the eddy current losses described in Ref. [6], Nonmagnetic materials will be incorporated in the SPRE engine. A hydrodynamic gas bearing has been successfully demonstrated on the power piston of the SPRE over the range of operating conditions. What makes the concept challenging is the lack of experimental data whereby a rotating hydrodynamic bearing- supported piston is simultaneously required to reciprocate axially while under the influence of a varying pressure gradient across the bearing length. Reciprocation is about 20 mm total at about 100 Hz frequency. The hydrodynamic bearing—based on early test data—appears to be stable on the power piston due to the side pull of the piston-plunger magnets. There are no such stabilizing magnets on the displacer and the preferred method of developing a gas bearing on the displacer—whether it be hydrodynamic or hydrostatic—is not known at this time. MTI is also conducting tests on various regenerator configurations in the SPRE engine. These tests will experimentally evaluate the impact on engine power and efficiency and be used in conjunction with code predictions. The next sequence for the MTI SPRE—as shown in Fig. 3 is upgrading the cold end of the engine. The primary purpose of this upgrade is to verify the mechanical integrity and operation of the cold end of the 1050 K. SSE engine by operating the cold end at 525 K. A second objective
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