I just got the email from Union Pacific about this video:
York1 John
Very interesting, although I wish he'd gone more into how the various parts were proportioned, which is a key. The video has been properly set up so that the arrow keys step you a few seconds forward and back, which you'll want to do to appreciate some of the technical features.
The basic burner is Thomas pattern, not von Boden-Ingles (which has a wider flame pattern) or something mechanical from industrial practice. Note the circular venturi for primary air, which is important in defining the initial plume. It is mounted at the front, firing backward, if you're confused about the orientation.
The secondary-air tuyeres, carefully tremie'd in with high-temperature cement as you see in a later picture, are angled vertically to induce proper flow development; notice their location and how the panels 'angle out' relative to the plume emitted by the burner. They are not open; they are fed from a plenum space with a smaller-area rectangular damper each side; I suspect this has an effect on the mass flow through the array. Note the curved heavy brick wall at the rear of the firepan, which flow-shapes and reverberates the plume around the backhead and forward between the crown and water legs.
I suspect that the plume has been designed to work with the substantial extended radiant absorbing surface ("direct" in older language) that characterizes the Challenger's relatively shallow firebox and chamber (to fit over the rear driver pairs) optimized to burn subbituminous coal. To that end, the combustion and droplet size have to be arranged to occur over a longer time-of-flight so that luminous flame (yellow to white) persists until close to the rear tubesheet in the boiler. The reason a 'light grey haze' is what you normally fired for is that it represents just past the point this condition was likely occurring in the firing; shy of it with a clean stack represents additional primary and secondary air that is only diluting the plume and removing some of its available radiant heat, so 'in practice' you might be encouraged to avoid it.
The burner has an unexpected quality, which I observed in West Chicago: the natural circulation from the venturi and tuyeres through the front end is sufficient to maintain boiler pressure with the engine standing and necessary auxiliaries running. Only slight use of blower is needed to add back heat when the whistle is being (at times, a bit enthusiastically) blown.
Incidentally the 'revised' cab specs include "DB" at the end, where the stoker information was on the coal-fired version. This stands for "Dickens-Barker", the two people responsible for developing the system.
You know, they are not using locomotive 4014 to make the big climb out of Ogden with 4000+ tons hooked to the tender, so if the light-oil firing is not competely optimized, the thing, well, runs and entertains crowds and has accomplished its mission, because wants to send half-a-tender-load of brown coal up the stack every time they take it out?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
I do not know if the burner lacks sufficient capacity to make full use of sustained cylinder horsepower; I do think it would be possible to use supplemental venturis or additional mechanical burners to the arrangement without fouling up the secondary-air arrangements, if necessary.
I have no complaint in theory if better turndown efficiency is a design priority on a locomotive nominally if much greater power than 'necessary for mission'. The interesting thing about the current DB design is that it might be both, without causing excessive weird thermal effects in the gas-pass structure anywhere...
Were any Big Boys delivered by Alco as oil burners? I'm thinking not.
Lithonia OperatorWere any Big Boys delivered by Alco as oil burners? I'm thinking not.
The only conversion of a Big Boy to oil (in the days of the late '40s when full coal strikes were threatened and nearly every railroad, including N&W, developed oil firing plans) was on locomotive 4005, and it was notoriously unsuccessful. That makes the development of the DB system all the sweeter...
No.
The UP Historical Society has made scanned engineering drawings for the Big Boys available on CD ROM for purchase. These include drawings developed by the railroad for the oil firing conversion in 1946. Comparing the drawings with the published videos, it doesn't look like the Steam Crew has deviated significantly from the 1946 oil firing system design. Interestingly, the original UP drawings show that the 800 class Northerns, the big Challengers, and oil-fired 4000 class locomotives all used the same Thomas oil burner. I think I remember Ed Dickens saying in one of his restoration videos prior to 2019 that they had some new burner assemblies manufactured (they are actually pretty simple components). If they took the opportunity to tweak the burner design, the changes were likely very minor. The main difference I see is that they decided to leave the security circulators in the firebox, whereas UP steam era practice was to remove the circulators on oil-fired power. Incidentally the 3977 Challenger, preserved at North Platte, NE, was retired as an oil burner and does not have circulators in the firebox. I believe the Steam Crew decided to keep the 4014's circulators in an effort to reduce temperature gradients across the crown sheet by promoting increased water circulation. To the extent that they can be seen in the Youtube video, the burner location, refractory brick layout, air supply holes in the firepan in the 4014 all look very much like the original UP oil-burning 4000 class arrangement drawings.
Scott Griggs
Louisville, KY
Our community is FREE to join. To participate you must either login or register for an account.