Abstract:
An aircraft propulsion assembly includes an engine, a nacelle surrounding the engine, and a system for extinguishing a fire that may occur in the engine and/or in the nacelle. The extinguishing system has means for supplying an extinguishant to at least one extinguishant distribution pipe which opens into a cavity of the engine and/or a cavity of the nacelle. The extinguishing system also includes means for supplying said at least one pipe with air so as to ventilate the or each cavity.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of ventilation of an aircraft propulsion assembly. 
       PRIOR ART 
       [0002]    An aircraft propulsion assembly comprises an engine and a nacelle surrounding said engine, which is generally a turbine engine. The nacelle comprises a rotationally symmetrical casing which defines an annular flow duct for a flow of air around the engine, this flow of air being referred to as the secondary flow in the case of a bypass turbine engine. The nacelle defines a first annular cavity around the casing. Some equipment in the propulsion assembly is mounted in the nacelle, i.e. in the aforementioned annular cavity, and can be fastened to the casing of said nacelle. The external wall of the nacelle generally comprises removable cowls for allowing access to this equipment during a maintenance operation. 
         [0003]    The engine comprises an internal annular flow duct for a flow of air referred to as the primary flow in the case of a bypass turbine engine. The engine comprises rotationally symmetrical coaxial casings which are surrounded by a rotationally symmetrical wall, the inside of which defines the duct for the secondary flow. This wall extends at a distance from the engine casings and defines a second annular cavity around said casings. Some equipment is mounted in this second annular cavity. 
         [0004]    The equipment mounted in the cavities in the propulsion assembly is sensitive to heat to a greater or lesser extent and is ventilated during operation. This is in particular the case for an EEC-type on-board computer which in particular allows actuators of the engine to be monitored with a view to optimising the turbine-engine performance (FR-B1-2 960 912). This computer is generally mounted in the nacelle together with other equipment (accessory gearbox (AGB), exchangers, etc.). 
         [0005]    In order to ventilate the internal cavity in the nacelle, said nacelle comprises a scoop for drawing off air during flight, the drawn-off air then being discharged through an air outlet grating of the nacelle. However, on the ground, this ventilation is virtually non-existent and the natural convection in the annular space in the nacelle may prove to be insufficient to ensure the ventilation of the equipment thereof. During operation, the computer generates significant thermal power which it has to dissipate regardless of whether the engine is in operation or is not running. Moreover, even when the engine is not running after having been in operation, the hot parts of the engine continue to radiate heat and heat up the peripheral cooler parts of the engine, which cooler parts can therefore reach temperatures when the engine is not running that are close to or greater than the temperatures thereof when the engine is in operation. 
         [0006]    Therefore, there is a real need for a system which is capable of ventilating this type of cavity in a propulsion assembly even when the engine is not running. 
         [0007]    Moreover, an aircraft propulsion assembly is provided with a system for extinguishing a fire which may break out in the engine and/or in the nacelle. This extinguishing system comprises means for supplying an extinguishing agent to at least one pipe which is intended for dispensing said extinguishing agent and leads into a cavity in the engine and/or a cavity in the nacelle. This extinguishing system is generally connected to a fire detection system (of the FDU type (fire detection unit)) which comprises sensors which are mounted on the engine and/or the nacelle and are intended for emitting an alert signal for the attention of the aircraft pilot when at least one of the sensors detects a fire breaking out. 
         [0008]    In the current art, the sole purpose of the pipe of the extinguishing system is to dispense extinguishing agent. Given the fact that fires rarely break out, this pipe is generally never used. However, an aircraft propulsion assembly always comprises said pipe for reasons of safety and certification. 
         [0009]    The present invention provides a simple, effective and economical solution to the above-mentioned need from the prior art. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention proposes an aircraft propulsion assembly comprising an engine, a nacelle surrounding the engine, and a system for extinguishing a fire which may break out in the engine and/or in the nacelle, this extinguishing system comprising means for supplying extinguishing agent to at least one pipe which is intended for dispensing said extinguishing agent and leads into a cavity in the engine and/or a cavity in the nacelle, characterised in that said propulsion assembly further comprises means for supplying air to said at least one pipe in order to ventilate the cavity/cavities. 
         [0011]    The invention therefore consists in giving a new additional function to a known means. Indeed, as is the case in the prior art, the pipe for dispensing the extinguishing agent of the fire extinguishing system is used for dispensing this agent into the cavity/cavities in the propulsion assembly if a fire breaks out. According to the invention, this pipe is also used to ventilate this cavity/these cavities. For this purpose, the pipe is connected to air supply means which provide the pipe with an air flow, which air flow thus being conveyed via the pipe as far as the cavity/cavities to be ventilated. The invention thus makes it possible to use an existing means (pipe) to convey ventilation air as far as a cavity in the nacelle and/or the engine, this existing means being used for a completely different purpose in the prior art (dispensing extinguishing agent). As described above, the extinguishing system of a propulsion assembly is rarely used. The pipe thereof can therefore be used to ventilate the cavities in the propulsion assembly even when the engine is not running. Indeed, the air supply means of the pipe advantageously operate independently of the engine and can therefore operate when the engine is not running. The equipment mounted in the cavities in the propulsion assembly can therefore be ventilated when the engine is not running, and this makes it possible to increase the service life of this equipment. 
         [0012]    The air supply means preferably comprise a ventilator fan. This ventilator fan may be an electric ventilator fan. 
         [0013]    The supply means may be connected to said at least one pipe by a valve and/or non-return flap. They may be connected to said pipe by means of a Y-shaped bypass for example. 
         [0014]    The supply means can be housed in the nacelle. 
         [0015]    In a variant, the supply means can be housed in a strut for connecting the propulsion assembly to the aircraft. The connection between a propulsion assembly and the strut thereof generally consists of a fire-resistant wall which is suitable for minimising the spread of a fire which may break out in the propulsion assembly. The supply means are thus protected from a fire which may break out in the nacelle. 
         [0016]    The supply means may be designed to output an air flow rate of between 1 and 500 g/s. 
         [0017]    The pipe may advantageously comprise at least one outlet located close to an air intake scoop of the nacelle or engine. 
         [0018]    The present invention also relates to a method for ventilating a cavity in an engine and/or a cavity in a nacelle of an aircraft propulsion assembly, this propulsion assembly comprising a system for extinguishing a fire which may break out in the engine and/or in the nacelle, this extinguishing system comprising means for supplying extinguishing agent to the least one pipe which is intended for dispensing said extinguishing agent and leads into the cavity in the engine and/or the cavity in the nacelle, characterised in that said method comprises supplying air to said at least one pipe. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention will be better understood and other details, features and advantages of the invention will emerge upon reading the following description given by way of non-limiting example and with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  is a schematic side view of an aircraft propulsion assembly, 
           [0021]      FIG. 2  is a highly schematic front view of an aircraft propulsion assembly, 
           [0022]      FIG. 3  is a view which corresponds to  FIG. 2  and shows an embodiment of the invention, and 
           [0023]      FIG. 4  is a view which corresponds to  FIG. 2  and shows a variant of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Reference is first made to  FIG. 1 , which shows an aircraft propulsion assembly  10 , this propulsion assembly comprising a strut  12  for connection to a structural part of the aircraft, which is in this case a wing  14  of the aircraft. 
         [0025]    The propulsion assembly  10  comprises an engine  16  of the turbine engine type which is surrounded by a nacelle  18 , the nacelle  18  defining a first annular flow duct  20  for a secondary flow around the engine which comprises a second internal flow duct (not shown) for a primary flow. 
         [0026]    The engine  16  typically comprises, from upstream to downstream, in the direction of the flows, a fan, at least one compression module, a combustion chamber, at least one turbine module, and an exhaust nozzle for ejecting combustion gases. 
         [0027]    The fan of the engine  16  is surrounded by a casing  22  of the nacelle  18 , which is itself surrounded by a rotationally symmetrical wall  24  of the nacelle. Equipment is mounted in the annular cavity  26  defined by the external wall  24  and the casing  22  of the nacelle  18 . 
         [0028]    The compression module, the combustion chamber and the turbine module comprise external casings  28  which are surrounded by a rotationally symmetrical wall  30 . The inside of this wall  30  defines the duct  20  for the secondary flow and extends at a distance from the external casings  28  so as to define an annular cavity  32  therewith, in which cavity equipment is also housed. 
         [0029]    The propulsion assembly  10  further comprises a system for extinguishing a fire which may break out in the engine  16  and/or in the nacelle  18 . This extinguishing system comprises means  34  for supplying extinguishing agent to the at least one pipe  36  for dispensing said extinguishing agent. 
         [0030]    As can be seen in the figure, this pipe  36  may comprise a plurality of inlets (in this case two) which are each connected to supply means  34 , and a plurality of outlets  38  (in this case two). In the example shown, the pipe  36  comprises a first outlet  38  in the cavity  26  in the nacelle  18  and a second outlet  40  in the cavity  32  in the engine  16 . In this figure, each outlet  38 ,  40  is Y-shaped and comprises two outlet openings for spraying extinguishing agent in directions substantially tangential to the casing  22  or casings  28 . The outlet  38  is preferably located close to an air intake scoop of the nacelle  16  (for ventilating the cavity  26  when the engine is in operation) and the outlet  40  is preferably located close to an air intake scoop of the engine (for ventilating the cavity  32  when the engine is in operation). 
         [0031]    The outlets  38  and  40  are oriented so as to coact with the air intake scoops of the nacelle  18  and of the engine  16 , respectively, in order to generate flows in similar directions. 
         [0032]    This makes it possible to prevent the extinguishing agent from leaving the regions to be extinguished before this has been achieved. Moreover, by virtue of the invention, aeration by means of the scoop or by means of the invention is similar and makes it easier to manage the ventilation flows. 
         [0033]    The pipe  36  is made of a material which is resistant to fire and in particular to very high temperatures (for example above 1000° C.). 
         [0034]    The supply means  34  may comprise a pressurised tank for extinguishing agent (consisting of halon for example), an outlet of which is connected to an inlet of the pipe  36  by means of a priming system, for example a pyrotechnic primer. This priming system is controlled remotely by the aircraft pilot from the cockpit of the aircraft. 
         [0035]    The extinguishing system is connected to a fire detection system  42  (for example of the FDU type) which is connected to sensors  44  which are mounted on the engine  16  and the nacelle  18  and are each intended to emit an alert signal for the attention of the aircraft pilot when at least one of the sensors  44  detects a fire breaking out. The sensors  44  comprise thermocouples, for example. 
         [0036]    As is schematically shown in  FIG. 2 , the supply means  34  are generally mounted on the perimeter of the aircraft, this perimeter being schematically defined in this case by the broken lines  46  and comprising the strut  12 . The pipe  36  extends from the supply means  34  as far as the cavities  26 ,  32 . The pipe  36  therefore has to pass through the duct for the secondary flow  20  and can, for this purpose, be housed in a tubular arm through which support systems of an intermediate casing of the engine pass. The broken lines  46  represent a fire-resistant wall to be passed through, and therefore there must be the minimum amount of pipe at this location in order to minimise the number of openings in the wall. 
         [0037]    Reference is now made to  FIG. 3 , which shows a first embodiment of the invention. 
         [0038]    According to the invention, means are provided for supplying air to the pipe  36 , this air being intended for being conveyed via the pipe  36  as far as the cavities  26 ,  32  in order to ventilate said cavities. 
         [0039]    In the example shown, the air supply means comprise an electric ventilator fan  48 , the air outlet  50  of which is connected to the pipe  36  in the region of the inlet  52  thereof connected to the supply means  34 . This connection can be produced by means of a Y-shaped bypass (preferably upstream of the fire-resistant wall) of which one of the lateral legs is connected to the ventilator fan  48 , the other lateral leg of which is connected to the supply means  34 , and the central leg of which is connected to the cavities  26 ,  32 . The connection between the ventilator fan  48  and the pipe  36  may consist of an electromagnetic valve or a non-return flap. 
         [0040]    The ventilator fan  48  may be designed to output an air flow rate of between 1 and 500 g/s. 
         [0041]    The ventilator fan  48  is preferably electrically controlled by control means which are independent of the engine  16  such that said ventilator fan can operate when the engine is not running. These control means are for example integrated in the electronic network of the aircraft. 
         [0042]    In the example shown in  FIG. 3 , the ventilator fan  48  is housed in the strut  12 . 
         [0043]    The variant of the invention shown in  FIG. 4  differs from the above-described embodiment basically in that the ventilator fan  48  is housed in the nacelle  18 , i.e. in the annular cavity  26  in the nacelle. The ventilator fan  48  may be electrically controlled by control means of the engine which are designed to operate and remain in operation when the engine is not running. 
         [0044]    As shown in  FIG. 1 , the invention may be applied to a propulsion assembly  10  fastened to a wing  14  of an aircraft, the strut  12  therefore being located at  12  (twelve o&#39;clock) using a clock face analogy. In a variant and as shown in  FIGS. 3 and 4 , the invention may be applied to a propulsion assembly  10  which is fastened to the fuselage of the aircraft, the strut  12  therefore being located at 3 o&#39;clock or 9 o&#39;clock for example. It is also conceivable to apply the invention to other types of propulsion assemblies such as those that are inside the fuselage of the aircraft at least in part.