Rolls-Royce has designed, built, and continues to test a high pressure (HP) turbocharging system specifically designed for a hybrid solid oxide fuel cell system being developed by Rolls-Royce Fuel Cell Systems, Ltd. This turbocharger is comprised of a two-spool machine with a shaft speed motor/generator on the low speed spool. Each spool contains a centrifugal compressor driven by a radial inflow turbine. The two spools run independently, but are physically close coupled for a smaller, more efficient system. The spools are mounted into a basic structure to provide structural rigidity, as well as sound and heat isolation. In its current test rig form, the system runs on oil lubricated bearings; is equipped with a liquid fueled slave combustor; and is controlled with a digital control system. Although never intended to be a “stand alone” microturbine — it is simply a high pressure turbocharger; if one wanted to — with a proper fuel and control system installed, it is capable of operation in such a stand alone mode. However, without heat recovery it would be a highly inefficient microturbine and therefore, was not considered in this application. Multiple units have been built and continue developmental testing. Initial matching to a fuel cell stack is scheduled for operation later in 2006.

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