U.S. patent application number 10/954482 was filed with the patent office on 2005-05-12 for burner.
Invention is credited to Gutmark, Ephraim, Paschereit, Christian Oliver.
Application Number | 20050100846 10/954482 |
Document ID | / |
Family ID | 9949080 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050100846 |
Kind Code |
A1 |
Gutmark, Ephraim ; et
al. |
May 12, 2005 |
Burner
Abstract
A burner 1 for a heat generator comprises an outlet 10
connectable to a combustion chamber 9, wherein at least part of an
inner surface of the outlet 10 is provided with corrugations 11
which are adapted to facilitate the production of axial vorticity
in the region of the outlet 10.
Inventors: |
Gutmark, Ephraim;
(Cincinnati, OH) ; Paschereit, Christian Oliver;
(Berlin, DE) |
Correspondence
Address: |
CERMAK & KENEALY LLP
P.O. BOX 7518
ALEXANDRIA
VA
22307
US
|
Family ID: |
9949080 |
Appl. No.: |
10/954482 |
Filed: |
October 1, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10954482 |
Oct 1, 2004 |
|
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10725614 |
Dec 3, 2003 |
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Current U.S.
Class: |
431/159 ;
431/350 |
Current CPC
Class: |
F23D 2210/00 20130101;
F23R 3/286 20130101; F23R 3/16 20130101; F23R 2900/00014 20130101;
F23C 2900/07002 20130101 |
Class at
Publication: |
431/159 ;
431/350 |
International
Class: |
F23D 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2002 |
GB |
0228320.8 |
Claims
What is claimed is:
1. A burner for a heat generator comprising: an outlet having an
inner surface, the outlet connectable to a combustion chamber;
wherein at least part of the inner surface of the outlet comprises
corrugations adapted to facilitate the production of axial
vorticity in the region of the outlet.
2. A burner as claimed in claim 1, wherein the corrugations are
provided over substantially all of the inner surface of the
outlet.
3. A burner as claimed in claim 2, wherein the outlet comprises a
nozzle.
4. A burner as claimed in claim 1, wherein the corrugations
comprise lobes.
5. A burner as claimed in claim 1, wherein the corrugations are
rectangular in cross-section.
6. A burner as claimed in claim 1, wherein the ratio of the length
to the depth of the corrugations is from 1:1 to 10:1.
7. A burner as claimed in claim 6, wherein the ratio of the length
to the depth of the corrugations is from 1:1 to 3:1.
8. A burner as claimed in claim 1, further comprising: a mixing
section; and wherein the corrugations extend over at least 20% of
the mixing section of the burner.
9. A burner as claimed in claim 1, wherein the corrugations are
triangular in cross-section.
Description
[0001] This application is a Continuation of, and claims priority
under 35 U.S.C. .sctn. 120 to, U.S. application Ser. No.
10/725,614, filed 3 Dec. 2003, and claims priority under 35 U.S.C.
.sctn. 119 to GB application no. 0228320.8, filed 4 Dec. 2002, the
entireties of both of which are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a burner for generating a
hot gas, and in particular to a pre-mix burner connectable to a
combustion chamber.
[0004] 2. Brief Description of the Related Art
[0005] Many gas burners rely on swirling to produce efficient
mixing of reactants. However, interaction between the complex flow
patterns within the swirling fluid and acoustic resonant modes in
the combustion chamber can lead to undesired thermoacoustic
pulsations or vibrations. These pulsations are associated with
coherent vortical flows in the combustion chamber. The vortical
flows introduce periodicity into the mixing process, which may lead
to periodic heat release and resonant coupling with the combustor
acoustic resonant modes. Vortical mixing of the reactants also
tends to be limited to large scale mixing with the result that
mixing in regions between vortices in the vortical flow tends to be
poor.
[0006] Thermoacoustic vibrations are problematic in combustion
processes, since they can lead to high-amplitude pressure
fluctuations, as well as to a limitation in the operating range of
the burner in question and to increased emissions from the burner.
Many combustion chambers do not possess adequate acoustic damping
to account for such thermoacoustic vibrations.
[0007] In conventional combustion chambers, the cooling air flowing
into the combustion chamber acts to dampen noise and therefore
contributes to the damping of thermoacoustic vibrations. However,
in modern gas turbines, an increasing proportion of the cooling air
is passed through the burner itself in order to achieve low
emissions. The cooling air flow within the combustion chamber is
thus reduced, resulting in reduced damping of the thermoacoustic
vibrations in the chamber.
[0008] Another method of damping is the coupling of Helmholtz
dampers in the combustion chamber, preferably in the region of the
combustion chamber dome or in the region of the cold air supply.
However, such dampers require a considerable amount of space in
order to allow them to be accommodated in the combustion chamber.
Since modern combustion chambers tend to be relatively compact, it
is usually impossible to incorporate Helmholtz dampers in the
combustion chamber without substantial re-design of the
chamber.
[0009] A further method of controlling thermoacoustic vibrations
involves active acoustic excitation. In this process, a shear layer
which forms in the outlet region of the burner is acoustically
excited. A suitable phase lag between the thermoacoustic vibrations
and the excitation vibrations makes it possible to achieve damping
of the combustion chamber due to the superimposition of the
vibrations and the excitation. However, a considerable amount of
energy is expended in generating such acoustic excitation.
[0010] A further means of providing damping in the combustion
chamber is to modulate the fuel mass flow in the burner. Fuel is
injected into the burner with a phase shift relative to measured
signals in the combustion chamber so that additional heat is
released at a minimum pressure. This reduces the amplitude of the
thermoacoustic vibrations. However, this technique also leads to
high emissions due to the increased fuel.
[0011] A further alternative is to inject air into the burner via
nozzles to disturb and break up the vortical flow. However, the
required additional pipes and plumbing complicates the design of
the combustor. Furthermore, the required additional air flow
reduces the overall efficiency.
[0012] In a similar technique, the vortical flow is broken up by
baffles which are located inside the burner in order to disturb the
vortical flow. However, the inclusion of such baffles increases the
constructional outlay of the burner, which is disadvantageous.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a burner in
which the above disadvantages are overcome.
[0014] The invention provides a burner for a heat generator
comprising an outlet connectable to a combustion chamber, wherein
at least part of the inner surface of the outlet is provided with
corrugations which are adapted to facilitate the production of
axial vorticity in the region of the outlet.
[0015] In an exemplary embodiment of the invention, the
corrugations are provided over substantially all of the inner
surface of the outlet. The corrugations are preferably in the form
of lobes. Alternatively, the corrugations are rectangular or
triangular in cross-section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention will now be described in detail with reference
to the accompanying drawings, in which:
[0017] FIG. 1 is a perspective view of an outlet of a burner
according to the invention;
[0018] FIG. 2 is a cross-sectional view of the burner of FIG. 1
along the line A-A;
[0019] FIG. 3 is a diagram of the flow in the region of an outlet
of the burner of FIGS. 1 and 2;
[0020] FIG. 4 is a graph showing the effect of the invention on
pressure fluctuations, and
[0021] FIG. 5 is a graph showing the effect of the invention on
emissions.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0022] In FIG. 1, a heat generator has a burner 1 with a swirl
generator 2. The swirl generator 2 generates a swirl 3 with an
axial flow component facing toward a downstream burner outlet 4.
Mixing takes place in an area 5 of the generator 2, so as to ensure
adequate mixing of fuel and combustion air. The axial flow
cross-section of the area 5 widens in the direction of the outlet
4; this configuration facilitates attainment of a constant swirl 3
in the area 5 with an increasing combustion air mass flow in the
direction of the longitudinal axis B of the burner 1. The generator
2 comprises two hollow partial cones (not shown) arranged offset to
one another. The offset of the respective centre axes of the
partial conical bodies creates two tangential air channels 6. A
combustion air flow 7 flows, with a relatively high tangential
velocity component, through the two tangential channels 6 into the
area 5, thus generating the swirl 3. Fuel is introduced into the
burner 1 via a fuel inlet 8 in the form of a nozzle.
[0023] The burner 1 is attached to a combustion chamber 9 via an
outlet 10 through which the swirl 3 passes. The swirl 3 contains
vortical flow, which causes flow instabilities including
thermoacoustic vibrations which result in low performance of the
combustion chamber.
[0024] An inner surface of the outlet 10 is provided with
corrugations 111 in the form of lobes. The preferred range of the
ratio of the length to the depth of the lobes is 1:1-3:1, but can
be as high as 10:1. The corrugations 11 can cover the entire mixing
section of the burner, or as little as 20% of the length of the
mixing section. As the swirl 3 passes through the outlet 10, it
passes through elongations 12 between the lobes 11. Opposing radial
velocity components arise in the swirl 3 as a result of the lobes
11 and cause radial shear, which produces a relatively intense
axial vorticity. The axial vorticity is superimposed on the
vortical flow in the swirl 3 in order to break up the vortical
flow, thus decreasing the coherence of the vortical flow and
increasing turbulence in the region of the outlet 10. This results
in increased flow stability. In addition, the axial vorticity
provides enhanced small scale mixing in the region of the outlet
10. The flow in the region of the outlet 10 is shown in FIG. 3.
[0025] FIG. 4 shows the effect of the burner according to the
invention on pressure fluctuations according to variation in Lambda
number. Line 13 is effectively a baseline, i.e. it represents a
burner which has not been modified in any way. Line 14 represents a
burner having a corrugated nozzle with a post (not shown), i.e. an
extension of the fuel inlet 8 along approximately {fraction (2/3)}
of the length of the swirl generator 2, and fuel injection. Line 15
represents a burner having a corrugated nozzle with a post in the
head region of the outlet 7 without fuel injection. Line 16
represents a corrugated nozzle without a post.
[0026] FIG. 5 shows the effect of the burner according to the
invention on emissions according to variation in Lambda number.
Line 13a is effectively a baseline, i.e. it represents a burner
which has not been modified in any way. Line 14a represents a
burner having a corrugated nozzle with a post (not shown) and fuel
injection. Line 15a represents a burner having a corrugated nozzle
with a post without fuel injection. Line 16a represents a
corrugated nozzle without a post.
[0027] It will be appreciated that variations of the embodiment
described above are possible. Alternative configurations of pre-mix
burners are well-known to persons skilled in the art. Similarly, it
would be possible to replace the conical swirl generator 2 with a
cylindrical swirl generator. It is also known to arrange a
displacement body, tapering towards the outlet 10, inside the swirl
generator; this could provide a further alternative embodiment of
the invention.
[0028] Although the corrugations 8 are in the form of lobes, they
could also be of rectangular, square, triangular or trapezoidal
cross-section. The lobes can be tapered and rounded at the edge,
straight and rounded at the edge, half-circular, half-elliptic,
half-oval, or stepped. They can also be tapered along their ridges
or straight.
[0029] While the invention has been described in detail with
reference to exemplary embodiments thereof, it will be apparent to
one skilled in the art that various changes can be made, and
equivalents employed, without departing from the scope of the
invention. Each of the aforementioned documents is incorporated by
reference herein in its entirety.
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