Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BURNER FOR A HEATING DEVICE COMPRISING AN IMPROVED HEAT SHIELD
The invention relates to a burner for a heater, especially for use in motor
vehicles, with
an essentially axially symmetrical combustion chamber, and a baffle plate
which is located in
the combustion chamber.
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 start to make
available a relatively rich
fuel-air mixture in the starting zone, on the other hand however making
available a sufficient
amount of primary combustion air is necessary to ensure transport of 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 be specifically 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 down 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.
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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 features of the independent claim.
Advantageous developments of the invention are given in the dependent claims.
The invention is based on a generic burner in that the baffle plate has a
defined curvature
into the axial direction and that there is a curvature in the direction of the
burnout zone. Based
on the curvature of the baffle plate there is defmed 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 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. By
arching in the
direction of the burnout zone 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.
According to one especially preferred embodiment of the invention, it is
provided that
there is a burner nozzle for supplying fuel and primary air, that there is 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 that the openings are provided
with air guide
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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 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. In this way on
the one hand 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.
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. Defmed
flow states in the combustion chamber are formed by the collective alignment
of the clips.
The invention is furthermore 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.
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It is furthermore provided that the heat shield has an opening for routing an
ignition
element through.
According to an 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 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
moreover 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 is between 0.5 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 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.
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
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combustion chamber wall with fuel so that the combustion chamber wall and
adjacent
components after their heating are used as wall vaporizers.
The invention is based on the fmding that the novel curved baffle plate,
especially in
combination with the novel fuel supply and the novel heat shield, 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.
The invention is explained by way of example with reference to the
accompanying
drawings using preferred embodiments.
Figure 1 shows a sectional view of the burner as claimed in the invention;
Figure 2 shows a perspective of a burner flange with the heat shield inserted
into it; and
Figure 3 shows a perspective of the heat shield.
In the following description of preferred embodiments of the invention the
same
reference numbers label the same or comparable components.
Figure 1 shows a sectional view of the burner as claimed in the invention. The
burner 10
as claimed in the invention 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
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 supply
of primary
combustion air into the fuel nozzle 20 which 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 fmally into the combustion chamber 22. The radial widening of the
air guide
achieves improves atomization due to the Venturi effect. Within the combustion
chamber 22
there is furthermore 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
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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 a 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.
Figure 2 shows a perspective of a burner flange with the heat shield inserted
into it, and
Figure 3 shows a perspective of the heat shield. Furthermore reference is
likewise made below
to burner components as shown in Figure 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 for routing the
ignition element
20 through. On the heat shield 24 there are furthermore 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 labelled with reference number 28
are aligned at a
large angle to the radius of the heat shield 24, i.e. their alignment is
essentially or ahnost
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 in their
alignment has a smaller angle 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 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.
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Thus a novel spray burner is made available which is improved with respect to
the
possible installation positions, the starting behavior and behavior in
continuous operation.
Furthermore problems with respect to the temperature-induced changes of 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.
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Reference number list
burner
12 burner nozzle
14 fuel needle
16 combustion air supply
18 starting zone
ignition element
22 combustion chamber
24 heat shield
26 opening
28 air guide element
air guide element
32 burnoutzone
34 opening
36 baffle plate
38 flame tube
burner pipe
42 outer pipe
44 attachment pin
46 attachment pin
48 opening
fuel supply
52 metal pipe
