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Draughting arrangements for Bulleid Pacifics including the Giesl ejector

Discussion in 'Steam Traction' started by jamesd, Oct 14, 2014.

  1. Nigel Day

    Nigel Day Member

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    Below is a graph of tests of FR draughting test done in the 1980’s. There is other types as a comparison.

    The comment of 242A1 and the Bure valley plus other instances of doing a full package of improvements I highly recommend.
    3BA27795-CB25-45A8-86C8-7C0863BC2B94.jpeg
     
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  2. Allegheny

    Allegheny Member

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    This graph shoes the "pressure lift ratio" which is the relationship between smokebox vacuum and blastpipe pressure. The graphs attached to post #184 show the "entrainment ratio", which is the relationship between the mass of smokebox gas and exhaust steam.
    A good design should do well on both measurements. Normally if you reduce the nozzle diameter, (without changing anything else) you would improve the entrainment ratio, but make the pressure lift ratio worse. (or vice versa).
     
  3. srapley

    srapley New Member

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    For those that might be following this thread (I appreciate the last comment on here was over a year ago) I have been leading some CFD analysis of the exhaust of an original/unrebuilt Merchant Navy, looking at design modifications for improving the locomotives exhaust performance, both in terms of draughting and exhaust clearance. Check out this webpage for a start https://35011gsn.co.uk/Technical an...versity-projects/loughborough-university.html
     
  4. class8mikado

    class8mikado Part of the furniture

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    Interested as to what Rapley Giesl lampor is. Since Lempor is is an abbreviation of Lemaitre-Porta its difficult to see how thats on the same 'page' as Giesl.

    All these different 'propiatry' arrangements work in similar fashion - creating a facsimile of several smaller chimneys with an ideal system height in place of a single large one which cannot be tall enough in the available space to work as effectively. All them work if , whether by formula or happy coincidence the individual components are of the right geometry and size both in relationship to one another and the loco. in question. The trick is coming up with the right dimensions for the solution required both in terms of minimum back pressure, efficient creation of vacuum and the third side of the triangle sufficient energy allowed to be wasted for the purpose of smoke lifting.

    To say that different systems are to be tested in simulation will not tell you anything about the efficacy of either system, only that of the examples you have chosen to simulate. the effort might be better directed by choosing a particular system and simulating different configurations towards achieving the best compromise of the the three desired outcomes. There is plenty of field data and available Formulae for Lem-Por, some for the Koopmans CF Lemaitre. Not sure if there is anyone left who professes to be qualified in configuring a Giesl...
     
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  5. Allegheny

    Allegheny Member

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    Were there any examples where the Giesl was "configured correctly"?
    My impression of the Giesl is that it was more a case of sales hype over substance.
     
  6. Sheff

    Sheff Resident of Nat Pres

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    You could well be right. The ‘tunability’ element - a sliding shutter - could only serve to increase back pressure and so reduce cylinder efficiency if closed by any amount.
     
  7. 242A1

    242A1 Well-Known Member

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    It appears that it was impossible to fully optimise the Giesl ejector. D Wardale devotes some time to this device in his book and the Comparison of Exhaust System Curves which covers from the BR Standard Class 7 plain up to the SAR Modified 19D No. 2644 is worth a few moments of your time. There are Giesl fitted types and Kylchap fitted types shown: there is also one Lemaitre fitted type, and yes, it is the BR Merchant Navy Class. I will let people who are responsible for, or who are admirers of, these machines have a look at Fig. 34 in the book in question and make their observations.
     
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  8. class8mikado

    class8mikado Part of the furniture

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    Indeed, and in spite of this they are very capable locomotives with impressive steam output - the potential to retain or improve this performance and at the same time create a more forceful blast to improve smoke clearance is entirely possible - even with a Giesl (34092)
    Think most agree that a w/c /bb is also a remarkable locomotive for its size, and the Giesl on City of Wells adds just a bit extra in general performance and the required 'volcanic activity', IIRC its installation was supervised by the Doctor himself.

    There are people out there today who can make a very good stab at the correct configuration for a multi nozzle exhaust system given some decent data from a locomotive, and the fine tuning /bias towards the three outcomes arrived at by using interchangeable nozzles and a very easy to fit smokebox sensor - but its the 'geometry' not the brand thats the key.
     
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  9. 242A1

    242A1 Well-Known Member

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    The 'volcanic activity' as you describe it is most definitely not required particularly in the present times. It could be argued that it was never either wanted or required; it only existed because of misplaced thinking or rather non existent thinking. We have to be aware that we are under scrutiny and act accordingly remembering that the world today is beholden to very loud and influential minorities who frequently have populist sound bites at their fingertips as opposed to a broad spread of knowledge, understanding and appreciation. Cancellation is very much the order of the day and any group or individual could be next. So poor exhaust and combustion system are simply unacceptable for day to day use.
     
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  10. Sheff

    Sheff Resident of Nat Pres

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    +1.
     
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  11. Richard Roper

    Richard Roper Well-Known Member

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    +2
     
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  12. Allegheny

    Allegheny Member

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    I think it depends on how you interpret "volcanic activity". If you mean generating large volumes of clagg, then indeed it would be unacceptable. If you mean generating sufficient draught to steam the boiler under all reasonable conditions and blow the exhaust clear so that it doesn't obscure the drivers vision, then I would agree.
     
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  13. 30854

    30854 Resident of Nat Pres

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    I'd interpret it as "the crap so beloved of many photographic types solid particulates in the exhaust which knacker the comparatively delicate moving parts of a Giesl ejector" .... and do nothing for coal consumption figures either!
     
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  14. Jamessquared

    Jamessquared Nat Pres stalwart

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    Just for clarity, there are two different things here. The "crap so beloved of many photographic types" is actually soot from partially burnt volatile components of the coal. That should be an absolute no-no in today's climate, but by and large is controllable by the fireman. Indeed, controlling smoke has been a feature of legislation and training right back to the earliest days of railways - think of the stipulation in the Rainhill Trials for locomotives to "effectively consume their own smoke".

    The "solid particulates in the exhaust" is slightly different: it is caused by small amounts of coal being lifted off the grate by the draft and swept through to the smokebox - whether they then emerge in the exhaust or are collected in the smokebox depends on various factors of smokebox design. They are less controllable: inherently, if you work a locomotive hard, eventually you get to a point where the boiler efficiency goes down because the draught is so fierce that large amounts of coal get swept through the tubes without burning. The only real solution is to work the loco less hard or, if the traffic demands, use a bigger loco. (It is one reason why for a given demand, a loco that is a bit too big will be more efficient than one that is a bit too small - the word "bit" being important in there).

    Tom
     
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  15. Richard Roper

    Richard Roper Well-Known Member

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    I well remember 34092 - The Volcano - on the S&C in the early '80s before it was Giesl-fitted... And many other Locos too - which were routinely producing clag for runpasts or special lineside requests which would have given Mount St. Helens a run for its money. Even as a kid back then, I couldn't understand the need for the blackout - My Dad had already trained me well with maintaining the coal fire at home. I remember my Dad and I taking photos of 5407 one time at Blea Moor, and as he remarked when we got our slides back "It looked like it was coming out of a Middle Eastern oilfield fire". You couldn't see any background whatsoever, just a full-frame of blackness with some added steam around the Loco!

    Richard.
     
  16. srapley

    srapley New Member

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    To answer some of the recent posts mine stimulated: the name of the exhausts (Lempor/Giesl/Lemaitre) I've used is to give the reader an idea/image to latch onto, the only design we simulated that is true to it's namesake is the Bulleid-Lemaitre. The Lempors we simulated are much squatter than the ideal in order to have the same diameter outlet as the original design, and it has 5 nozzles instead of 4, to allow easier comparison and to partially overcome the height problem. Additionally the nozzles are pointed towards the centre of area at the diffuser exit of the segment that they reside in. The Giesl started off as a single nozzle ejector with a long shallow diffuser, which was then sliced down it's axis and stretched to make an oblong, it has 7 nozzles with each nozzle feeding an equal diffuser exit area. Further details will be given in "The Packet" issue 16 (issue 15 is being written now and provides details of the external aerodynamics study) which is available for free to members of the 35011 GSNLRS. My aim with any potential change to the draughting of GSN is can we introduce something that either improves the power or efficiency (or both) of our locomotive without altering the aesthetic of our machine, whilst being mindful on the impact it may have on exhaust clearance? Or conversely can we make a change to the exhaust that improves the exhaust clearance without reducing the power or efficiency? The black smoke from 34092 could well be a sign that it was draughting too well I guess...
    Steve
     
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  17. 30854

    30854 Resident of Nat Pres

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    The 'claggiest' locos I've experienced first hand have been (30)120, during it's stint on the MHR and K&ESR's charming old MW Charwelton, mind you, it's impossible not to work a loco hard on either the MHR or up Tenterden Bank! The pyrotechnics displayed during 34092's first Giesl-equipped mainline sorties were of a different order of magnitude and there are very many images of it's Vesuvius impressions back then.
     
  18. srapley

    srapley New Member

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    Was '64 Fighter Command as "claggy" once it had a Giesl fitted?
     
  19. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    I'm slightly at a loss to understand this 'clag' business with CoW and the implication that the ejector either helps or hinders smoke effects.

    I'm not a fireman so I won't get into technicalities but if you look at this video on the S&C (start at 1 minute in) under what is clearly a loaded set of circumstances, you can see what the exhaust is like when the loco is being fired and not being fired. In both situations the exhaust is being lifted clear of the locomotive far more than would have been the case with a conventional unrebuilt light pacific. That's the bonus of a Giesel.

     
  20. JJG Koopmans

    JJG Koopmans Member

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    I am tempted to reply since in August 2015 I gave a lecture in Swanage of which one of the slides is attached:
    Regards
    Jos
     

    Attached Files:

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