**b. The fuel choice**

The fuel used, suggested, chosen for all prototype is a liquid hydrocarbon (pentane-butane or similar). The kerosene use or other jet-fuel appears perfectly compatible. For the operational prototype, the possibility is being studied to use methane or hydrogen, but this last one generates problems of tank design (high pressure, low power density).

### **c. Design problems**

The analysis of existing prototypes indicates as the main design problems that can be previewed to this point are the following ones:


### **d. Technological and manufacturing problems**

They are generally correlated to the availability of opportune high resistance materials (high thermo mechanical stresses) as well as the combustion chamber, turbine, regenerator, ecc. And to the productive technologies. While such problems will not have great influence on the realization of the prototypes, an engineering study to pass "to the productive" part (post-prototypal phase) will be necessary. Finally, the economic impact of these devices will be dependent on the performance levels and the manufacturing costs, both of which have yet to be proven. It is certainly possible, however, that UMGTs may, one day, be competitive with conventional machines in a cost per installed kilowatt. Even at much higher costs, they will be very useful as compact power sources for portable electronics, equipment, and small vehicles.
