Abstract:
A burner ( 10 ) for a heater, especially for use in motor vehicles, with a burner nozzle ( 12 ) for supplying of fuel and primary air, a combustion chamber ( 22 ), and a heat shield ( 24 ) between the burner nozzle and the combustion chamber, the heat shield having openings ( 26 ) for supplying secondary air to the combustion chamber. The openings ( 26 ) are equipped with air guide elements ( 28, 30 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The invention relates to a burner for a heater, especially for use in motor vehicles, with a burner nozzle for supplying fuel and primary air, a combustion chamber, and a heat shield between the burner nozzle and the combustion chamber, the heat shield having openings for supplying secondary air to the combustion chamber. 
         [0003]    2. Description of Related Art 
         [0004]    These burners which are also called atomization burners or spray burners are used especially in auxiliary heaters and independent heaters for motor vehicles. 
         [0005]    There are numerous requirements for these burners, especially with respect to reliable and largely emission-free starting behavior and stable combustion operation. Furthermore, an effort is made to build heaters which can be used in different installation positions. 
         [0006]    With respect to starting behavior, various operating parameters must be matched to one another. On the one hand, it is necessary during burner starting to provide a relatively rich fuel-air mixture in the starting zone, on the other hand, however, to provide a sufficient amount of primary combustion air is necessary to ensure transport of the fuel from the fuel needle to the starting zone. 
         [0007]    The requirement of allowing different installation positions of the heater is associated with problems relating to starting behavior. In order to specifically be able to transport fuel into the starting zone with little primary air supply, in the past, orienting the fuel needle with the outlet opening pointed downward had to be tolerated; this resulted in the entire burner having to be mounted in the vertical installation position. 
         [0008]    To ensure stable combustion operation of the burner, likewise, mutually contradictory requirements must be satisfied. On the one hand, good intermixing of the fuel and air is always required, on the other hand, in the core region of the flame and there, especially during the starting phase, it is undesirable to cause overly high air proportions and overly high swirling. 
       SUMMARY OF THE INVENTION 
       [0009]    The object of the invention is to overcome the described problems of the prior art at least in part and especially to enable reliable and low-emission starting behavior with little dense smoke in different installation positions. 
         [0010]    This object is achieved with the openings in a heat shield between the burner nozzle and the combustion chamber for supplying secondary air to the combustion chamber being equipped with air guide elements. 
         [0011]    The invention is based on a generic burner in that the openings are equipped with air guide elements. A heat shield is fundamentally useful to shield the nozzle and the fuel supply against the heat energy present in the combustion chamber. Furthermore, secondary air is supplied to the combustion space via the heat shield. By the openings for secondary air supply being provided with air guide elements, this secondary air can be supplied in a controlled manner so that combustion operation, both with respect to starting operation and also for continuous operation, can be influenced in a specific manner. 
         [0012]    It is useful for the air guide elements to be formed by tabs which are made integrally with the heat shield and which project in the direction of the combustion chamber. This heat shield can be easily produced, for example, by the tabs being formed with a v-shaped punching tool and being bent out of the plane of the heat shield after or with the punching process. 
         [0013]    The invention is also usefully developed in that the tabs are made at different angles to the surface of the heat shield and/or to the radius of the heat shield. If the tabs extend almost perpendicularly to the radius of the heat shield, this delivers strong angular momentum, while tabs with a smaller angle to the radius deliver less angular momentum. Tabs which assume a small angle to the surface of the heat shield produce air flows which have a large radial component and a small axial component, while for tabs with large angles to the surface of the heat shield the axial component dominates. In this way, it is possible to route secondary air with low angular momentum into the core region of flame formation, and on the one hand, the air which is required for combustion is supplied; but there is no excess angular momentum which would adversely affect stabilization of the flame. In particular, the secondary air can be divided depending on the alignment of the individual air guide elements. 
         [0014]    According to another embodiment, it is provided that the tabs are grouped at essentially identical angles to the surface of the heat shield and/or to the radius of the heat shield. Defined flow states in the combustion chamber are formed by the collective alignment of the tabs. 
         [0015]    Furthermore, the invention is usefully executed such that the burner has a burnout zone and that the secondary air which is supplied to the burnout zone has higher angular momentum than the secondary air which is supplied to the starting zone. High angular momentum is desired in the burnout zone. In particular, a radially inside swirled backflow region improves the burnout and provides for the combustion chamber volume being effectively used. 
         [0016]    It is also provided that the heat shield has an opening for routing an ignition element through. 
         [0017]    According to one especially preferred embodiment of the invention, it is provided that the burner nozzle has a fuel needle for supplying fuel to the burner and a primary air supply for supplying combustion air to the burner and that, by choosing the inside diameter of the fuel needle, the exit speed of the fuel is predetermined such that during the starting phase of the burner fuel in essentially unatomized form reaches the starting zone. By reducing the inside diameter of the fuel needle as compared to fuel needles in the heaters of the prior art, at the same fuel delivery volume, the exit speed of the fuel is increased. In this way, for any installation position, it is possible for the fuel jet to reach the starting zone from the exit opening of the fuel needle. In particular, for a small primary air amount, for which the supplied primary air should have only little angular momentum, an essentially unatomized fuel jet can reach the starting zone. Consequently, the burner starts reliably and formation of dense smoke during starting is distinctly reduced. 
         [0018]    It is preferred that the inside diameter of the fuel needle be between 0.5 mm and 0.7 mm. Compared to exit speeds for fuel needles of the prior art in which the inside diameter is in the region of 0.8 mm, the exit speed for inside diameters between 0.5 and 0.7 mm can be almost doubled or even more than doubled. 
         [0019]    It is especially preferred that the inside diameter of the fuel needle be about 0.6 mm. At this inside diameter, in full load operation, i.e., at a fuel mass flow of 0.5 kg/h, exit speeds of more than 0.6 m/s are possible, while for an inside diameter of 0.8 mm, the exit speed is in the region of 0.35 m/s. The exit speed in partial load operation rises accordingly, i.e., for a fuel mass flow of 0.2 kg/h, from roughly 0.14 m/s to roughly 0.25 m/s. For a corresponding choice of construction properties or of operating parameters the goal of an essentially unatomized jet which reaches the starting zone when the heater is being started can also be achieved with a conventional fuel needle with an inside diameter of roughly 0.8 mm. 
         [0020]    It is useful for the starting zone to be made as a starting chamber into which an ignition element projects. The wall of the combustion chamber can surround the ignition element in this way. During starting operation the “ballistic” fuel jet can then wet the ignition element and the combustion chamber wall with fuel so that the combustion chamber wall and adjacent components after their heating are used as wall vaporizers. 
         [0021]    In one especially preferred embodiment of the invention, it is also provided that the combustion chamber is essentially axially symmetrical, that there is a baffle plate in the combustion chamber, and that the baffle plate has a given curvature into the axial direction. Due to the curvature of the baffle plate, there is defined shaping of the baffle plate which is independent of temperature. For the baffle plates of the prior art which are made flat, this is, among other things, not the case since, depending on the temperature, spontaneous changes of shape can occur which can adversely affect the combustion behavior of the burner. 
         [0022]    It is preferred that there is a curvature in the direction of the burnout zone. In this way, a sufficient space in the region of the starting chamber is made available. Furthermore, it has been found that the curvature in the direction of the burnout zone does not have an adverse effect on the flow behavior in this zone. In particular, the pronounced swirled backflow region is maintained in the radially inside region of the burnout zone. 
         [0023]    According to one preferred embodiment of the invention, it is provided that the outer periphery of the baffle plate defines a plane and that the ratio between the maximum axial distance of the baffle plate from this plane and the diameter of the baffle plate is between 0.07 and 0.21. The most heavily arched point of the baffle plate is preferably essentially in the center of the arrangement with respect to the radial coordinate. From the plane which is defined by the outer periphery of the baffle plate, this point has an axial distance which is defined by the indicated ratio to the diameter. 
         [0024]    In this connection, it is especially preferred that the ratio between the maximum axial distance of the baffle plate from the plane and the diameter of the baffle plate is roughly 0.14. For example the round diameter of baffle plate is roughly 40 mm, while the curvature has a value of roughly 5.7 mm. 
         [0025]    The invention is based on the finding that the novel heat shield with air guide elements, especially in combination with the novel fuel supply and the novel baffle plate can dramatically improve the operating behavior of a burner. This relates especially to the starting behavior, the stability of burner operation and the possibilities with respect to the installation position of the burner in the motor vehicle. 
         [0026]    The invention is explained by way of example using preferred embodiments and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a sectional view of the burner in accordance with the invention; 
           [0028]      FIG. 2  is a perspective view of a burner flange with the heat shield inserted into it; and 
           [0029]      FIG. 3  is a perspective of the heat shield. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    In the following description of preferred embodiments of the invention, the same reference numbers label the same or comparable components. 
         [0031]      FIG. 1  shows a sectional view of the burner in accordance with the invention which has a nozzle  12  which is securely joined to the heat shield  24 . The heat shield  24 , together with a burner pipe  40  which is connected to the heat shield  24 , defines the combustion chamber  22 . The combustion chamber pipe  40  is surrounded by an outer pipe  42  which forms the burner flange. A flame tube  38  is attached to this outer pipe  42 . The connections between the heat shield  24  and the combustion chamber pipe  40  or between the combustion chamber pipe  40 , the outer pipe  42  and the flame tube  38  are generally welded connections. 
         [0032]    On the fuel nozzle  12 , there is the fuel supply  50  which has a metal pipe  52  for supplying of fuel and a fuel needle  14  for injection of fuel into the combustion chamber  22 . Furthermore, in the region of the fuel nozzle  16 , there are channels for supplying of primary combustion air to the fuel nozzle  20 . The combustion air flows past the fuel needle  14  in order to then flow along the radially widening air guide of the fuel nozzle  12  in the direction of the combustion chamber and finally into the combustion chamber  22 . The radial widening of the air guide achieves improved atomization due to the Venturi effect. Within the combustion chamber  22 , there is also a baffle plate  36  which has an advantageous curvature. This curvature in the direction of the burnout zone  32  is advantageous since, in this way, heat-induced spontaneous changes in the shape of the baffle plate  36  are prevented. By curving the baffle plate  36  in the direction of the burnout zone  32 , moreover, sufficient space is available for accommodating the starting chamber  18 . The wall which defines the starting chamber  18  is welded to the baffle plate  36 . 
         [0033]      FIG. 2  shows a perspective of a burner flange with the heat shield inserted into it, and  FIG. 3  shows a perspective of the heat shield. Furthermore, reference is also made below to burner components that are shown in  FIG. 1 . 
         [0034]    The heat shield  24  has a central opening  48  through which the fuel-air mixture which has been delivered from the nozzle  12  enters the combustion chamber. Furthermore, there is a laterally arranged opening  34  through which the ignition element  20  is routed. Furthermore, on the heat shield  24 , there are attachment pins  44 ,  46  to which the nozzle  12  is attached. The heat shield  24  furthermore has a host of openings  26  through which secondary air can enter the combustion chamber  22 . On the side of the heat shield  24  facing the combustion chamber  22 , there are triangular air guide elements  28 ,  30 . They cause division of the secondary air based on the different angles to the radius of the heat shield  24 . A first group of air guide elements with members partially labeled with reference number  28  are aligned at a large angle relative to the radius of the heat shield  24 , i.e., their alignment is essentially or almost tangential. Based on this alignment, the secondary air passing through the corresponding openings  26 , with an exit flow direction indicated by the arrow, will overflow into the burnout zone  32  past the baffle plate  36  with a high angular momentum. This air which is provided with a high angular momentum flows in the radially outlying region of the burnout zone  32  into the posterior region of the combustion chamber  22 , i.e., into the region of the combustion chamber  22  which faces away from the heat shield  24 , and then with high swirling in the central region back in the direction of the baffle plate  36 . Consequently, advantageous mixing of the gaseous components in the burnout zone  32  occurs. 
         [0035]    Another group of air guide elements  30  is aligned with a smaller angle relative to the radius of the heat shield  24 . These air guide elements are partially identified with reference number  30 . Moreover, these air guide elements  30  have a smaller angle relative to the surface of the heat shield  24  than the air guide elements  28 . Consequently, these air guide elements  30  route the secondary air with an exit flow direction, indicated by another arrow, with low angular momentum into the core region of the flame; this especially benefits stable combustion chamber behavior. 
         [0036]    Thus, a novel spray burner is provided which is improved with respect to the possible installation positions, the starting behavior and the behavior in continuous operation. Furthermore, problems with respect to the temperature-induced changes in the shape of the baffle plate are avoided. 
         [0037]    The features of the invention disclosed in the above specification, the drawings and the claims can be important to the implementation of the invention, both individually and also in any combination for implementation of the invention.