Steam Generator locomotives?

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Steam Generator locomotives?

Postby D Alex » Sat Nov 10, 2018 2:28 pm

I was reading a story about the Doble steam car recently, how it differed from other steam autos by using a steam generator rather than a boiler. Now, I know that a good number of diesel locomotives used small steam generators to heat passenger coaches, but did anybody ever run a locomotive with a large steam generator? It would seem to be a good idea where water might be scarce, or a smaller locomotive with full power was needed. Also, a steam generator takes only a couple of minutes to raise a head of steam, whereas a boiler takes probably an hour or more. Of course, you need a fluid fuel source (oil or gas), which might be more efficiently used in an internal combustion engine. I'm sure at some point, an engineer at least did a study...
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Re: Steam Generator locomotives?

Postby D Alex » Sun Nov 11, 2018 4:13 pm

Sorry, but that is not a steam generator, it is an electric generator powered by a steam engine; BIG difference.
https://en.wikipedia.org/wiki/Steam_generator_(boiler)
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Re: Steam Generator locomotives?

Postby phillyrube » Sun Nov 11, 2018 5:00 pm

The old GG-1 had an oil fired steam generator. Seems funny with all that electricity to use oil to heat water, but it's more efficient.
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Re: Steam Generator locomotives?

Postby D Alex » Mon Nov 12, 2018 6:48 pm

Oil-fired steam generators were in a LOT of 1st generation diesels, but not as a power unit. From what I've read about the Doble, it could get a head of steam up from cold in about 90 seconds, which might be useful in a small switcher. Or the need for much less water might've been helpful in a very dry climate. Perhaps it might've worked in a self-propelled car?

Oh, BTW, they probably used an oil-fired SG so that it could heat the cars on the consist when parked, and the caternary was down.
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Re: Steam Generator locomotives?

Postby Pneudyne » Mon Dec 17, 2018 10:48 pm

As I understand it, the Doble “steam generator” was basically a form of forced draught water-tube boiler, sometimes of the single-tube (monotube) type. Water-tube boilers were/are the norm for stationary and marine applications, but never found favour for locomotive applications. Hybrid combinations of water-tube fireboxes coupled with normal fire-tube boilers were tried here and there, notably by the B&O, but were never attractive enough to justify their wider use.

For a passenger auto with its relatively small steam demand, a boiler or “steam generator” and control system could be made with sufficiently low thermal inertia that it could work on an “immediate demand” basis. Not really so with the Stephensonian-type locomotive boiler relying on exhaust steam to create the draft, and which was required to be a thermal reservoir capable of supplying steam beyond its production capability for short periods of time. I imagine that the thermal reservoir requirement may have explained the hybrid of water-tube firebox with fire-tube boiler; the latter would have provided the thermal reservoir.

The apparent water economy of the Doble system was I think due to its use of a condenser for water recovery. Condensing has been used on conventional steam locomotives, with some fleet-scale applications, the best known of which is probably the South African Railways (SAR) 25 class, which was built for operation over the non-electrified sections that traversed the dry interior region known as the Karoo. Where water was very scarce and other solutions were not readily available, condensing could be made to work, but it was probably too much hassle for use where it was not unavoidably necessary. In the SAR case, a combination of electrification and dieselization made the condensing steam locomotive redundant, and most of the 25 class fleet was converted to non-condensing form (25NC class).


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