What would the “perfect” IMLEC competitor model be like?

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What would the “perfect” IMLEC competitor model be like?

This topic has 5 replies, 3 voices, and was last updated 14 November 2011 at 14:23 by Alf Jones.

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14 November 2011 at 09:31 #77815
Alf Jones
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@alfjones33318
Hello all.

I was reading the history of the IMLEC competition:

http://tinyurl.com/bsc3h2n

and I found it fascinating. The quote at the start appeals to me a lot. True experimental engineering.

Reading recent ME’s, it seems that absolute scale isn’t so much a requirement – as long as it looks and acts fairly like a train.

So I was wondering what the result would be if a person, or group of people, set out to design a train purely with IMLEC efficiency in mind. Would it look like an existing train? I’m assuming that, just like anything else in the world of engineering, loco’s were designed with a mixture of opposing challenges in mind? So I would assume that none of the existing model designs – the LBSC type – would be focused entirely on efficiency, as opposed to top speed or other factors.

What are the key components in the design of a strong, highly efficient loco? Is it the boiler design? The power train? The weight of the loco?

Are there absolutes in this question? Would it be reasonable to say something like “A good competitor would always use (for example) Stephenson valve gear, and would never use Joy valve gear?” or would this type of decision be based on a number of other factors?
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14 November 2011 at 09:31 #1049
Alf Jones
Participant
@alfjones33318
IMLEC efficiency questions
14 November 2011 at 10:00 #77817
Richard Parsons
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@richardparsons61721
The primary problem for an ILMEC locomotive was stated In part 10 of his constructional article for the ‘Fair Rosamund’[i] by the late Mr Neville Evans with his remark that:-

“The efficiency of the boiler counts for more than that of the cylinders because the combined efficiency is based on that of the boiler, times the cylinder efficiency, expressed as a percentage. In other words’ if the boiler efficiency is 70% and the cylinder efficiency is 10%’ then the total efficiency is 7%’ lf the boiler efficiency is 55% and the cylinder efficiency is 11% then the total efficiency is 6%”.

Mr Evans then wrote “No less a person than André Chapelon ‘to whom we doff our caps’ stated that most of the heat from the fire that passed into the water was through direct radiation, in other words through the firebox. In his opinion (M. Chapelon’s), the main reason for the fire tubes was to carry the products of combustion ‘along with the used up drafting air’ forward to the blast pipe’. From here it was ejected, together with the spent steam, to create a vacuum which draws air through the furnace. He (M. Chapelon) showed that the heating surface contained in the fire tubes contributed little to the boiler’s capacity for raising steam.” This is supported by the work of Mr K.N.Harris where he states the criteria for a successful boiler is to make the fire box as big as possible.

This comes from an un-submitted paper by YH called “Mulling about Boilers”. In it I discuss the very problem of redesigning the model boiler used on our locomotive. These boilers originated in the 1920s and were mostly the Work of LBSC

For an ILMEC locomotive I would look carefully at the boiler design (in particular the Fire box where according to Mr Chapelon 90-95% of the heat transfer occurs and the drafting mechanism which gets the steam out of the cylinders. As the great G.J. Churchward, said that “Any fool can get steam into the cylinder the trick is to get it out afterwards”. This is what the drafting system must do.

To summarise the “Boiler is the Heart of the Locomotive”. We need to rethink this

[i] Model Engineer Vol 204 No 4376 – 23^rd April – 6May 2010
14 November 2011 at 12:35 #77824
Alf Jones
Participant
@alfjones33318
Richard,

Do those idea’s apply only to firetubes, or to water tubes as well?

I believe I have read that the stroke rate of a cylinder, if it was designed for absolute efficiency, should either be significantly slower ( in the 10’s of strokes per minute ) or significantly faster, in the 000’s of strokes a minute, and that the middle ground inhabited by Loco’s is a poor choice. I have read this in at least two different places now, but can’t currently find either one….

Is there any truth in that? It would suggest some type of gearing would be needed, which have never ( to the best of my knowledge ) ever existed on a full sized train.

I was also thinking about the drafting of a boiler. As I understand it, IMLEC is all about efficiency. Strong drafting of a boiler will certainly get the fire burning hotter, but also – I suspect – lead to a lot more heat disappearing up the chimmney. In my car, the engine designers have looked to eek out ever watt of power from the fuel in the name of efficiency, even to the point of re-burning some of the exhaust gases ( although this also helps with emissions ).

Would I be right in thinking that, if looked at purely in terms of efficiency – how much power can come out of a fixed amount of coal and turned into rotational work on a track – then there would be a careful balance to strike between too little draft and too much?
14 November 2011 at 13:39 #77827
Joseph Ramon
Participant
@josephramon28170
I suspect that a much more efficient system could be set up with some clever non-standard trickery, especially if the whole thing was under microprocessor control. This could allow the boiler to work on a much wider pressure range – run the fire hard and build up a lot of pressure, then damp it down and run on stored heat for a while. Monitor the smokebox temperature to detect if and when heat is being wasted up the chimney.

Use electrically operated poppet valves for steam admission and exhaust , so you dynamically adjust the timing and cut-off to give smooth efficient running despite varying pressure. Cut off the steam supply completely when ‘coasting’, or just allow through a small amount to keep the cylinders warm and the fire in.

I reckon a 50% increase in efficiency could be achieved this way with models, much less at full size.

Joey
14 November 2011 at 14:23 #77828
Alf Jones
Participant
@alfjones33318
Thanks Mr Ramon – some good idea’s.

a 50% increase in efficiency would only leave something like a 2.5% efficient Loco – I think full size work at around 7%?
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