Gas-Turbine Powerplants For Two-Phase Hydropropulsion 

 10 



V- 



Fig. 4Z - Variation of a and ig with e for 

 IR-F powerplant (4; = 0.9, p =: 12, a. p.) 



8 CONCLUSIONS 



The analysis of four basic powerplants for marine propulsion, that is, 

 hot-gas hydrojector, hot-gas pumpjector, cold-air hydrojector, and water jet, 

 allows the fundamental conclusion that a propulsive jet device powered by com- 

 pressed hot gas can be actually competitive with water jets, both in the pure 

 ejector configuration (hydrojector) and in the hybrid pump-ejector configuration 

 (pumpjector). 



When powered by cold air, the same device provides very poor and non- 

 competitive performance, its performance being strongly improved by the gas 

 temperature or specific volume. 



The pumpjector can be seen as a useful change of the water jet, the thrust 

 of which can be so improved without efficiency decrease. Essentially, the com- 

 parison between water jets and hydrojectors is favorable to the latter for the 



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