TABLE 2.6-1 MASS ANALYSIS OF 9 GW STIRLING ENGINE SYSTEM 2.6.4 Stirling Technical Discussion The theory and the technology of Stirling engines is advancing rapidly. Thus, predicting future performance is speculative at best. The following is based closely on the performance objectives of the intermediate demonstration engine. The design life of this system is of the order of 100,000 hours, and the SPS goal is a lifetime of 262,000 hours (30 years); by using conservative stress levels, such as in the ASME boiler code, this may be possible. It is assumed that a large number of 25^ efficient, 25 kW, double cylinder generators comprise the power generation component of an FPSE SPS.(3,5) The hot side temperature of 720 K is a conservative value. It is difficult to scale a single Stirling engine up to high power levels, as is done with other thermal cycles. The walls of the displacer cylinder transport heat between the working fluid and the outside. As the engine gets larger, the gas volume increases more rapidly than the wall area, so heating of the gas is slowed. The need for thicker walls with larger size compounds this effect. External heat exchangers improve the rate of thermal transport but add mass and increase the dead gas volume, which decreases power. The primary materials used in the engine are iron and Inconel 718.(6) Of the materials in the engine, only the working gas (helium) and some alloying elements in the Inconel 718 are non-lunar.
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