70014IronDuke
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- 13 Jun 2015
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Otherwise known as the thermodynamics of a conventional steam locomotive
Having lunch with friends yesterday, the lady-wife commented that it was "such a shame" that steam could not have survived, whereupon the man-hub asked if, with the very low price of oil on the market, was it possible that there might be an economic case for a steam comeback.
My main line of argument against was that, apart from the dirty jobs involved that few would take on (and I never mentioned the environmental issues), the steam engine was inherently of such low efficiency that even with oil prices at rock bottom, it would never be viable again, at least in the world as we know it. (after all, low oil prices feed into low diesel and low electricity generation prices too.)
I seem to remember reading that steam locomotives at best were about 10% efficient, even theoretically. But that got me thinking: where does all the 90% of energy actually end up?
Obviously, an awful lot of heat leaves the firebox and starts flying down the tubes - but it comes out still pretty hot over the blast-pipe, and then up the chimney.
Does anyone know the typical temperatures on entry into the tubes from a hard working locomotive? And the temperatures at the 'cool' end of the boiler, as the gases enter the smokebox?
I have little idea, but I assume the temperatures in the firebox would be in the region of 200-300C - just guessing. I presume these temperature differences could be measured to some degree in the days of working steam - and this could give a picture of the efficiency of the thermal transfer process in the boiler. But I don't know for sure.
Then, of course, the exhaust steam from the cylinders itself contains energy, whis is expired going up the blast-pipe and drawing flames through the boiler. Plus you have heat losses from the boiler and firebox, plus you have some coal that flies unburned straight through the tubes, out the chimney and into lineside vegetation, whereupon it prmptly starts a fire
Then of course, you have the mechanical losses from friction in the piston/cylinder and motion/bearings.
My personal bet would be that the worst losses are heat and unburned coal that flies straight up the chimney - but does anyone have a proper scientific estimation of all the losses?
Having lunch with friends yesterday, the lady-wife commented that it was "such a shame" that steam could not have survived, whereupon the man-hub asked if, with the very low price of oil on the market, was it possible that there might be an economic case for a steam comeback.
My main line of argument against was that, apart from the dirty jobs involved that few would take on (and I never mentioned the environmental issues), the steam engine was inherently of such low efficiency that even with oil prices at rock bottom, it would never be viable again, at least in the world as we know it. (after all, low oil prices feed into low diesel and low electricity generation prices too.)
I seem to remember reading that steam locomotives at best were about 10% efficient, even theoretically. But that got me thinking: where does all the 90% of energy actually end up?
Obviously, an awful lot of heat leaves the firebox and starts flying down the tubes - but it comes out still pretty hot over the blast-pipe, and then up the chimney.
Does anyone know the typical temperatures on entry into the tubes from a hard working locomotive? And the temperatures at the 'cool' end of the boiler, as the gases enter the smokebox?
I have little idea, but I assume the temperatures in the firebox would be in the region of 200-300C - just guessing. I presume these temperature differences could be measured to some degree in the days of working steam - and this could give a picture of the efficiency of the thermal transfer process in the boiler. But I don't know for sure.
Then, of course, the exhaust steam from the cylinders itself contains energy, whis is expired going up the blast-pipe and drawing flames through the boiler. Plus you have heat losses from the boiler and firebox, plus you have some coal that flies unburned straight through the tubes, out the chimney and into lineside vegetation, whereupon it prmptly starts a fire
Then of course, you have the mechanical losses from friction in the piston/cylinder and motion/bearings.
My personal bet would be that the worst losses are heat and unburned coal that flies straight up the chimney - but does anyone have a proper scientific estimation of all the losses?