Supercritical organic Rankine engines (SCORE)

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Supercritical organic Rankine engines (SCORE)

Boretz, J.E.

In the past, the approach to the design of organic Rankine cycle (ORC) engines has been fairly conservative. In general, subcritical cycle conditions have been selected and comparatively low component efficiencies have been assumed. This has resulted in low overall power conversion unit (PCU) efficiencies in the 18 % (DIPS) to 25 % (ORCEPS) range. With the selection of solar dynamic systems as possible candidates for the Space Station power modules, it has become obvious that increased power conversion unit efficiencies are desirable to reduce overall solar dynamic power module weights and volumes. This paper discusses the potential for increasing ORC engine efficiencies by the use of supercritical cycles and increased component efficiencies. Both CP-25 (toluene) and RC-1 (hexafluorobenzene-pentafluorobenzene) working fluids are considered. The technical issues of operating in the supercritical regime, as well as a comparison of the characteristics of the working fluids in achieving high component efficiencies, are discussed. The approach to achieving higher component efficiencies and the estimated achievable values are also described.