Auxiliary power unit passive cooling system

摘要

A passive cooling system for an auxiliary power unit (10) located in an aft compartment (20) of an aircraft is provided in which cooling air is drawn into the compartment through an aft opening (54) located in the rear of the aircraft and discharged back to the atmosphere through an exhaust duct (42) connecting to a rear exhaust opening (44). The aft opening (54) is located above the exhaust opening (44). Cooling air is drawn into the compartment using an eductor (46) that is connected between a turbine (14) and the exhaust duct (42). The eductor (46) creates a low-pressure region that suctions compartment air, which in turn, suctions atmospheric air in through the aft opening (54). The combined compartment air and combustion gases are exhausted out the exhaust duct (42). In auxiliary power unit embodiments in which the compartment is located in a rear portion of the aircraft fuselage, the cooling system further includes an inlet duct (50) having a forward end (56) and an aft end (52). The aft end (52) is connected to the opening (54); the forward end (56) is connected to the compartment (20). The inlet duct (50) defines an airflow passage through which ambient air is drawn into the compartment (20) for use in cooling various auxiliary power unit components.