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introduction 



In cu^iiderlng alternate fuels for future Navy use, hydrogen stands 

 out as a fuel with great potential In teres of usefulness, availability, 

 and product emissions. Hydrogen can be used in both internal and exter- 

 nal combustion engines; it can be burned for heating purposes; and it 

 can be used in fuel cells. It is a component of water which is avail- 

 able everywhere. Finally, the products of combustion with air are water 

 and ec=d° oxides of nitrogen (oxides of nitrogen are products whenever 

 combustion is sustained with rir at high temperatures). 



One of the greatest problems with hydrogen is its low energy den- 

 sity. As a gas at atmospheric pressure , hydrogen has aa energy density 

 of 29Z of that of natural gas. As a liquid stored at cryogenic tempera- 

 tures, hydrogen has an energy density of 28X of that of gasoline. These 

 low energy densities present inconveniences when mobility of the fuel is 

 a concern. 



In recent years much work has been done on the chemical storage of 

 hydrogen in metal hydrides. Energy densities of up to 40% of that of 

 gasoline appear possible. Energy densities at least as high as that of 

 liquid hydrogen have been demonstrated and without the problems that 

 accompany liquid hydrogen. 



The purpose of this study was to determine what metal hydrides are 

 availalle, and how applicable they night be to Navy needs. A survey and 

 compilation of the metal hydrides was carried out, and then a short lock 

 ,-. was taken into various uses of this type of storage. 



I 



COMPARISON OF ALTERNATE FUELS AND HYDROGEN STORAGE METHODS 



In tlse classification of chemical energy storage many possible 

 fuels reveal themselves. These possibilities take the form of synthetic 

 fe fuels and include methane, methanol, ethanol, ammonia, svnthetic gasoline, 



hydrazine, and hydrcgen. Table 1, taken from Reference 1 compares 

 |-| several of these fuels. 



Two of these chemical alternatives--hydrazine and ammonia- -must be 

 j - used with great care because of the great danger if they are released in 

 the air. These fuels have extremely low maximum allowable concentra- 

 tions of 1 ppm for hydra: ine and 100 ppm for ammonia in air [2]. In 

 addition, hydrazine is very dangerous to handle, except when diluted 

 with water in which case it makes an excellent fuel for fuel cells but 

 not for coabustion processes [1J. 



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