Thermodynamics, DBHP and related technical matters

Yeah, you are correct, forgot to divide by 4, 95 liters. Apart from that Postupalsky used .35 ato as back pressure,
this is different now.
kind regards
Jos

 

What is your evidence of that? I would expect the inside and outside engines to provide approximate balancing of the reciprocating masses, leaving the balance weights on the wheels to balance only the rotating masses, thus giving minimal hammer blow. Surely that was Churchward's reason for adopting the De Glehn layout.

 

What ? mean coming to the defence of the GWR ? better take some tablets
Impressive as the rebuilt Scots are, rebuilding it just gave it the kind of boiler the castle had used for years, once both had a double chimney and high superheat you have two very similar locomotives, with different numbers of cylinders agreed the Scott should have the edge...
Would chuck in the Lord Nelson and how that in theory should be there with the best of them. and then how the Kings had to go one better .. and that brings us nicely back to 6023.

 

so do i, with 25 on it must have been going downhill....

 

That was not the way they were balanced.
Each of the driving axles was balanced almost as a normal two cylinder loco to reduce bearing horizontal loads.
Both axles hammerblew heavily, but in anti phase.That is nice if You are a bridge but not at all if You are a rail.
A gentleman here dug out the bridge stress commity report that contains the balancing details anno ca 1923.
If You find a copy please give me one also.

 

Thank you

 

well , the Scot had better cyls better draughting , higher BP and more heating area ,and a bigger boiler , so yes , they did have the edge

for much of their career the Kings were limited to C 24000 lb per hour . only when Sam Ells took them in hand did they get around 30000 lb . as I said , I have never seen any max rate figures for the Scot ,but I would think that until the Kings last years the Scots were at least their equal . 46115 has produced work in preservation that is well into Pacific territory. hopefully we will see what 6023 is capable of .

The Nelsons were never as good as they should have been .

the Castles and Scots were built for different jobs . in many ways , comparisons do justice to neither

 

well,yeah , but the Duchess shares the same lineage . just shows what a great engineer GJC was

 

Seconded.

 

I'm guessing that'd be shortly before the technology to scan them into a computer file became a readily affordable option ..... in accordance with sod's law.

Leaving aside the likelihood that a 1945 election win by Churchill (doubtless ennobled as a Marquess or Duke) would most probably have rendered nationalisation a complete non-starter on idealogical grounds (don't forget, it was a Labour policy), it's an intriguing "what if". Following the years of wartime government control, an LMS board not facing imminent dissolution would, most likely, have looked at things very differently.

As it was, the Big Four's boards could (and did) make some 'interesting' decisions, many dictated by postwar shortages, others more by what we'd now call 'blue skies thinking' and I suspect matters might've played out rather differently, had long term responsibility remained with the directors. Here's just one look forward from the 1930's LMS which wasn't picked up again postwar:



(Image courtesy spellerweb.net)

 

Regarding the efficiency of different nos. of cylinders doing the same work.
Adolph Giesl-Gieslingen gives a curve for this in his interesting book "Lokomotiv-Athleten", Slezak 1976, the book is about all the 12- and 14-couplers in the world.
The curve gives the relative specific steam consumption (kg steam per indicated Hp hour) for cylinders of different swept volume.
The curve is quoted from Glasers Analen 1953, page 47, a paper about the optimal specific steam consumption of steam locos. Author not given.
From this curve follows that a three cyl. machinery has 4.7 % higher and a four cyl. 8 % higher steam consumption over a two cyl. machinery. All other parameter equal. As there were quite a number of loco types built with different versions of cylinders in Germany and other countries, these figures seem well verified. E.g. DR BR 01 and 03 and KPEV S10 (BR 17).
A closer examination of the curve reveals that it quite well follows a (1/V)^(1/9), i.e. the efficiency increases with the ninth root of the swept cyl. volume.
The physical background for this difference is that the cyclic cylinder condensation is less for a larger cyl., i.e. more of the steam is further away from the cylinder walls. And thus less effected by the varying temperature of the steel or iron surfaces.

Dag B

 

The metric system at its finest!

 

The unknown author is Postupalsky. There is another difference, the circumference of 2 cylinders of identical total volume compared to a single cylinder is different
so that entry and exit losses differ also.

 

The curve is generic, only stating the variance with size. Whatever unit you like: lb per kWh? ;-)

Absolutely, there is also an optimal ratio between the stroke and cyl. diameter to minimize the condensation losses.
I read about a guy really trying to do proper calculation on the heat transfer between the mass of steam in the cylinder and the cylinder walls, using a computer program for neutron diffusion in nuclear reactors. The physics is similar enough, but I never heard of any results of the study.

 

On the subject of maximum drawbar horsepower George Carpenter accepts the following:

LMS 6234 "Duchess of Abercorn" 1,770dbhp
LNER 4490 "Empire of India" 1750dbhp
SR 21C7 "Aberdeen and Commonwealth" 1870dbhp

The MN has a cylinder volume of 10.604 cubic feet whereas the Princess Coronation has 13.861 cubic feet and the boiler on the MN has both less evaporative and less superheater surface. It does as built however have a higher boiler pressure and larger valves. No one should be surprised at the performances of 35028 even though it now works at 250psi.

The Class 8 Pacifics all share a very similar adhesive weight, 65-68 tons, 2007 will be more in the region of 80 tons.

The MN class originally had a nominal tractive effort of 37,515 lbf later reduced by rebuilding to 33,495 lbf. The P2 will muster 43,684 lbf but tractive effort is only one part of the story.

As the steam locomotive developed better steam circuits and improved mechanical design allowed the creation of engines that no longer needed 8 ft. drivers to run fast. 6 ft 8 inch drivers allowed engines to be plenty fast enough and if you didn't have the need for that much speed then a 6 ft nominal driving wheel diameter was absolutely fine and this could be reduced still further as later events showed. And the improvement in steam circuit design allowed for more powerful, freer running machines. They should have been more economical but this didn't always work out first time.

Poppet valve gear can give a significant reduction in specific steam consumption, or to put it another way produces a design that produces more power from a given quantity of steam. David Elliot has not revealed his finalised design to the world but it cannot be too far away.

Significant changes took place between the production of the LMS Pacific and the building of the MN. Equally improvements have come about since the MN, and with a much increased cylinder volume, a steam circuit to make it effective, much higher adhesion, improved mechanical design the 2-8-2 should not only deliver an improved performance but it should also be viewed as a bit of a homage to Bulleid who really admired the type but regrettably was not free to build his own.

 

I can see this discussion leading towards the uniflow engine.

 

From Cox Locomotive panorama

Minimum indicated steam consumption per ihph

(Chapelon 2-8-2 11.2 lbs )

Std 7 13.2
King 13.8

Two cylinder compound rather.The exhaust porting of uniflow cylnders do not ease travel on shrinking english rails.
On the other hand :Caprotti on two small outside high pressure cylinders and Stumpf Uniflow on a single inside low pressure?
Anybody having a Webb 0-8-0 lying somewhere?

 

I'm not sure where the figure of 1,770 d.b.h.p. for the Stanier Pacific came from as it was measured at the dynamometer car as 2,511. The figures for the other engines also look low. All these could, and did, put out 3,000 i.h.p. or above, and transmission losses getting on for 50% do not sound right.

 

What Book?

Is this based on numbers from the 48 interchange trials?


They correspond very well with the one hour ,two firemen rating of a standard class 7 according to Cox in Locomotive Panorama Volume 2.

 

Refering to Roger J. Mannions book about the Duchess; locomotive "Duchess of Abercorn" with a special train weighing 604 tons in 1939. It was recorded a maximum drawbar horsepower of 2282 ,estimated to a indicated horsepower of 3333.