Abstract:
According to an embodiment, a heat detection system includes a graphene conductor, a housing containing the graphene conductor; and, a signal wire connected in electrical communication with the graphene conductor, the signal wire having a length that extends from the housing.

Description:
FIELD 
       [0001]    This disclosure is directed to heat and/or fire detection systems and methods generally and in particular for use in aerospace applications. 
       BACKGROUND 
       [0002]    There is a need for improved detection of heat and/or fire in difficult to access areas of an aircraft. There also are no fire detection systems that run throughout the entire aircraft because of cost, weight, and the durability requirements for aircraft certification and operation. 
         [0003]    Current heat and/or fire detection systems for aircraft can be easily damaged. The systems are highly susceptible to vibration during normal operating conditions. They can also be inadvertently damaged from maintenance, inspection, and repair and from loading and unloading of cargo. Current heat and/or fire detection systems are often attached to engine components and auxiliary power unit (APU) components, exposing them to maximum vibration loads. A typical heat and/or fire sensor is surrounded by an insulator. Due to the high vibration environment, the insulator can develop cracks which allows the vibration to be transmitted to the sensor causing it to break and fail. When such sensors fail, the possibility of detecting fire in the early stages is either substantially diminished or eliminated altogether. 
         [0004]    Many existing heat and/or fire detection systems for aircraft require the presence of visible flames or smoke to be detected. This allows conditions for a fire to occur and the conditions to grow without detection. In some cases, rapid propagation of a fire could make existing smoke and fire detection systems entirely ineffective. Adding additional sensors in the cargo compartment may not be effective because cargo could block the additional sensors, nulling their sensing capabilities. With the current construction of heat and/or fire detection sensors, adding large numbers of sensors to the aircraft cargo compartment may also undesirably increase the weight of the aircraft. 
       SUMMARY 
       [0005]    The heat detection systems and methods of this disclosure employ flexible, lightweight heat and fire sensors that are effective in sensing all types of overheating and fire situations. The flexibility and lightweight enables the sensors to be placed throughout the entire aircraft without significantly increasing the weight of the aircraft and without compromising the performance of the sensors. The heat detection systems and methods of this disclosure include overheat and/or fire detection sensors that employ a graphene conductor. According to an embodiment, a heat detection system includes a graphene conductor, a housing containing the graphene conductor, and a signal wire connected in electrical communication with the graphene conductor, the signal wire having a length that extends from the housing. 
         [0006]    According to another embodiment, a heat detection system includes a graphene conductor, the graphene conductor being a flexible, lightweight wire, an electrical resistivity monitor; and, an electric circuit electrically communicating the graphene conductor with the electrical resistivity monitor. 
         [0007]    According to yet another embodiment, a method of forming a heat detection system includes encapsulating a graphene conductor partially surrounded by a ceramic insulator and a metal housing to form a graphene thermal resistor, connecting a first signal wire in electrical communication with a first end of the graphene conductor and a second signal wire in electrical communication with a second end of the graphene conductor in the graphene thermal resistor, and extending the first and second signal wires from the graphene thermal resistor to an electric resistivity monitor to form an electric circuit. 
         [0008]    Further features of the heat detection system employing a graphene conductor are set forth in the following detailed description of the system and in the drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic representation of a heat detection system employing a graphene sensor in a resistivity monitoring circuit. 
           [0010]      FIG. 2  is a representation of an enlarged, cross-section view of the graphene conductor sensor of  FIG. 1 . 
           [0011]      FIG. 3  is a graphical representation of an exemplary electrical resistance change in a graphene conductor in response to temperature change. 
           [0012]      FIG. 4  is a representation of a perspective view of an aircraft employing a heat and/or fire detection system comprised of a matrix of the electrical resistivity monitoring circuits represented in  FIG. 1 . 
           [0013]      FIG. 5  is a flow chart representation of a method of forming a heat detection system. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  is a representation of a heat detection system  10  comprising a graphene thermal resistor  12  and forming a part of an electrical circuit  20 . Graphene is a series of carbon atoms arranged in a hexagonal pattern in a very thin layer that is one atom thick and nearly transparent. Graphene is remarkably strong, has a very low weight (about 100 times stronger than steel per pound) and it conducts heat and electricity with great efficiency. 
         [0015]    The graphene thermal resistor  12  is capable of detecting heat and fire in highly dynamic and extreme environments of an aircraft such as cargo compartments, fuel tanks, heat ducts, engines, engine support structures and strut areas (nacelle and engine system wing attachments). The graphene thermal resistor  12  is extremely durable in excessive vibration and high temperature environments. The graphene thermal resistor  12  is lightweight and has a small footprint. This enables fire detection systems such as that represented in  FIG. 1  to be easily placed throughout an aircraft via a matrix network configuration  14  such as that represented in  FIG. 4 , thereby providing early and reliable heat, smoke, and fire detection throughout the aircraft  16 . 
         [0016]    In the representation of  FIG. 1 , the graphene thermal resistor  12  includes a graphene conductor  18 . Electrical resistance properties of the graphene conductor  18  change with temperature. 
         [0017]    Referring to  FIG. 3 , there is shown a graphical representation of an exemplary resistance change in the graphene conductor  18  with respect to temperature change. As represented in  FIG. 3 , the resistance of the graphene conductor  18  increases in response to the graphene conductor being subjected to increasing temperature.  FIG. 3  represents that graphene can be used as an effective temperature sensor by monitoring the change in resistance with temperature. 
         [0018]    A graphene fire sensor such as the graphene thermal resistor  12  represented in  FIG. 1  can be used in many configurations. The graphene thermal resistor could be used in a continuous loop detection system configuration such as that represented in  FIG. 1 , or as a bridge resistor type sensor. 
         [0019]    In the heat detection system  10  represented in  FIG. 1 , the graphene thermal resistor  12  includes the graphene conductor  18  in the form of a lightweight wire. The graphene conductor  18  extends through a center of the graphene thermal resistor  12  between a first end  22  of the conductor and an opposite second end  24  of the conductor as shown in a partial phantom view of the graphene thermal resistor  12 . 
         [0020]    An insulating material  28  surrounds the graphene conductor  18 . The insulating material  28  partially surrounds the graphene conductor  18  as can best be seen in the representation of the partial phantom view of the graphene thermal resistor  12  in  FIG. 1  and the cross-section of the graphene thermal resistor  12  of  FIG. 2 . In the representation of the graphene thermal resistor  12  of  FIGS. 1 and 2 , the insulating material  28  may be constructed of a ceramic material. Asbestos paste or high temperature Teflon® insulation may also be used. When constructed of a ceramic material, the insulator  28  may be considered a ceramic insulator. 
         [0021]    A metal housing  32  encloses the graphene conductor  18  and the insulating material  28 . The housing  32  completely encloses the graphene conductor  18  and the insulating material  28  except for the exposed first end  22  and second end  24  of the graphene conductor at the opposite ends of the graphene thermal resistor  12 . Although the graphene conductor  18  is extremely strong, the housing  32  provides further damage resistance to the graphene conductor  18  enabling the graphene thermal resistor  12  to endure more airplane cycles than existing heat detection systems. The housing may be constructed of a metal alloy such as Inconel®, nickel, zinc or aluminum oxide. 
         [0022]    A first signal wire  36  is connected in electrical communication with the graphene conductor  18 . As represented in  FIG. 1 , the signal wire  36  is electrically communicated with the first end  22  of the graphene conductor  18 . The signal wire  36  extends from the graphene thermal resistor  12  and from the harsh environment of the aircraft where the graphene thermal resistor  12  is positioned, to an electrical resistivity monitor  42 . In the heat detection system represented in  FIG. 1 , a second signal wire  44  is also connected in electrical communication with the graphene conductor  18 . As represented in  FIG. 1 , the second signal wire  44  is connected in electrical communication with the second end  24  of the graphene conductor  18 . The second signal wire  44  extends from the graphene thermal resistor  12  and the harsh environment of the aircraft where the thermal resistor  12  is positioned to the electrical resistivity monitor  42 . 
         [0023]    In the simple schematic of the heat detection system  10  represented in  FIG. 1 , the graphene thermal resistor  12 , when subjected to heat, increases in electrical resistance. The electrical resistivity monitor  42  displays a representation of the increasing heat of the environment of the graphene thermal resistor  12  that causes the resistivity of the graphene conductor  18  to increase. In this manner, the electric circuit  20  of the heat detection system  10  provides a lightweight, durable, damage resistant fire detection system that is able to endure more airplane cycles than existing systems. 
         [0024]    The graphene fire detection system of  FIG. 1  will operate by monitoring levels of heat and detecting overheat conditions in different areas of an aircraft as well as by detecting fire situations in different areas of an aircraft. This information is communicated to the flight deck where it is monitored by the crew. The overheat warning, at a temperature well below the fire warning, indicates a general temperature rise due to hot bleed air leakage or combustion gases into an area of concern inside and outside of firewalls of an aircraft, and indicates a dangerous situation in areas highly sensitive to high temperature conditions. 
         [0025]    The graphene fire detection system will operate accurately to determine a temperature rise situation of concern starting at 100° C., and determining a temperature range of 100° C.-2,000° C. This eliminates any possibility of overheat damage and any risk associated with overheating. The system can also be programmed to operate to sense rate of temperature rise conditions as well as fixed temperature set points. 
         [0026]    For example, the graphene fire detection system can have an overheat set point typically around 500° C., and at that temperature will send overheat indication signals to the flight deck. The fire set point detection temperature will adhere to well published guidelines at 1,500° C. (and within ten seconds of flame onset) and 2,000° C. (within five seconds of flame onset). 
         [0027]    In conditions of a fire, the temperature increases substantially and the outer housing  32  of the graphene thermal resistor  12  heats up to close to the temperature of the fire. This in turn increases the temperature of the graphene conductor  18  contained in the housing  32 . The electrical resistivity of the graphene conductor  18  is proportional to its temperature as represented in  FIG. 3 . As the temperature increases, the resistivity of the graphene conductor  18  increases as well. Even a small amount of change in the resistivity in the graphene conductor  18  can be detected by the electrical resistivity monitor  48  which could include a four way bridge resistor or other equivalent device. 
         [0028]    Additionally, the increase in the resistivity of the graphene conductor  18  can also cause a voltage drop. In place of the electrical resistivity monitor  42 , an equivalent voltage monitor could be used. The voltage monitor could be calibrated to monitor changes in voltage of the electric circuit  20  that in turn could be used to monitor changes in temperature in the environment of the graphene thermal resistor  12  in the same manner as the electrical resistivity monitor  42  described earlier. 
         [0029]    The fire detection system of  FIG. 1  will increase aircraft reliability and safety. It will enable significant airplane fuel savings and efficiency due to its lightweight, and will be much easier to install in the small, constricted, and difficult to access spaces around different aircraft structures, such as aircraft engines due to its high flexibility and small size. The flexibility and small size of the system represented in  FIG. 1  will reduce installation and maintenance times for the fire detection system and other engine systems local to the fire detection system. The flexibility and the light weight of the graphene conductor wire further enables the sensor constructed of the graphene conductor wire to be positioned throughout an aircraft construction in difficult to access areas. The flexibility of the wire also enables the graphene wire sensors to be used in many configurations to conform to the configuration of the aircraft structure that is to be monitored by the graphene sensors. 
         [0030]    Furthermore, due to its flexibility and small size, a plurality of fire detection systems such as the fire detection system  10  represented in  FIG. 1  can be positioned throughout the different aircraft structures as part of a matrix network configuration. As one example, the heat detection system  10  may include the graphene conductor  18  being one of a plurality of graphene conductors, the electrical resistivity monitor  42  being one of a plurality of electrical resistivity monitors; and the electric circuit  20  being one of a plurality of electric circuits communicating each graphene conductor of the plurality of graphene conductors with an associated electrical resistivity monitor of the plurality of electrical resistivity monitors. The graphene wire is also extremely durable in excessive vibration and high temperature environments. Referring to  FIG. 4 , portions  48 ,  52  of such a matrix could be located in the cargo compartments, portions  54 ,  56  of the matrix could be located by the fuel tanks in the wings, portions  58  of the matrix could be located in auxiliary power units and portions of the matrix could be located in the engines  62  or engine cowlings of the aircraft  16 . 
         [0031]    Referring to  FIG. 5 , a method  500  of forming a heat detection system includes various steps. Method  500  begins with encapsulating a graphene conductor wire  18  that is partially surrounded by an insulator  28 . The insulator  28  could be a ceramic insulator. The graphene conductor  18  and the insulator  28  are then enclosed in a metal housing  32  to form a graphene thermal resistor  12 , as referenced in block  502 . A first signal wire  36  is connected in electric communication with a first end  22  of the graphene conductor  18 , and a second signal wire  44  is connected in electric communication with a second end  24  of the graphene conductor  18 , as referenced in block  504 . Method  500  continues with the signal wires ( 36 ,  44 ) are extended from the graphene thermal resistor  12  to an electric resistivity monitor  42  to form an electric circuit  20 , as referenced in block  506 . 
         [0032]    The housing  32  may be positioned within a region or at a structure of an aircraft  16  where temperature is to be measured. One or more of the thermal resistors  12  could be positioned at a plurality of different areas of the aircraft  16 , as referenced in block  508 . Furthermore, one or more of the thermal resistors  12  could be configured to conform to a configuration of the structure of the aircraft  16 , as referenced in block  510 . 
         [0033]    The method  500  concludes with the heat detection system being employed to monitor a change in temperature in one or more areas of the aircraft  16  and/or to monitor an occurrence of a fire. For example, the area or region of the aircraft  16  could be in or near an engine  62  or engine cowling, a cargo hold  52 , a crew rest area, a crown region, a bilge region, a cockpit panel or other cockpit region, an electrical panel, a lavatory, or any other area that may be difficult to reach or inconvenient to inspect, or where high temperature may be generated. The heat detection system may be employed to detect temperature and/or possible fire in other vehicles such as armored vehicles, boats, cars, trucks/trailers, military transports, ships, recreational vehicles, and trains. 
         [0034]    As described, the heat detection system  10  could be employed to monitor an occurrence of a fire in an area of an aircraft  16  or other vehicle. A rapid increase in temperature at a particular location and/or a progressive increase in temperature detected in one or more dimensions of the graphene thermal resistors  12  in a matrix  14  composed of a plurality of thermal resistors could indicate a spreading fire. 
         [0035]    As various modifications could be made in the construction of the apparatus and its method of operation herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.