Patent Publication Number: US-2019168886-A1

Title: Fuel tank with suction system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the European patent application No. 17382813.8 filed on Dec. 1, 2017, the entire disclosures of which are incorporated herein by way of reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a fuel tank with suction system. More specifically, the invention is relative to a Fuel tank with suction system able to feed an Auxiliary Power Unit. 
     BACKGROUND OF THE INVENTION 
     An APU (Auxiliary Power Unit) is a gas turbine engine which is used in aircraft to provide electrical and/or pneumatic power to various aircraft systems and components. The APU is controlled and monitored by an ECB (Electronic Control Box). 
     When an aircraft is in ground mode, its main source of electrical power and compressed air for cabin conditioning is provided by the APU. The APU is able to power the aircraft and the ECS (Environmental Control Systems), drive the pneumatic starters systems for the MES (Main Engines Start). When an aircraft is in flight mode, the APU is able to provide pneumatic and/or electric power to the aircraft. 
     APUs are generally located in the aft fuselage module of the aircraft, at or near the tail cone section, but the APU is commonly fed in fuel via the wings tanks. 
     Indeed, nowadays, a suction point is fixed and located in the lower part of a fuel tank of each main wing, mainly to guarantee that the APU will be fed by fuel even with low quantity of fuel in the tanks. 
     However, some water enters into the aircraft fuel tanks with the uplifted fuel, when the fuel is mixed or dissolved, and during in-breathing, when humid air enters the tank as tank gauge decreases. During the descent of the aircraft, water vapor becomes liquid with the increase of ambient temperature. 
     For large range aircraft, with a huge wing tanks, this quantity of water can be several hundred liters. 
     Due to the differences of density between water and Jet fuel, because water is denser than fuel, water precipitates to the lowest parts of the tanks, creating at least several phases, a lower layer of water, an upper layer of fuel, and between these layers a slight mixed-phase. 
     Aircraft fuel tanks are drained of water on a regular basis, but sometimes the amount of water between draining tasks can be significant. Free water in the tanks can give rise to some problems of engine performance, specifically for APU engines because they are much more susceptible to water ingestion than main engines. 
     SUMMARY OF THE INVENTION 
     In order to solve the drawbacks stated above, the present invention proposes that the APU be always supplied with the clearest, cleanest, and waterfree fuel from the upper level of the tank. The main advantage of the invention is to avoid suction from the lower area of the tank in which water and/or dirt tent to accumulate. 
     Another advantage of this invention, and not the least, is to keep the piping and the APU pump exactly as they presently are, but only adapt the current suction point. This would minimize the mechanical complexity and additional parts counts, the modifications required, and would be easy implementable to retrofit aircraft already on the market. 
     The present invention is relative to a fuel tank with a suction system, the tank comprising within at least two layers of fuel, with a lower layer being denser than the upper layer, the suction system comprising:
         a first pipeline comprising, respectively, a first and a second extremity, the extremities each comprising, respectively, a first and a second orifice,   a second pipeline comprising, respectively, a first and a second extremity, the extremities each comprising, respectively, a first and a second orifice,   a third pipeline comprising, respectively, a first and a second extremity, the extremities each comprising, respectively, a first and a second orifice,   the second orifice of the first pipeline is connected to the first orifice of the second pipeline via a vacuum pump,   the second orifice of the second pipeline is connected to the first orifice of the third pipeline via a valve,   the first orifice of the third pipeline is connected to a fuel engine,       

     characterized in that, the suction system comprises:
         a flexible hose comprising a first and a second extremity, the second extremity comprising an orifice configured to be connected to the first orifice of the first pipeline via a connection point,   the first extremity of the flexible hose being fastened to a floating system and comprising at least one orifice, the orifice comprising a suction point always able to supply the engine from the upper layer of fuel available in the tank, in order to avoid water and potential dirt from the lower layer.       

     According to the invention, the connection point is an articulation point, such that the hose is able to move freely with respect to the first pipeline; 
     According to the invention, the flexible hose is retractable, such as when the first extremity of the flexible hose is moving down according to the level of fuel available in the tank, the hose length is reducing, and when the first extremity of the flexible hose is moving up according to the level of fuel available in the tank, the hose length is increasing; 
     According to the invention, the floating system is a buoy; 
     According to the invention, the first extremity of the flexible hose is only able to move vertically via a fixed guiding element inside the tank, while the level of fuel available changes. 
     According to the invention, the guiding element can be a rail, a rod or a profile, made from metal or composite material. 
     According to the invention, the suction point of the first extremity of the flexible hose is located at some centimeters below the floating element, between 1 and 3 centimeters, in order to be sure that the suction point is fed with fuel air-free and dirt-free. 
     According to the invention, the tank can be housed inside an aircraft wing or a horizontal tail cone. 
     The present invention is also relative to an APU (Auxiliary Power Unit) fed with fuel via a fuel tank with suction system according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. The drawings form an integral part of the description and illustrate preferred embodiments of the invention. The drawings comprise the following figures: 
         FIG. 1 , is a schematic representation of a fuel tank with suction system according to the state of art; 
         FIG. 2 , is a schematic representation of a fuel tank with suction system according to one embodiment of the invention; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is directed generally toward a fuel tank with a suction system. A person skilled in the relevant art will understand, however, that the invention may have additional embodiments, and that the invention may be practiced without several of the details of the embodiments described below with reference to  FIGS. 1 and 2 . 
       FIG. 1  is a schematic representation of a fuel tank  200  with a suction system  100  according to the state of art.  FIG. 1  describes a part of aircraft wing, comprising inside the fuel tank  200  in order to feed a set of thermic/fuel engines  430  of the aircraft. Indeed, in commercial aircraft, fuel tank  200  is usually housed in the main aircraft wing and/or in the (HTP) Horizontal Tail Plane. In a non-exhaustive list, the set of thermic engines comprises at least the main engines and additionally the (APU) Auxiliary Power Unit. In this schematic representation, the tank  200  is not fully filled and comprises at least two layers  310 ,  320  of fuel  300 , an upper layer  310  and a lower layer  320 . The lower layer  320  is water or a mixture of water with fuel which is denser than the upper layer  310  which is pure fuel. The suction system  100  of the state of art comprises a set of pipelines  110 ,  120 ,  130  such as a first pipeline  110  comprising respectively a first  111  and a second  112  extremity, the extremities  111 ,  112  comprising respectively a first  113  and a second  114  orifice. The suction system  100  comprises a second pipeline  120  comprising respectively a first  121  and a second  122  extremity, the extremities  121 ,  122  comprising respectively a first  123  and a second  124  orifice. The suction system  100  comprises also a third pipeline  130  comprising respectively a first  131  and a second  132  extremity, the extremities  131 ,  132  comprising respectively a first  133  and a second  134  orifice. 
     The set of pipelines  110 ,  120 ,  130  are successively connected together, such as the second orifice  114  of the first pipeline  110  is connected to the first orifice  123  of the second pipeline  120  via a vacuum pump  410 . The second orifice  124  of the second pipeline  120  is connected to the first orifice  133  of the third pipeline  130  via a valve  420 . The first orifice  133  of the third pipeline  130  is connected to a set of fuel engines  430 , such as the APU (Auxiliary Power Unit) and/or the main aircraft engines. 
     This set of pipelines  110 ,  120 ,  130  is arranged and interconnected together such as according to the needs of the engines  430 , the vacuum pump  410  is able to lead the fuel  300  available in the tank  200  via the first orifice  113  of the first pipeline  110 , considered in the state of art as a suction point, to the engines  430  through the valve  420 . Unfortunately, the localization of the first orifice  113  is strategically positioned in the lower part of the tank  200  in order to guarantee that the engine  430  is supplied with fuel  300  during its operation. The main difficulty met in this kind of disposition of the suction point, according to the state of art, is an inappropriate ingestion of water or dirt by the engine  430 , which could lead to detrimental consequences for the engine  430 . 
     The present invention wishes to overcome the disadvantages of the suction system  100  of the state of art by adding a retrofit technical solution, as shown in  FIG. 2 . The suction system  100  according to the invention comprises a flexible hose  150  comprising a first  151  and a second  152  extremity, the second extremity  152  comprising an orifice  154  configured to be connected to the first orifice  113  of the first pipeline  110  via a connection point  440 . The first extremity  151  of the flexible hose  150  is fastened to a floating system  155  and comprises at least one orifice  153 , such as the orifice  153 , which becomes a suction point always able to supply the engine  430  from the upper layer  310  of fuel  300  available inside the tank  200 , in order to avoid water and dirt from the lower layer  320 . The set of orifices  153  presents a real advantage in order to avoid the blockage of the suction if one these orifices  153  was clogged because of the presence of dirt. This set of orifices  153  work consequently as a filter. Another advantage of this embodiment is to allow to the flexible hose  150  to follow, dynamically, the level of fuel  300  available in the tank  200  and particularly the best layer, the upper one 310. 
     In another embodiment, the connection point  440  is an articulation point, such that the hose  152  is able to move rotationally freely with respect to the first pipeline  110 . 
     In another embodiment, the flexible hose  150  is retractable, such that when the first extremity  151  of the flexible hose  150  is moving down according to the level of fuel  300  available in the tank  200 , the hose length is reducing. When the first extremity  151  of the flexible hose  150  is moving up according to the level of fuel  300  available in the tank  200 , the hose length is increasing. 
     In another embodiment, the floating system  155  is a buoy. 
     In another embodiment, the first extremity  151  of the flexible hose  150  is only able to move vertically via a guiding element  156  inside the tank  200 , while the level of fuel  300  available in the tank  200  changes. 
     In another embodiment, the guiding element  156  can be a rail, or a rod with a ring or a profile, the guiding element  156  being made from metal or composite material. 
     In another embodiment, the suction point of the first extremity  151  of the flexible hose  150  is located some centimeters below the floating system  155  in order to be sure that the suction point is fed with fuel  300  without air and potential dirt. 
     In another embodiment, the fuel tank  200  can be housed inside an aircraft wing or a HTP (Horizontal Tail Plane). 
     Another object of the invention is an Auxiliary Power Unit  430  fed with fuel  300  via a suction system  100  according to the invention. 
     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. Although advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages. Additionally, none of the foregoing embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited except as by the appended claims. 
     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.