Work is being done on engines with the "Ranque-Hilsch" Vortex Effect of double "cold" and "hot" flow for small reactors with speeds of between 350 and 450 km / hr, ideal for cruise missiles.

-Also they are very low cost, as they are disposable.

"Schematic of a simple version"

-The main advantage is that by not having an expensive turbine exposed to the heat of combustion (up to 2500° C) the total cost of the engine is lower.

“The above engine with fairing”

-The Vortex Effect creates two currents, one cold and the other hot, the latter being that of 2500° C and the “cold” one, from 850 to 900° C,

"Version of a possible real engine"

-The last illustration is of a two-stage turbofan, axial compressor, multiple chambers taking advantage of the cold return current to introduce it into a centrifugal turbine -of cheaper materials-.