Abstract:
A fuel tank inerting system is provided including an air flow comprising air from a first source having a first temperature and air from a second source having a second temperature. The second temperature is cooler than the first temperature. At least one separating module is configured to separate an inert gas from the air flow.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention generally relates to the aircraft on-board systems, and more particularly, to a temperature control system for on-board fuel tank inerting systems. 
         [0002]    Fuel tank inerting systems are used to introduce an inert gas, such as nitrogen, into the fuel tanks of a vehicle, such as an aircraft. The inert gas displaces potentially dangerous fuel and air mixtures, thereby reducing the risk of explosion or fire. Typically, on board fuel inerting systems process air from an air source, such as bleed air taken from the engines of an aircraft. The bleed air is provided to a hollow fiber membrane where it is separated into nitrogen and oxygen. The separation efficiency of the membrane is directly dependent on the temperature of the air. However, there is a maximum allowable temperature of the bleed air to maintain the safety of the components downstream of the bleed air, such as filter, valves, and sensors, as well as safety relative to the fuel tank. Bleed air leaving the engines is extremely hot and therefore must be cooled before being processed. However, existing systems for cooling the bleed air to a safe temperature for inerting requires expensive processing equipment and negatively impacts the performance of the environmental control system of the aircraft. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one embodiment, a fuel tank inerting system is provided including an air flow comprising air from a first source having a first temperature and air from a second source having a second temperature. The second temperature is cooler than the first temperature. At least one separating module is configured to separate an inert gas from the air flow. 
         [0004]    According to an alternate embodiment of the invention, a fuel tank inerting system includes an air flow and at least one air separating module configured to separate an inert gas from the airflow. The air flow is cooled within a heat exchanger prior to being provided to the air separating module. A fluid arranged in a heat transfer relationship with the air flow within the heat exchanger is not RAM air. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0006]      FIG. 1  is a schematic diagram of a fuel tank inerting system; 
           [0007]      FIG. 2  is a schematic diagram of an environmental control system of an aircraft associated with a fuel tank inerting system according to an embodiment; 
           [0008]      FIG. 3  is a schematic diagram of an environmental control system of an aircraft associated with a fuel tank inerting system according to another embodiment; 
           [0009]      FIG. 4  is a schematic diagram illustrating various air flow paths within an aircraft compatible for use with a fuel tank inerting system according to an embodiment; and 
           [0010]      FIG. 5  is a schematic diagram of a heat exchanger for cooling a temperature of the bleed air according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Referring now to  FIG. 1 , an example of a basic fuel tank inerting system (FTIS)  20  for controlling a supply of inerting gas to a fuel tank  22  is illustrated. The FTIS  20  uses an on-board supply of air  24  to generate the inerting gas. In the illustrated, non-limiting embodiment, the air  24  provided to the FTIS  20  is bled from one or more engines  26  of an aircraft. The bleed air  24  flows through a filter  28  before being provided to one or more air separation modules (ASM)  30 . The ASMs  30  typically include a permeable membrane  32  having two sides. The oxygen rich bleed air passes across a first side of the membrane  32  and a secondary fluid flow passes over a second, opposite side of the membrane  32  to create a pressure differential across the membrane  32 . The pressure differential causes oxygen to diffuse from the bleed air to the secondary fluid stream, and a magnitude of the pressure differential may therefore be used to control how much oxygen is diffused from the stream of bleed air. The secondary fluid flow may be provided from any suitable system having a low pressure airflow. 
         [0012]    To maintain safety and a desired level of efficiency of the membrane  32  of the ASM  30  by controlling the temperature thereof, the bleed air  24  provided to the FTIS  20  is partially cooled prior to passing through the ASM  30 . In an embodiment the air provided to the membrane  30  is between about 150° F. and about 250° F., and more specifically between about 150° F. and about 215° F. As shown in  FIG. 1 , the bleed air  24  may be mixed with a supply of cool air  32  to achieve a desired temperature. The cool air  32  to be mixed with the bleed air  24  in the FTIS  20  may be provided from any suitable cool air source. In the illustrated, non-limiting embodiment of  FIG. 2 , the cool air  32  is provided from the primary heat exchanger  34  of an environmental control system (ECS)  40  of an aircraft. However, other cool fluid sources within an ECS  40  are within the scope of the disclosure. For example, as shown, a portion of the cool air  32  output from the primary heat exchanger  34  and upstream from an air cycle machine  36  may be diverted to the FTIS  20 . Alternatively, the primary heat exchanger  34  may be configured with two distinct flow paths, as shown in  FIG. 3 , arranged in a heat transfer relationship with a RAM air source. In such embodiments, the primary heat exchanger  34  may include one or more additional headers such that one or more passes within the heat exchanger  34  is coupled to an outlet  38  associated with and dedicated to the FTIS  20 . 
         [0013]    A flow control valve  42 , best shown in  FIG. 1 , may be positioned within the conduit providing the cool air  32  to the FTIS  20 . The valve  42  is operable to control the amount of cool air  32  supplied to the FTIS  20  and mixed with the bleed air  24 . In an embodiment, the valve  42  is operated in response to a temperature of the air upstream of or within the ASM  30 , as measured by a sensor, illustrated schematically at  44 . If the sensed temperature is below a desired operating temperature, a controller or actuator (not shown) associated with the valve  42  and the sensor  44  will partially or fully close the valve  42  to limit or completely block the flow of cool air  32  to the FTIS  20 . As a result, the temperature of the mixture of cool air  32  and bleed air  24  will increase. If the sensed temperature is greater than a maximum operating temperature, the controller or actuator will increase the ratio of cool air  32  to bleed air  24  provided to the FTIS  20  to reduce the temperature of the mixture of cool air  32  and bleed air  24 . In an embodiment, the controller associated with the valve  42  may be a controller configured to control at least a portion of the ECS  40 . 
         [0014]    Alternatively, the bleed air  24  provided to the FTIS  20  may be partially cooled prior to passing through the ASM  30  through a heat transfer operation with a cool fluid source. In an embodiment, the bleed air  24  is cooled through a heat exchanger where the cool fluid source is located outside of a RAM circuit  50  (see  FIGS. 2 and 3 ) of the ECS  40 . With reference to  FIG. 4 , examples of suitable sources that may be used to cool the bleed air  24  within a heat exchanger include, but are not limited to, cabin recirculation air, as illustrated schematically by a heat exchanger located at  52 , cabin exhaust air as illustrated schematically by a heat exchanger located at  54 , and conditioned ECS outlet air as illustrated schematically by a heat exchanger located at  56 . It should be further understood that although a single heat exchanger for cooling the bleed air  24  is illustrated and described herein, embodiments where a plurality of heat exchangers configured to provide multiple stages of cooling to achieve a desired temperature are also within the scope of the disclosure. 
         [0015]    In embodiments where the bleed air  24  is cooled via one or more heat exchangers, such as heat exchanger  52 ,  54 , or  56  for example, located outside of the RAM air circuit, a bypass conduit  58  may extend from upstream of the heat exchanger, as shown in  FIG. 5 . A valve  60 , such as a three way valve for example, may be arranged at the upstream end or within the bypass conduit  58  to direct the flow of the bleed air  24  between the heat exchanger and the bypass conduit  58 . As previously described, the valve  60  may be operated in response to a sensed temperature of the bleed air upstream of or within the ASM  30 . If the sensed temperature is below a desired operating temperature, the valve may be operated to divert at least a portion of the bleed air  24  through the bypass conduit  58  to increase the temperature of the bleed air  24  provided to the FTIS  20 . If the sensed temperature is greater than a maximum allowable operating temperature, the position of the valve is adjusted to reduce the amount of flow through the bypass conduit  58  and increase the flow of bleed air  24  that passes through the heat exchanger to reduce the temperature of the bleed air  24  provided to the FTIS  20 . 
         [0016]    Although mixing a cool air  32  with the bleed air  24  and including a heat exchanger to cool the bleed air  24  are illustrated and described separately, embodiments including both a cool air source  32  to be mixed with the bleed air  24  and a heat exchanger, such as heat exchangers  52 ,  54 , and  56  for example, to cool the bleed air  24  are contemplated herein. In an embodiment, the bleed air  24  may be partially cooled in one or more heat exchangers before being mixed with a separate supply of cool air  32  and then supplied to an ASM  30 . Alternatively, the bleed air  24  may be mixed with a supply of cool air  32 , and then the mixture may be further cooled via a heat exchanger prior to being supplied to the ASM  30  of the FTIS  20 . 
         [0017]    The FTIS  20  described herein is configured to operate at a temperature to optimize efficiency of the ASM membrane  32  while maintaining a desired level of safety with at the fuel tank  22 . The cooling air sources disclosed may be used to achieve the desired temperature with minimal impact to the ECS  40  of an aircraft  20 . Accordingly, the FTIS  20  may be used in both new and retrofit applications. 
         [0018]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.