Method and architecture for supplying air to an auxiliary power unit for an aircraft

Description

Technical Field

[0001] The present invention relates to the field of auxiliary power units (APU) comprising a gas generator and installed in aircraft and it relates more particularly to a method of supplying air to an auxiliary power unit from a pressurized cabin of the aircraft and the associated architecture. Prior art

[0002] The reinjection of cabin air into the high pressure (HP) compressor of an APU is known in particular from application WO2014118455A1, the objective of which is to facilitate the ignition at altitude of this APU, the cabin air being mixed with outside air (atmospheric air) in a channel upstream of this HP compressor. Different operating modes depending on the flight phases of the aircraft are envisaged, including: a start-up mode, where the HP compressor is supplied only with cabin air; a stabilized mode, where the APU is supplied mainly with outside air; and a transient mode where the outside air is gradually injected into the channel. This solution improves the operability of the APU by facilitating its re-ignition.However, air supply from the cabin becomes a problem especially in case of failure of the cabin ventilation system and high altitude performance is not improved in any way, as power generation capacity (operability) is in fact reduced at high altitude.

[0003] Furthermore, with such an air supply configuration from the aircraft cabin, the available flow rate that can be injected into the APU is necessarily limited by that provided to ventilate the cabin. However, particularly for commercial aircraft, this flow rate is relatively low and, by constraining the operation of the APU, therefore significantly degrades its performance.

[0004] Document US5722229 proposes the injection of cabin air into the high pressure compressor from a load compressor powered by an electric motor.

[0005] Documents US20070234731 and WO2014118455 propose an architecture according to the preamble of claim 5.

[0006] Document US20190367173 proposes an architecture for supplying air to an auxiliary power unit from cabin air and a pressurized air system. Statement of the invention

[0007] The main aim of the present invention is therefore to overcome these drawbacks by proposing a method and an air supply architecture making it possible to optimize the benefits of cabin air recirculation on the performance of the APU. The invention also aims to improve specific consumption, particularly at high altitude.

[0008] This aim is achieved by a method of supplying air to a high-pressure compressor of an auxiliary gas generator from a pressurized cabin of an aircraft, a load compressor being driven in rotation by a common rotation shaft providing a mechanical connection between the high-pressure compressor and a high-pressure turbine of the auxiliary gas generator, characterized in that a second air flow from the load compressor is added to a first flow of air extracted from the cabin.

[0009] Thus, by providing a source of pressurized air flow complementary to the high pressure compressor, the present invention makes it possible to increase the power that can be extracted from the auxiliary gas generator while facilitating its re-ignition at high altitude and thus increasing its overall efficiency without significantly impacting its installation.

[0010] Advantageously, a third air flow from another load compressor also driven in rotation by the common rotation shaft of the auxiliary gas generator is added to the first and second air flows to supply the high pressure compressor.

[0011] Preferably, the first air flow extracted from the cabin is limited to a determined maximum value and the second air flow further supplies an air conditioning system of the aircraft.

[0012] The invention also relates to an architecture for supplying air to a high-pressure compressor of an auxiliary gas generator from a pressurized cabin of an aircraft, characterized in that it comprises: a charge compressor driven in rotation by a common rotation shaft providing a mechanical connection between the high-pressure compressor and a high-pressure turbine of the auxiliary gas generator and supplied by an external air intake; a first control valve mounted at the outlet of the charge compressor to control all or part of the air flow delivered by the charge compressor; a second control valve mounted at the outlet of the pressurized cabin to control the air flow taken from the pressurized cabin; a mixer receiving the outlets of the first and second control valves to add the air taken from the pressurized cabin to all or part of the air delivered by the charge compressor;and a third control valve mounted at the outlet of the mixer to control the flow of air injected into the high pressure compressor of the auxiliary gas generator.;

[0013] Preferably, this air supply architecture further comprises another load compressor also associated with the auxiliary gas generator and a fourth control valve mounted at the outlet of this other load compressor to control all or part of the air flow delivered by this other load compressor to the mixer receiving, in addition to the outlets of the first and second control valves, the outlet of this fourth control valve.

[0014] Advantageously, it further comprises a discharge valve associated with each of the load compressors to ensure the stability of each of the load compressors by discharging into the atmosphere all or part of the air delivered by each of the load compressors.

[0015] Preferably, it further comprises at the outlet of the pressurized cabin a flow limiter to limit the flow of air extracted from the pressurized cabin.

[0016] Advantageously, the charging compressor is connected to an air conditioning system of the aircraft and there is further provided at the outlet of the charging compressor an air flow control valve mounted if necessary in series with an isolation valve to deliver a determined air flow to an air conditioning system of the aircraft.

[0017] Preferably, the third control valve is further configured to, if necessary, adapt the flow of air injected into the high-pressure compressor to the flow available at the outlet of the mixer.

[0018] Advantageously, it also includes a selection valve mounted at the inlet of the high-pressure compressor to select the highest pressure flow rate between the external air intake and the outlet of the third regulating valve.

[0019] Preferably, it further comprises at the outlet of the pressurized cabin a discharge valve to the atmosphere.

[0020] Finally, the invention also relates to an aircraft comprising a pressurized cabin, an auxiliary gas generator and an air supply architecture as mentioned above. Brief description of the drawings

[0021] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting character and in which: [ Fig. 1 ] there figure 1 schematically illustrates an air supply architecture of an auxiliary gas generator according to the invention, and [ Fig. 2 ] there figure 2 shows the ratio between the extracted mechanical power and the nominal power for different operating conditions of an auxiliary gas generator according to the invention. Description of the embodiments

[0022] There figure 1 schematically illustrates in an aircraft 10 comprising a pressurized cabin 12 and an auxiliary gas generator 14 conventionally comprising a high-pressure compressor 140, a combustion chamber 142 and a high-pressure turbine 144, an air supply architecture for the high-pressure compressor of this auxiliary gas generator according to the invention. The term "high pressure" is used herein to specify the compressor of the auxiliary gas generator, even if the latter only comprises a single compressor supplying compressed air to the combustion chamber, and thus distinguish it from the load compressor defined below and associated with the auxiliary gas generator.

[0023] More particularly, this architecture comprises: a charge compressor 16 associated with the auxiliary gas generator 14 (i.e. driven in rotation by the common rotation shaft 146 ensuring the mechanical compressor-turbine connection of the auxiliary gas generator) and supplied by an outside air intake 18; a first regulating valve 20 mounted at the outlet of the charge compressor to control all or part of the air flow delivered by this charge compressor; a second regulating valve 22 mounted at the outlet of the pressurized cabin 12 to control the air flow taken from the pressurized cabin; a mixer 24 receiving the outlets of the first and second regulating valves 20, 22 to add the air taken from the pressurized cabin 12 to all or part of the air delivered by the charge compressor 16;and a third regulating valve 26 mounted at the outlet of the mixer 24 to control the flow of air injected into the high pressure compressor 140 of the auxiliary gas generator 14.;

[0024] The third regulating valve 26 allows, if necessary, the flow of air injected into the high pressure compressor 140 of the gas generator to be adapted to the flow available at the outlet of the mixer 24 by adjusting the ingestion pressure.

[0025] The load compressor 16 is provided at the inlet with guide valves 160 (IGV for Inlet Guide Vanes) to regulate its operation and ensure its supply from the outside air intake 18 which also supplies air directly to the high-pressure compressor via a selection valve 28 receiving on the one hand this outside air on a first inlet and on the other hand the air leaving the third regulating valve 26 on a second inlet (it will be noted that the high-pressure compressor is here without guide valves). This valve selects the flow rate of higher pressure between the outside air intake and the outlet of the third regulating valve.

[0026] An electric generator 30 is mounted on the common rotation shaft 146, possibly via a reduction box 32, to deliver electrical power to various electrical systems of the aircraft and in particular to an air conditioning system 34 (ECS for Environmental Control System) of the aircraft ensuring the ventilation of the pressurized cabin 12.

[0027] Downstream of the load compressor is mounted a set of valves to ensure various functions of the architecture. First of all, a discharge valve 36 (SCV or Surge Control Valve) intended to ensure the stability of the load compressor 16 by discharging all or part of the air delivered by this load compressor to the atmosphere. Then, the load compressor being connected to the air conditioning system, it can be provided, when necessary for the air conditioning system, an air flow control valve 40 (ABRV for Aircraft Bleed Regulation Valve) which can be mounted in series with an isolation valve 38 (LCV for Load Control Valve) to deliver a determined air flow to the air conditioning system 34. These valves as well as the first control valve 20 (RCV for Recirculation Control Valve) are mounted on the same pipe 42 emanating from the load compressor 16.

[0028] Upstream of the second regulating valve 22, therefore at an outlet of the pressurized cabin 12, a flow limiter 44 may be provided to limit the flow of air extracted from this pressurized cabin, the air content of which may also be discharged to the atmosphere if necessary by a discharge valve 46 placed at another outlet of the pressurized cabin.

[0029] All of these valves are of course controlled from a control module 48 which acts on their opening according to the different flight phases of the aircraft, as will now be explained further.

[0030] In applications where the air flow from the charge compressor 16 proves insufficient to supply the high-pressure compressor 140 (for example in the case of a business jet), an additional air flow can be added from an additional air supply source 50, comprising another charge compressor 52 also associated with the auxiliary gas generator 14 via the common rotation shaft 146, and a set of valves whose control is carried out in an identical manner to that of the first charge compressor 16 via the control module 48.

[0031] More particularly, an additional control valve 54 is mounted at the outlet of this load compressor to control all or part of the air flow delivered to the mixer 24 which, in addition to the outlets of the first and second control valves 20, 22, will receive the outlet of this additional control valve.

[0032] Like the first load compressor 16, this additional load compressor 52 is provided at the inlet with guide valves 520 to regulate its operation and ensure its supply from an external air intake 58 which may be the same as that of the first. Similarly, a discharge valve 56 is provided to ensure the stability of this additional load compressor 52 by discharging all or part of the air that it delivers into the atmosphere.

[0033] The operation of this air supply architecture is as follows. In the majority of current applications of auxiliary power units (APUs), the latter only provides mechanical power in flight (and electrical power via generator 30), and the air sampling for the air conditioning system (ECS 34) is done on the main engines of the aircraft (valves 38 and 40 are then closed).

[0034] With the present invention, the APU comprises a charge compressor 16 associated with the gas generator and the hot air from this charge compressor is diverted to the mixer 24 which mixes it with the colder air from the pressurized cabin 12. For example, the temperature of the hot air could be close to 450K, while the temperature of the colder air would remain below 400K. However, by means of the isolation valves 38 and regulation valves 40, the charge compressor can also supply pneumatic energy to the air conditioning system 34, in order to distribute the available flow between this system 34 and the high pressure compressor 140 when necessary.

[0035] The advantage of this solution is that it supplies the high-pressure compressor with pressurized air and with a sufficient flow rate so as not to over-constrain the operation of the auxiliary gas generator. In addition, in nominal operation, the auxiliary gas generator then operates over a reduced operating range (cabin temperature and pressure being regulated over all flight phases) for which it can be optimized. This solution does not require adding major components to current architectures and uses a component currently unused in flight (the load compressor), which facilitates its installation. The load compressor will always provide a maximum flow rate, within the limits of its stability domain and a compression ratio compatible with the cabin pressure, a greater recirculated flow rate allowing for optimized flight performance.

[0036] On the ground and at low altitude, the control valves 20, 22 and 26 are closed, the high pressure compressor 140 is supplied with outside air from the intake 18 via the selection valve 28 and the auxiliary gas generator 14 operates in a “classic” mode, then being able to provide electrical power and nominal pneumatic power via its load compressor.

[0037] In flight and in nominal operation, the control valves 20 and 26 are open as well as the control valve 22 connecting the pressurized cabin to the auxiliary gas generator 14, the high pressure compressor 140 is supplied with a mixture of cabin air and air from the load compressor according to the selection made at the highest pressure by the selection valve 28, and the flow rates are controlled by the opening of the valves in order to maintain the cabin pressure at an acceptable level. It should be noted that in flight, the air conditioning system 34 is generally not supplied with pressurized air by the load compressor, since this pressurized air is taken from the engine(s) of the aircraft. As a result, the isolation valve 38 and the air flow control valve 40 will generally remain closed in flight, which makes it possible to supply the mixer 24 with the entire air flow provided by the load compressor 16, via the control valve 20.The guide valve 160 is also piloted so that the charge compressor 16 can provide the required flow rate at a pressure compatible with the flow from the cabin, optimum performance being obtainable when the charge compressor provides maximum flow rate to the high pressure compressor, its flow rate capacity being a function of altitude.

[0038] In the event of cabin depressurization, the control valve 22 is commanded to close or closes automatically and the cabin is isolated from the air recirculation circuit from the charging compressor. The auxiliary gas generator 14 is then supplied from the outside air intake 18, and can generate electrical and / or pneumatic power nominally.

[0039] In the event of the auxiliary gas generator going out, the control valve 20 closes and the cabin air is reinjected into the compressor in order to facilitate the re-ignition of the auxiliary gas generator 14 regardless of the altitude.

[0040] There figure 2presents an example of the ratio between the mechanical power extracted from the auxiliary gas generator and its nominal power in steady state, for different altitudes and according to four distinct architectures: a "classic" architecture where the high-pressure compressor is supplied only with outside air (curve 60), an architecture where the high-pressure compressor is supplied only and without flow limitation by air from the cabin (curve 62), an architecture where the high-pressure compressor is supplied only by cabin air whose flow rate is saturated between 0.4 and 1.0 kg / s (curves 64, 66, 68, 70) and an architecture in accordance with the invention where the high-pressure compressor is supplied by cabin air whose flow rate is saturated between 0.4 and 1.0 kg / s (curves 72, 74, 76, 78) and mixed with air from the load compressor (the intermediate curves correspond to flow rates of 0.6 and 0.8 kg / s).

[0041] It can be noted that the contribution of the charge compressor makes it possible to increase the mechanical power that can be extracted from the auxiliary gas generator, the power taken by the charge compressor from the rotation shaft being compensated by the flow rate that it provides (reducing the constraint on the operation of the auxiliary gas generator). For the different levels of cabin air flow rate retained, it can also be noted that an input of available power corresponds to a reduction in the specific consumption of the auxiliary gas generator.

[0042] Comparison of the extracted powers gives the transition altitude from a "conventional" mode (supply by outside air - curve 60) to the supply mode of the invention (supply by cabin air mixed with recirculated air from the load compressor - curves 72-78). In the illustrated case, the transition takes place between approximately 3 km (10000 ft - case of a cabin air flow rate of 1.0 kg / s) and 10 km (35000 ft - case of a cabin air flow rate of 0.4 kg / s). In the case of nominal operation with an available cabin air flow rate of 1.0 kg / s (corresponding to an application to medium-haul aircraft), a virtually constant available mechanical power is thus obtained for altitudes between 0 and approximately 15 km (51000 ft), thus eliminating the pressure-altitude effect on the power supply by the gas turbine.

[0043] It will be noted that the addition of one or more heat exchangers can be considered to increase the power generated by the load compressor, and reduce its consumption. In particular, a heat exchanger (not shown) can be placed upstream of the control valve 20 and / or downstream of the mixer 24 between the cabin air and the air from the load compressor. The coupled heat source could be, for example, the engine oil circuit.

[0044] Similarly, the use of batteries (not shown) downstream of the electric generator 30 can also be considered in order to size the auxiliary gas generator on an average load, and therefore to optimize its operation on a nominal point.

Claims

1. A method for supplying air to a high-pressure compressor (140) of an auxiliary gas generator (14) from a pressurized cabin (12) of an aircraft, a load compressor (16) being rotationally driven by a common rotation shaft (146) providing a mechanical coupling between the high-pressure compressor and a high-pressure turbine (144) of the auxiliary gas generator, a second air flow coming from the load compressor (16) being added to a first air flow extracted from the cabin.

2. The method for supplying air as claimed in claim 1, characterized in that a third air flow coming from another load compressor (52) also rotationally driven by the common rotation shaft (146) of the auxiliary gas generator (14) is added to the first and second air flows to supply the high-pressure compressor (140).

3. The method for supplying air as claimed in claim 1, characterized in that the first air flow extracted from the cabin is limited to a given maximum value.

4. The method for supplying air as claimed in any of claims 1 to 3, characterized in that the second air flow further supplies an air conditioning system of the aircraft (34).

5. An architecture for supplying air to a high-pressure compressor (140) of an auxiliary gas generator (14) from a pressurized cabin (12) of an aircraft, comprising load compressor (16) supplied by an outside air intake (18), a common rotation shaft (146) providing a mechanical coupling between the high-pressure compressor (140) and a high-pressure turbine (144) of the auxiliary gas generator and a mixer (24) to add the air drawn from inside the pressurized cabin to the air delivered by the load compressor to be injected into the high-pressure compressor of the auxiliary gas generator, characterized in that the load compressor is rotationally driven by a common rotation shaft (146); and in that the architecture for supplying air further comprises a first regulation valve (20) assembled at the outlet of the load compressor to control all or part of the air flow delivered by the load compressor; a second regulation valve (22) to be assembled at the outlet of the pressurized cabin to control the air flow drawn from inside the pressurized cabin; the mixer (24) receiving the outputs of the first and second regulation valves to add the air drawn from inside the pressurized cabin to all or part of the air delivered by the load compressor; and a third regulation valve (26) assembled at the outlet of the mixer to control the air flow injected into the high-pressure compressor of the auxiliary gas generator.

6. The architecture for supplying air as claimed in claim 5, characterized in that it further comprises another load compressor (52) also associated with the auxiliary gas generator (14) and a fourth regulation valve (54) assembled at the outlet of this other load compressor to control all or part of the air flow delivered by this other load compressor to the mixer (24) receiving, in addition to the outputs of the first (20) and second (22) regulation valves, the output of this fourth regulation valve (54).

7. The architecture for supplying air as claimed in claim 5 or claim 6, characterized in that it further comprises a bleed valve (36, 56) associated with each of the load compressors (16, 52) to ensure the stability of each of the load compressors by bleeding into the atmosphere all or part of the air delivered by each of the load compressors.

8. The architecture for supplying air as claimed in any of claims 5 to 7, characterized in that it further comprises at the outlet of the pressurized cabin a flow limiter (44) to limit the air flow extracted from the pressurized cabin.

9. The architecture for supplying air as claimed in any of claims 5 to 8, characterized in that the load compressor (16) is connected to an air conditioning system (34) of the aircraft.

10. The architecture for supplying air as claimed in claim 9, characterized in that it further comprises at the outlet of the load compressor an air flow regulation valve (40) assembled, if necessary, in series with a shutoff valve (38) to deliver a given air flow to an air conditioning system (34) of the aircraft.

11. The architecture for supplying air as claimed in any of claims 5 to 10, characterized in that the third regulation valve (26) is further configured to, if necessary, adapt the air flow injected into the high-pressure compressor (140) to the flow available at the outlet of the mixer (24).

12. The architecture for supplying air as claimed in any of claims 5 to 11, characterized in that it further comprises, assembled at the inlet of the high-pressure compressor a selector valve (28) to select the flow with the highest pressure between the outside air intake and the outlet of the third regulation valve.

13. The architecture for supplying air as claimed in any of claims 5 to 12, characterized in that it further comprises at the outlet of the pressurized cabin a bleed valve bleeding into the atmosphere (46).

14. An aircraft including a pressurized cabin, an auxiliary gas generator and an architecture for supplying air as claimed in any of claims 5 to 13.