The fill density of automotive cryo-compressed hydrogen vessels

Cryo-compressed hydrogen storage promises to deliver highest system storage density leading to fundamental cost and safety advantages. However, cryogenic vessels are complex systems, continuously drifting in thermodynamic space depending on use patterns, insulation performance, vessel characteristics, liquid hydrogen pump performance, and para-H-2 to ortho-H-2 conversion. This paper shows a comprehensive evaluation of all factors affecting cryogenic vessel fill density, in an effort to evaluate system performance vs. operational parameters over a broad range of conditions. The results confirm previous experiments and models indicating that cryogenic vessels have maximum fill density of all available storage technologies, and fill density is most sensitive to daily driving distance and insulation performance. It is finally predicted that para-H-2 to ortho-H-2 conversion will affect most automobiles, increasing fill density by up to 5.3%. In a future world dominated by cryogenic H-2 fueled vehicles, para-H-2 to ortho-H-2 conversion inside the vessel will be the closest contact an average person will have with quantum mechanics outside of consumer electronics. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.