it very well, but that is roughly my understanding.

Most stationary and marine engines were compounds, often of the triple expansion variety, and most locomotives ended up being simples, I think probably due to the problems of packaging the equipment in the available space. There is a lot more to be said on this subject, but I've tried to keep it simple in this post.

 

One point about a railway locomotive is the requirement to provide a draft - which requires energy (i.e. the energy required to provide a given mass-flow rate of gas through the boiler, against all the resistance of the firebed, tubes etc.)

That energy has to come from somewhere, so in practical terms you can't fully expand the steam in the cylinders: you have to leave something back to provide the energy needed for the draft. So the overall cylinder efficiency would be less than in marine practice.

(The other point about locomotives is that they work at widely variable power output; whereas marine engines would typically work at long periods of constant output, and can be optimised for that duty).

Tom

 

Good points, though obviously some very successful compound locomotives have been built. In my post above I was just trying to provide a brief reply to class8mikado's post. Reams have been written on the subject of simple versus compound expansion, and I imagine the invention of the Kylchap exhaust was largely driven by a requirement to provide a low back pressure for French compound locomotives.
One other point to add is that the majority of stationary or marine engines would have been condensing, which would allow much more expansion.

 

The Final verdict made by the germans concerning compounding or not was made by Professer Nordmann 1941 in Die Lokomotive page 153 an on.
He did not like the verdict.
http://anno.onb.ac.at/cgi-content/anno-plus?aid=lok&datum=1941&page=218&size=45

 

I don't either - I can't bloody read it!

Richard.

 

That's the trouble with us Brits. I do know some German, but not enough to tackle that sort of document.

 

Given the ever present need to translate UK Acts of Parliament into comprehensible English, that's absolutely no admission of any failure, chaps!

 

Same here, but technical German doesn't normally come up in the average conversation German class!.

 

I am able to work some things out, especially if there's an accompanying photograph or diagram... My Girlfriend is German too, but she doesn't know the technical terminology, so can't really translate it for me. And I certainly won't be relying on Messrs. Google's translation facilities!

Richard.

 

When I was a student, I used to read a lot of papers in Zeitschrift für Naturforschung, Teil B and Angewandte Chemie, which somewhat stretched my schoolboy German, but you soon learnt the key vocabulary, and to a degree, the writing was quite formulaic. My French was better, but there was no-one publishing in my field in French!

Doubt I could do it quarter of a century on

Tom

 

It was maybe a job for one of the steam magazines to translate it and have a competent thermodynamicist to explain and comment.
We can also have some entertaining discussions if we do it ourselves.
I can raw- translate it if some born english-speaker will correct and arange text and tabel and numbers in a readable fashion.

 

That would be good, please can you do this.

 

I asked a German born former colleague to take a look at this. To ask for a full word-for-word translation was a rather extreme sot I requested that she provide a summary of the article - as follows (my emphasis):

Tests on a Norwegian compound engine.

An idealised compound engine (no heat loss, mass-less cylinders) has no thermodynamic advantage over a machine of simple steam expansion, and can only such a lower loss in a real machine can bring an advantage of compound action (Verbundwirkung).

Discussion of losses in a steam cylinder. Real effect cannot be calculated, steam consumption must be measured. Same for compound engine.

Discussion of losses in a compound engine.

Retrospect of wet steam compound engines.

Hot steam and compound compound action – tests so far

Tests on the Norwegian engine – description/comparison against new German locomotives (simple steam expansion) – descriptions and discussions.

Verdict: The compound engine is more sensitive to increase of revolutions and decrease of power, but more efficient in some areas and should therefore be considered again. One thing is clear: the compound action's near universal reign at the time of wet steam will never even come close to returning.

I am assuming "hot" steam means superheated....

Essentially - the development of reliable superheating removed any need for the complications of compounding in practical terms - except perhaps in certain niche applications.

 

Nordmann had been very much pro two simple,outside superheated cylinders so the remarkable thing is that he comments on this foreign unnessecary compoundery.
The important numbers are in the tables 4, 5 and 6 on page164.
57kg/m2 was max allowable load for boilers
50kg/m2 has only one point(The big threecylindr 06(White Elephant)) doing 120km per hour, where simple is better than compound.
30kg/m2 is lousy return on investment and need not influence our choice compound versus simple
For me his defence for the Reichsbahn Steam policy 1920 -40 fells flat on stomach but he tries and is an honest man that does not manipulate data.

 

Would it be possible for someone to provide a translation for the headings of the tables on pages 163 and 164 of the document?

Thanks in anticipation.

 

Was it better to start a new subject called something like Simple Locomotive Compounding or something like that?

 

If its anything like 'Simple Harmonic Motion' its a bit of a misnomer

 

How complicated do you want this to be? Experiments with superheated steam can be traced back to 1705 according to a document produced by the Technical Staff of The Superheater Co. Ltd. Manchester. You then end up with chasing names, Hornblower, Woolf, Bramah, Maudslay, Roentgen and many, many more in order to try to obtain a reasonable picture of the development of compound engines. You need a substantial document if not a book to even attempt to cover it all.

 

For a railway locomotive, what was the perceived advantage of compounding? You can only expand the steam a certain amount whether you do that through one stage or two, so on the face of it, it just looks like extra material (cylinders, steam passages) in which to have heat losses. Was it just that you potentially ended up with a smaller heat drop across each cylinder, with the high and low pressure thermally isolated from each other? Given the quote above: One thing is clear: the compound action's near universal reign at the time of wet steam will never even come close to returning. I'm wondering if there is some particular advantage of compounding with saturated steam that isn't there with superheating; if so it must presumably be in relation to the propensity of steam to condense in the cylinders if it is over-expanded?

Tom