[GZG] Gas turbine efficiency. (Was: Scale Creep)

Gas turbines are notoriously fuel-inefficient, but that's not the  
only consideration in the choice of power-plant. Gas turbines are  
mechanically simple, can be brought quickly up to full power from  
cold, and typically have high power-to-weight and power-to-size  
ratios. Presumably it was those features that attracted the designers  
of the M-1 Abrams.

 From a fuel-economy point of view, something like the turbo-compound  
Napier Nomad diesel turbine would be ideal as a tank engine, but  
keeping so complex a power-plant running in the field might present a  
difficult challenge. An ordinary turbo-diesel might well be a better  
compromise.
http://en.wikipedia.org/wiki/Turbo-compound_engine
http://en.wikipedia.org/wiki/Napier_Nomad

Essentially the crucial problem with gas-turbine engines, from an  
efficiency point of view, is that they throw too much energy away in  
their hot exhaust (creating incidentally a large infra-red  
signature). "Combined Cycle" gas turbine systems use heat exchangers  
to capture some of this wasted energy to drive steam-turbines, and  
can achieve very high efficiencies. However, such systems are bulky,  
complex, and have so far only really been used in fixed electricity- 
generation applications.
http://en.wikipedia.org/wiki/Combined_cycle

Best regards, Robert Bryett

On 11/04/2008, at 16:48 , Richard Bell wrote:

> Tubines guzzle fuel at start because, during startup, the turbine  
> is idling.  Driving the compressor (running for zero mechanical  
> power out) consumes 30-40 % of the fuel used at max rated power.   
> Gas turbines in ground vehicles only make sense in racecars and  
> hybrids that can switch off the turbine whenever it cannot be run  
> flat out.

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