Fire extinction design for an auxiliary power unit compartment of an aircraft

1. An auxiliary power unit compartment ( 1 ) of an aircraft, comprising:

an auxiliary power unit ( 2 ) placed in the auxiliary power unit compartment ( 1 ) and having a turbine ( 3 );

an intake duct ( 4 ) having an intake door ( 10 ), the intake duct ( 4 ) for providing external air only to the turbine ( 3 ) and not to the auxiliary power unit compartment ( 1 );

an exhaust ( 5 ) for expelling combustion gases;

an aperture ( 7 ) providing a passage between the auxiliary power unit compartment ( 1 ) and an inside of the exhaust ( 5 ), and

a temperature dependent fire detection system associated with the auxiliary power unit compartment ( 1 ) for detecting a fire within the auxiliary power unit compartment ( 1 ),

wherein the auxiliary power unit compartment ( 1 ) is constructed as an air tight compartment and includes a conduit ( 9 ) for providing external air only to the portion of the space inside the auxiliary power unit compartment ( 1 ) that is outside of the auxiliary power unit ( 2 ), a door ( 8 ) for closing the conduit ( 9 ) inlet, and a control unit ( 6 ) being configured to independently close and open both the intake door ( 10 ) and the door to conduit ( 9 ) and also configured to close the door ( 8 ) while maintaining the intake door ( 10 ) open when a fire is detected by the fire detection system, such that when the door ( 8 ) is closed and while the auxiliary power unit ( 2 ) is in operation, the air contained in the auxiliary power unit compartment ( 1 ) is pulled out through the aperture ( 7 ) and expelled out of the auxiliary power unit compartment ( 1 ) through the exhaust ( 5 ) to thereby extinguish the fire.

2. The auxiliary power unit compartment ( 1 ) of claim 1 , wherein the control unit ( 6 ) is operable to shut off the auxiliary power unit ( 2 ) once the fire is extinguished.

3. The auxiliary power unit compartment ( 1 ) of claim 1 , wherein the control unit ( 6 ) is operable to close the intake door ( 10 ) when the auxiliary power unit ( 2 ) is shut off.

4. The auxiliary power unit compartment ( 1 ) of claim 1 , wherein the conduit ( 9 ) is formed as a part of the intake duct ( 4 ).

5. The auxiliary power unit compartment ( 1 ) of claim 1 , wherein the auxiliary power unit ( 2 ) has an oil cooler ( 11 ), and wherein said oil cooler ( 11 ) comprises the aperture ( 7 ).

6. The auxiliary power unit compartment ( 1 ) of claim 1 , wherein the door ( 8 ) is provided at a fuselage ( 12 ) of the rear end of an aircraft.

7. The auxiliary power unit compartment ( 1 ) of claim 1 , wherein the intake duct ( 4 ) is provided at a fuselage ( 12 ) of the rear end of an aircraft.

8. A method for extinguishing a fire in an auxiliary power unit compartment ( 1 ) of an aircraft, the method comprising the steps of:

providing an auxiliary power unit ( 2 ) located in the auxiliary power unit compartment ( 1 );

detecting a fire within the auxiliary power unit compartment ( 1 ) based on a temperature change within the compartment ( 1 );

providing the auxiliary power unit compartment ( 1 ) as an air tight compartment;

providing a conduit ( 9 ) having a door ( 8 ) for introducing external air only into the auxiliary power unit compartment ( 1 ) and a separate intake duct ( 4 ) having an intake door ( 10 ) for providing external air only to the auxiliary power unit;

closing the door ( 8 ) to the conduit ( 9 ) to prevent the entrance of external air into the auxiliary power unit compartment ( 1 ) when a fire is detected while maintaining the intake door ( 10 ) in an open position to provide external air to the auxiliary power unit, and

when a fire is detected inside the auxiliary power unit compartment ( 1 ) maintaining the auxiliary power unit in an on condition thereby pulling the air contained inside the auxiliary power unit compartment ( 1 ) out through an aperture ( 7 ) of the auxiliary power unit ( 2 ), the aperture ( 7 ) providing a passage between the auxiliary power unit compartment ( 1 ) and an exhaust ( 5 ) of the auxiliary power unit ( 2 ), the pulling of air lasting for a period of time until a pressure differential between the inside of the exhaust ( 5 ) and the auxiliary power unit compartment ( 1 ) is compensated, thereby removing the air contained in the auxiliary power unit compartment ( 1 ) and also extinguishing the fire.

9. The method for extinguishing a fire of claim 8 , further comprising:

shutting off the auxiliary power unit ( 2 ) once the fire is extinguished.

10. The method for extinguishing a fire of claim 9 , further comprising:

closing the intake door ( 10 ) to prevent the entrance of external air through the intake duct into the auxiliary power unit ( 2 ) once the fire is extinguished.