Patent Application
20120151933
The invention relates to a method for feeding and ventilating with air an aircraft auxiliary power source plant centred on an auxiliary power unit (abbreviated as APU) or equivalent for supplying power on an aircraft. The invention also relates to an APU air feed and ventilation system capable of using such a method.
An APU can supply power to the items of equipment (alternators, pumps, pressure compressors, air conditioning) of the aircraft, directly and/or indirectly via a power transfer box, abbreviated as BTP, with multiple outlets, notably during the transitional flight phases (take-off, acceleration, stationary flight for helicopters, etc.). During the stable phases, for example cruising, the main engines can generate the electricity necessary for the items of equipment via the APU running as a generator or via a standalone generator.
The APUs are dedicated particularly to starting the main engines of the aircraft. For this purpose, the APUs supply energy to the gas generators of the engines until the running cycle of these gas generators is operational. They also supply non-propulsive energy (pneumatic, electrical and/or hydraulic) to the ground during the starting or standby phase. Certain secure APU units can also intervene in flight in the event of a failure of an engine in order to try to restart it or to supply energy to the items of equipment.
Like any turbine engine, an APU conventionally comprises a compressor/combustion chamber/turbine assembly forming a gas generator. Cool air is introduced into the compressor, then the compressed air, mixed with the fuel, causes the combustion in the dedicated chamber. The hot gases expand in the turbine which partially transmits the mechanical power produced to the compressor via a transmission shaft, the residual power being directed via a BTP to the items of equipment. In another type of architecture, the kinetic power of the exhaust gases may also drive a free turbine which, in its turn, transmits the power, via a shaft, to the items of equipment (alternators, pumps, pressure compressor, etc.). The residual gases are discharged via an exhaust nozzle.
Installing an APU in a compartment that is dedicated thereto, usually in the tail unit in an aeroplane or in the top portion of the cell of a helicopter, requires an arrangement of the air feed of the gas generator but also ventilation in this compartment. Specifically, the ventilation of the items of equipment connected to the gas generator and the feeding with air of the exchangers (air/oil or more usually air/fluid) must be provided in the compartment.
In particular, the new generations of APU of the “all electric” type require proportionally higher cooling air flow rates in the presence of additional alternators to be cooled, for example instead of a pressure compressor, and greater powers to be dissipated originating from the BTP and from the items of equipment.
The flows of air and of other fluids may interact in the compartment and their interactions must be thermally controlled in the complete operating range of the APU which can then cover considerable and sudden temperature variations. These flows may be generated mechanically—electroventilator, fan driven by the BTP—or by a vacuum caused by a jet pump effect induced by a discharger on the gas exhaust nozzle.
Known from patent document U.S. Pat. No. 7,364,117 is a passive cooling system for an APU arranged in a nacelle by an oil cooler. This cooler is placed in an air-flow duct which travels, by piping the outlet of the cooler, to the outlet discharger of the nacelle. The mounting of the cooler on pipework incorporating the discharger requires complex and bulky sheet metalwork which adversely affects the effectiveness of the ventilation and induces an increase in weight and cost.
Moreover, patent documents EP 0 968 918 and EP 0 626 039 provide that the air flow that traverses the oil cooler originates from an air inlet close to the discharger. The cooler is also mounted on pipework connected to the discharger. This solution causes the same drawbacks.
The object of the invention is precisely to prevent these drawbacks while achieving optimized ventilation of the compartment. To do this, the invention proposes to ventilate the compartment in an independent manner and to individualize the air feed of each item of equipment.
More precisely, the object of the invention is a method for feeding and ventilating with air an aircraft auxiliary power source plant comprising an auxiliary power unit APU and items of equipment connected to the APU, this plant being arranged in an aircraft compartment. In this method, the air feed is supplied to the APU and to each item of equipment that may require an air feed through an independent and separate passageway. The external ventilation of the APU and of the items of equipment of the plant is carried out through at least one ventilation air passageway that is independent and separate from the other air passageways.
In these conditions, the various feeding and ventilating air flows are captured separately at air inlets of the aircraft: the problems of distributing flow rates from a common inlet are thus avoided. Moreover, the use of internal mobile systems (valves, flaps, gates, etc.) can be dispensed with: reliability is increased and costs reduced accordingly.
According to preferred embodiments:
The invention also relates to a system for feeding and ventilating with air an aircraft auxiliary power source plant comprising an auxiliary power unit APU and items of equipment mounted in connection with the APU, this plant being arranged in an aircraft compartment. The APU is fitted with an exhaust nozzle which leads into a gas discharger mounted outside the compartment, from an opening of this compartment. In this system, separate and independent ducts channel the air between air inlets, made through the compartment, and respective inlets of the gas generator and items of equipment which may require an air feed. At least one ventilation duct that is separate and independent from the other ducts is coupled to an air inlet of the compartment in order to ventilate the APU and the items of equipment of the plant.
According to particular embodiments:
Other aspects, features and advantages of the invention will appear in the non-limiting description of the following embodiment, with reference to the appended drawings which represent respectively:
In
In
In this description, the “upstream-downstream” qualifier follows the direction defined by the gas flows in the gas generator, the “downstream-upstream” qualifier follows the reverse direction.
With reference to
As appears also in the upstream-downstream view of
The ducts 3a to 3c are box assemblies which aspirate the air directly. These box assemblies may be components of the items of equipment or, as illustrated, extensions formed by ducts up to the inlets 4a to 4c. The same applies for the exhaust outlet 6 for the air flow Fe of the alternator 13.
In operation, the combustion gases G of the APU 10 which escape through the discharger 20 via the nozzle 3 generate a vacuum in the compartment 2. The vacuum is caused by the jet pump effect induced by the appropriate shape of the mouth 22 of the discharger 20 resting on the opening 21. This vacuum in its turn causes an aspiration of air originating from the air inlet 4c via the exchanger 14. Leaving the exchanger, the air then ventilates the compartment 2 and all of the items of equipment via the air flows Fv.
In certain cases, the air flow rate through the exchanger 14 may be too much for the requirements of the exchanger. Advantageously, the exchanger incorporates a thermostatic valve gate which makes it possible to divert the oil flow below a determined temperature threshold.
Advantageously, the exchanger 14 is arranged upstream in the compartment so that the vacuum, which draws the air towards the discharger 20 downstream, causes the air flows Fv to flow onto the items of equipment and the gas generator in an evenly distributed manner. Moreover, the items of equipment are distributed in the compartment so that the ventilation of the items of equipment and of the APU is maximized.
The exchanger 14 is arranged as close as possible to its air inlet 4c so that the duct 3c for connection to the exchanger is of minimal length in order to optimize heat exchange, pressure losses, weight and bulk.
By virtue of the air feed passageways formed by the ducts 3a to 3c, the air flows F1 to F3 dedicated to the specific feeds are independent and totally separate from the ventilation flows Fv for the items of equipment of the compartment.
The invention is not limited to the embodiment described and shown. It is for example possible to provide several ventilation ducts arranged upstream, in the compartment of the APU. Moreover, the air inlets may be distributed over several walls of the compartment and not on a single wall as shown in the appended figures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 60603 | Dec 2010 | FR | national |
