Abstract:
A fire-suppression system for use in an aircraft having at least one cargo compartment is disclosed. Methods of suppressing a fire in the cargo compartment are also disclosed. The fire-suppression system, under one aspect of the present invention, can include at least one fire-suppressant vessel, at least one discharge conduit coupled to the at least one fire-suppressant vessel, and a valve arrangement coupled to the fire-suppressant vessel and the discharge conduit. The valve arrangement can have a first setting to discharge a fire suppressant at a first discharge rate after activation of the fire-suppression system, a second setting to discharge the fire-suppressant at a second discharge rate less than the first discharge rate, and a third setting to discharge the fire-suppressant at a third discharge rate greater than the second discharge rate during descent of the aircraft.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a divisional of U.S. application Ser. No. 10/786,285, filed Feb. 25, 2004 and incorporated herein in its entirety by reference thereto. 

   TECHNICAL FIELD 
   The present invention is directed to fire-suppression systems and, more particularly, to apparatuses and methods for suppressing a fire condition in an aircraft. 
   BACKGROUND 
   Current commercial jetliners with cargo compartments have fire-suppression systems as a safety feature in the event of a fire in the cargo compartment. The fire-suppression systems typically disperse Halon 1301 (bromotrifluoromethane—CF 3 Br) as the suppressant. The conventional fire-suppression systems also have multiple bottles of Halon 1301, each with its own discharge mechanism. In the event of a fire in the cargo compartment, fire suppression is achieved by an initial rapid discharge of Halon into the cargo compartment to establish a minimum Halon concentration of 5% or more by volume in the compartment. This initial high Halon concentration level provides effective and fast initial flame knockdown. Sustained fire suppression against deep-seated fire and conflagrations is achieved by maintaining the Halon concentration in the cargo compartment at or above 3%. 
   The typical fire-suppression systems on large commercial aircraft achieve the initial high Halon concentration level by very quickly releasing the entire contents of one or more high-rate discharge (HRD) bottles of Halon into the cargo compartment. After the HRD bottle(s) are discharged, the Halon concentration peaks and then slowly decreases toward approximately 5% during a period of approximately 20 minutes. In one fire-suppression system used on a Boeing 747-400, two HRD bottles are immediately emptied into a cargo compartment upon activation of the fire-suppression system. The HRD bottles provide approximately 110 pounds of Halon (55 pounds from each HRD bottle) into the cargo compartment to establish an initially high Halon concentration level, which is intended to slowly drop to at least 5%. 
   The Halon concentration in the cargo compartment is then maintained by providing a substantially continuous, regulated flow of Halon from a plurality of “metered” bottles over an elongated period of time. The metered bottles begin to discharge at a selected time delay after the HRD bottles are discharged. The metered bottles release Halon over an extended time period so the Halon concentration level is maintained at approximately 5%-7%, at least until the aircraft begins its descent to a safe landing. 
   When a commercial aircraft descends from a cruise altitude, the cargo compartment undergoes a repressurization. The cargo compartment also typically experiences an increase in a compartment leakage rate due to outflow valve effects. The repressurization and increased leakage rate effectively result in additional air being added into the cargo compartment, which causes the Halon concentration to decrease as the aircraft descends. 
   The conventional fire-suppression systems compensate for the decrease in Halon concentration during descent by maintaining a higher Halon concentration in the cargo compartment during the cruise phase before the descent phase. Accordingly, the Halon concentration level has room to drop as the aircraft descends, while not dropping below the 3% concentration minimum. For example, the metered bottles provide a continuous flow of Halon into the cargo compartment to maintain an elevated Halon concentration level of over 6% through the majority of the aircraft&#39;s flight after activation of the fire-suppression system. The Halon concentration level is maintained at this elevated level to compensate for the Halon concentration drop that will occur during descent of the aircraft to a safe landing. Accordingly, the conventional fire-suppression systems, when activated, must contain enough Halon to maintain the intentionally elevated Halon concentration during the flight time prior to descent. The aircraft, therefore, must carry hundreds of pounds of Halon on each flight to ensure that the fire-suppression system will have enough Halon to meet the minimum Halon concentration level requirements at all times in the event a fire condition occurs in one of the cargo compartments. The weight of the Halon negatively impacts the aircraft&#39;s fuel efficiency. 
   SUMMARY 
   Aspects of embodiments of the invention are directed to fire-suppression systems for an aircraft. One aspect of the invention includes a fire-suppression system for use in an aircraft having a cargo compartment. The fire-suppression system can include at least one fire-suppressant vessel, at least one discharge conduit coupled to the at least one fire-suppressant vessel, and a valve arrangement coupled to the fire-suppressant vessel and to the discharge conduit. The valve arrangement can have a first setting to discharge fire suppressant at a first discharge rate after activation of the fire-suppression system, a second setting to discharge the fire suppressant at a second discharge rate less than the first discharge rate, and a third setting to discharge the fire suppressant at a third discharge rate greater than the second discharge rate during descent of the aircraft. 
   Another aspect of the invention includes a method of suppressing a fire condition in a cargo compartment of an aircraft. The method can include detecting a fire condition in the cargo compartment, delivering fire suppressant into the cargo compartment at a first discharge rate after detection of the fire condition, delivering fire suppressant into the cargo compartment at a second discharge rate less than the first discharge rate, and delivering fire suppressant into the cargo compartment at a third discharge rate greater than the second discharge rate during descent of the aircraft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic top isometric view of an aircraft with a cargo compartment and a fire-suppression system in accordance with one embodiment of the present invention. 
       FIG. 2  is a schematic view of the fire-suppression system of  FIG. 1 . 
       FIG. 3  is a schematic view of a fire-suppression system in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The following disclosure describes fire-suppression systems for use in a cargo compartment of an aircraft. Certain specific details are set forth in the following description and in  FIGS. 1-3  to provide a thorough understanding of various aspects and embodiments of the invention. Other details describing well-known structures and systems often associated with aircraft, including cargo compartments, smoke detection and warning systems, and fire-suppression systems, are not set forth in the following description to avoid unnecessarily obscuring the description of the various embodiments of the invention. 
   Many of the details, dimensions, and other specifications shown in the figures are merely illustrative of particular embodiments of the invention. Accordingly, other embodiments can have other details, dimensions, and specifications without departing from the spirit or scope of the present invention. In addition, other embodiments of the invention may be practiced without several of the details described below. 
     FIG. 1  is a schematic top isometric view of an aircraft  10  with a fuselage  12  that contains cargo compartments, including a forward cargo compartment  16   a  and an aft cargo compartment  16   b . The cargo compartments  16   a  and  16   b  are sized to receive cargo containers or pallets (not shown) that can include a vast assortment of different items, containers, and materials. A conventional fire detection system  20  (shown schematically) is provided in the cargo compartments  16   a  and  16   b . The fire detection system  20  includes a plurality of detectors  22  configured to provide a signal to an aircraft control system  24  (shown schematically) upon detecting an actual or potential fire condition in one or both of forward and aft cargo compartments  16   a  and  16   b . For purposes of clarity, the cargo compartment in which a fire condition is detected will be referred to in the following disclosure as “the target compartment  16 .” The control system  24  is configured to provide a warning to the operator of the aircraft  10  in the event at least one of the detectors  22  is activated in the target compartment  16 . 
   The aircraft  10  also includes a fire-suppression system  26  in accordance with at least one embodiment of the invention. The fire-suppression system  26  is coupled to the control system  24  and is activated manually or automatically by the control system if a fire condition is detected. The fire-suppression system  26  is configured to disperse a fire suppressant, such as Halon 1301, into the target compartment  16 . The fire suppressant is initially dispersed into the target compartment  16  at elevated levels to extinguish any flame that may be present in the target compartment  16 . The fire suppressant is also dispersed into the target compartment  16  over an extended period of time after the initial fire suppressant dispersal to maintain a selected fire suppressant concentration level that prevents any subsequent flare-ups. As the aircraft  10  begins its descent toward a safe landing, the amount of fire suppressant dispersed into the target compartment  16  is increased, thereby maintaining the selected fire suppressant concentration level throughout the descent. 
   The fire-suppression system  26  in accordance with one embodiment of the present invention includes a main line  28  that carries a flow of fire suppressant to the target compartment  16 . The flow of fire suppressant through the main line  28  can be directed to the target compartment  16 , whether it is the forward cargo compartment  16   a  or the aft cargo compartment  16   b , in response to a command from the pilot or from an automatic command from the control system  24 . 
   A plurality of distributing lines  30  branch off from the main line  28  and are spaced apart from each other within the forward and aft cargo compartments  16   a  and  16   b . Each of the distributing lines  30  terminates at a discharge nozzle  32  configured to disperse the fire suppressant into the respective forward cargo compartment  16   a  or the aft cargo compartment  16   b . The distributing lines  30  and the discharge nozzles  32  are positioned so that, when the fire-suppression system  26  is activated, the fire suppressant will be dispersed substantially uniformly to rapidly achieve a uniform concentration of fire suppressant throughout the target compartment  16 . 
   As best seen in  FIG. 2 , the main line  28  is connected to a plurality of pressurized bottles  34  that contain the fire suppressant. In other embodiments, the bottles  34  may contain Halon 1301 as the fire suppressant material, although fire suppressants other than Halon 1301 can be distributed through the main line  28 , the distributing lines  30 , and the discharge nozzles  32  into the target compartment  16 . The bottles  34  of the illustrated fire-suppression system  26  include two high-rate discharge (HRD) bottles  36  coupled to the main line  28 . In the illustrated embodiment, the fire suppressant is Halon 1301 and each HRD bottle  36  contains approximately 55 pounds of Halon 1301. Other embodiments can utilize HRD bottles  36  containing more or less fire suppressant per bottle. The HRD bottles  36  are configured to quickly discharge the fire suppressant into the main line  28  for delivery to the target compartment  16  when the fire-suppression system  26  is activated. 
   The HRD bottles  36  of the illustrated embodiment have valve mechanisms with a valve setting that allows the bottles to fully discharge into the main line  28  over a very short period of time (e.g., 2-3 minutes) as soon as the fire-suppression system  26  is activated. The fire suppressant from the HRD bottles  36  is distributed through the main line  28  and the distributing lines  30  and is dispersed from the discharge nozzles  32  throughout the target compartment  16 . The HRD bottles  36  in one embodiment delivers enough Halon into the target compartment  16  to provide an initial elevated concentration by volume of fire suppressant that peaks at approximately 5%-30% or more. The volume and concentration levels of the fire suppressant can be different in other embodiments, including embodiments using a fire suppressant other than Halon. 
   The high initial concentration level of fire suppressant extinguishes any flames that may be in the target compartment  16 . After the fire suppressant from the HRD bottles  36  is rapidly dispersed to suppress or extinguish any flames, no additional fire suppressant is added to the target compartment  16  for a selected time period (e.g., 18 minutes). During this time period, the fire suppressant concentration in the target compartment  16  is allowed to slowly drop to a predetermined acceptable level. For example, when the fire suppressant is Halon, the concentration is allowed to drop to the range of approximately 5%-9%, inclusive. 
   The bottles  34  in the fire-suppression system  26  also include a plurality of metered bottles  38  coupled to the main line  28  and also to the aircraft&#39;s control system  24 . Each of the metered bottles  38  of the illustrated embodiment contains approximately 80 pounds of Halon 1301 as the fire suppressant, although pressurized containers can be used that contain more or less fire suppressant. The metered bottles  38  are activated at a selected time by the control system  24  to dispense the fire suppressant into the target compartment  16  at a controlled discharge rate over an elongated period of time. The discharge rate of the fire suppressant from the metered bottles  38  is substantially less than the discharge rate of the fire suppressant from the HRD bottles  36 . In one embodiment, the metered bottles  38  are activated approximately 20 minutes after activation of the fire-suppression system  26 . Accordingly, the flow of fire suppressant from the metered bottles  38  is dispersed into the main line  28  and to the target compartment  16  after the HRD bottles  36  have been substantially emptied. 
   The metered bottles  38  are coupled to at least one regulator  40  that controls the flow of fire suppressant to the target compartment  16 . In the illustrated embodiment, one regulator  40  controls the flow of fire suppressant toward the forward cargo compartment  16   a , and another regulator controls the flow of fire suppressant to the aft cargo compartment  16   b . The regulators  40  provide a substantially continuous, metered flow of Halon to the target compartment  16  as the aircraft is flying along a cruise phase prior to descent toward a safe landing area. 
   In one embodiment wherein the fire suppressant is Halon, the metered bottles  38  and the regulators  40  can be configured to provide a flow of Halon into the target compartment  16  for up to 420 minutes or more while maintaining the Halon concentration level above 3%. In one embodiment, the metered bottles  38  provide Halon into the target compartment  16  to maintain a fire suppressant concentration level in the range of approximately 3.5%-4%, inclusive, after activation of the fire-suppression system  26  and prior to descent of the aircraft toward landing. 
   In one embodiment, the metered bottles  38  and the regulators  40  are configured with a setting to provide 0.9 pounds of Halon per minute into the target compartment  16 . Other embodiments can provide greater or fewer metered bottles  38  and regulators  40  or other flow restricting devices with valve settings that provide a flow of Halon greater or less than 0.9 pounds per minute, so as to maintain the concentration of Halon within the cargo compartment above the 3% minimum during at least the cruise phase and prior to descent of the aircraft. 
   The fire-suppression system  26  of the illustrated embodiment also includes at least one supplemental bottle  42  of fire suppressant coupled to the main line  28 . One or more flow restricting devices  44  are provided between the supplemental bottle  42  and the main line  28  to control the flow of fire suppressant from the supplemental bottle toward the target compartment  16 . The restriction devices  44  can include regulators or other flow control devices. The supplemental bottle  42  and the restriction devices  44  are coupled to the aircraft&#39;s control system  24  and are configured to be activated to disperse additional fire suppressant into the target compartment  16  as the aircraft  10  ( FIG. 1 ) begins to make its descent toward landing. 
   When the supplemental bottle  42  is activated in one embodiment, fire suppressant from the supplemental bottle is directed into the main line  28  and is added to the flow of fire suppressant from the metered bottles  38  flowing toward the target compartment  16 . Accordingly, fire suppressant is added to the target compartment  16  at a greater rate during the descent phase as compared to the rate at which the fire suppressant is delivered from the metered bottles  38  alone prior to descent. In another embodiment, the entire flow of fire suppressant to the target compartment  16  is only provided from one or more supplemental bottles  42  during descent. Accordingly, the flow rate of fire suppressant from the one or more supplemental bottles  42  can be greater than the flow rate of fire suppressant from the metered bottles  38 . In a further aspect of this embodiment, the flow rate of fire suppressant from the supplemental bottle  42  is less than the flow rate from the HRD bottles  36 . 
   In the illustrated embodiment, the fire-suppression system  26  is configured so the supplemental bottle  42  begins to disperse the fire suppressant at approximately the initiation of the aircraft&#39;s descent toward a safe landing area. The supplemental bottle  42  contains enough fire suppressant to be dispersed into the target compartment  16  for up to approximately 20 minutes, which corresponds to the duration of an aircraft&#39;s typical descent. 
   As the aircraft  10  ( FIG. 1 ) descends, the forward and aft cargo compartments  16   a  and  16   b  are repressurized, which results in air being adding into the cargo compartments. The forward and aft cargo compartments  16   a  and  16   b  may also experience increased compartment leakage because of the outflow valve effects during descent. Accordingly, adding additional air through repressurization and losing fire suppressant through increased leakage would ordinarily result in a decrease in the fire suppressant concentration level within the target compartment  16  if the discharge rate of fire suppressant into the target compartment were not increased. The supplemental bottle  42  provides an increased discharge rate of fire suppressant into the target compartment  16  to maintain the fire suppressant concentration above the 3% minimum during the entire descent to counteract the decrease in concentration that would otherwise result. 
   The supplemental bottle  42  of the illustrated embodiment contains approximately 55 pounds of Halon and provides a flow of Halon lasting for approximately 20 minutes during the aircraft&#39;s descent. Accordingly, as an example, the flow of Halon from the supplemental bottle  42  provides an increased discharge rate of Halon during the descent phase so the Halon concentration level in the aft cargo compartment  16   b  remains in the range of approximately 3.5%-4%, inclusive. In one embodiment, the supplemental bottle  42  adds an additional 1.1 pound per minute of Halon 1301 flowing to the target compartment  16  during descent. In other embodiments, the supplemental bottle  42  can provide more or less additional fire suppressant at greater or lesser flow rates. 
   The fire-suppression system  26  of the illustrated embodiment is configured so the supplemental bottle  42  is activated either automatically or in response to a operator&#39;s command at approximately the beginning of the aircraft&#39;s descent. In other embodiments, the fire-suppression system  26  can be configured to activate the supplemental bottle  42  at a trigger point other than at the beginning of the aircraft&#39;s descent. For example, the supplemental bottle  42  can be activated based upon the aircraft&#39;s altitude, the aircraft&#39;s descent rate, the temperature in the target compartment  16 , or other triggering event. 
   The supplemental bottle  42  in the fire-suppression system  26  is configured to provide the extra fire suppressant into the target compartment  16  when needed during the descent phase to compensate against a concentration drop resulting from the concurrence of increased air pressure and compartment leakage. Accordingly, excessive amounts of Halon do not need to be provided into the target compartment  16  for an extended time period prior to descent to maintain an overly high concentration level that can compensate for a drop in the fire suppressant level during the descent. Therefore, less fire suppressant needs to be carried in the fire-suppression system  26 , which provides significant weight and cost savings for the aircraft. 
   In another embodiment, shown in  FIG. 3 , the supplemental bottle  42  can be eliminated and its function carried out by the regulators  40  and the metered bottles  38 . The regulators  40  control the fire-suppressant flow rate from the metered bottles  38 , which is substantially less than the fire-suppressant flow rate from the HRD bottles  36 . In this embodiment, a bypass line  46  is provided between the metered bottles  38  and the main line  28 . The bypass line  46  allows at least a portion of the fire suppressant from the metered bottles  38  to bypass the regulators  40  and flow toward the target compartment  16  at an increased flow rate. 
   At least one restriction device  48  can be connected to the bypass line  46  and configured to provide a fire-suppressant flow rate to the main line  28  greater than the fire-suppressant flow rate through the regulators  40  but less than the flow rate from the HRD bottles  36 . The restriction device  48  can be a regulator, a flow diverter, an adjustable flow valve, or other flow control device. The restriction device  48 , when activated, allows a flow of fire suppressant from the metered bottles  38  to bypass the regulators  40 , so an increased flow of fire suppressant is carried through the main line  28  and delivered to the target compartment during the aircraft&#39;s descent phase. 
   The restriction device  48  can be activated automatically or in response to a command from the operator. The restriction device  48  can be activated at a trigger point corresponding to, for example, a selected amount of time after activation of the fire-suppression system  26 , at the initiation of the aircraft&#39;s descent phase, at a selected altitude, at a selected descent rate, or at another selected trigger point. Accordingly, additional fire suppressant is provided into the target compartment  16  during the aircraft&#39;s descent phase to maintain the fire suppressant concentration at a generally constant level throughout the descent. 
   When the fire-suppression system  26  of the foregoing embodiment is activated in response to an actual or potential fire condition in the forward or aft cargo compartment  16   a  and  16   b , the fire suppressant from the HRD bottles  36  is quickly discharged and dumped into the target compartment  16 , as discussed above. Approximately 20 minutes after the activation of the HRD bottles  36 , the metered bottles  38  are activated. Fire suppressant from the metered bottles  38  flows through the regulator  40  to provide the metered flow of fire suppressant through the main line  28  to the target compartment  16 . The fire suppressant from the metered bottles  38  is dispersed into the target compartment  16  at a selected rate to maintain the fire suppressant concentration above the 3% minimum. In one embodiment wherein the fire suppressant is Halon, the flow of Halon from the metered bottles  38  maintains the Halon concentration in the range of approximately 3.5%-4%, inclusive, over a time period of up to 420 minutes or more. 
   When the aircraft  10  ( FIG. 1 ) begins its descent phase, the restriction device  48  is activated by the control system  24  to allow fire suppressant from the metered bottles  38  to flow through the bypass line  46  to the main line  28 , bypassing the regulators  40 . The fire suppressant from the bypass line  46  provides an increased fire-suppressant flow rate to the target compartment  16  as compared to the fire-suppressant flow rate prior to descent and activation of the restricting device  48 . Accordingly, increased amounts of fire suppressant from the metered bottles  38  are provided into the target compartment  16  to maintain the fire suppressant concentration in a selected range. When the fire suppressant is Halon, the Halon concentration in the target compartment  16  is maintained in the range of approximately 3.5%-4%, inclusive, and at least above the 3% minimum, during the entire descent phase of the aircraft&#39;s flight until landing. 
   In one embodiment, the restricting device  48  can be sequentially or continuously adjusted to provide an increasing fire-suppressant flow rate into the target compartment  16  during the entire descent of the aircraft  10  ( FIG. 1 ). The fire-suppression system  26  can minimize the amount of fire suppressant needed in the metered bottles  38  to provide the fire-suppression protection required for the aircraft&#39;s forward and aft cargo compartments  16   a  and  16   b.    
   In still another embodiment, the regulators  40  in this embodiment can include one or more adjustable devices controlled by the control system  24  or another controlling device. The regulators  40  can be adjusted at selected times during an actual or potential fire condition to change the fire-suppressant flow rate to the target compartment  16 . The regulators  40  can be adjusted prior to or during descent of the aircraft, so the fire-suppressant flow rate is sequentially or substantially continuously increased throughout the descent phase. 
   In another embodiment, the multiple bottles of fire suppressant and multiple regulators or restriction devices can be eliminated and their functions carried out by a single tank or container of fire suppressant and a valve arrangement that controls the fire-suppressant flow rate into the target compartment  16 . The valve arrangement can then be adjusted to provide a high flow rate of fire suppressant into the target compartment  16  immediately after activation of the fire-suppression system  26 . The valve arrangement can be adjusted to reduce the fire-suppressant flow rate during the aircraft&#39;s cruise phase for efficient distribution of the fire suppressant. The valve arrangement can also be adjusted at a selected time, such as at the beginning of the aircraft&#39;s descent, to increase the fire-suppressant flow rate throughout the aircraft&#39;s descent until landing. Accordingly, the fire suppressant concentration is maintained at a generally constant level during descent, thereby compensating for the effects of repressurization and increased leakage in the target compartment 
   The fire-suppression system  26  of the embodiment discussed above provide benefits over the prior art. As an example, the fire-suppression system  26  is configured to provide increasing amounts of fire suppressant into the target compartment  16  only when needed to maintain the fire suppressant concentration within a selected range to compensate for the effects of pressurization and increased leakage in the target compartment. Accordingly, reduced amount of fire suppressant can be efficiently dispersed into the target compartment  16  as needed to maintain the fire suppressant concentration at or slightly above a selected minimum during the cruise and descent phases of the aircraft&#39;s flight. The fire-suppression system  26 , therefore, provides highly desirable cost and weight savings for the aircraft because excessive fire suppressant need not be carried by the fire-suppression system  26 . 
   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 systems and methods described above or the context of particular embodiments can be combined or eliminated in other embodiments. Many of the foregoing embodiments were described in the context of particular fire suppressant, particular suppressant concentration levels, particular flow rates and particular capacities. In other embodiments, any of the foregoing systems can be configured to handle different fire suppressants, maintain different fire suppressant concentrations, deliver different flow rates and/or share different capacities of fire suppressants. Accordingly, the invention is not limited except as by the appended claims.