BURNER FOR A HEATER WITH IMPROVED HEAT SHIELD

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

1. Field of Invention

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.

2. Description of Related Art

These burners which are also called atomization burners or spray burners are used especially in auxiliary heaters and independent heaters for motor vehicles.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

It is also provided that the heat shield has an opening for routing an ignition element through.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The invention is explained by way of example using preferred embodiments and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the burner in accordance with the invention;

FIG. 2 is a perspective view of a burner flange with the heat shield inserted into it; and

FIG. 3 is a perspective of the heat shield.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of preferred embodiments of the invention, the same reference numbers label the same or comparable components.

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.

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.

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.

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.

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.

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.

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.

Claims

1-14. (canceled)

15. Burner for a heater for use in motor vehicles, comprising:

a burner nozzle for supplying of 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,

wherein the openings are equipped with air guide elements.

16. Burner as claimed in claim 15, wherein the air guide elements are formed by tabs which are made integrally with the heat shield and which project in a direction toward the combustion chamber.

17. Burner as claimed in claim 16, wherein at least some of the tabs are arranged at a different angle than other of the tabs with respect to at least one of the surface of the heat shield and the radius of the heat shield.

18. Burner as claimed in claim 16, wherein the tabs are arranged in groups, the tabs of each group being arranged at an essentially identical angle relative to at least one of the surface of the heat shield and the radius of the heat shield, the angle at which the tabs of one of the groups is arranged being different from that at which the tabs of another of the groups is arranged.

19. Burner as claimed in claim 15, wherein

the burner has a starting zone and burnout zone and

wherein the secondary air is supplied to the burnout zone with a lower angular momentum than secondary air which is supplied to the starting zone.

20. Burner as claimed in claim 15, wherein the heat shield has an opening through which an ignition element is routed.

21. Burner as claimed in claim 15, wherein

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

wherein the inside diameter of the fuel needle is set to produce a predetermined exit speed of the fuel such that fuel in essentially unatomized form reaches the starting zone during a starting phase of the burner.

22. Burner as claimed in claim 21, wherein the inside diameter of the fuel needle is between 0.5 mm and 0.7 mm.

23. Burner as claimed in claim 21, wherein the inside diameter of the fuel needle is about 0.6 mm.

24. Burner as claimed in claim 19, wherein the starting zone is a starting chamber into which an ignition element projects.

25. Burner as claimed in claim 15, wherein

the combustion chamber is essentially axially symmetrical,

wherein a baffle plate is located in the combustion chamber, and

wherein the baffle plate has a curvature in an axial direction.

26. Burner as claimed in claim 25, wherein the curvature is in a direction toward a burnout zone.

27. Burner as claimed in claim 26, wherein

an outer periphery of the baffle plate defines a plane and

a ratio between a maximum axial distance of the baffle plate from said plane and the diameter of the baffle plate is between 0.07 and 0.21.

28. Burner as claimed in claim 27, wherein the ratio between the maximum axial distance of the baffle plate from the plane and the diameter of the baffle plate is about 0.14.