1/ Thermal considerations
The CAPSTONE electrical generator is not build between the
compressor and the turbine, but on the compressor side.
On top of that, the generator is built with a large gap between
rotor and stator :
That makes a large inductance in the circuit and ease the
thyristor turn off,
but also allows to make all the air sucked by the compressor to
go through the generator and keep it cool.

2/ Energetic efficiency
With low pressure, the power efficiency of the CAPSTONE gas
turbine alone (about 30%) is due to the regenerative cycle :
The compressed air is heated first by the exhaust gases through
the heat exchanger and secondly by the combustion.
Without this heat exchanger, the efficiency should be sa low as
22%

3/ Electric turbo compounding not adapted for aircraft use
I agree that turbo compounding through a mechanical transmission
to the propeller or Wankel shaft will be lighter than the
electrical solution,
and probably more reliable in case of atmospheric perturbations
(lightnings), and then better for aircraft use.

However, standard generators (belt driven alternators) used in
cars are a shame in terms of mass to power ratio and power
efficiency.


Philippe Dejean

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