The Locomotive Boiler

[Overmod]

timz

"On locomotives with type E superheaters the smokebox gases are from 100 to 150 degrees lower than the steam temperature."

Two things:

First, on its face, that the gas temperature measured all the way forward of the front tubesheet, presumably at a location where the combustion gas is about to pass through the cinder screens (where present) and then be entrained in the exhaust steam is lower than the steam temperature measured at the superheater header.

Second, that a type E element is a multiple-pass heater with a significant proportion of its area back toward the firebox, and two of the passes are countercurrent, so there is a significant amount of heat transfer to the steam before the fourth-power lolog heat transfer through the walls of the tubes and flues has lowered the average gas temperature.

Note that the gas temperature is still very high at the indicated "100 to 150F" -- with superheat temperature at the peak of the range the English accepted as advisable with piston-valve lubrication, about 835F, that is a great mass of gas well above the ignition point of many substances.  That is the heat that an economizing system like Franco-Crosti can recover... and even there, the exhaust temperature was frequently kept safely over the 'dew point of sulfuric acid' to preclude corrosion.

[Erik_Mag]

I was amused to read the description of the Velox boiler, namely it involved a compressor driven by an exhaust gas turbine. In other words, a turbocharged steam locomotive.

The timing of the article was interesting for a couple of reasons, one being after start of hostilities in Europe and also shortly after the devlopment of general purpose diesel locomotives. OTOH, the author noted that proven oil reserves at that time were equal to ~15 years at the current production. Hence the emphasis on non-petroleum fuel sources.

[timz]

Toward the bottom of page 387:

"On locomotives with type E superheaters the smokebox gases are from 100 to 150 degrees lower than the steam temperature."

What does that mean?

[L-105]

Here is a link to a very informative piece by C. A. Brandt entitled "The Locomotive Boiler" published in the American Society of Mechanical Engineers July, 1940 Vol 62 No.5

https://cybra.lodz.pl/Content/6095/Trans_vol.62_no.5_1940.pdf

 

It is the second article, starting from 379.

The first section by E. G.Bailey is also about steam boiler performance but mainly covers marine/stationary watertube boilers along with diagrams and detailed test data including large ones with grate/furnace areas in excess of 300-400+ sq ft.

The section entitled "The Locomotive Boiler" by C. A. Brandt discusses locomotive boiler design and proportions. Among the things discussed, the importance of maximum boiler diameter is particularly emphasized, or as C. A. Brandt puts it:

"In the past either the heating surface or the grate area has been the basis on which the size of the other component parts of the boiler has been determined. This is not the most logical prodecure as the dimensions of these parts do not control the limit of size to which the boiler can be built, since they may be increased with the length of the boiler within considerable limits. The diameter and gas area through the boiler constitute the limiting factors because the height, width, and weight are fixed and cannot be exceeded" 

and:

"The capacity of the locomotive boiler is limited by its diameter because this determines the gas area of the flues through which all the gases of combustion must pass"

Also, the maximum boiler diameter doesn't just determine the amount of flues and tubes you can fit in the barrel, it also influences the height and width of the combustion chamber (if the boiler has one) as well as the height and width of the upper portion of the firebox itself, thereby having an affect on firebox volume and heating surface. 

Detailed boiler stats of many prominent locomotives built up to 1940 are also given.

The Great Northern R-2 is an odd one out, as the boiler O.D. large course is given as 111.125", which contradicts the more commonly seen figure of 109" as given in the R-2 diagram. I suspect that for some odd reason, only the inside diameter of the R-2 is given in the diagram and that when you add up the sheet thickness of 1 1/16", you get to 111.125". This seems to be the case with R-1 as well.