Patent Publication Number: US-2020291854-A1

Title: Aircraft propulsion system including a heat exchanger system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the European patent application No. 19162017.8 filed on Mar. 11, 2019, the entire disclosures of which are incorporated herein by way of reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an aircraft propulsion system including a heat exchanger system, together with an aircraft including at least one such propulsion system. 
     BACKGROUND OF THE INVENTION 
     In order to supply hot air whether for a system of air, conditioned so as to guarantee the comfort of the passengers, or for a de-icing system for de-icing the outside surfaces of an aircraft, this system includes a heat exchanger system, which is schematically illustrated in  FIG. 4 . 
     The heat exchanger system  500  is disposed in the vicinity of the turbojet of the aircraft and includes a heat exchanger  502 . The turbojet is fixed to the structure of the wing thanks to a pylon, and the heat exchanger  502  is located between the pylon and the pylon fairing. 
     The heat exchanger  502  is supplied with hot air through a first supply pipe  504 , which bleeds hot air from the high pressure stage  506  or at the intermediate pressure stage  508  of the turbojet, respectively through a first valve  510  and a second valve  512 . The first supply pipe  504  also includes a regulating valve  514 , which enables regulation of the pressure at the inlet of the heat exchanger  502 . 
     The heat exchanger  502  is supplied with cold air by a second supply pipe  516 , which bleeds cold air from the fan duct of the turbojet. The second supply pipe  516  also includes a regulating valve  518 , which regulates the quantity of cold air introduced into the heat exchanger  502  so as to regulate the temperature of the hot air exiting the heat exchanger  502 . 
     After having passed through the heat exchanger  502 , the cold air, which has been heated, is expelled to the outside through an evacuation pipe  520 . 
     After having passed through the heat exchanger  502 , the hot air, which has been cooled, is directed through a transfer pipe  522  to the air management systems like the air conditioning system or the de-icing system. 
     The heat exchanger system  500  includes a temperature sensor  523 , which measures the temperature of the hot air exiting the heat exchanger  502  and a control unit  524 , which controls the valves according to the temperature measured by the temperature sensor  523  and the temperature desired for the hot air exiting the heat exchanger  502 . 
     The heat exchanger  502  is with cross flow, that is to say, the hot air and the cold air enter the heat exchanger  502  and exit the heat exchanger  502  along two globally perpendicular directions. 
     EP-A-0 934 876, US-A-2012/045317 and WO-A-2018/002855 disclose propulsion systems of the state of the art. 
     Actually, the size of the turbojet increases due to the necessity to increase the bypass ratio and the overall pressure ratio. Due to this increasing of the turbojet, the space allocated to the heat exchanger  502  is reduced and the air exhaust of the heat exchanger  502  is close to the leading edge of the wing, creating perturbations to the boundary layer. 
     SUMMARY OF THE INVENTION 
     An aim of the present invention is to propose an aircraft propulsion system including a heat exchanger system, which is less bulky and thus enables better integration in the propulsion system. 
     To that effect, an aircraft propulsion system is proposed, the aircraft propulsion system including a turbojet including an intermediate pressure stage and a high-pressure stage, a fan duct, and a heat exchanger system which includes:
         a main heat exchanger including a main hot supply connection, a main hot transfer connection pneumatically connected to the main hot supply connection through the main heat exchanger, a main cold supply connection and a main cold evacuation connection pneumatically connected to the main cold supply connection through the main heat exchanger,   a supply pipe which is connected to the main hot supply connection, and which supplies the heat exchanger with the hot air, and which includes a regulating valve,   a high pressure pipe which bleeds hot air from the high-pressure stage through a first valve,   an intermediate pressure pipe which bleeds hot air from the intermediate pressure stage through a second valve, wherein the high-pressure pipe and the intermediate pressure pipe are connected to the inlet of the regulating valve,   a transfer pipe which is connected to the main hot transfer connection, and which is adapted to transfer the hot air that has passed through the main heat exchanger to an air management system of the aircraft,   a main supply pipe which is connected to the main cold supply connection, which supplies the main heat exchanger with cold air from the fan duct, and which includes a main regulating valve,   an evacuation pipe which is connected to the main cold evacuation connection and is adapted to expel the air to the outside,   a sub heat exchanger including a sub hot supply connection, a sub hot transfer connection pneumatically connected to the sub supply connection through the sub heat exchanger, a sub cold supply connection and a sub cold evacuation connection pneumatically connected to the sub cold supply connection through the sub heat exchanger, wherein the high pressure pipe issued from the first valve goes through the sub heat exchanger between the sub hot supply connection and the sub hot transfer connection,   a sub supply pipe which is connected to the sub cold supply connection, which supplies the sub heat exchanger with cold air from the fan duct and which includes a sub regulating valve,   a sub evacuation pipe which is connected to the sub cold evacuation connection and expels the air to the fan duct,   a temperature sensor, which measures the temperature of the hot air exiting the main heat exchanger through the transfer pipe, and   a control unit which controls the main regulating valve and the sub regulating valve according to the temperature measured by the temperature sensor and the temperature desired for the hot air exiting the main heat exchanger through the transfer pipe.       

     The embodiment including two separate heat exchangers induces a size reduction of the main heat exchanger and a better integration in the reduced space between the pylon and the pylon fairing. 
     Advantageously, the propulsion system includes a pylon with a primary structure which supports the turbojet, the main heat exchanger is located above the primary structure and in the fan duct and the sub heat exchanger is below the primary structure and in the fan duct. 
     The invention also proposes an aircraft including at least one propulsion system according to one of the preceding variants. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned characteristics of the invention, as well as others, will emerge more clearly on reading the following description of an embodiment example, the description being made in relation to the attached drawings, among which: 
         FIG. 1  is a side view of an aircraft including a heat exchanger system according to the invention, 
         FIG. 2  is a schematic illustration of a heat exchanger system according to the invention, 
         FIG. 3  shows a side view of the heat exchanger system according to the invention in its environment, and 
         FIG. 4  is a schematic illustration of a heat exchanger system of the state of the art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description that follows, the terms relating to a position are taken with reference to an aircraft in normal flight position, that is to say, as illustrated on  FIG. 1 , and the positions “forward” and “aft” are taken in relation to the front and rear of the turbojet. 
     In the description that follows, and by convention, X is the longitudinal axis of the turbojet, which is parallel to the longitudinal axis of the aircraft, Y is the transversal axis, which is horizontal when the aircraft is on the ground, and Z is the vertical axis, which is vertical when the aircraft is on the ground, these three directions X, Y and Z being orthogonal to each other. 
       FIG. 1  shows an aircraft  10 , which includes a fuselage  11 , on either side of which a wing  13  is fastened that supports at least one propulsion system  15  which is shown on  FIG. 3  and which includes a pylon  12  and a turbojet  70 . The pylon  12  is fastened under the wing  13  and supports the turbojet  70 , which conventionally includes a compression stage  72  and a fan duct  74 . The pylon  12  includes a primary structure  50 , which is fastened at its upper part to the structure of the wing  13  and which supports the turbojet  70  through different fastening points. The primary structure  50  is disposed above the turbojet  70  and its front edge is attached to the turbojet  70  inside the fan duct  74 . 
     The compression stage  72  includes a high-pressure stage  206  and an intermediate pressure stage  208 . For example, in cruise conditions at 41000 ft, the intermediate pressure at 205° C. is 35 psia, and the high pressure at 517° C. is 174 psia. 
     The aircraft  10  includes an air management system like, for example, an air conditioning system and/or a de-icing system. 
     The propulsion system  15  also includes a nacelle  14 , which includes a fairing  76 , which surrounds the turbojet  70 , and an aerodynamic fairing of the pylon  12 , which surrounds the primary structure  50 . 
       FIG. 2  shows a heat exchanger system  200  according to the invention. 
     The heat exchanger system  200  includes a main heat exchanger  202  which comprises a main hot supply connection  201 , a main hot transfer connection  203  pneumatically connected to the main supply connection  201  through the main heat exchanger  202 , a main cold supply connection  205  and a main cold evacuation connection  207  pneumatically connected to the main cold supply connection  205  through the main heat exchanger  202 . 
     The heat exchanger system  200  includes a supply pipe  204  connected to the main hot supply connection  201  and which supplies the main heat exchanger  202  with hot air and which includes a regulating valve  214 , which enables regulation of the pressure at the hot supply connection  201 . 
     The heat exchanger system  200  includes a high-pressure pipe  250  which bleeds hot air from the high-pressure stage  206  through a first valve  210 . 
     The heat exchanger system  200  includes an intermediate pressure pipe  252  which bleeds hot air from the intermediate pressure stage  208  through a second valve  212 . 
     The high-pressure pipe  250  and the intermediate pressure pipe  252  are connected together to the inlet of the regulating valve  214 . 
     The heat exchanger system  200  includes a main supply pipe  216  connected to the main cold supply connection  205  and which supplies the main heat exchanger  202  with cold air and which bleeds cold air from the fan duct  74  of the turbojet  70 . The main supply pipe  216  also includes a main regulating valve  218 , which regulates the quantity of cold air introduced into the main heat exchanger  202  so as to regulate the temperature of the hot air exiting the main heat exchanger  202 . 
     The heat exchanger system  200  includes an evacuation pipe  220  connected to the main cold evacuation connection  207 . After having passed through the main heat exchanger  202 , the cold air, which has been heated, is expelled to the outside through the evacuation pipe  220 . 
     The heat exchanger system  200  includes a transfer pipe  222  connected to the main hot transfer connection  203 . After having passed through the main heat exchanger  202 , the hot air, which has been cooled, is directed through the transfer pipe  222  to the air management systems like the air conditioning system or the de-icing system. 
     The heat exchanger system  200  includes a temperature sensor  223 , which measures the temperature of the hot air exiting the main heat exchanger  202  through the transfer pipe  222  and a control unit  224 , such as a controller, which controls the valves according to the temperature measured by the temperature sensor  223  and the temperature desired for the hot air exiting the main heat exchanger  202  through the transfer pipe  222 . 
     The main heat exchanger  202  is here with cross flows, that is to say, the hot air and the cold air enter the main heat exchanger  202  and exit the main heat exchanger  202  along two globally perpendicular directions. But in another embodiment, the passage of the hot air through the main heat exchanger  202  from the supply pipe  204  to the transfer pipe  222  takes place along a first transfer direction and the passage of the cold air through the main heat exchanger  202  from the main supply pipe  216  to the evacuation pipe  220  takes place along a second transfer direction parallel to the first transfer direction but in the opposite direction. 
     The heat exchanger system  200  includes also a sub heat exchanger  230  connected between the first valve  210  and the regulating valve  214  on the high-pressure pipe  250 . 
     The sub heat exchanger  230  comprises a sub hot supply connection  231 , a sub hot transfer connection  233  pneumatically connected to the sub hot supply connection  231  through the sub heat exchanger  230 , a sub cold supply connection  235  and a sub cold evacuation connection  237  pneumatically connected to the sub cold supply connection  235  through the sub heat exchanger  230 . 
     The high-pressure pipe  250  issued from the first valve  210  goes through the sub heat exchanger  230  between the sub hot supply connection  231  and the sub hot transfer connection  233 . 
     The heat exchanger system  200  includes also a sub supply pipe  232  connected to the sub cold supply connection  235  and which supplies the sub heat exchanger  230  with cold air and which bleeds cold air from the fan duct  74  of the turbojet  70 . The sub supply pipe  232  also includes a sub regulating valve  234 , which regulates the quantity of cold air introduced into the sub heat exchanger  230  so as to regulate the temperature of the hot air exiting the sub heat exchanger  230 . 
     The heat exchanger system  200  includes a sub evacuation pipe  236  connected to the sub cold evacuation connection  237 . After having passed through the sub heat exchanger  230 , the cold air, which has been heated, is expelled to the fan duct  74  through the evacuation pipe  236 . 
     The sub regulating valve  234  is also controlled by the control unit  224 . 
     The separation of the heat exchanger into a main and a sub heat exchanger induces a size reduction of the main heat exchanger  202  and the integration of this main heat exchanger  202  in a reduced space is easier. 
     The main heat exchanger  202  is sized for the intermediate pressure stage  208 , and as soon as the high-pressure stage  206  is used, the sub heat exchanger  230  is used to complement the main heat exchanger  202 , and each heat exchanger  202 ,  230  has its own cold air inlet  216 ,  232  and its own regulating valve  218 ,  234  to modulate independently the cold air flow. 
     The cooling of the hot air from the intermediate pressure stage  208  is performed by the main heat exchanger  202  and the quantity of cold air introduced in the main heat exchanger  202  is controlled by the main regulating valve  218  to achieve the targeted outlet temperature. 
     When air is bled from the high-pressure stage  206 , the sub regulating valve  234  is controlled to be open as soon as the main regulating valve  218  is fully open and the air flow in the sub heat exchanger  230  is modulated by the sub regulating valve  234  to achieve the targeted outlet temperature. If bleed temperature becomes too low or if the system switched back to the intermediate pressure stage  208 , the sub regulating valve  234  is closed and the main regulating valve  218  takes back control on the temperature control. 
     In the embodiment shown on  FIG. 2 , the sub heat exchanger  230  is with cross flows but in another embodiment not illustrated, it can be with counter flows. 
       FIG. 3  shows the heat exchanger system  200  of the propulsion system  15  in its environment. 
     The main heat exchanger  202  is located above the primary structure  50  and in the fan duct  74  and the sub heat exchanger  230  is below the primary structure  50  and in the fan duct  74 . More precisely, the main heat exchanger  202  is located between the pylon and the pylon fairing. 
     The primary structure  50  comprises a window through which the supply pipe  204  goes through to connect itself with the high-pressure pipe  250  and the intermediate pressure pipe  252 . 
     In the embodiment shown on  FIG. 3 , the regulating valve  214  is also arranged below the primary structure  50 . 
     The main regulating valve  218  and the sub regulating valve  234  take here the form of a scoop including a door, which is mobile between an open position in which it does not blank off the scoop and a closed position in which it blanks off the scoop so as to regulate the quantity of cold air captured by the scoop. 
     Each door is motorized so as to ensure its movement and each motor is controlled by the control unit  224 . Each door acts as a valve. 
     Each scoop is oriented so as to be able to capture the cold air that circulates in the fan duct  74 . 
     The new implementation allows a design of the main heat exchanger with low bleed air side pressure drop. This lower pressure drop allows an improvement of the engine start performance due to higher pressure delivered to the starter turbine, a higher inlet pressure to air conditioning pack allowing the pack to operate with less ram air and thus reducing induced ram drag, and the challenging of the position of the intermediate pressure stage port, using a lower compressor stage that improves engine specific fuel consumption. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.