This is a description of the performance tests of a Lysholm engine completed at the Lawrence Livermore National Laboratory at the University of California. The Lysholm engine is a rotary displacement engine which can accept a low quality (vapor fraction) two-phase mixture. Generally, the well-head condition of geothermal fluids is a mixture of liquid and vapor, with quality up to 40 percent, although for most liquid dominated geothermal resources the vapor fraction is considerably less than 40 percent. As a thermodynamic process, using mixed phase flow has the potential for using significantly more of the available energy output per pound of fluid, as contrasted with other processes that either transfer heat energy to a second fluid, or use only the vapor fraction and discard the liquid. In our tests, the quality was varied between 8 and 27 percent. Our results indicate that the Lysholm engine can operate well with a two-phase mixture as a working fluid. The maximum observed engine efficiency was 53 percent at 8000 rpm, with an inlet pressure of 190.6 psia, 22.2 percent quality, and an exhaust pressure of 30.6 psia. The best results were observed at the higher speeds and with exhaust to an above-atmospheric backpressure.

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