Air-Water Jet (Mist-Jet) for Ship Propulsion 



0.50 



10 15 



MIXTURE RATIO, 



Fig. 13 - Propulsion efficiency versus 

 water-to-air mass flow ratio 



Another characteristic of a propulsion device is system volume, which is 

 directly related to thrust density. Figures 8 and 9 show thrust per unit mass of 

 air versus mass augmentation ratio and ship speed, respectively. It can be seen 

 that for any ship speed and pressure ratio there is an optimum water -to -air 

 augmentation ratio. The thrust used here is net thrust, which accounts for 

 losses, both internal and external, arising from adding the liquid phase. These 

 figures show the normal decrease in thrust per unit energy added with increase 

 in speed and also indicate that net thrust increases of more than a factor of two 

 may result from water-augmentation of an air jet. Figure 10 illustrates the 

 variation of thrust intensity, i.e., thrust per unit exit area versus nozzle pres- 

 sure ratio. Here it can be seen that for a given thrust intensity there is an op- 

 timum pressure ratio and mass augmentation ratio combination resulting in 

 highest overall efficiency. It is this information that can be used in vehicle de- 

 sign where size and weight are balanced against system efficiency. Generally it 

 can be seen that a nozzle thrust intensity of 1000 lb/ft ^ is a reasonable upper 

 value for the practical range of propulsive efficiencies. 



1075 



