Originally Posted by Mr Optimistic
No compressor and the heated gas, which is now at higher pressure (pv=nkt) sees lower and equal pressure at either end of the tube
No.
This is a very common misunderstanding of turbine engine.
The gas heating is done
at constant pressure not at constant volume !
The temperature increase is exactly compensated by a density decrease.
Without compressor, the heated air would just remain at atmospheric pressure and expand in both forward and backward direction and wouldn't produce any work (no pressure differential).
Luc