US Boiler Design and Combustion Chambers

I'm working on a piece about Churchward's pacific, and one doesn't get far into that topic without considering Churchwards's paper "Large Locomotive Boilers", read the previous year. This paper is basically a survey of the then state of the art, including examples from various British lines, Canada, France, but most especially US practice.

Studying the paper for my purpose, one thing that struck me was that there was no mention of combustion chambers, and none of the examples that Churchward featured had one. This surprised me, because the 'Kruger' class built under Churchward's direction in 1899-1903 had featured one, albeit apparently unsuccessfully. We know of course that the combustion chamber was a feature of pretty much all later successful Pacifics in the UK.

So that got me thinking, what was the state of the art with combustion chambers in the UK? Consulting Ahrons' "The British Steam Locomotive" it seems to be one of those things that was tried and abandoned a number of times in the 19thC. Another reference had it that they were found in US practice at the time, and certainly later US design incorporated very substantial combustion chambers.

So does anyone here know much about US design at this period? Or can point me at a good US forum where they discuss this sort of technical information? I went hunting but didn't find anything that didn't seem to be either entry level or discussing games.

 

The attached is from Alfred Bruce's "The Steam Locomotive in America". He notes that combustion chambers were generally adopted by 1916.. "to obtain a practical tube length" for the longer boilers then in use.

 

Are you aware of Locomotive Cyclopedia?

 

Excellent. Found it on line. The 1905 and 1909 editions (called American Master Mechanics Dictionary at that date) states the combustion chamber is "not commonly used", but the 1912 edition says "The combustion chamber is used extensively on Mallet locomotives with long boilers". Thank you.

 

A late American friend had an almost full set...his widow offered me them, but it meant getting them back to the UK. I perused one or two...fabulous reading. Glad I could help.

 

1905 https://babel.hathitrust.org/cgi/pt?id=chi.12086918
1906 https://babel.hathitrust.org/cgi/pt?id=mdp.39015021799567
1909 https://babel.hathitrust.org/cgi/pt?id=mdp.39015021799575
1916 https://babel.hathitrust.org/cgi/pt?id=chi.098469222
1922 https://babel.hathitrust.org/cgi/pt?id=chi.098469345

 

Google "Edward C Poultry steam". He's mentioned in Graces Guide and has commented in books about boiler design.

 

Looking at the 1905 edition. How embarrassing: one of Mr Drummond's Gobblers on page 505. And a section of the weird and wonderful water tube boiler fitted to one of the Grasshoppers on page 517 (I knew that DD tried to get the Yanks interested, but I never guessed that they would go so far!).
Pat

 

So looks like combustion chamber boilers gradually came into general use in USA between 1900 & 1920 as a response to the arrival of much larger locomotives, particularly the Mallets but possibly also 4-8-2s and 2-10-2s?

An issue with Mallets was the overhang of the boiler at the front end, leading to some curious "flexible boiler" designs. J T van Riemsdijk ("Compound Locomotives") describes a Santa Fe 2-6-6-2:

"These boilers had relatively short tubes leading to a tube plate roughly above the pivot between the two sets of running mechanism. A forward portion of boiler contained a matching set of tubes between its own tube plates, the front one of which was the true smokebox tube plate. The two portions of the boiler were joined by a metallic bellows which made it possible to attach the front part to the front motion framing."

More info here:

https://www.steamlocomotive.com/locobase.php?country=USA&wheel=2-6-6-2&railroad=atsf#13787

It was some time later before combustion chamber boilers became common in Europe. I don't think any of the pre-1914 European Pacific designs featured combustion chambers. In some cases , the front tube plate was set well back, keeping the barrel and tube length fairly short (17ft 3in in the case of the Bavarian S3/6). The Belgian Type 10 took this approach to an extreme, with the smokebox behind the bogie:

https://en.wikipedia.org/wiki/SNCB_Type_10

Gresley's A1 of 1922 may have been the first European Pacific design to have a combustion chamber boiler, but I'm open to correction if anyone knows different. Gresley's design is said to have been influenced by the Pennsylvania RR Class K4 design of 1914.

One final snippet about European pre-1914 Pacific designs. They all, like Great Bear, had 4 cylinders, albeit a mix of simple and compound.

 

It took me a while to find those pages. Printed page 505 is 613 of the digital copy, and 517 is 624.

 

This is all interesting stuff, and tending to change my thinking. One of the things that comes out loud and clear from Churchward's Large locomotive Boilers paper is a considerable concern for leaking tubes, which he considers to be a bigger problem in wide firebox boilers due t proximity of the fire. Combustion chambers weren't a new idea, and had been tried intermittently in the 19thC, especially, I think, around the coke to coal era.

[Continued in the Bear Thread : https://www.national-preservation.c...t-bear-and-surrounding-controversies.1420223/]

 

I wonder how effective some of them were in their stated purpose. I've seen various diagrams of Beattie locos (a noted exponent of coal burning trials); in one arrangement, there is a short nest of tubes (probably about a foot long) from the firebox to an intermediate combustion chamber; then the tube nest-proper through to the front tube plate. The difficulty of such an arrangement (apart from construction, maintenance etc!) is that the gases get cooled so much as to be below the ignition point on reaching the combustion chamber: in other words, if they haven't fully combusted in the firebox or first foot of tubes, why will they do so in the combustion chamber?

A later iteration is on the LNWR "Greater Britain" class by Webb. This comes from much later than the coal / coke burning trials era. The boiler design was said to have a "combustion chamber" though I am very dubious that it worked as such. (In GWR terms, the "Greater Britain" predated the "Krugers" by eight years). OS Nock described it thus:

But the salient characteristic of the engine was that extraordinary boiler. The grate area was the same as the "Dreadnoughts" and "Teutonics", 20 sq. ft.; but the tube heating surface, totalling 1,348 sq. ft. (against 1,242,4 sq ft. in the "Dreadnoughts") was made up in two sections: from the firebox tubes there was first a nest of 156 tubes 5 ft. 10in. long, leading into an intermediate combustion chamber, which afforded a further 39 sq. ft. of heating surface, and from this chamber there extended a further nest of 156 tubes 10 ft. 1 in. long to the smokebox tube plate. The total heating surface was 1,505.7 sq. ft. against a total of 1,361 in the earlier engines. Webb needed enhanced boiler capacity, and as, presumably, he was not at that time allowed to exceed the previous maximum load of 15 1/2 tons per axle, the boiler had to be made long, so as to distribute the weight. In view of the great length of tube compared with that of previous engines the tubes were 2 1/8 in. outside diameter, instead of 1 7/8 in., to afford a better draught. The combustion chamber was stated to have the effect of arresting the gases as they pass from the firebox, thus securing more perfect combustion. Whether any benefits were obtained in this way is a very doubtful point; what is more likely is that the presence of the intermediate combustion chamber sadly interfered with the draught.

(My emphasis)
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I tend to agree with Nock; to which I'd also add one wonders how Webb felt he would achieve more boiler power from the same grate area. Ultimately boiler power comes back to how much coal you can burn, and once you have the draught sorted, that in turn comes back to grate area. Of course, there is more to boiler design than that, but if you want more sustained power, just lengthening the tubes isn't going to do it.

(The projection on the bottom of the combustion chamber was apparently to enable removal of ashes. Whether it also admitted supplementary air I do not know).



Tom

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The USRA standard locomotive range perhaps gives a snapshot of typical USA design practice as it was around 1918.

https://en.wikipedia.org/wiki/USRA_standard

Looking at the photos, it appears that the 4-8-2 and 2-10-2 classes had combustion chamber boilers (the entry for the Heavy 2-10-2 includes a diagram). But I'm not sure that the USRA 4-6-2 and 2-8-2 boilers had that feature.

 

I've not read any of the various papers referenced above but I would doubt that the GWR would have any need for a combustion chamber in their boilers. A combustion chamber is provided to allow for complete combustion of the volatile gases produced by the fire. These are the the flames that we see in a fire and As Tom has intimated, once the gases enter the tubes any combustion will cease. It is the same principle as found in a miners safety lamp. The gases need time to burn and the distance between firebed and tubeplate is critical in this respect. With a straight throatplate boiler there is little distance between the firebed and the tubes so a combustion chamber would be an advantage. However, with the invention of the brick arch this advantage largely disappeared. With a narrow firebox boiler, the flame path around and over the brick arch is generally sufficiently long to provide the necessary distance and time for combustion to take place. With a wide firebox, the length of the grate is much shorter and thus, so is the length of brick arch and the length of the flame path is reduced so a combustion chamber is generally necessary.
An additional point to consider is the length of flame produced by the coal. This is one of the variables that you get with coal and is related to the amount of volatiles. Welsh coals were generally considered to be short flame coals, unlike the long flame coals of Yorkshire and the Midlands, and, as the GWR generally used the former, there would be little need for a combustion chamber.

 

In what lovely book do You have this Webb 2-4-2 drawing ?ISBN or to early?

 

Not my book - a Facebook find, apparently from "International Railway Congress fifth session London : June-July 1895. Proceedings volume II."

Tom

 

A Bill Baily, a kingdom for a Bill Baily drawing of same quality.



A gentleman Peter Davis has promised to publish a book of fourcylindered Compound Webbs.
Has that happened yet?

 

I don't know but my wife has bought me the book covering the three-cylinder Compounds. It's currently all wrapped up under the tree so I have to wait a few more days.

 

The mice might get there first....

 

They'd have to get past the cat first!