Well, the topic is LEMPOR EXHAUST NOZZLES, so that doesn't seem to be uninclusive of any experts contribution. I suppose Nigel's point is it seems to have started as being just about his way of applying it to one specific case study, and now other approaches on other cases are being voiced......I find that interesting and comparisons enlightening, but perhaps he feels his toes are being stepped on by a broader discussion. I'm sorry for us all that he has chosen to remove himself from the subject for now, he's done a lot of this work in many places and has a lot of valuable insight.

If we must we could start another thread, but it would reference this one since much is already posted here. Might make more sense for it to keep going if it can. If Michael would like to post more about how his approach is different and what the differences result in from a practical POV, I know that would interest many of us.

I find it very interesting tha Nigel said he did what Michael is doing 20 years ago and it didn't work for him, but it is working for Michael. I think perhaps they actually didn't do the same thing, and there's a lot of misunderstandsing going on, unless the design is different in smaller scale, in which case we ought to explore that, or if Canada has odd applications of the laws of physics which makes them culturally nicer than we are as well.

dave

When I first became interested in the Lempor exhaust, it was because finally (I thought at the time) someone had produced a way to design an exhaust system that wasn't a lot of obscure black magic - you could calculate the important bits. I was disappointed on two fronts, one was the unfortunate departure of Porta himself a year or so earlier and the fact that my maths skills were not up to the job of doing the calculations! This led to my collaboration with Richard Stuart who could do the math and the end result was the lempor calculator spreadsheet. Now it was finally possible for me to determine nozzle and throat dimensions with a few minutes work of entering data. Lots of different combinations of things could be entered to see what resulted without getting lost in hours of math work. After that it was fascinating to read Koopmans book and to correspond with him as I went through the process of designing and testing some nozzles and diffusers on a live steam loco in my driveway at home. This I wrote up and posted online, it forms a basic lempor cookbook of sorts.

In my opinion the best way to learn about lempor ejectors is to pick a known locomotive and go through the design process yourself as an academic exercise. Download a copy of the sheet and have at it.

Apologies to the group if it was my fault that Nigel went off in a huff. Again, if anyone has specific questions I will do my best to answer them.

Cheers,
Michael.

Dennis, if you are still reading this thread, the sketch shown on July 29th for measuring cylinder back pressure is incorrect. The pressure will be affected by the gas velocity (the gauge will read high) using a bent pitot tube like that. A simple side connection to the manifold is all that is required to get static pressure. See: http://en.wikipedia.org/wiki/Pitot_tube

Regards,
Michael.

Michael,

The pitot tube as shown is not really "incorrect" but it will measure velocity pressure, not static pressure. IIRC, Porta believed this was a useful number to have as it is the actual pressure available for work in the exhaust system. It will also show the effect of streamlining of the exhaust circuit between the valves and the exhaust stand (better streamlining = higher velocity pressure). A poorly streamlined steam circuit will actually show LOWER velocity pressure at this point than a more streamlined one.

All data can be useful as long as you know what it means and what to do with it.

And this is why we need more than one qualified contributor to this thread.

dave

Hugh, I am at work and at a disadvantage but take a look in Koopmans book page 95, reference 22.

- later.
Michael.

Hi ,
I am new here. Let me introduce myself. From about 1985 to 2005 I studied the available literature on 200 years of front-end research. I added some theory, previously unused, from standard text books on fluid dynamics like Fox and White and defended the combination to a couple of tough academic characters in the U.K. They really showed me all corners in scientific space. So I am quite familiar with the work of generations of locomotive engineers and it is up to you to form your opinion on my qualifications to join this thread.
If find the discussions fascinating, mostly because of its lack of unasked questions.
This thread is about a Fowler 0-6-0 tank locomotive built 1886. It has a firebox heating surface of 39.269 sq.ft and 115 tubes of 1.5 in.(38 mm) o.d and 8 ft(2.4 m) long . It was provided with an exhaust orifice of 2.835 in.(72 mm). First question: why 72 mm??
My small data base of heated surfaces and corresponding orifices shows me that for the combined heating surface of 409 sq.ft ( 38 m2) orifices were used in the 3 inch range. The probably inappropriate formula by Ell results in 99 mm(4 in.) and that of the German Nordmann gives 70.6 mm( 2.78 in.) so that the 72 mm orifice passes some scrutiny. Apart from that the length/diameter ratio of the tubes is 2500/31.4 or 79,6. The A/S ratio would be 1/(4*79.6). Quite a few locomotives have l/d ratios of about a 100 and the tube bundle appears to have a lower resistance than average. So, if the locomotive is not steaming there are other causes. On July 21st a picture is shown of the blast pipe with 2 holes of each 0,625 inch. To my surprise there is no further discussion. However, these holes were not visible at the backside of the blast pipe, so they were wasting steam against the direction of the flow of combustion gases into the smokebox if not plugged. Further calculation shows that these holes equal 10% of the orifice area, so that amount of steam is lost at the orifice. This results in a momentum which is reduced to 81% of the value needed and now has to eject also the 10% wasted steam in addition to the combustion gases. All of this contributes to a dysfunctional front-end.
Since we all agree that a Lempor is superior to a single orifice system, Dennis wanted a Lempor. Any sensible investigation would have assumed that an improved exhaust system would have resulted in an increased orifice area and a lowered back pressure. The equivalent diameter from the Lempor calculator of 75.65 mm (2.798 in.) appears to fulfill those expectations. However, Mr Nigel Day comes with an area of 4.75 sq.inches, 75% of the original area or 2.46 in. (62.5 mm) diameter and de Laval nozzles for the transsonic velocities he expects. Transsonic velocities and pressures were situations that generations of locomotive engineers avoided like the plague. I must say that I have very mixed feelings about such a power boosting solution for a heritage locomotive of 1886.

Regarding the discussion on diffuser(tapered stack) entry conditions, I would like to point out that all diffuser performance data are based on research with models. After all one has to prove only once that the data gathered are applicable to larger units. Note that the data books stress that fully developed flow should enter the diffuser. The textbook by Fox (Introduction to fluid dynamics, third edition page 368) even states “Diffuser pressure recovery with uniform inlet flow is somewhat better than that for fully developed inlet flow”. It is up to you to decide what to prefer, nozzles inclined towards the wall or inclined to cover the throat area in a uniform way.

As for the tube for the velocity/pressure measurement in the blast pipe, I value Porta’s opinion highly, however Bernouilli and Pitot higher. The single tube measures velocity pressure and static pressure together and as a consequence different combinations of these pressures could give identical readings. Front-end research has used static pressure only from a blunt orifice in the wall of the blast pipe. Additional information could be gained from a combination of the two tubes, it would be a Pitot instrument and would supply velocity pressure and static pressure separately by subtraction. One of the finer points would be that the curved tube would need a round tip, as it is it would give an extra stagnant pressure from the flat front of the tube.

Kind regards
Jos Koopmans

I have received a number of requests to for me to continue making posts in this thread about the Fowler and its Lempor but I am yet to be totaly conviced.

As the thread has come to an abrupt stop as the expert discution seams to have simply run out of steam I wish to 'Ask the Experts' the following questions.

MR Guy, From the work of Mr Wardale espeshaly re 3450 and shown in the Red Devil book what is page number and fig no showing the correct nozzle aiming point for lempor blast pipe nozzles thus setting the angle?

Mr Wardale in a private conversation with me was very adiment and discribed in detail the best way of testing for front end preformance. It was the way Porta did it and was the only way that all front ends could then be compered with limitted resorces. That is the reason why I posted that method. Is it thus I asume that you have used another method and thus you figures may or may not be comparatable to others?
If you have used a Pitot tube to measure the back pressure in your small loco I would be intrested how you got a comparativly large device into the comparitivly small exhaust pipe without afecting the exhuast flow and thus the reading it gives.

Mr Koopman, Since your thesis was published Mr Dave Wardale who in my opinion is the absolute master of the mathmatics of draughting made coments and corrections to the thesis which I understand where placed on The 5AT web site. (I dont know if they are still there.) Please would you tell us when a revised adition of the thesis is to be published including the above.

You question the method of obtaining the blast pipe size. Your method is related to the boiler serface but is it not that the blast pipe is conected to the cylinders that has more direct affect on the back pressure and mass flow of the exhaust steam? Please would you list the conciderations and fetures which are in the exhaust system which affect the blast pipes ability to breath and are of an antiquated design on this locomotive. As one of the items for concideration is the shape of the blast pipe orifice I am sure Mr Austin would give us a lecture on the 'coefficents of discharge through orifices'.

Please would you also tell me why I should state the obvious to Dennis an intelegent man with much experiance on steam about the bolt holes in the stand pipe needing blocking off? In any case one of them will be used for test gear.

As a further question open to all I am going to get a picture of a boiler posted. I would welcome every coment on it from what loco it came off where it is and what it was used for. It is wrongly stored at anagle and was never ment to be so in use.

What ever the Lempor for the Fowler is progressing well and Dennis is doing a good job in private.

I'm fairly definite it isn't a Yank boiler based on its overall massing, the removable steam dome, and the bottom of the front end as more noticable details. I notice the water inlet port is plugged - perhaps this was used in stationary service after being removed from the frame and running gear, or somebody stored it that way. Doesn't look as if the stack was covered for storage, though......and I wonder about the line with the valve with the LOOOOOONG rod running back from the front end towards the backhead. The shape of the stack is very interesting, though.....which is probably what resulted in its posting here.

Welcome back.

dave

It is not a yankie boiler, The boiler fittings are missing but nothing pluged off. I dont know what its off or even if it was built in the country it resides in. Thats what I want to know. Yes the front is significant and there was a specific use and reason for the long handle. Yes it is very relivent in a way to this thread.

It looks typical of Beyer Peacock

It could very well be B/P as the railway system in that country is very British in many respects.

Very interesting. Well, it has a narrow (Belpaire) firebox, so I'd guess it came off of something like a 4-6-0 or a 2-6-0, and that looks like the stack of a Lempor ejector. That's not the remains of Porta's project engine from Paraguay, is it?