Abstract:
An ignition device, in particular for an atomizer burner of a motor vehicle heating appliance, comprises a glow ignition member and screening material, which can take up fuel and which surrounds the glow ignition member at least over a region.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
           [0003]    1. Background of the Invention  
           [0004]    The present invention relates to an ignition device, particularly for an atomizer burner of a motor vehicle heating appliance.  
           [0005]    2. Technical Field  
           [0006]    In heating appliances, such as are used as so-called supplementary heaters or auxiliary heaters in motor vehicles, fuel is fed together with combustion air into a combustion chamber and is combusted there. The combustion is ignited by so-called spark gaps, such as also find application in heating burners in heating installations of buildings. The spark gaps provided for ignition, as used in particular in connection with so-called atomizer burners, in which the fuel to be burned is injected together with the combustion air at high speed and thus atomized, are comparatively expensive and thus represent a not inconsiderable cost factor, particularly for smaller kinds of heating devices.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has as its object to provide a cost-efficient ignition device which in particular can also be used in connection with atomizer burners.  
           [0008]    This object is attained according to the invention by an ignition device, particularly for an atomizer burner of a motor vehicle heating appliance, including a glow ignition member and screening material which can take up fuel and which at least partially surrounds the glow ignition member.  
           [0009]    Departing from the procedure, known from the prior art, of using spark gaps for the ignition of atomizer burners, the present invention takes the path of using an ignition device, working on the principle of a glow ignition device, which is markedly more cost-effective to obtain and to build in. This was heretofore not possible, since the removal of heat from a glow ignition member was very great due to the flow speed of the materials injected into the combustion chamber in the case of atomizer burners, so that the glow ignition member could no longer produce, even in its immediate neighborhood, the temperature required for the ignition of the combustion materials. Since however according to the invention the glow ignition member is screened by screening material, the heat transfer to the material flowing at high speed is markedly reduced. Instead of this, the fuel injected at high speed together with combustion air and thus atomized is taken up in the screening material, so that fuel collects in the immediate surroundings of the glow ignition member, which is screened from a high speed flow, and can now be ignited by the glow ignition member.  
           [0010]    It should be mentioned here that as used in the present invention, the expression “material which can take up fuel” includes material which because of its design forms cavities in which the fuel can collect; a direct impingement of the fuel into the material itself does not necessarily have to take place. Nevertheless, materials are also included which have a bodily structure such that the fuel is taken up into them and thus, for example, absorbed, as is the case for a porous material.  
           [0011]    In order to be able as far as possible to exclude heat removal from the glow ignition member due to the flow, it is proposed that the glow ignition member is substantially completely screened against direct flow onto it of material delivered by an atomizer nozzle.  
           [0012]    When the screening material is arranged spaced from the glow ignition member at least in a region, an atmosphere whose flow is calmed down can be produced in the space region between the screening material and the glow ignition member, and can very easily be ignited by the glow ignition member.  
           [0013]    In a further embodiment of the ignition device according to the invention, it can be provided that the glow ignition member is carried by a support arrangement and that screening material is arranged spaced from the support arrangement at least in a region. By this measure, heat transfer from the screening material to the support arrangement is made difficult, so that the ignition efficiency of the ignition device according to the invention can be further improved.  
           [0014]    For example, it can be provided that the glow ignition member is elongate, and that the screening material extends at least along a free end region of the glow ignition member. In order to be able to thereby attain as good as possible a screening action, it can be provided that the screening material extends out over the free end region of the glow ignition member. The screening material can form a screening material member substantially cylindrically surrounding the glow ignition member.  
           [0015]    As materials for the screening material, for example, porous materials can be used, foamed ceramic material being a useful material here because of its thermal and mechanical resistance. The use of mesh-like material such as e.g., wire mesh, is also possible. It should be mentioned that the expression “mesh” is to express the fact that material sections are present which interengage or overlap one another in the manner of a mesh, warp knit fabric, weft knit fabric, or woven fabric. A limitation to a given manner of production of this mesh-like material is not thereby introduced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The present invention is described hereinbelow with reference to the accompanying drawings, in which:  
         [0017]    [0017]FIG. 1 shows a sectional view of a first embodiment of an ignition device according to the invention,  
         [0018]    FIG. 2  shows a view corresponding to FIG. 1, of an alternative embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    A glow ignition member is generally denoted in FIG. 1 by the numeral  10 . The glow ignition member  10  comprises a glow plug or a glow pin  12  of conventional construction, which can thus have, for example, a heating coil and if necessary a control coil as well as insulating powder or the like, in a heat-resistant glow tube. The glow pin  12  is supported in a support member  16  provided with an external thread  14 , and projects over this support portion  16  with its free end region  18 , which for example then contains the heating coil. The support member  16  is supported in a substantially cylindrical support sleeve  20  with an internal thread  21 . The support sleeve  20  can be installed on a housing  22 , shown schematically, of a heating burner  24 . This heating burner  24  furthermore has an atomizer nozzle  26 , shown schematically. Combustion air is introduced at high speed into the combustion chamber  28  of the heating burner  24  by means of the atomizer nozzle  26 . The combustion air, flowing in, entrains the fuel and atomizes it, so that a mixture of combustion air and very fine fuel particles, denoted by  30  in FIG. 1, is produced and flows at high speed into the combustion chamber  28 .  
         [0020]    In the variant embodiment shown in FIG. 1, the free end region  18  projects beyond the housing wall  22  into the combustion chamber  28 . In order to protect this free end region of the glow pin  12  from the air/particle stream flowing in at comparatively high speed, a substantially cylindrical screening member  32  is provided. This extends, with the formation of an interspace  34 , at a spacing along the free end region  18  of the glow pin  12 , and thus along that region of the glow pin  12  which projects beyond the support member  16 . The screening member  32 , in its section extending along the support sleeve  20 , then abuts on, and is supported on, the inner surface of the support sleeve  20 . The screening member  32  extends, together with the free end region  18  of the glow pin  12 , into the combustion chamber  28 , and in fact in the embodiment example shown, as far as the free end region  18  of the glow pin  12  extends also. In this manner, at least a portion of the air/particle stream  30  delivered from the atomizer nozzle  26  is prevented from directly striking the surface of the glow pin  12 .  
         [0021]    The screening member  32  is such, or is formed of such material, that fuel which is contained in the air/particle stream  30  striking this screening member  32  can be taken up in this screening member  32 . For example, the use is possible of a member formed of wire mesh, or of a porous material such as, for example, foamed ceramic. The fuel taken up in the screening member  32  or absorbed into it is transported to the inside, i.e. the side toward the glow pin  12 , of the screening body  32 , on the one hand by the fuel newly flowing on from the outside, and possibly on the other hand by capillary action. An atmosphere enriched with fuel is thus formed in this region and also in the space region  34 . Since the glow pin  12  or its free end region  18  is now extensively screened against the air/particle stream  30 , the removal of heat from the glow pin  12  due to flow is reduced to such an extent that the glow pin  12  can produce a temperature in its surroundings which is sufficient for the ignition of the fuel present there. After the resulting ignition, the combustion immediately propagates over the whole combustion chamber  28 .  
         [0022]    The present invention thus provides the possibility, even in so-called atomizer burners, of employing glow pins, which are very cost-effective in comparison with spark gaps, for the ignition of the injected air/fuel mixture, since the region of the glow pin relevant for igniting this mixture is extensively screened against the mixture flowing on at high speed and thus against an excessive removal of heat induced by flow.  
         [0023]    In the embodiment variant shown in FIG. 2, the glow pin  12 , or its free end region  18 , is arranged such that it does not project into the combustion chamber  28 , or does not project so far into the combustion chamber  28  as in the embodiment according to FIG. 1. The screening material surrounding the free end region  18  of the glow pin  12 , i.e., the screening member  32  of substantially cylindrical constitution, however extends out over the free end region  18  of the glow pin  12  here, and if necessary even into the combustion chamber  28 . A still better screening of the free end region  18  of the glow pin  12  is thus attained. Here an extension of the screening member  32  like a hood in its region projecting beyond the free end region  18  of the glow pin  12  could also be considered, thus completely excluding the direct flow of the air/particle stream  30  onto the glow pin  12 .  
         [0024]    It can furthermore be seen in FIG. 2 that an interspace  36  is created between the support sleeve  20  and the screening member  32  in the end region of the support sleeve  20  near to the housing wall  22 . This interspace leads to an improved thermal insulation of the screening member  32  with respect to the support sleeve  20  and thus reduces the removal of heat from the region relevant for ignition.  
         [0025]    It should be mentioned that in both embodiments described hereinabove, the material which can take up fuel particles, i.e., the screening member  32 , can contact the glow pin  12  or its free end region  18  at least over a region, so that the screening member  32  can already be brought to a markedly higher temperature. It is also of course possible to adapt both the glow pin  12  and also the screening member  32  as regards their design, dimensions, and positioning with respect to the atomizer nozzle.  
         [0026]    In addition to markedly lower material costs in comparison to an ignition device constituted with spark gaps, the ignition device according to the invention, working on the principle of a glow ignition, can be operated with comparatively lower electrical power.