U.S. patent application number 11/719572 was filed with the patent office on 2009-09-03 for burner for a heater with improved fuel supply, improved heat shield and improved baffle plate.
This patent application is currently assigned to Webasto AG. Invention is credited to Michael Poehner, Jan Steffens, Steffen Weber, Friedrich Widemann.
Application Number | 20090220901 11/719572 |
Document ID | / |
Family ID | 35994656 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090220901 |
Kind Code |
A1 |
Poehner; Michael ; et
al. |
September 3, 2009 |
BURNER FOR A HEATER WITH IMPROVED FUEL SUPPLY, IMPROVED HEAT SHIELD
AND IMPROVED BAFFLE PLATE
Abstract
A burner for a heater, especially for motor vehicles, has an
essentially axially symmetrical combustion chamber, a burner nozzle
for supply and atomization of fuel, a fuel needle for supplying
fuel to the combustion chamber, a combustion air supply for
supplying combustion air to the combustion chamber, a starting zone
in which ignition of the fuel to start the burner takes place, a
heat shield between the burner nozzle and the combustion chamber,
the heat shield having openings for supplying secondary air to the
combustion chamber, and a baffle plate located in the combustion
chamber. 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. The openings have air guide elements,
and the baffle plate has a defined curvature in the axial
direction.
Inventors: |
Poehner; Michael; (Muenchen,
DE) ; Widemann; Friedrich; (Muenchen, DE) ;
Weber; Steffen; (Anklam, DE) ; Steffens; Jan;
(Isenwang, DE) |
Correspondence
Address: |
ROBERTS MLOTKOWSKI SAFRAN & COLE, P.C.;Intellectual Property Department
P.O. Box 10064
MCLEAN
VA
22102-8064
US
|
Assignee: |
Webasto AG
Stockdorf
DE
|
Family ID: |
35994656 |
Appl. No.: |
11/719572 |
Filed: |
November 16, 2005 |
PCT Filed: |
November 16, 2005 |
PCT NO: |
PCT/DE2005/002061 |
371 Date: |
May 6, 2009 |
Current U.S.
Class: |
431/171 ;
431/258 |
Current CPC
Class: |
F23D 11/24 20130101;
F23D 11/406 20130101; F23D 9/00 20130101; F23D 2900/11401 20130101;
F23D 11/408 20130101 |
Class at
Publication: |
431/171 ;
431/258 |
International
Class: |
F23M 9/06 20060101
F23M009/06; F23Q 7/06 20060101 F23Q007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2004 |
DE |
10 2004 055 438.2 |
Claims
1. Burner for a heater, especially for use in motor vehicles, with
an essentially axially symmetrical combustion chamber (22), a
burner nozzle (12) for supply and atomization of fuel, which has a
fuel needle (14) for supplying fuel to the combustion chamber (22)
and a combustion air supply (16) for supplying combustion air to
the combustion chamber, a starting zone (18) in which ignition of
the fuel to start the burner takes place, a heat shield between the
burner nozzle and the combustion chamber, the heat shield having
openings for supplying secondary air to the combustion chamber, and
a baffle plate which is located in the combustion chamber, wherein
the inside diameter of the fuel needle (14) is sized to produce a
predetermined exit speed of the fuel such that, during the starting
phase of the burner (10), fuel in essentially unatomized form
reaches the starting zone (18), the openings are equipped with air
guide elements, and the baffle plate has a defined curvature in an
axial direction.
2. Burner as claimed in claim 1, wherein the inside diameter of the
fuel needle (14) is between 0.5 and 0.7 mm.
3. Burner as claimed in claim 1, wherein the inside diameter of the
fuel needle (12) is roughly 0.6 mm.
4. Burner as claimed in claim 1, wherein the starting zone is made
as a starting chamber (18) into which an ignition element (20)
projects.
5. Burner as claimed in claim 1, wherein the air guide elements are
formed by tabs (28, 30) which are made integrally with the heat
shield and which project toward the combustion chamber.
6. Burner as claimed in claim 5, wherein the tabs (28, 30) are made
at different angles relative to at least one of the surface of the
heat shield and the radius of the heat shield (24).
7. Burner as claimed in claim 5, wherein the tabs (28, 30) are
grouped at essentially identical angles relative to at least one of
the surface of the heat shield and the radius of the heat
shield.
8. Burner as claimed in claim 1, wherein the combustion chamber of
the burner (10) has a burnout zone (32) and wherein the secondary
air is supplied to the burnout zone with a higher angular momentum
than secondary air is supplied to the starting zone.
9. Burner as claimed in claim 1, wherein the heat shield (24) has
an opening (34) for routing the ignition element through.
10. Burner as claimed in claim 1, wherein the curvature of the
baffle plate (36) extends toward the burnout zone (30).
11. Burner as claimed in claim 1, wherein an outer periphery of the
baffle plate defines a plane and wherein 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.
12. Burner as claimed in claim 11, wherein the ratio between the
maximum axial distance of the baffle plate (36) from the plane and
the diameter of the baffle plate (36) is roughly 0.14.
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 an essentially axially symmetrical
combustion chamber, a burner nozzle for supply and atomization of
fuel, which has a fuel needle for supplying fuel to the combustion
chamber and a combustion air supply for supplying combustion air to
the combustion chamber, a starting zone in which ignition of the
fuel to start the burner takes place, a heat shield between the
burner nozzle and the combustion chamber, the heat shield having
openings for supplying secondary air to the combustion chamber, and
a baffle plate which is located in the combustion chamber.
[0003] 2. Description of Related Art
[0004] Burners of the initially described type, 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 start to make available a relatively rich
fuel-air mixture in the starting zone, and on the other hand,
providing a sufficient amount of primary combustion air is
necessary to ensure transport of 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. Specifically, to be able to transport fuel into the
starting zone with low primary air supply, in the past, orienting
the fuel needle with the outlet opening pointed down had to be
tolerated; this resulted in the entire burner having to be mounted
in a 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, and on the other hand, especially during the starting
phase, it is undesirable to cause overly high air proportions and
overly high swirling in the core region of the flame.
[0009] Commonly-owned, U.S. patent application Ser. No. 10/466,683
discloses a reformer with a reaction space in which a breaker body
is located that can be made conical and/or convex and/or concave at
least in sections. The breaker body comprises a baffle plate in
which openings can be made in the form of defined perforations. The
baffle plate can have a chamber into which at least one heating
element extends and can be used as a starting chamber, in which
case the heating element is formed by a glow pin and/or a glow plug
that can be activated to initiate burner operation of the reformer
system. Additionally, an air guidance means can be provided in the
air inlet area to impart a swirl to the in-flowing air. The air
guidance means can comprise an air-guiding device with swirl blades
that are located on a carrier mounted on a Venturi nozzle assembly,
and the blades can have triangular base surfaces with rounded
corners.
SUMMARY OF THE INVENTION
[0010] 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.
[0011] This object is achieved by choosing the inside diameter of
the fuel so that 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 the heat shield
having openings that are equipped with air guide elements, and by
the baffle plate having a defined curvature in the axial
direction.
[0012] The invention is based on a generic burner in 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 reaches the starting zone in essentially unatomized
form, that the openings in the heat shield are equipped with air
guide elements, and that the baffle plate has a defined curvature
in the axial direction. 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. 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. For the baffle
plates of the prior art which are made flat, this is among others
not the case since depending on the temperature spontaneous changes
of shape can occur which can adversely affect the combustion
behavior of the burner.
[0013] It is preferred that the inside diameter of the fuel needle
be between 0.5 mm and 0.7 mm. As 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
mm and 0.7 mm can be almost doubled or even more than doubled.
[0014] It is especially preferred that the inside diameter of the
fuel needle is roughly 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 be achieved
even with a conventional fuel needle with an inside diameter of
roughly 0.8 mm.
[0015] 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.
[0016] 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.
[0017] The invention is also usefully developed in that the tabs
are made at different angles relative 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 smaller 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. Thus, the air 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.
[0018] 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.
[0019] The invention is also 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.
[0020] 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.
[0021] 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.
[0022] In this connection, it is especially preferred that a ratio
of about 0.14 is produced between the maximum axial distance of the
baffle plate from the plane and the diameter of the baffle plate.
For example, the round diameter of baffle plate is roughly 40 mm,
while the curvature has a value of roughly 5.7 mm.
[0023] The invention is based on the finding that the novel fuel
supply with a fuel needle with a reduced exit cross section, the
novel heat shield with air guide elements and the novel, curved
baffle plate can greatly improve the operating behavior of a
burner. This relates especially to the starting behavior, the
stability of burner operation and possibilities with respect to the
installation position of the burner in the motor vehicle.
[0024] The invention is explained by way of example with reference
to the accompanying drawings using preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a sectional view of the burner in accordance with
the invention;
[0026] FIG. 2 is a perspective of a burner flange with the heat
shield inserted therein; and
[0027] FIG. 3 shows a perspective of the heat shield.
DETAILED DESCRIPTION OF THE INVENTION
[0028] In the following description of preferred embodiments of the
invention, the same reference numbers label the same or comparable
components.
[0029] FIG. 1 shows a sectional view of a burner 10 of the
invention. The burner 10 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 a
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 a
fuel supply 50 which has a metal pipe 52 for supply 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 primary combustion air into the fuel nozzle
20. The primary 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. Moreover, by curving the baffle plate 36 in
the direction of the burnout zone 32, 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.
[0030] FIG. 2 is a perspective view of the burner flange with the
heat shield 24 inserted into it, and FIG. 3 shows a perspective
view of heat shield 24. Furthermore, reference is likewise made
below to burner components as 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. Also, there is a laterally arranged opening 34 through
which the ignition element 20 is routed. On the heat shield 24,
there are attachment pins 44, 46 to which the nozzle 12 is
attached. Additionally, the heat shield 24 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 their different angles relative 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 high angular momentum.
[0031] 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 32, 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 arranged at a smaller
angle relative to the radius of the heat shield 24. These air guide
elements are partially identified with the 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.
[0032] Thus, a novel spray burner is made available which is
improved with respect to the possible installation positions, the
starting behavior and the behavior in continuous operation.
Furthermore, problems with respect to temperature-induced changes
of the shape of the baffle plate are avoided.
[0033] 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.
* * * * *