Abstract:
A solid propellant gas generator releases a flowing mixture from a solid propellant, separated from a surrounding area, into the surrounding area. The solid propellant gas generator includes a cooling system for cooling the flowing mixture. The cooling system has at least one feed device for feeding a gas from the surrounding area to the flowing mixture in order to mix the flowing mixture prior to entering into the surrounding area with the gas from the surrounding area.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    Exemplary embodiments of the present invention relate to a solid propellant gas generator, an extinguishing device, a method for cooling a flowing mixture and a method for extinguishing a fire. 
         [0002]    Solid propellant gas generators are known in systems for extinguishing fires. In this case an extinguishing medium, which is present in the form of a solid propellant in a capsule, is ignited, so that the ignition process causes a flowing mixture of, for example, aerosols and gases, which are suitable for extinguishing or suppressing a fire, to develop from the solid propellant. In addition, the ignited solid propellant acts as a propellant for expelling the mixture from the capsule, in order to help extinguish or suppress the fire by means of the resulting increased kinetic energy of the mixture. An exemplary solid propellant gas generator for use in extinguishing fires is described in German patent document DE 31 22 897 A1. 
         [0003]    The process of igniting the solid propellant, however, causes a significant rise in the temperature of the aerosols or rather the gases, so that the flowing mixture is released into the surrounding area at a high temperature. Such a situation should be avoided, especially if persons or temperature sensitive machines may be found in the outlet area of the flowing mixture. 
         [0004]    Therefore, the solid propellant gas generators that are currently available on the market use cooling systems that cool the flowing mixture down to acceptable temperatures. Frequently solid thermal storage mediums, such as metal or ceramic, that can absorb the heat of the flowing mixture, are used for such cooling purposes. In that case the amount of thermal energy that can be stored is usually directly proportional to the weight of the storage medium. 
         [0005]    However, the net effect is an increase in the weight of the solid propellant gas generators, so that they are less suitable for use in the design and construction of aircrafts. 
         [0006]    Therefore, exemplary embodiments of the present invention are directed to an improved solid propellant gas generator. 
         [0007]    A solid propellant gas generator is designed for releasing a flowing mixture from a solid propellant, separated from a surrounding area, into the surrounding area and comprises a cooling system for cooling the flowing mixture. In this case the cooling system has at least one feed device for feeding and mixing a gas from the surrounding area with the flowing mixture prior to entering into the surrounding area. 
         [0008]    When the flowing mixture is released from the solid propellant gas generator, the flowing mixture absorbs energy and, in so doing, heats up too much. By supplying a gas, which has a lower energy content, from the surrounding area, the flowing mixture can be cooled to lower temperatures. In the case of the solid propellant gas generator according to the invention, the cooled gas from the surrounding area is mixed with the flowing mixture before the flowing mixture enters into the surrounding area. This arrangement reduces the risk of persons getting burned and/or the risk of temperature sensitive machines being damaged in the outlet region into the surrounding area. Accordingly, heavy cooling systems made of metal or ceramic for cooling purposes are not required. As a result, the solid propellant gas generator can also be used in the field of aeronautics. 
         [0009]    Preferably the cooling system comprises an acceleration device for accelerating the flowing mixture, an introducing device for introducing the flowing mixture into the surrounding area and preferably a linear contact region of acceleration device and introducing device. In one advantageous embodiment the feed device is arranged at the contact region. 
         [0010]    Thus, the kinetic energy, which the flowing mixture absorbs upon acceleration in the acceleration device, can be utilized through a reduction in the pressure for the purpose of drawing in cooling gas from the surrounding area by means of the feed device. 
         [0011]    Preferably the feed device is arranged radially to the contact region. In particular, it is provided that the cross-section of the feed device tapers off from the surrounding area in the direction of the contact region. 
         [0012]    Hence, the cooling gas from the surrounding area can be fed preferably essentially perpendicular to the flow direction of the flowing mixture, as a result of which the cooling gas mixes with the flowing mixture. 
         [0013]    Due to the advantageous design of the feed device in the tapering form, the gas from the surrounding area is additionally accelerated in the direction of the flowing mixture, as a result of which an even better mixing of the mixture and gas is achieved. 
         [0014]    Preferably the acceleration device connects an interior of the solid propellant gas generator with the contact region. At the same time it is provided that the cross-section of the acceleration device tapers off from the interior in the direction of the contact region. 
         [0015]    Due to the advantageous design of the acceleration device the flowing mixture from the interior is accelerated in the direction of the contact region, where the mixture mixes with the cooling gas from the surrounding area. 
         [0016]    Furthermore, the introducing device connects the contact region with the surrounding area. In this case the cross-section of the introducing device expands from the contact region in the direction of the surrounding area. 
         [0017]    Due to the advantageous expansion of the introducing device, the previously accelerated flowing mixture is introduced into the surrounding area with dissimilar directional components and can mix there with the cooling gas from the surrounding area. The net effect is a drop in the temperature of the flowing mixture. 
         [0018]    In a preferred embodiment the cooling system comprises a sealing mechanism for sealing off the interior from the surrounding area. In particular, the sealing mechanism is a water impermeable foil. This arrangement prevents contaminants from the surrounding area from penetrating into the cooling system or more specifically the solid propellant gas generator and, for example, clogging the cooling system. 
         [0019]    It is most highly preferred that the feed device is arranged at the cooling system in the flow direction of the flowing mixture downstream of the sealing mechanism. Thus, on igniting the solid propellant the sealing mechanism can be blasted free by means of the flowing mixture that is generated. Therefore, it is even more preferred that the sealing mechanism be disposed in the region of the acceleration device, in particular at the place, where the flowing mixture reaches a maximum speed. 
         [0020]    The cross-section of the cooling system is designed so as to taper off in the flow direction of the flowing mixture. Due to the advantageous outer shape of the cooling system, cool ambient air is conveyed along the tapering outer walls of the cooling system to the region, in which the flowing mixture enters into the surrounding area. Hence, it is possible to generate turbulence that enables the cool ambient air to mix with the flowing mixture. 
         [0021]    Preferably a solid propellant storage device is provided for storing the solid propellant; and the housing of this solid propellant storage device is provided with a thermal insulation. With this solid propellant storage device the solid propellant can be separated from the surrounding area; and at the same time a thermal insulation is also on hand. During the ignition process this thermal insulation can ensure that the activating energy, generated by the ignition process, is used to generate the flowing mixture and is not released into the surrounding area. This minimizes both a rise in the temperature of the generator jacket and the risk of injuring persons and damaging material. 
         [0022]    To this end an igniting device for igniting the solid propellant for generating the flowing mixture is provided. 
         [0023]    In a preferred embodiment the solid propellant gas generator has a solid propellant for generating a gas and/or an aerosol and/or a gas-aerosol mixture, in particular for producing an extinguishing agent. 
         [0024]    It is most highly preferred that a filter unit, in particular a metal mesh, is arranged between the cooling system and the solid propellant. With this arrangement it is possible to prevent the solid particles, which are produced when the solid propellant is ignited or when the solid propellant does not completely burn off, from clogging the cooling system, in that the solid particles are retained on the filter unit in the interior of the solid propellant gas generator. 
         [0025]    An extinguishing device for extinguishing a fire comprises the solid propellant gas generator described above. 
         [0026]    In a method for cooling a flowing mixture the following steps are carried out: 
         [0000]    a) accelerating the flowing mixture;
 
b) feeding a cooling gas into the flowing mixture; and
 
c) distributing the cooled flowing mixture into a surrounding area in such a way that additional cooling gas is supplied.
 
         [0027]    The acceleration of the flowing mixture, the supply of cooling gas and the distribution of the cooled flowing mixture is made possible by providing the solid propellant gas generator described above. 
         [0028]    In this respect it is highly preferred that the flowing mixture be filtered. 
         [0029]    In an advantageous method for extinguishing a fire preferably the steps a) to c) of the above described method are carried out. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0030]    The invention is explained in detail below with reference to the accompanying drawings. The drawings show in 
           [0031]      FIG. 1  a solid propellant gas generator; 
           [0032]      FIG. 2  flow conditions at and in a solid propellant gas generator from  FIG. 1  after ignition. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]      FIG. 1  shows a solid propellant gas generator  10  with a solid propellant storage device  12  in the form of a housing  14 , in which a solid propellant  16  is disposed. The housing  14  comprises an igniting device  18  for igniting the solid propellant  16 . 
         [0034]    When the solid propellant  16  is ignited by means of the igniting device  18 , a flowing mixture  20  is released in the solid propellant gas generator  10 ; and this mixture issues from the housing  14  into a surrounding area  22  and can be used as the extinguishing agent  24  for extinguishing a fire  26 , shown in  FIG. 2 . 
         [0035]    In order to be able to use the activating energy, generated by the ignition process, in its entirety for igniting the solid propellant  16 , the housing  14  has a thermal insulation  28 . 
         [0036]    Following the release of the flowing mixture  20 , this flowing mixture passes through a cooling system  30 , in which it is cooled down, and then exits into the surrounding area  22 . First, however, the flowing mixture  20  is filtered by means of a filter unit  32 , so that any larger particles that may be present in the flowing mixture  20  do not clog the cooling system  30 . In the embodiment shown in  FIG. 1 , a metal mesh  34  is provided as the filter unit  32 . 
         [0037]    The cooling system  30  has a feed device  36 , by means of which the gas  38  from the surrounding area  22 , for example the air  39 , can be fed to the flowing mixture  20 , before it leaves the cooling system  30  and enters into the surrounding area  22 . 
         [0038]    The cooling system  30  is designed in such a way that it has an acceleration device  42 , in which the flowing mixture  20  is accelerated, in the region, in which the flowing mixture  20  from an interior  40  of the housing  14  enters into the cooling system  30 . In the acceleration device  42  the inner walls  44  of the cooling system  30  taper off, as seen in the flow direction, so that the acceleration device  42  forms a narrowing  46 , in which the flowing mixture  20  exhibits a high speed due to the acceleration. 
         [0039]    Connected to the acceleration device  42  is an introducing device  48 , by means of which the accelerated flowing mixture  20  is introduced into the surrounding area  22 . 
         [0040]    The acceleration device  42  and the introducing device  48  are connected to each other in a contact region  50 . In the embodiment of the solid propellant gas generator  10  depicted in  FIG. 1 , the introducing device  48  is formed in that the inner walls  44  expand away from each other in the flow direction. 
         [0041]    The feed device  36  conveys the gas  38  from the surrounding area  22  in the contact region  50  between the acceleration device  42  and the introducing device  48  into the cooling system  30 . 
         [0042]    A sealing mechanism  52  (in the present example in the form of a water impermeable foil  54 ) is disposed in the flow direction above the feed device  36 . This foil prevents contaminants from the surrounding area  22  from passing into the interior  40  of the housing  14  and, in so doing, clogging, for example, the cooling system  30 , in particular, for example, at the narrowing  46 . 
         [0043]    In the present embodiment in  FIG. 1  the contact region  50  has a linear construction. That is, the contact region connects the acceleration device  42  and the introducing device  48  to each other on a straight line, so that the maximum speed of the flowing mixture  20  prevails in the contact region  50 . The feed device  36  is arranged radially to this linear contact region  50 , so that the supplied gas  38  from the surrounding area  22  impinges on the flowing mixture  20  in essence with a perpendicular directional component. This arrangement allows the flowing mixture  20  and the gas  38  from the surrounding area  22  to mix. In addition, the feed device  36  tapers off in the flow direction of the supplied gas  38  and accelerates this gas  38  in such a way that the generation of turbulence upon impinging on the accelerated flowing mixture  20  in the cooling system  30  is reinforced. 
         [0044]    The introducing device  48  expands from the contact region  50  in the flow direction of the flowing mixture  20 , which is now cooled down, and, in so doing, distributes the flowing mixture  20  with dissimilar directional components into the surrounding area  22 . 
         [0045]    The outer walls  56  of the cooling system  30  also taper off in the flow direction of the flowing mixture  20 . 
         [0046]    This arrangement allows the air  39  of the surrounding area  22  to be conveyed, as shown by the large arrows in  FIG. 2 , preferably in the direction of the region, in which the flowing mixture  20  enters into the surrounding area  22 . The net effect is additional mixing of the flowing mixture  20  with the cooler ambient air  39 , so that the flowing mixture  20  cools down even more. 
         [0047]    When the solid propellant  16  is ignited, aerosols are released in the interior  40  of the housing  14 . These aerosols mix with the gas, which may be found in the interior  40 , to form a gas-aerosol mixture  58 . This gas-aerosol mixture  58  is mixed, as indicated by the small arrows in  FIG. 2 , with the cooling gas  38  from the surrounding area  22  and then issues into the surrounding area  22 . The mixing of, for example, the air  39  with the gas-aerosol mixture  58  acts as an extinguishing agent  60 , which can extinguish, for example, the fire  26  shown in  FIG. 2 . Hence, an extinguishing device  22 , which can be used even in aerospace engineering due to its negligible weight, is formed by the particular design of the solid propellant gas generator  10 . 
         [0048]    In the above described solid propellant gas generator  10  a possible alternative cooling principle is proposed for a gas and/or an aerosol. Such an alternative cooling principle makes it possible to use the solid propellant gas generator  10  even in aircrafts and to replace the fire extinguishing systems that are currently used in the freight compartments of aircrafts. 
         [0049]    The current solid propellant gas generators  10  are, in principle, too heavy for the construction of aircrafts. The reason lies in the heavy cooling system. This cooling system reduces the temperature of the generated gas or aerosols, before they leave the solid propellant gas generator  10 , a feature that is necessary in order to prevent the risk of injuring persons and damaging machines. An alternative cooling principle can significantly reduce the weight of the solid propellant gas generator  10 . 
         [0050]    The current cooling systems of solid propellant gas generators  10  are based on the absorption of heat into a storage medium, such as metal or ceramic. The amount of heat that can be stored is, in principle, directly proportional to the weight of the storage medium. The result is that the solid propellant gas generators  10  are extremely heavy, because large amounts of heat are often generated by the solid propellant gas generator  10 . Furthermore, it has been found that a storage-based cooling system can lead to a loss of extinguishing agent. Such a loss could decrease the efficiency of the solid propellant gas generator  10  and at the same time be associated with an increase in the weight of the solid propellant gas generator system. 
         [0051]    Therefore, what is now proposed is to cool by mixing with the air  39  of the surrounding area  22 . To this end it is provided that coarse particles be filtered out and that the extinguishing agent  60  be accelerated, for example, with a Laval nozzle. To this end the air  39  is drawn in and premixed with the extinguishing medium inside this exemplary Laval nozzle. An additional mixing at the outlet from the Laval nozzle is also possible. 
         [0052]    In comparison to the current systems that are available on the market, the advantage of the proposed solid propellant gas generator  10  consists of the significantly reduced weight. This weight loss is achieved by the fact that with the air-cooled principle a thermal storage device does not have to be present in the solid propellant gas generator  10 , because the air  39  absorbs the heat. 
         [0053]    There is also the additional advantage that significantly fewer aerosol particles are lost due to the short straight outlet channel than in the currently existing cooling systems. Since the particles achieve the extinguishing effect predominantly by impinging on a fire  26  in a central manner, the loss incurred by a conventional cooling system leads to a reduction in the efficiency. 
         [0054]    In summary, the solid propellant gas generator  10  is significantly lighter, more efficient and smaller than the currently existing systems. 
         [0055]    A relatively new extinguishing system is the so-called aerosol or gas generators. This extinguishing method is based on various extinguishing effects, such as inhibition and inertization. In both cases the extinguishing medium is generated by igniting a quantity of solid propellant, the propellant charge. This process is associated with the development of a temperature that may present a particular concern for persons and machines. Current systems use solid storage mediums for cooling down to acceptable temperatures. 
         [0056]    Due to the proposed alternative cooling principle of the present invention the weight of the generators is significantly reduced compared to that of solid propellant gas generators  10  with solid storage mediums. 
         [0057]    As an alternative to a cooling system that stores heat, the cooling is achieved by mixing with air  39 . The conveyance by means of, for example, a Laval nozzle, is suitable for this purpose. Due to this alternative cooling principle, the weight of the generators is drastically reduced. 
         [0058]    The gas generating solid propellant  16  is positioned, as shown, for example, in  FIG. 1 , in a cylinder on a metal mesh  34 . The metal mesh  34  serves as the filter in order to retain larger particles. Such an arrangement prevents the Laval nozzle, which is positioned so as to be connected thereto, from being clogged. As soon as the gas generating solid propellant  16  is ignited by means of, for example, an electric igniter, the solid propellant  16  begins to burn. The gas or aerosol that is generated flows through the mesh into the Laval nozzle, where it is accelerated. According to Bernoulli&#39;s energy equation, the static pressure decreases as the flow rate increases. A skillful selection (as shown in  FIG. 1 ) of the nozzle geometry and the supply air channels allows the air  39  to be drawn into the nozzle in the course of conveyance; and this air mixes with the generated gas or aerosol. The net effect of this mixing is a significant reduction in the temperature of the extinguishing medium that is generated. 
         [0059]    Moreover, a water impermeable protective foil is provided in order to prevent the gas generating solid propellant  16  from making contact with moisture. The generator jacket has internally a thermal insulation. 
         [0060]    In this respect  FIG. 1  shows the basic design of an air-cooled solid propellant gas generator. 
         [0061]    Since the mixture of air and extinguishing agent leaves the Laval nozzle at a high speed, the net result is an additional mixing with the air  39  following the outflow of said air-extinguishing agent mixture. The flow conditions of the air-cooled solid propellant gas generator  10  can be seen in  FIG. 2 . In this case the arrows indicate the flow direction of the gases. The head of the generator is optimized with respect to flow in such a way that the result is a fast additional mixing of the air  39  and the extinguishing agent  60 . 
         [0062]    The net effect of the sequence presented above is a significant drop in the temperature of the generated extinguishing medium to temperatures that do not present a hazard. In summary it can be said that the generator is significantly lighter in weight, more efficient and smaller than those used in the currently existing systems. 
         [0063]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10  solid propellant gas generator 
           12  solid propellant storage device 
           14  housing 
           16  solid propellant 
           18  igniting device 
           20  flowing mixture 
           22  surrounding area 
           24  extinguishing agent 
           26  fire 
           28  thermal insulation 
           30  cooling system 
           32  filter unit 
           34  metal mesh 
           36  feed device 
           38  gas 
           39  air 
           40  interior 
           42  acceleration device 
           44  inner wall 
           46  narrowing 
           48  introducing device 
           50  contact region 
           52  sealing mechanism 
           54  foil 
           56  outer wall 
           58  gas-aerosol mixture 
           60  extinguishing agent 
           62  extinguishing device