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

Abstract

The invention refers to an APU compartment, and a method for extinguishing a fire in an APU compartment. The APU compartment (1) comprises an APU (2), an exhaust (5), an aperture (7) providing a passage between the APU compartment (1) and the inside of the exhaust (5), and a fire detection system, wherein the APU compartment (1) of the invention is constructed as an air tight compartment, and additionally comprises a conduit (9) for providing external air to the APU compartment (1), a door (8) for closing the conduit (9) inlet, and a control unit (6) configured to close the door (8) when a fire is detected, such that when the door (8) is closed and the APU (2) is in operation, the air contained in the APU compartment (1) is sucked through the aperture (7) to be expelled out of the APU compartment (1) to extinguish the fire.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better comprehension of the invention, the following drawing is provided for illustrative and non-limiting purposes, wherein:

(2) FIG. 1 shows a schematic view of an APU compartment according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

(3) FIG. 1 shows a side schematic view of an APU compartment 1 according to the invention. Regarding the invention, the APU compartment 1 comprises a part of the fuselage of the rear end of an aircraft, the space contained inside thereof and, all components and systems contained therein. As shown in FIG. 1, the APU compartment 1 is delimited by the fuselage 12 and a firewall 13 of the aircraft that separates the APU compartment 1 from the rest of the aircraft. The firewall 13 prevents fire propagation in the event that it occurs.

(4) Conventionally, the APU compartment 1 comprises an auxiliary power unit 2 provided with a turbine 3, an intake duct 4 for providing external air to the turbine 3, an exhaust 5 for expelling combustion gases, and an aperture 7 providing an airflow between the APU compartment 1 and the inside of the exhaust 5. Also, the APU compartment 1 is conventionally provided with a fire detection system responsible for triggering a fire detection alarm when the temperature sensed by the system is considered as fire indication.

(5) In addition to these, the design of the APU compartment 1 is constructed as a fireproof air tight compartment. Such air tight construction embraces an initial air tight configuration for the fuselage 12 of the APU compartment 1, and also any adaptation required by conventional APU compartments to become air tight, such as sealing any gap or opening provided in the fuselage 12 of the APU compartment 1.

(6) Additionally, the APU compartment 1 of the invention comprises means for preventing the entrance of external air inside the APU compartment 1. Said means enable controlling the air contained in the APU compartment. Thus, in the event of a fire, said means avoid feeding the fire with more oxygen than that already contained in the APU compartment. According to the invention, said means comprise a conduit 9, a door 8 for closing the conduit 9 inlet, and a control unit 6 for controlling the door 8. The conduit 9 is suitable for providing external air to the APU compartment 1. Thus, the conduit 9 also serves for providing cooling air to the APU compartment 1, helping to maintain an acceptable APU compartment air temperature.

(7) When a fire is detected, the control unit 6 is programmed to activate the closing of the door 8. Hence, the APU 2 operation causes the air contained in the APU compartment 1 to be sucked through the aperture 7 by venturi effect until the difference of pressure between the inside of the exhaust 5 and the APU compartment 1 is compensated. This absorption of air occurs instantly. Thus, the air comprised in the space contained in the APU compartment 1 and the outside of the APU 2, is expelled out of the APU compartment 1 by the exhaust 5. This way, the invention removes the oxygen contained in the APU compartment 1 to perform the fire extinction. Therefore, the invention achieves fire extinction without producing any damage to the environment.

(8) According to a preferred embodiment, the control unit 6 is also operable to shut off the APU 2 once the fire is extinct. Doing the control unit 6 responsible for shutting off the APU 2 after a predetermined time, the invention ensures a safe final state for the APU compartment 1.

(9) According to another preferred embodiment, the intake duct 4 comprises an intake door 10, and the control unit 6 is operable to close said intake door 10 when the APU 2 is shut off. Once the fire is extinct and the APU 2 is shut off, the control unit 6 can be configured to close the intake door 10 because the turbine 3 of the APU 2 no longer needs external air. Additionally, closing the intake door 10 helps protecting the APU compartment, especially when the APU is not going to be restarted for a while.

(10) According to another preferred embodiment, the conduit 9 is formed as a part of the intake duct 4. Thus, the inlet of the intake duct 4 that is conventionally provided in the APU compartment 1, can be used both for providing external air to the to the APU compartment 1 and to the turbine 3. This embodiment avoids providing another inlet for the conduit 9.

(11) As shown in FIG. 1 and according to another preferred embodiment, the APU 2 comprises an oil cooler 11, wherein said oil cooler 11 comprises the aperture 7.

(12) In another preferred embodiment, the door 8 that closes the conduit 9 inlet is provided at the fuselage of the rear end of an aircraft, preferentially, at the fuselage 12 of the APU compartment 1.

(13) Additionally, according to another preferred embodiment, the intake door 10 that closes the intake duct 4 inlet is provided at the fuselage of the rear end of an aircraft. Likewise, preferentially, said intake door 4 is provided at the fuselage 12 of the APU compartment 1.