WO2006053537A1

WO2006053537A1 - Burner for a heating device comprising an improved heat shield

Info

Publication number: WO2006053537A1
Application number: PCT/DE2005/002053
Authority: WO
Inventors: Michael PÖHNER; Friedrich Widemann; Steffen Weber; Jan Steffens
Original assignee: Webasto Ag
Priority date: 2004-11-17
Filing date: 2005-11-16
Publication date: 2006-05-26
Also published as: CA2595016A1; CN101103227A; JP2008520947A; RU2359171C2; EP1812749A1; KR20070086041A; US20090220903A1; DE112005003408A5; RU2007122478A

Abstract

The invention relates to a burner (10), for a heating device, in particular, for application in motor vehicles, comprising a burner nozzle (12), for the introduction of fuel and primary air, a combustion chamber (22) and a heat shield (24), between the burner nozzle and the combustion chamber, whereby the heat shield comprise openings (26), for the introduction of secondary air into the combustion chamber. According to the invention, the openings are provided with air guide elements (28, 30).

Description

Burner for a heater with improved heat shield

The invention relates to a burner for a heater, in particular for use in motor vehicles, having 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 into it having the combustion chamber.

Such burners, which are also referred to as atomizing burners or as spray burners, are used in particular in auxiliary heaters and auxiliary heaters for motor vehicles. There are numerous requirements for such burners, in particular with regard to a safe and largely emission-free starting behavior and a stable combustion operation. Furthermore, efforts are being made to design heaters that can be used in different mounting positions.

With regard to the starting behavior, different operating parameters must be coordinated with each other. On the one hand, it is necessary to provide a relatively rich fuel-air mixture during burner start-up in the starting zone, but on the other hand provision of a sufficient amount of primary combustion air is required to transport the fuel from the fuel needle to ensure the starting zone.

The requirement to allow different installation positions of the heating appliance is connected with the problems with regard to the starting behavior. In fact, in order to be able to transport fuel into the starting zone with little primary air supply, it has hitherto been accepted to orient the fuel needle with the outlet opening facing downwards; This had the consequence that the entire burner had to be mounted in a vertical installation position.

In order to ensure a stable combustion operation of the burner, contradictory requirements are sometimes also to be met. On the one hand, a good mixing of fuel and air is always required, on the other hand, it is in the core area of the flame and there especially during _ 2 -

the start-up phase undesirable to cause high levels of air and excessive turbulence.

The object of the invention is to at least partially overcome the described problems of the prior art and, in particular, to enable a reliable and low-emissivity or low-smoke starting behavior with different installation positions.

This object is achieved by the features of the independent claim.

Advantageous embodiments of the invention are indicated in the dependent claims.

The invention builds on the generic burner in that the openings are equipped with air guide elements. A heat shield is generally useful for shielding the nozzle and fuel supply from the heat energy present in the combustion chamber. Secondary air continues to be fed into the combustion chamber via the heat shield. By the openings for secondary air supply are equipped with air guide elements, the supply of this secondary air can be targeted, so that the burning operation, both in terms of the start-up operation as well as during continuous operation can be selectively influenced.

Usefully, it is provided that the air guiding elements are formed by tabs formed in the direction of the combustion chamber and integrally formed with the heat shield. Such a heat shield can be manufactured in a simple manner, for example by using a V-shaped punching tool. can be formed, which are bent out of the plane of the heat shield after or with the punching operation.

The invention is also advantageously further developed in that the tabs are formed at different angles to the surface of the heat shield and / or to the radius of the heat shield. If the tabs extend almost perpendicular to the radius of the heat shield, a strong twist is introduced by the latter, while a lesser twist is introduced by tabs with a smaller angle to the radius. Tabs, which occupy a small angle to the surface of the heat shield, produce Luftströ¬ rules, which have a large radial component and a small axial component, while in tabs with large angles to the surface of the heat shield, the axial Kompo¬ nents dominated. In this way it is possible to direct secondary air with little swirl into the core region of the flame formation. As a result, on the one hand, the air required for combustion is supplied; however, there is no excessive swirl which would adversely affect the stabilization of the flame. In particular, a division of the secondary air can take place as a function of the orientation of the individual air guiding elements.

According to a further embodiment, it is provided that the tabs are formed in groups at substantially identical angles to the surface of the heat shield and / or to the radius of the heat shield. The collective alignment of the straps results in defined flow states in the combustion chamber. The invention is further useful in that the burner has a burnout zone and that the secondary air supplied to the burnout zone has a higher swirl than the secondary air supplied to the start zone. In the Ausbrandzone a high twist is desired. In particular, a radially inwardly swirled backflow region improves the burnout and ensures that the combustion chamber volume is well utilized.

It is further provided that the heat shield has an opening for the passage of an ignition element.

According to a particularly preferred embodiment of the invention it is provided that the burner nozzle has a fuel needle for supplying fuel into the burner and a primary air supply for supplying combustion air into the burner and that the outlet speed is selected by the choice of the inner diameter of the fuel needle of the fuel is predetermined so that during a starting phase of the burner fuel in a substantially undusted form reaches a starting zone. By reducing the inner diameter of the fuel needle in comparison to fuel needles in heating devices of the prior art, the exit speed of the fuel is increased for the same fuel delivery volume. This makes it possible in any installation position that a fuel jet from the outlet opening of the fuel needle in the start zone ge reached. In particular, with a small amount of primary air, wherein the primary air supplied should also still have only a slight twist, so a substantially non-atomized fuel jet can reach the starting zone. Consequently starts the burner safely, and the smoke formation during takeoff is significantly reduced.

It is preferable that the inner diameter of the fuel needle is between 0.5 and 0.7 mm. In comparison to exit speeds in fuel needles of the prior art, in which the inner diameter is in the range of 0.8 mm, the exit velocity at inner diameters between 0.5 and 0.7 mm can be almost doubled or even more than doubled ,

It is particularly preferred that the inner diameter of the fuel needle is about 0.6 mm. With such an inner diameter, exit speeds of more than 0.6 m / s are possible in full-load operation, ie at a fuel mass flow of 0.5 kg / h, while at an inner diameter of 0.8 mm, the exit velocity is in the range of 0.35 m / s. Correspondingly, the exit speed increases during part-load operation, that is to say at a fuel mass flow of 0.2 kg / h from approximately 0.14 m / s to approximately 0.25 m / s. With a corresponding selection of structural properties or operating parameters, the goal of a substantially non-atomized jet, which reaches the starting zone when starting the heater, can also be achieved with a conventional fuel needle with an inner diameter of approximately 0.8 mm.

Usefully, it is provided that the starting zone is designed as a starting chamber into which an ignition element protrudes. The wall of the combustion chamber can surround the ignition element in this way. During the starting operation, the "ballistic" fuel jet then the ignition element and wet the combustion chamber wall with fuel, so that the combustion chamber wall and adjacent components serve as wall evaporator after their heating.

In a particularly preferred embodiment of the vorlie¬ ing invention is further provided that the Brenn¬ chamber is substantially axially symmetrical, that in the combustion chamber, a baffle plate is arranged and that the baffle plate has a predetermined curvature in the axial direction. Due to the curvature of the baffle plate, there is a temperature-independent defined shaping of the baffle plate. In the case of newly formed baffle plates of the prior art, this is sometimes not the case since, depending on the temperature, spontaneous changes in shape can occur, which can adversely affect the combustion behavior of the burner.

It is preferred that the curvature is provided in the direction of the burnout zone. As a result, a sufficient space is provided in the region of the starting chamber. Furthermore, it has been found that the curvature in the direction of the burn-out zone does not adversely affect the flow behavior in this zone. In particular, the turbulent pronounced return flow region remains in the radially inner region of the burn-out zone.

According to a preferred embodiment of the invention, it is provided that the outer circumference 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 furthest bulging point of the baffle plate lies with respect to the radial coordinate, preferably substantially in the center of the arrangement. From the plane defined by the outer circumference of the baffle plate, this point has an axial distance defined by the specified ratio to the diameter.

In this connection, it is particularly preferred that 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. For example, the round diameter of the baffle plate is about 40 mm, while the bulge has a value of about 5.7 mm.

The invention is based on the finding that the operating behavior of a burner can be markedly improved by the novel heat shield with air guide elements, in particular in combination with the novel fuel feed and the novel baffle plate. This applies in particular to the starting behavior, the stability of the burner operation and the possibilities with regard to the installation position of the burner in the motor vehicle.

The invention will now be explained by way of example with reference to the accompanying drawings with reference to preferred embodiments.

Showing:

FIG. 1 is a sectional view of a burner according to the invention; FIG. 2 is a perspective view of a burner flange with a heat shield inserted therein; and

Figure 3 is a perspective view of a heat shield.

In the following description of the preferred embodiments of the invention, the same reference numerals designate the same or comparable components.

FIG. 1 shows a sectional view of a burner according to the invention. The burner 10 according to the invention has a nozzle 12 which is fixedly connected to a heat shield 24. The heat shield 24, together with a burner tube 40 connected to the heat shield 24, defines a combustion chamber 22. The combustion chamber tube 40 is surrounded by an outer tube 42, which forms the burner flange. At this outer tube 42, a flame tube 38 is attached. The connections between the heat shield 24 and the combustion chamber tube 40 or between the combustion chamber tube 40, the outer tube 42 and the flame tube 38 are generally welded joints. At the fuel nozzle 12, a fuel feed 50 is arranged, which has a metal tube 52 for supplying fuel and a fuel needle 14 for injecting fuel into the combustion chamber 22. Furthermore, in the area of the fuel nozzle 16, there are provided channels for supplying primary combustion air into the fuel nozzle 20, which flows past the fuel needle 14 and then along the radially expanding air guide of the fuel nozzle 12 in the direction of the combustion chamber and finally into the fuel nozzle Burner chamber 22 to flow. Due to the radial expansion of the air duct ei¬ ne improved atomization due to the Venturi effect achieved. Within the combustion chamber 22, a baffle plate 36 is further arranged, which has an advantageous curvature. This curvature in the direction of the burn-out zone 32 is advantageous because it prevents heat-induced spontaneous changes in shape of the baffle plate 36. Due to the curvature of the baffle plate 36 in the direction of the Ausbrandzone 32 is also a sufficient space for the accommodation of the start chamber 18 is available. The wall defining the start chamber 18 is welded to the baffle plate 36.

FIG. 2 shows a perspective view of a burner flange with a heat shield inserted therein, and FIG. 3 shows a perspective view of a heat shield. It will also be pointed to components of the burner according to Figure 1 below. The heat shield 24 has a central opening 48, through which the fuel-air mixture discharged from the nozzle 12 enters the combustion chamber. Furthermore, a laterally arranged opening 34 for the passage of the ignition element 20 is provided. On the heat shield 24 fastening pins 44, 46 are further provided, on which the nozzle 12 is attached. The heat shield 24 also has a plurality of openings 26 through which secondary air can enter the combustion chamber 22. On the combustion chamber 22 facing side of the Hit¬ zeschildes 24 triangular air guide elements 28, 30 are provided. These cause due to the different angles to the radius of the heat shield 24, a division of the secondary air. A first group of air guiding elements whose members are designated by the reference numeral 28 are aligned at a large angle to the radius of the heat shield 24, that is, their orientation is in the Essentially or almost tangentially. On account of this orientation, the secondary air which passes through the corresponding openings 26 and whose outlet flow direction is indicated by an arrow, passes with high swirl past the impact disk 36 into the burn-out zone 32. This air, which is provided with a high swirl, flows radially outer region of the Ausbrandzone 32 in the rear region of the combustion chamber 22, that is in the heat shield 24 facing away from the combustion chamber 22, and then with great turbulence in the central region back towards the baffle plate 36. Consequently, it comes to a vor¬ geous Mixing of the gaseous components in the burn-out zone 32. Another group of air-guiding elements 30 has a smaller angle to the radius of the heat shield 24 in their orientation. These air guide elements are partially identified by the reference numeral 30. In addition, these air guide elements 30 have a smaller angle to the surface of the heat shield 24 than the air guide elements 28. Consequently secondary air, the outlet flow direction of which is indicated by a further arrow, is conducted into the core region of the flame by means of these air guide elements 30 , which in particular favors a sta¬ biles burning behavior.

Thus, a novel spray burner is provided which is improved with regard to the possible installation positions, the starting behavior and the behavior in continuous operation. Furthermore, problems with regard to temperature-induced changes in shape of the baffle plate are avoided. The features of the invention disclosed in the foregoing description, in the drawings and in the claims may be essential to the realization of the invention both individually and in any combination.

LIST OF REFERENCE NUMBERS

10 burners

12 burner nozzle

14 fuel needle

16 combustion air supply

18 start zone

20 ignition element

22 combustion chamber

24 heat shield

26 opening

28 air guide

30 air guide

32 burn-out zone

34 opening

36 baffle plate

38 flame tube

40 burner tube

42 outer tube

44 fixing pin

46 fixing pin

48 opening

50 fuel feed

52 metal pipe

Claims

EXPECTATIONS

1. Burner for a heater, especially for use in motor vehicles

a burner nozzle (12) for supplying 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 into the combustion chamber,

characterized in that the openings are equipped with air guiding elements (28, 30).

2. Burner according to claim 1, characterized in that the air guide elements (28, 30) are formed by tabs (28, 30) which project in the direction of the combustion chamber (22) and are formed in one piece with the heat shield.

3. Burner according to claim 1 or 2, characterized in that that the tabs (28, 30) are formed at different angles to the surface of the heat shield (24) and/or to the radius of the heat shield.

4. Burner according to one of the preceding claims, characterized in that the tabs are formed in groups at essentially identical angles to the surface of the heat shield and / or to the radius of the heat shield.

5. Burner (10) according to one of the preceding claims, characterized in that the burner has a start zone (18) and a burnout zone (32) and

that the secondary air supplied to the burnout zone (32) has a lower swirl than the secondary air supplied to the starting zone (18).

6. Burner according to one of the preceding claims, characterized in that the heat shield has an opening (34) for the passage of an ignition element (20).

1. Burner according to one of the preceding claims, characterized in that

that the burner nozzle (12) has a fuel needle (14) for supplying fuel into the burner (10) and a primary air supply for supplying combustion air into the burner and that by selecting the inner diameter of the fuel needle (14), the exit speed of the fuel is predetermined so that during a starting phase of the burner (10), fuel in essentially unatomized form reaches a starting zone (18).

8. Burner according to claim 7, characterized _in that the inner diameter of the fuel needle (14) is between 0.5 and 0.7 mm.

9. Burner according to claim 7 or 8, characterized in that the inner diameter of the fuel needle is approximately 0.6 mm.

10. Burner according to claims 5 to 9, characterized in that the starting zone (18) is designed as a starting chamber into which an ignition element projects.

11. Burner according to one of the preceding claims, characterized in that

that the combustion chamber is essentially axially symmetrical,

that a baffle plate is arranged in the combustion chamber (22) and

that the baffle plate (36) has a predetermined curvature in the axial direction.

12. Burner according to claim 11, characterized in that the curvature is provided in the direction of the burnout zone (32).

13. Burner according to claim 11 or 12, characterized in that

that the outer circumference 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.

14. Burner according to claim 13, characterized in that the ratio between the maximum axial distance of the baffle disk (36) from the plane and the diameter of the baffle disk (36) is approximately 0.14.