Turbo-compound engine

A turbo-compound engine is a reciprocating engine that uses a turbine to recover energy from the exhaust gases and return it as mechanical power to the engine. Instead of using that energy to drive a turbocharger, as in many high-power aircraft engines, the recovered energy is mechanically transmitted to the crankshaft to increase the total power delivered by the engine. Major aircraft examples include the Wright R-3350 Duplex-Cyclone and the Napier Nomad.

As this recovery process does not increase fuel consumption, it has the effect of reducing the specific fuel consumption, the ratio of fuel use to power. Turbo-compounding was used for commercial airliners and similar long-range, long-endurance roles before the introduction of turbojet engines. Examples using the Duplex-Cyclone include the Douglas DC-7, Lockheed L-1049 Super Constellation, and Lockheed L-1649 Starliner, while other designs did not see production use for commercial flight.