Re: Turbines

[bearbvd@domain.elided (Greg Hermann)]

>
>The Pennsy S-2 was actually more efficient than diesel-electrics above 40
>mph.  But it cost a mint to stop it anywhere!  So they never built another
>one.  The UP messed around with them a lot.  But all the RR units were steam
>turbines, which I don't think is the same thing as a gas turbine.
>
NO--although I am not familiar with the Pennsy S-2's. The UP's "big blows"
were GAS_NOT_ STEAM_ turbine electrics.  And the "big blows" were more than
"messed around with"--they saw main line freight service between Ogden and
Cheyenne for many years. Mostly on the big grades between Ogden and Green
River and between Cheyenne and Laramie (the "Sherman" grade). The combined
cycle locomotive I mentioned seeing--which was not publicized that I know
of--appeared to be a gas turbine electric with a (condensed) recip steam
bottoming cycle.

The problem with gas turbine economy is not AS much with variable speed
operation, although that is certainly a factor,  as it is with part LOAD
operation. Turbines are grotesquely inefficient at part load unless they
use a regenerative cycle. (A regenerator is a heat exchanger which captures
heat from the exhaust to pre- heat the compressed air prior to the
combustor.)

Regards, Greg