Structure for feeding air to an auxiliary power unit in an aircraft

Abstract

The invention concerns a structure (3) for feeding air to an auxiliary power unit (2) of an aircraft (1) comprising a pressurized cabin (10) and an auxiliary power unit (2), the structure comprising: a pipe (30) for feeding air to the auxiliary power unit; a unit (4) for controlling the airflow fed to the auxiliary power unit; and a valve (31) for the intake of air outside the aircraft, disposed at the inlet of the feed pipe (30), the opening of the valve being driven by the control unit (4). The structure is characterized in that it further comprises a circuit (32) for injecting air from the pressurized cabin into the auxiliary power unit feed pipe. The invention also concerns a method for feeding air to an auxiliary power unit.

Claims

1. An architecture for supplying air to an auxiliary power unit of an aircraft, comprising a pressurized cabin, a circuit for exhausting air from the cabin to the outside of the aircraft, and an auxiliary power unit of the type including a combustion chamber for fuel, the architecture including: a supply duct for supplying air coming from outside the aircraft to the auxiliary power unit, a unit for controlling the flow of air supplied to the auxiliary power unit via said supply duct, a first valve for admitting air from outside the aircraft, positioned at the inlet to the supply duct, the opening of said first valve being controlled by the control unit, a circuit for injecting air coming from the pressurized cabin into the supply duct, wherein the circuit for injecting air is connected to the circuit for exhausting air toward the outside of the aircraft through a distribution valve, the opening whereof is controlled by the control unit to draw a proportion of a flow of air circulating in the exhaust circuit and to inject said proportion of the flow of air into the supply duct through a nozzle located at the exit of the of the injection circuit, wherein the control unit controls the distribution valve to provide a continuously variable proportion of air between a first proportion wherein the entirety of the flow of air circulating in the exhaust circuit is drawn, and a second proportion wherein a zero proportion of air circulating in the exhaust circuit is drawn, wherein said first valve and said distribution valve are each progressively controlled by said control unit so that the flow of air supplied to the auxiliary power unit is a determined variable mixture of air supplied from said air from outside the aircraft and said air from said pressurized cabin, said determined variable mixture determined by operation of said control unit.

2. The architecture according to claim 1, wherein the control unit is designed to control the opening of the outside air admission valve and the opening of the distribution valve depending on a phase of operation of the auxiliary power unit.

3. The architecture according to claim 1, wherein the control unit is designed to control the opening of the outside air admission valve and the opening of the distribution valve according to a rotation speed of a rotating shaft of the auxiliary power unit.

4. An aircraft comprising a pressurized cabin and an auxiliary power unit, wherein said aircraft further includes an architecture for supplying air to the auxiliary power unit according to claim 1.

5. A method for supplying air to an auxiliary power unit of the type having a combustion chamber for fuel, in an aircraft comprising a pressurized cabin, an exhaust circuit for exhausting air from the cabin to the outside of the aircraft, an auxiliary power unit of the type including a combustion chamber for fuel, and an injection circuit for injecting air coming from the pressurized cabin into a supply duct of the auxiliary power unit, said method comprising steps of: supplying a flow of air coming from outside the aircraft to the auxiliary power unit through the supply duct, controlling the flow of air supplied to the auxiliary power unit via said supply duct by: controlling opening of a first valve for admitting air from outside the aircraft, said first valve being positioned at an inlet to the supply duct, injecting air coming from the pressurized cabin into the supply duct, controlling an opening of a distribution valve to provide a continuously variable proportion of air between a first proportion wherein the entirety of the flow of air circulating in the exhaust circuit is drawn, and a second proportion wherein a zero proportion of air circulating in the exhaust circuit is drawn, wherein the distribution valve connects the circuit for injecting air is connected to the circuit for exhausting air toward the outside of the aircraft to draw a proportion of a flow of air circulating in the exhaust circuit and to inject said proportion of the flow of air into the supply duct through a nozzle located at the exit of the of the injection circuit, wherein said controlling of said first valve and said distribution valve is progressive so that the flow of air supplied to the auxiliary power unit is determined variable mixture of air supplied from said air from outside the aircraft and said air from said pressurized cabin, said determined variable mixture determined by operation of a control unit.

6. The method according to claim 5, wherein the proportion of flow of air circulating in the exhaust circuit and the proportion of flow of air into the supply duct are controlled according to a rotation speed of a rotating shaft of the auxiliary power unit.

7. The method according to claim 5, wherein, during a starting phase of the auxiliary power unit, the supply of air to said unit comes exclusively from the air recovered from the pressurized cabin, and during a transitional phase between the starting phase and a stabilized operation phase, the supply of air to the auxiliary power unit includes an increasing flow of air coming from the outside and an increasing flow of air coming from the pressurized cabin.

8. The method according to claim 7 wherein, during a stabilized operation phase, the supply of air to the auxiliary power unit comes solely from the pressurized cabin, or comes partly from the cabin and partly from outside air.

Description

DESCRIPTION OF THE FIGURES

(1) Other features, aims and advantages of the invention will be revealed by the description that follows, which is purely illustrative and not limiting, and which must be read with reference to the appended drawings wherein:

(2) FIG. 1 shows schematically an aircraft equipped with an architecture for supplying air to an auxiliary power unit according to one embodiment of the invention.

(3) FIG. 2 shows the principal steps of the method for supplying air to an auxiliary power unit according to one embodiment of the invention.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

(4) With reference to FIG. 1, we have shown an aircraft 1 comprising a pressurized cabin 10, a passenger cabin for example. By pressurized cabin is meant a cabin in which the air that it contains is pressurized with respect to the outside, particularly when the aircraft is in flight.

(5) The aircraft further comprises a circuit 11 for exhausting air contained in the cabin to the outside of the aircraft, comprising in particular a valve 12 for exhausting air toward the outside, to allow renewal of the air contained in the cabin.

(6) A certain flow of air, depending on the size of the cabin, flows continuously in this circuit, to be exhausted so as to allow renewal of the air contained in the cabin.

(7) The aircraft also includes an auxiliary power unit 2, which includes a combustion chamber for fuel, a turbine for driving an air compressor through a rotating transmission shaft shown schematically in the figure under reference 21, an exhaust nozzle 22 and a duct 23 for exhausting the gasses.

(8) The auxiliary power unit also comprises a circuit for supplying fuel (not shown) and an architecture for supplying air 3.

(9) This architecture includes a duct 30 for supplying air to the auxiliary power unit, at the inlet thereto, and a valve 31 for supplying air from outside the aircraft to the inlet to the duct 30, in order to supply the auxiliary power unit with air.

(10) The architecture further comprises a control unit 4 configured to control the opening of the valve 31 so as to regulate the flow of outside air supplying the auxiliary power unit.

(11) Finally, the architecture 3 for supplying air to the auxiliary power unit also includes a circuit 32 for injecting air recovered from the pressurized cabin into the duct 30 for supplying the auxiliary power unit. This circuit comprises a distribution valve 33 allowing its connection to the circuit 11 for exhausting air from the pressurized cabin, and a nozzle 34 for injecting the air recovered from the pressurized cabin into the supply duct 30.

(12) Advantageously, the control unit 4 is also configured for controlling the opening of the distribution valve 33, through a plurality of configurations to vary the proportion of air drawn from the flow of air circulating in the exhaust circuit, from a configuration of the valve, called closed, wherein a zero flow of air is drawn from the exhaust circuit, to a second configuration, called open, wherein the entirety of the flow of air in the exhaust circuit is drawn to supply the auxiliary power unit.

(13) Advantageously, the proportion of air taken from the exhaust circuit is continuously variable between the open and closed configurations of the distribution valve 33.

(14) In this manner, the auxiliary power unit can benefit at the same time from being supplied with outside air which, while the aircraft is in flight, is poor in oxygen and cold but can have a high flow rate, and from being supplied with air coming from the cabin, which is richer in oxygen and at a higher temperature but at a lower flow rate.

(15) The control unit 4 advantageously controls the opening of the outside air admission valve 31 and the distribution valve 33 according to a phase of operation of the auxiliary power unit APU 2. Indeed, while it is starting, the APU unit 2 does not require a high air flow rate, and in addition this flow must be controlled so as to ensure a large enough starting window. On the other hand, when the APU unit is started and operating, the required flow of air needed for its operation is larger.

(16) The control unit is therefore configured to implement the method for supplying air to the auxiliary power unit described hereafter with reference to FIG. 2.

(17) During starting 100, to ignite the combustion chamber of the auxiliary power unit, the control unit 4 controls the valve 31 so that it remains closed and opens the valve 33 so that the entire supply of air to the APU unit comes from the cabin. The proportion of air drawn from the exhaust circuit 11 is variable depending on the dimensioning of the aircraft and of its different components. In circumstances where the start of the APU group takes place while the aircraft is in flight in altitude, the air coming from the cabin facilitates the start because it is richer in oxygen and has a higher temperature than outside air (e.g. of the order of 20 C. while the outside air has a negative temperature).

(18) In the transitional phase 200, once the combustion chamber of the auxiliary power unit 2 is ignited and begins to diverge, the control unit 4 can then progressively open the valve 31 and the valve 33 to cause a greater flow of air, coming both from the cabin and from the outside atmosphere.

(19) Finally, in the stabilized phase 300, the control unit 4 can, according to a first implementation mode 310, progressively close the distribution valve 33 so that the air supplied to the auxiliary power unit comes exclusively from outside, in which case a zero proportion of air is drawn from the exhaust circuit 11.

(20) As a variant 320, the control unit can maintain the two valves 31 and 33 open so that the air supplied to the auxiliary power unit includes both air coming from the outside and air recovered from the cabin 10.

(21) Very advantageously, for better accuracy in controlling valves 31 and 33, their control by the control unit is slaved to the rotation speed of the rotating shaft of the auxiliary power unit.

(22) The architecture proposed therefore facilitates the starting of the auxiliary power unit of an aircraft when it is in flight, and particularly when it is at altitude in an atmosphere poor in oxygen, because supply of air during starting has a low flow rate and is richer in oxygen than that of air in the atmosphere. Starting is facilitated.