Abstract:
A nozzle for atomization of liquid fuel by air flowing through the nozzle ( 20 ), with an air entry area ( 50 ), an air exit area ( 52 ) and a flow path ( 54 ) which connects the air entry area ( 50 ) to the air exit area ( 52 ), the nozzle ( 20 ) being made of ceramic material, an air guidance device ( 56 ) being provided in the air entry area ( 50 ) which imparts a swirl to the inflowing air, and the air guidance device ( 56 ) being an integral part of the nozzle ( 20 ). Furthermore, there is a heater ( 10 ) equipped with such a nozzle ( 20 ) for mobile applications.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The invention relates to a nozzle for atomization of liquid fuel by means of the air flowing through the nozzle, with an air entry area, an air exit area and a flow path which connects the air entry area to the air exit area.  
         [0003]     2. Description of Related Art  
         [0004]     Generic nozzles are used, for example, in vehicle heaters. These vehicle heaters can be used, for example, as auxiliary heaters and/or stationary heaters.  
         [0005]     The nozzle is used to supply combustion air, due to the flow of combustion air the liquid fuel, for example, diesel or gasoline, being entrained from a fuel nozzle and atomized. In this way, a mixture of combustion air and fuel is obtained which can be burned, optionally, after mixing with air supplied on other flow paths, by which the heat necessary for heating operation is produced. This heat generated by a burner then heats a heat transfer medium, for example, water or air.  
         [0006]     Nozzles of the prior art often are made of metal, e.g. as cast parts or turned parts. The disadvantage in these components is the comparatively high production cost and the generally high thermal conductivity of the metals. The thermal conductivity can pose problems when the temperature in the area of the fuel nozzle rises unduly as a result of the heat produced in the burner. To solve the problems which are associated with metallic nozzles, it has been proposed that a ceramic nozzle be used.  
         [0007]     The flow behavior of the combustion air is important for the mixing of the combustion air with the fuel on the common path. In order to improve the flow behavior of the combustion air, it was already proposed in DE 100 39 152 A1 and corresponding U.S. Patent Application Publication 2003/0022123 A1 that a swirl be imparted to the combustion air. In this way, it is possible to distinctly improve the atomization quality and thus the efficiency of the burner, since the combustion air speed is increased as a result of the pronounced tangential component of motion. In order to impart this swirl, a carrier with swirl blades is connected upstream of the input area of the nozzle. However, the disadvantage in this carrier with upstream swirl blades is that an additional component is needed, for which reason the tolerances which exist for undisturbed operation of the nozzle can sometimes be exceeded.  
         [0008]     In heaters of the prior art it is, furthermore, problematical to maintain narrow tolerances with respect to positioning of the glow plug with regard to the inflowing fuel/air mixture.  
       SUMMARY OF THE INVENTION  
       [0009]     The object of the invention is to make available a nozzle which can be economically produced, which has thermal conductivity which is low compared to metal, and which induces advantageous properties with respect to the flow behavior of the combustion air, and calibration problems are to be avoided.  
         [0010]     This object is achieved by the nozzle being made of ceramic material and having an air guidance means formed as an integral part thereof in the air entry area so as to impart a swirl to the inflowing air  
         [0011]     The invention is based on the generic nozzle in that the nozzle is made of ceramic material and the air entry area has air guidance means which impart a swirl to the inflowing air but improves thereon by the air guidance means being made as an integral part of the nozzle. In this way a nozzle is provided which can be economically produced. The ceramic material can be easily worked, numerous versions with respect to shaping being possible. In particular, the air guidance means which delivers a swirl to the combustion air outside of the air entry area can be made integrally with the nozzle. As a result of using a ceramic, there is the additional advantage that the area of the nozzle around the fuel needle which is located in the nozzle does not assume overly high temperatures, so that amounts of fuel which may be emerging from the nozzle cannot ignite. The integral execution of the air guidance means makes it possible to easily adhere to tolerances, since miscalibration of the air guidance means when the burner is being assembled is no longer possible.  
         [0012]     The invention is advantageously developed in that the nozzle has means for holding a glow plug. The positioning of the glow plug with respect to the nozzle is an important parameter with regard to good starting behavior of the burner. In heaters of the prior art, the glow plug was generally held by the burner housing, so that, in this way, fluctuations of the positioning with respect to the nozzle could occur. These tolerances can be precluded by the property of the nozzle of the present invention in that the nozzle itself has means for holding the glow plug so that the glow plug always has the same position with respect to the nozzle.  
         [0013]     Furthermore, the nozzle in accordance with the invention is advantageously developed in that the nozzle has at least in part an essentially cylindrical shape and that the air guidance means forms channels which are offset with respect to the radial directions. The air which is flowing in perpendicular to the axis of the nozzle is therefore not radially supplied, but supplied with an offset. This offset determines the swirl which is delivered to the combustion air, and thus, the flow behavior and ultimately also the properties and quality of combustion.  
         [0014]     It is especially useful for the air guidance means to have essentially triangular base surfaces, the corners being rounded. In this way, the channel offset can be easily implemented. The rounding of the corners is advantageous for uniform flow behavior.  
         [0015]     It can also be useful for the air guidance means to be made as blades. These blades can likewise provide offset channels so that, in this way, the combustion quality is benefited.  
         [0016]     In another preferred embodiment of this invention, it is provided that the means for holding the glow plug are made as a hole which runs obliquely to the cylinder axis. The glow plug must then be simply inserted into the hole for suitable positioning. A stop on the glow plug and/or within the hole provides for the glow plug to be guided into its optimum position with respect to the nozzle.  
         [0017]     The nozzle in accordance with the invention is developed especially advantageously in that an at least essentially cylindrical part of the nozzle has an essentially cylindrical shoulder with an increased diameter and that the means for holding the glow plug are made as a hole which penetrates the shoulder which runs obliquely to the cylinder axis. In this way, the glow plug can be held in an area in which it influences the flow behavior of the inflowing fuel/air mixture as little as possible. This can be easily managed by the cylindrical stop which has a greater diameter than the remaining nozzle body.  
         [0018]     Likewise, it is especially advantageously provided that an at least essentially cylindrical part of the nozzle has an essentially cylindrical shoulder with an increased diameter and that the cylindrical shoulder has recesses for holding the mounting pins. These mounting pins can be securely attached, for example, to the heat shield of the burner. The relative positioning of the nozzle is fixed in this way by recesses in the shoulder and the position of the mounting pins. Thus, installation is especially simple and is possible with only low tolerances.  
         [0019]     In an especially advantageous manner, it can be provided that the nozzle is a Venturi nozzle. The Venturi effect for atomization of the fuel emerging from the fuel needle can be advantageously combined in this way with the swirl delivered to the combustion air. The effects support one another and thus lead to high-quality combustion.  
         [0020]     The invention is based on the finding that a nozzle which can be economically produced provided with a shape which can be varied within wide limits using a ceramic material. The shaping of the nozzle can be completed such that the air guidance means which imparts a swirl to the entering combustion air can be made integrally with the nozzle. Furthermore, the ceramic has the advantage that an undesirably high temperature can be avoided in the area of the fuel needle.  
         [0021]     Another object consists in devising a heater for mobile applications which can be economically produced.  
         [0022]     This object is achieved by a heater for mobile applications, especially motor vehicles which is provided with a burner for combustion of a fuel/air mixture having a nozzle in accordance with the present invention.  
         [0023]     The invention is explained in greater detail below with reference to the accompanying drawings which shows a preferred embodiment of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a partially cutaway schematic of a heater in which the nozzle of the present invention can be used;  
         [0025]      FIG. 2  cross-sectional side view of one embodiment of a nozzle in accordance with the invention;  
         [0026]      FIG. 3  is a plan view of the air entry area of a nozzle in accordance with the invention; and  
         [0027]      FIG. 4  shows a nozzle in accordance with the invention mounted on a burner. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     In the following description of the drawings, the same reference numbers identify the same or comparable components throughout the various figures.  
         [0029]      FIG. 1  shows a heater  10  for use with the nozzle of the invention which has a burner  12  for combustion of a fuel/air mixture. The heater comprises an annular channel fan  14  with a fan motor  36 . Combustion air  42  is taken in through the annular channel fan  14  via an air entry connection  16  and is blown into a combustion air collecting space  18  on the pressure side. The combustion air which is available in the combustion air collecting space  18  is divided into primary air and secondary air. The primary air is conveyed into the combustion chamber  24  by a nozzle  20  which is made as a Venturi nozzle in this example. The secondary air is conveyed through secondary air holes  22  into the combustion chamber  24 . The division of the combustion air into primary air and secondary air is useful in order to provide a rich, ignitable mixture at the outlet of the nozzle  20 .  
         [0030]     The nozzle  20  comprises a settling zone  26  and a diffusor  30  in order to produce the Venturi effect. Within the nozzle  20 , there is a fuel needle  28 . The fuel needle  28  is supplied with fuel  44  via a fuel line  82 . Due to the high flow velocity of the combustion air in the settling zone  26 , the fuel which is emerging almost unpressurized from the fuel needle  28  is pulled into filaments which then break down into droplets. The high air speeds which are necessary for good atomization can be achieved by good pressure recovery of the diffusor  30 .  
         [0031]     Furthermore, over the course of the diffusor  30 , the flow velocity of the fuel/air mixture is drastically reduced, by which low flow velocities are accomplished in the area of the glow plug  62  which is indicated in  FIG. 2 . This supports the formation and propagation of a pilot flame. After the starting process, i.e., ignition of the system by the glow plug  62 , the glow plug is turned off. It is used subsequently with the aid of resistance measurement for flame monitoring.  
         [0032]     Within the fuel chamber  24 , there is a baffle disk  32 . The latter constitutes a flow barrier so that the air emerging from the nozzle  20  is forced to the outside. In this way, good mixing of the primary air with the secondary air takes place; this is useful with respect to good final combustion. The area between the nozzle  20  and baffle disk  32  is thus used as a mixing zone  34  and the area on the other side of the baffle disk  32 , i.e., the area which is downstream with respect to the baffle disk  32 , is used as a reaction zone  38 . The mixture produced burns in the further course of the combustion pipe  40  and is routed out of the heater  10  by the parts which carry the exhaust gas. The heat generated heats the entering cold water  46  in heat exchange with the exhaust gas-carrying parts so that hot water  48  emerges from the heater  10 . For example, air can also be used as a heat transfer medium instead of water.  
         [0033]      FIG. 2  shows a partially cutaway side view of one embodiment of a nozzle  20 . This nozzle  20  can be used, for example, in a heater  10 , as is shown in  FIG. 1 . The nozzle  20  is made of a ceramic material; this simplifies the production of the nozzle  20  as compared to metal nozzles. The nozzle  20  has an air entry area  50  and an air exit area  52 . The air entry area  50  is connected to the air exit area  52  via the flow path  54 . This flow path  54  is divided in this example into a settling zone  26  and a diffuser  30 .  
         [0034]     In the air entry area, there is air guidance means formed of air guidance elements  56 . These air guidance elements  56  are made integrally with the ceramic nozzle  20 . The air guidance elements  56  are aligned such that a swirl is imparted to the supplied air; this is explained below with reference to  FIG. 3 . In the settling area  26 , there can be a fuel needle  28  (see,  FIG. 4 ) so that a mixture of fuel and air emerges from the nozzle  20 . This mixture can be ignited via a glow plug  62  which can be inserted into a hole  58  of the nozzle  20 . The positioning of the glow plug  62  is thus fixed with respect to the nozzle  20 , since the glow plug  62  is held by a hole  58  of the nozzle  20 , i.e., especially not by any other parts. Thus, very low tolerances can be maintained with respect to the installation position of the glow plug  62 . The hole  58 , advantageously, penetrates a cylindrical shoulder  64  of the nozzle  20 , which shoulder has an enlarged radius; this has the advantage that the flow behavior of the nozzle  20  is influenced only slightly by the hole  58  or by the glow plug  62  which is located in the hole  58 .  
         [0035]      FIG. 3  shows an overhead view of the air entry area  50  of a nozzle. One possible configuration of the air entry area  50  by air guidance elements  56  is shown. The air guidance elements  56  form channels  60  for the inflowing air. These channels  60  are positioned with respect to the radii of the structure which is located essentially on an axis such that there is an offset. Air flowing in from the outside thus undergoes a swirl; this entails advantageous properties with respect to atomization of the fuel which is emerging from the fuel needle which can be located in the settling area  26 . Furthermore, in this representation, the arrangement of the opening  58  for holding the glow plug can be recognized. The opening  58  penetrates the essentially cylindrical shoulder  64 . Furthermore, the shoulder  64  is provided with recesses  66 . These recesses  66  define the installation position of the nozzle  20 ; this is explained below with respect to  FIG. 4 .  
         [0036]      FIG. 4  shows a partially cutaway view of a device in accordance with the invention. One end of the burner  12  facing the nozzle  20  is shown.  
         [0037]     The burner  12  is bordered by a heat shield  78 . On this heat shield  78 , there are two mounting pins  68  in this sample embodiment. These mounting pins  68  can be welded to the heat shield  78  or to the burner  12 . The mounting pins  68  define the positioning of the other components which are described below. First of all, there is a seal  76  which preferably is formed of a mica layer and a graphite layer, the mica layer facing the burner  12  and the graphite layer facing the nozzle  20 . The ceramic nozzle  20  follows and is positionally fixed on the mounting pins  68  with its recesses  66  ( FIG. 3 ). A fuel feed  70  is connected to the fuel needle  28  and is seated on the nozzle  20 . This fuel feed  70  is positioned, likewise, by mounting pins  68  by means of holes  84  which are provided in a side flange. The fuel feed  70  is supplied with fuel by a fuel line  82  in which there is a fuel sensor  80 . The fuel feed  70  is followed by a spring  72  which is also seated on the mounting pins  68 . The spring  72  is held by clamping disks  74  which sit immovably on the mounting pins  68 . The spring  72  is shown in the tensioned state in which the legs of the spring  72  are, for example, parallel to the interposed disk. In the relieved state of the spring  72 , the legs of the spring  72  are bent up in the direction to the interposed disk. The glow plug, which is not shown in  FIG. 4 , is positioned in agreement with the embodiment of nozzle  20  shown in  FIG. 2  by this nozzle and is held by a wire spring (not shown) which is supported on the nozzle  20 .  
         [0038]     The fuel feed  70 , and thus, the fuel needle  28  are automatically aligned in this way with respect to the nozzle  20 . Therefore, only two components are involved which influence the fuel feed and mixing of the fuel with the combustion air, so that very small tolerances can be maintained; this is possible by axial mounting on the same mounting pins  68 . Likewise, the glow plug  62  can be positioned exactly with respect to the nozzle  20  and the burner  12 . The production of the structure shown in  FIG. 4  can be completely automated. In particular, the mounting direction is uniformly axial so that only “threading” of the components  76 ,  20 ,  70 ,  72  and  74  need be performed. The seal  76  makes available heat insulation, coupling of the nozzle ceramic  20  to the metal of the heat shield  78 , and tolerance compensation. The structure can be advantageously mounted by power-controlled pressing of the clamping disks  74  onto the mounting pins  68  so that, with respect to the heat and temperature properties of the structure, uniform prerequisites can be created. Imparted by the spring force of the spring  72 , tolerances due to the varied heating of the components, different final temperatures of the components and different coefficients of temperature expansion can be compensated.  
         [0039]     The features of the invention disclosed in the description above, in the drawings and in the claims can be important to the implementation of the invention both individually and also in any combination.