Got a reference for that?
DLM-AG.ch
Weird. Not even the manufacturer expected that result.
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The odd thing about steam engine nomencalture is that the steam part is the transmission - really they would be coal-steam ( like diesel-electric ) or whatever. That sounds a bit daft though... although it does leave room for things like electric-steam, as the swiss once did.
Depends what you mean by the transmission. There are two stages.
- Conversion of chemical into mechanical potential energy.
- Transmission of mechanical energy into power at the rail.
With electric traction, stage 1 takes place at the power station by the burning of fuel.
Stage 2 comprises the heating of water to make it into steam (the working substance), its conversion to electricity in a turbine, transmission down the distribution system, conversion into rotary motion in the trains' motors and transmission of the rotary motion via the gearing system or drive shafts into power at the rail. Efficiency is 2*
With a diesel mechanical system, the conversion of chemical energy to mechanical energy takes place inside the cylinders of the internal combustion energy. The hot combustion gases are the working substance. This cuts out the need for steam boilers, turbines, and distribution grids. All that is needed is to convert reciprocal motion to rotary motion, and the power can be transmitted to the rails by a clutch and gearbox. But the nature of the system means that only limited power can be transferred to the rails in this way and more powerful diesel traction units use the engine to drive an electric generator and the electricity drives the motors. Efficiency is 3*.
In a steam locomotive the combustion of fuel takes place in a combustion chamber just as it does in a power station. The potential energy of the steam is converted to reciprocating motion in the cylinders and there is a direct drive to the wheels. In a locomotive the conversion of the energy in the steam to reciprocating motion is relatively less efficient than in the turbines of a power station or the cylinders of an internal combustion engine, so overall efficiency is only 1*. However, the conversion of reciprocating energy to power at the rail is very efficient as there is no intervening transmission system - just connecting rods and cranks. Combustion systems have also become more efficient in recent years, which has driven up overall thermal efficiency at little. It also happens to be easier to meet increasingly strict emission standards with external combustion as there is better control of the chemical process than with internal combustion, which is explosive.
The initial cost of steam locomotives is also around one-third of that of other traction of the same power, due to their greater simplicity. A steam locomotive consists of a chassis, a combustion chamber, a pressure vessel, a means of converting the potential energy of hot steam into mechanical energy and a system for transmitting this to the wheel-rail interface. The pressure vessel acts as an energy reservoir, allowing a relatively fixed combustion rate but variable power output.
There were obvious technical issues with steam locomotives which led to them largely going out of use in the 1950s but most of the others were resolved in the 1970s. The relatively low thermal efficiency is inherent, but even this has been much improved.
At some point one it would be reasonable to expect this realisation to dawn on those who make decisions about traction policy.
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