million project to prove the technology is not only possible but commercially viable.
Public Investment Kick-Starts Development
REL Inc., with a long history of squeeze casting, was
capable of infi ltrating metal into ceramic preform struc- tures, fi lling gaps as small as 10 microns. Adam Loukus, vice president, REL, saw potential in casting a tank with a thin internal structure to minimize the amount of wall material while still maintaining the structure’s ability to hold natural gas held at high pressures. “Conventionally, you use cylindrical geometry when
storing gas at high pressure,” said Josh Loukus, presi- dent, REL Inc. “That’s nature’s shape. Put those cylin- drical tanks in the trunk, and as soon as you do that, you can’t put your groceries in there. With a conformable design, with a box, you can pack fuel more efficiently inside a vehicle.” With the idea of a conformable CNG tank, REL ap-
plied for funding under the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) program. In July 2012, REL Inc. was awarded a $3 million grant to pursue its research. T e fi nal goal being a design improvement from the
standard cylindrical tanks, REL Inc.’s design team started with a squared structure. Initially, the corners were rounded to minimize high stress points. T rough numerous itera- tions—including designs with pillar and bubble shaped
The Schwarz P design, found in the skeletal plate of sea urchins, required a number of cores to be stacked on top one another to produce the minimalist internal structure.
internal structures—the REL Inc. team eventually pursued a path that already existed in nature. T e so-called Schwarz P surface features two inter-
twined cubic lattices. T is design, which consists of two fully independent and intertwined cavities, features a high surface-to-volume ratio. Such a design is found in the skeletal plate of sea urchins, a fact that reinforced the REL Inc. team’s belief it was a naturally effi cient design. T e constant curvature, though, meant the Schwarz P design
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Southwestern Energy, with its own fl eet of CNG-fueled vehicles, invested in the project in hopes of producing a commercially vi- able storage tank.
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Mar/Apr 2016 | METAL CASTING DESIGN & PURCHASING | 23
Image courtesy Anders Sandberg.
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