Abstract: A system is provided for an aircraft. This aircraft system includes an engine, a fuel system and an air system. The fuel system includes a fuel circuit, a fuel source, a heat exchanger and a turboexpander. The fuel circuit is configured to direct fuel from the fuel source, through the heat exchanger and the turboexpander, to the engine for combustion. The heat exchanger is configured to transfer heat energy from combustion products generated by the combustion of the fuel in the engine into the fuel in the fuel circuit. The air system is discrete from the engine. The air system includes an air compressor and the turboexpander. The air system is configured to expand the fuel directed across the turboexpander by the fuel circuit to power operation of the air compressor.

Abstract: A method of bleeding air from a gas turbine engine having a compressor section with a downstream centrifugal compressor is described, which includes bleeding air from a first location upstream of the centrifugal compressor's outlet, when the compressor is operating in a first pressure range, and bleeding air from a second location upstream of the centrifugal compressor's outlet, when the engine is operating in a second pressure range.