Draughting arrangements for Bulleid Pacifics including the Giesl ejector

I would be alarmed if you did accept things in an unquestioning manner.

Drawing the gas flow through its path in the Smokebox absorbs part of the vacuum created by the exhaust system and compared with the exhaust steam flow this path is rather indirect. We can measure the vacuum at various points in the boiler system and so see where our precious vacuum is being used - or lost in the case of spark arresters - bringing about a serious rethink of either the design of arrester or exhaust system. Or failing that an acceptance of lower power output.

The strands of flow from the individual tubes are drawn together, some will turn far more than others (but I don't think that any execute a 180 degree turn). The gas flow from the tube bank area is expelled through a much smaller area in the mixing chamber (has it purely been accelerated?) How much impact the loss of momentum of the gas flow due to the path it takes has on the co flowing mixture in the ejector has we do not know. Is it important? We will not know unless we address the question.

As to people being slack in their applications and calculations. We are all victims of this on a regular basis. Welcome to a dark side of the human condition.

 

How about the "Double Ister", or "Double Star", as fitted to many of the MAV (Hungary) Class 424's (4-8-0)? When looking at an approaching loco, the exhaust is ejected at 45 degrees to the vertical - quite comical when the loco's working hard!

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Interesting, does it have a sloping front tubeplate to completely eliminate any kinks in the post tube gas flow....?
and here we start to wonder ponder the practicalities of other methods to mitigate this flow loss.
a transverse array of the required number and size of nozzles roughly a third of way up the smoke box and as far forward towards the smokebox door
end as poss would do it, would allow a very simple spark arrestor arrangement( but a bit awkward to empty) and you could probably get away with it on a spam- can to boot.
Seriously as the vacuum achievable with most 'advanced' systems is sufficient to liquify the firebed on a first gen arrangement and still deliver a low back pressure im not sure that the loss of energy in changing the direction and or slowing the firebox gases on entering the smokebox is a significant event other than it is a useful mechanism for shedding its particular load ?

 

Strange how the subject of a thread gets lost for a while...... Sometimes permanently.

We should be thankful for the work carried out on exhaust systems by those who have tried to produce improved designs, better theories and have worked hard to make use of material from other fields of research. Those good people that have worked to apply the results of the more enlightened ideas that have stemmed from the results of many man hours of academic toil by producing practical applications should also be saluted.

Though no theory may be perfect there have been numerous applications that show that locomotives can be substantially improved at little cost. Whether you choose to do so or not with respect to those machines for which you are responsible, well that is your choice.

The gas flow through the smokebox interests me. How does the flow behave throughout the whole range of combustion rates? The box on each class could exhibit its own flow patterns. Some designers favoured larger smokebox volumes though the DC fitted A4 appears to suffer no ill effects from having a relatively small volume. Spark arresters, self cleaning mechanisms both have an impact on the smokebox vacuum and this can be measured. The internal design of the box has an impact on the flow of gasses. You are wanting large diameter main steam pipes. There is all manner of other plumbing that can obstruct the gas flow. Does the resistance to gas flow plus the that offered by the flow route taken by the gas taken from the tubes to the mixing chamber entrance form a loss that might be major in the great scheme of draughting things? Are there any compression artefacts present in the gas flow under certain conditions? Does it matter?

 

Some interesting questions there 242A1. Mr Koopmans asked a question earlier upthread regarding the placing of the blastpipe orifices in a linear - i.e. front to back arrangement as in a Giesl, how about a layout where the orifices are tangential - as in side to side? Bear with me. Yes, sacrilege could well be a deserved accusation here and forget smoke lifting for this exercise, but, think about it, a Giesl or row of orifices that are in the same plane as the tubeplate and the flow of the gases from the tubes, would entrain the gases with less resistance than the existing arrangement. A 25NC in South Africa was modified in the early 80s with two Lempor exhausts and they were side by side, much in the way that I have described. I don't think that there was much in the way of testing of this locomotive, but, anecdotal evidence shows it to have performed better than a standard 25NC, which was probably inevitable given the superiority of a Lempor arrangement..

The semi-good news with what I have outlined is that a Giesl or other ejector arrangement arranged tangentially, would hardly show on a, ahem, unmodified Bulleid!! I'm ducking for cover here, but, as you have said, a good many man-hours have been spent on improving the designs of the front-end of the steam locomotive. It would be a great pity if some of this priceless research is forgotten and never applied, particularly today, as despite a relative feast of main line steam, things will surely get harder as time marches on.

cheers

Alan

 

another way of saying
'a transverse array of the required number and size of nozzles roughly a third of way up the smoke box and as far forward towards the smokebox door
end as poss would do it, would allow a very simple spark arrestor arrangement( but a bit awkward to empty) and you could probably get away with it on a spam- can to boot.'

There you go, two of us think its a good idea, think we should take out a patent (Raglado ejector ?)

 

Surely the long thin "curtain" of steam entrains flue gasses on both sides, so turning the "curtain" sideways would only present one side to the tubeplate, whereas the for-aft alignment allows both sides to work evenly.

 

The volume of a smokebox and its contents is relatively uninportant. It acts as a soothing chamber with small velocities.
Around the early 1900's there was a suggestion for large smokeboxes and some were even extended in the USA. It did
not work and the suggestion was withdrawn and smokeboxes shortened.
My point about the gas flow in the smokebox is that in a Lempor the orifice is as low as possible and the chimney entrance
at the same level! As a consequence the flow from the tubes/flues has to be downwards, to be reversed near the orifices and
inhaled by the chimney. Since the Lempor equation has a component for the momentum contribution of the gases, next to that of the exhaust steam, I am merely questioning the wisdom of that.
As for compression, since the Giesl throat is too narrow, there must be some compression!

Regarding a transverse Giesl type, another Austrian by the name of Golsdorf, tried that from 1915 and BBo 80.990 ran with
it for a couple of years. It was not repeated which tells it all!
(NB both Gols- and BBo should have an "umlaut", double dots on top)
Kind regards
Jos Koopmans

 

The entrance to the mixing chamber has to be as low as possible to allow for the necessity of making the best use of the height available in order to incorporate the best ejector design.
Yes this does mean that the gas flow from the tubes makes quite a tight turn.
It would perhaps be advantageous to have an exhaust system that had a series of entrainment levels so that the gases from the superheater tubes took a similar shape of flow path to that of the gases from the lower levels of smoke tubes. Gets back to Chapelon's intentions with the Kylchap exhaust.
ET was a proponent of the large smokebox school. Strange that he was so far out of date. His predecessor on the other hand, his engines had modest smokeboxes.
If the Lempor theory allowance comfortably accounts for the peculiarities of gas flow within the smokebox it is perhaps more important to make sure that there is no slack application of the Theory. If there are some aspects that need further measurement and analysis well and good. But that is no reason not to apply the knowledge as it currently stands whilst those who want to enhance exhaust system theory are aided in doing so by granting them access to the results of ever improving applications both in numbers and in performance.

 

Go

Good point Lplus, there is the possibility of losing one side of the blast, so to speak. However, such thinking is not going to get the newfangled Raglado Ejector (thanks for that one class8mikado) accepted for installation on all overhauled locos in future.

Of course, each Raglado Ejector will be fitted with it's own builder's plate; now what shape and colour should it be.....................

Cheers

Alan

 

Make me an offer, I am slightly fed up with these armchair discussions!
Kind regards
Jos Koopmans

 

I think I have said on here before that this is one area where the engineers should look to motorsport. Over the last 40-50 years many millions have been spent optimising bell mouths and their immediate relationship to the box that surrounds them and how the pulsed gasses change direction entering it. Rules of thumb for this are well understood by the experts although empirical testing of slightly different profiles is still used to gain the last couple of per cent of efficient flow. From what little I know on this subject, even steam loco's that are of an improved design seem to often use a very basic bell mouth shape into the mixing chamber so there must be opportunity for further improvement. Designing an exhaust where the bell mouth profile could be swapped or its height raised and lowered slightly to measure its effect on smoke box vacuum or flow would not be difficult as it is a simple cheap'ish component. I guess though that would be another variable in what is already a complicated relationship between the various exhaust components so could never be fully exploited to its ultimate without a full test rig.

 

There must be a difference between a low volume high velocity resonant motorcycle exhaust system and that of
a high volume low velocity steam locomotive exhaust. As for the bell mouth, shapes and distances have been tested
from Goss in the 1890's onwards. I cannot image how to add something useful in 2014/2015.
Kind regards
Jos Koopmans

 

A few weeks ago there was a proposal for a 'National Preservation' locomotive, which ultimately came to nothing. Would there be an appetite for something a little less ambitious (and costly), namely for the Nat Pres community to jointly sponsor such modifications? What would it cost, and are there enough people on the forum who are sufficiently curious in seeing how a modern, well designed front end would get on against the original design and the Giesl, to chip in a few quid? I know I might be interested.

 

I'm sure we at the 5AT group would be interested in becoming involved with such an initiative should it gain traction. We have up-to-date costings for the Lempor we designed for the S160 at the KWVR, and are currently looking at the implications of applying a Lempor to a 3 cyl loco - something that hasn't been done historically to our knowledge. I'll keep a watching brief on this for further developments. Good luck!

 

Seconded! I asked for a quote a couple of days ago, as I like to know where I step into. But know-how would be greatly served
if something serious could be tried 60 years after S.O.Ell.
Kind regards
Jos Koopmans

 

With all due respect I think the ball is in your court as far as making offers is concerned. If you are prepared to fund the cost of the modifications, the trial running, loss of income during the conversion and reversion to original form if the modifications prove not worthwhile then we could possibly start talking. A very detailed proposal will be needed before anything can be considered.

 

A detailed proposal is no problem, but I am not aware of your local fabrication costs. It is volunteer work or outsourced,
cost of coal and the like. I am sure that any test train will attract customers, so not really a problem there. Reversion to
the original if needed is a condition sine qua non and any Bulleid Lemaitre would be of great advantage given the size
of the smokebox hole. On the 92squadron website I saw the castings for the new lemaitre orifices and a new chimney,
price?
If the modifications prove to be worthwhile do I get a fair addition to my pension from your coal/water savings?
Kind regards
Jos Koopmans

 

We won't be getting any coal and water savings as the host railway pays those bills so you would need to talk to them regarding any additions to your pension.. The new chimney was fabricated by our own work force. The new Lemaitre blast pipe cap has yet to be cast owing to a problem with the pattern. The old one has been cleaned up just in case we need it before the new one is available. The new casting will be outsourced.
At the end of the day we are very happy with the loco as she is and whilst there will be interest in how modifications would affect her performance, the fact she is not a main line loco will mean she'll never have to work hard for a living so how effective any trials would be is open to question.