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Locomotive Performance and Tractive Effort Discussion

Discussion in 'Steam Traction' started by MellishR, Nov 26, 2022.

  1. 242A1

    242A1 Well-Known Member

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    Hello there. It took me a while to step outside what we might refer to as UK thinking and I did start the journey many years ago.

    Chapelon observed that the Rankine Theory did not appear to predict what he could achieve in practice, no matter, let us look at what was achieved.

    PO Pacific 3566 underwent reconstruction which was completed in 1929. Due to circumstances outside of its creator's control this project ran some two years late. As built the ihp of these standard Pacifics was around 1,850. Chapelon had a series of modifications to apply to these engines which he calculated would be able to raise this figure to 3,000. On trials 3566 could achieve this figure at speeds between 75 and 80 mph. How was this done?

    It was important to minimise the steam chest pressure drop during admission and so these chests were greatly increased in volume. Steam passages were enlarged to reduce both pressure loss and back pressure. The level of superheat was increased by 100 degrees centigrade to ensure that the l.p. cylinders were using superheated steam. In order to have full valve opening at short cut-offs poppet valves and gear were fitted. The boiler performance was addressed by means of the fitting of a double Kylchap exhaust and this also had the benefit of reducing back pressure on the pistons. Chapelon never claimed that he was original in his thinking and was always at pains to acknowledge those who had made it possible such as Du Bousquet, Schmidt and Crampton amongst others.

    With a slight increase in cylinder dimensions following the application of the Houlet type superheater the output of these rebuilt engines reached 3,700 hp. sustained. Chapelon doubled the power output of the original design by applying a modest and cost effective series of improvements. The boiler pressure was a little under 250 psi and the next jump to 20 bar was for another Pacific rebuild but these Pacifics were of a smaller wheeled type and these became 4-8-0s and produced 4,000 hp which after enlargement of the l.p. cylinders and fitting of mechanical firing could maintain 4,400 cylinder horsepower as a sustained output.

    The Pacifics had trapezoidal fireboxes which were slightly larger (46.6 sq ft) in grate area than the 4-8-0 types which had a narrow box.
    To produce a high power output at low speeds you need a slightly different approach. A 2-12-0 was produced rebuilt from a PO 2-10-0 and with six cylinders it could produce 3,000 cylinder horsepower at a speed of 25 mph and it achieved high thermodynamic efficiency which is also what Chapelon wanted. This locomotive, 160A rode well and ran at 90 kmh. Because the power output was spread out over the six cylinders the components involved were relatively light and this feature was much appreciated by those who worked on the machine.

    There are so many ways you can make things better, you just have to look for them.
     
  2. Jamessquared

    Jamessquared Nat Pres stalwart

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    So
    1. What was the overall thermal efficiency claimed for those locos?
    2. Over how long were those power outputs sustained? (And under what firing conditions?)
    Tom
     
  3. 242A1

    242A1 Well-Known Member

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    Thank you for doing some work on this and I agree with you. The GL is unlikely to have achieved 3,000ihp and cannot help but wondering if punters wagered their shirt on the tractive effort horse.
     
  4. 242A1

    242A1 Well-Known Member

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    The route over the "threshold of Burgundy"from Laroche to Dijon is around 83 miles and contains long sections of 1:125 and is a part of the old PLM. It was one of the trial or testing grounds of the French railways a difficult and challenging route. The hand fired 4-8-0 out performed the PLM 4-8-2 241C1 when in competition on this line. The Pacifics when working on their home line between Paris and Toulouse faced a difficult 200 mile section over the southern 200 miles of this route which consisted of long sections at 1:100 and constant curvature. Here they could keep time with 500 ton express passenger trains. The French railways had a speed limit due to a decree of Napoleon lll which limited mechanical transport to a maximum speed of 75 mph. To maintain the 70 mph schedules between stops which were required in order to keep time the locomotives had to accelerate well and maintain speed. There was no climbing of the banks at 55 mph and then racing downhill at 85+ mph. These engines and their crews could maintain constant outputs, they had to. Martin Bayne posted some French gradient profiles, you can find them with an image search or look at his old website. these might give you some idea of what the crews faced. Sadly I know of no French equivalent to my Ian Allan Gradient profiles

    Some Chapelon compounds could exceed 12% efficiency and were capable of being significantly improved. In the years 1930 to 1960 the typical steam locomotive had an efficiency of some 6%.
     
  5. Jamessquared

    Jamessquared Nat Pres stalwart

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    If the locos were doing similar speed up banks as down, then by definition they were not operating at constant output. They were doing bursts at high power output, and then recovering at low output down the other side. (By contrast, slower speed up hill and then hell for leather down the other side is closer to a constant power output).

    So the answer to my question about how long those power outputs were sustained is not for long periods. You’ve described what is a well known capability of steam locomotives, which is to run at well beyond a sustainable power output for a few minutes by dropping the water level or running down the fire.

    For efficiency: my fag packet calculation of 2000hp off a 40 sq ft grate was based on 10% efficiency. If the French locos could go 12% then that number goes up to 2400hp for the same combustion rate. Each sq ft of grate is generating 24hp per pound of coal burnt per hour. So to get to 4000hp off 40 sq ft, you’ve got to get to 167lb of coal per sq ft per hour.

    That poses two problems. Firstly, to burn 167% as much coal, you need 167% more mass flow rate of air through the fire. How was that achieved without simply throwing the fire out of the chimney? If you drive the fire too hard, you don’t get increased power output, and I simply can’t see why a French loco should be able to cope with almost double the airflow as a British one and yet somehow still preserve its fire.

    Secondly there is the small consideration of the fireman: your numbers imply a firing rate of over 6,600lb of coal per hour on that size grate, or 3 tons per hour. I’d suggest that is physically unattainable.

    While those locomotives may have been capable of short periods of very high output, nothing you have said has convinced me that your oft-quoted figure of a sustained 4000hp on a 40 sq ft grate is remotely attainable. At best, a 12% thermal efficiency might get you up towards 2500hp.

    Tom
     
  6. RAB3L

    RAB3L Member

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    They would have been fitted with mechanical stokers.

    https://static1.squarespace.com/static/55e5ef3fe4b0d3b9ddaa5954/t/55e6373fe4b04afd122b821d/1441150783767/#+DOMS-1_Chapelon.pdf

    The 242A1 was capable of sustained drawbar horsepower in excess of 4,000 between 50 and 63mph. Compared to the remarkable S-1b “Niagara” class of the New York Central, not only was the drawbar power to grate area ratio 50% greater on the 242.A.1, but the horsepower to adhesive weight ratio was 30% greater.

    If ever there was case for recreating a lost locomotive, 242A1 would be it. I am not sure that there any drawings remaining though.
     
    Last edited: Nov 29, 2022
  7. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    A theme seen for many years, not just with enthusiasts. See: 1923, Wembley Empire Exhibition, 4472 Flying Scotsman versus Caerphilly Castle.
     
  8. Eightpot

    Eightpot Resident of Nat Pres Friend

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    Chapelon claimed that Fireman Marty on 4-8-0 3566 shovelled 4 tons of coal in an hour and refused assistance with other footplate duties. This equates to a ton every 15 minutes or 1 - 1/3 cwt every minute. I find this unbelievable when compared with BR reckoning that a British fireman could shovel only 1-1/2 ton of coal continuously, or 2 tons for one hour. See Colonel Rogers book on Chapelon, or Chapelon's own book for confirmation.
     
    Last edited: Nov 29, 2022
  9. 30854

    30854 Resident of Nat Pres

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    I'd be most interested in how (or if) the ergonomics which the two design schools threw up have any effect on the firemen's job. It can't all be down to the benefits of wine and garlic in the diet!
     
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  10. Eightpot

    Eightpot Resident of Nat Pres Friend

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    Perhaps they got the message from Popeye - eat spinach.
     
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  11. 240P15

    240P15 Well-Known Member

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    It`s amazing what you can achieve if you really want it:)
     
    Last edited: Nov 29, 2022
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  12. WD196

    WD196 New Member

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    O.T. but: Ergonomics? The French? They cared even less for ergonomics than the GWR ;-). The advent of the 141R must 've caused quite a shock with French footplate crews in showing that it is possible to have some level of comfort in the cab of a steam locomotive (cover from the elements, seats, lighting) and still get the job done.
     
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  13. RAB3L

    RAB3L Member

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    What are you comparing the 141Rs with? 19th century French steam? I am not too sure that you know much about French steam locomotives! The 141Rs required less maintenance than the equivalent French locomotives but they were nowhere near as efficient.
     
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  14. WD196

    WD196 New Member

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    I am comparing ergonomics, i am not talking about steam efficiency. And for the record, yes i do know quite a bit about French steam, do you?
    You go in the cab of a SNCF150P (built 1940 - 1950) , compare that to the contemporary 141R and tell me which one you would prefer?
     
  15. RAB3L

    RAB3L Member

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    No seats, no electric lighting?

    http://www.martynbane.co.uk/2003Trips/Brienzetc/museum3a.htm

    The 141R would win on weather protection but the cab wouldn't be appreciated in summer in the south of France!
     
    Last edited: Nov 29, 2022
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  16. Maunsell907

    Maunsell907 Member

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    I think the BR figures recognised lengthy non stop runs eg Euston Carlisle, Paddington Plymouth,
    the varying quality of coal and above all a conservative figure for the purposes of time tabling.

    Undoubtedly there were occasions when fireman shovelled above this rate ( Stoker Marty’s effort
    has long been regarded as the epitome ! ). Certainly much UK day to day performance in the 1930s
    required more. At times some performances were almost super human.

    There is a record in the 1939 Railway Gazette of A4 No.4490 ( not then fitted with a Kylchap
    exhaust) at the time of the Munich Crisis, taking three extra carriages on the ‘Flying Scotsman’.
    17/593/635 tons. Stops at Grantham, and York, intermittent schedules of 110, 83 and 90 minutes.
    Actual running times: 107 minutes 55 seconds, 84-55 (83 net) and 86.
    Typical of the work involved was an average EDHP of 1800-1900 for the 15 miles up to Stoke,
    a firing rate of. 5500-6000 lbs hr, obviously there were easier sections. It is fortunate that
    C.J.Allen was on board., He noted the tender was very low at Newcastle.
    Suggests at least 8 tons used i.e.with an average speed of 57.5mph c. 65lbs/ minute i.e.
    3900lbs/hr for four and a quarter hours ( and of course if nine tons was used then pro.rata .

    There have been many instances on both the WCML and S&C where high firing rates have
    been achieved with Preservation steam. Earlier this year a Merchant Navy ran at IHPs >2200
    from MP7.5 to Shap Summit, other than the easing through the Lune Gorge. This required
    c 2500 lbs of coal in a 23 minute duration. The calorific value of the coal is unknown and
    presumably the box was full at the beginning of the effort and perhaps the Inspector took a
    hand

    Certainly Driver Dalrymple and Fireman had no such help in 1938..

    Michael Rowe
     
    Last edited: Nov 29, 2022
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  17. 242A1

    242A1 Well-Known Member

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    And next to nobody wants to look at which of the locomotives involved in the Interchange Trials which shortly followed achieved the highest horsepower.
     
  18. 242A1

    242A1 Well-Known Member

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    Read " La Locomotive A Vapeur", it is readily available and has indicator diagrams, performance logs (which include gradient profiles) and much else. It is a little dated but it illustrates the direction of thinking at the time and if you read Porta's papers you can see how these ideas and some new ones developed. R H N Hardy's experiences on French Railways are also of interest. A sustained effort is just that, no dropping of water level or boiler pressure.

    2007 is going to be a P2 as it should have been built in the 1930s in terms of the chassis and valve gear development. It is still a bolted plate frame construction with conventional spoked wheels and, yes, the boiler is of welded construction. There is also a substantial quantity of electronic and electrical equipment on the engine but essentially it is a P2. Some "French" thinking is included in the design but only some. A compound version with a 300 psi boiler pressure and a more developed steam circuit would have been more interesting. The locomotive was from the British school of locomotive design with a little French thrown in. To understand how the French locomotive designers achieved what they did you have to understand how their thinking was different. If you approach their designs with a British mindset from the British school of locomotive design you will not understand what was done and how it was achieved. The same goes for looking at US practice though there are fewer language difficulties here.

    The 50 sq ft grate area on the P2 should not present much difficulty on regular duties so long as the exhaust system is optimised. This is another area where some fine tuning adjustments might be needed. The engine will not produce the outputs of a 231E, a 240P or a 141P. These all have a smaller grate area but the 4-8-0 and 2-8-2 have a mechanical stoker and could deliver 4,000 hp or more and though the P2 has been calculated to give 3,400 hp it is less efficient. A mechanical stoker might have been welcome here too but this machine will not be in daily use. We don't know what this engine might achieve and it always better to under promise and over deliver. Time will in due course reveal all.
     
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  19. 242A1

    242A1 Well-Known Member

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    I've been to Mulhouse and viewed a few other locomotives around France. They did things in their own way and though the cabs are different they are just as, if not more, fit for purpose than those inflicted on GW crews.
     
  20. Steve

    Steve Resident of Nat Pres Friend

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    Inflicted being the right word. :)
     

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