Engine assembly for an auxiliary power unit

An engine assembly for use as a power unit for an aircraft, the engine assembly comprising:

• at least one internal combustion engine in driving engagement with an engine shaft;
• a generator having a generator shaft in driving engagement with the engine shaft to provide electrical power for the aircraft;
• a gearbox drivingly connecting the engine shaft to the generator shaft;
• a compressor having an outlet in fluid communication with an inlet of the at least one internal combustion engine;
• a first stage turbine having an inlet in fluid communication with an outlet of the at least one internal combustion engine;
• and
• a second stage turbine having an inlet in fluid communication with an outlet of the first stage turbine;
• wherein at least one of the turbines is in driving engagement with the compressor.

A method of providing electrical power to an aircraft, the method comprising:

• flowing compressed air from an outlet of a compressor to an inlet of at least one internal combustion engine of an engine assembly;
• rotating an engine shaft with the at least one internal combustion engine;
• driving a generator providing electrical power to the aircraft with the engine shaft through a drive engagement between a shaft of the generator and the engine shaft, the shaft of the generator being driven at a different speed than a rotational speed of the engine shaft;
• and
• driving a turbine of the engine assembly with exhaust from the at least one internal combustion engine.