U.S. patent application number 11/245853 was filed with the patent office on 2007-04-12 for inshot burner flame retainer.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Duane D. Garloch, Ninev Karl Zia.
Application Number | 20070082309 11/245853 |
Document ID | / |
Family ID | 37911396 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070082309 |
Kind Code |
A1 |
Zia; Ninev Karl ; et
al. |
April 12, 2007 |
Inshot burner flame retainer
Abstract
A flame retainer for an inshot burner has a plurality of
secondary openings that take full advantage of the space available
to limit their size in one dimension to prevent flashbacks but are
sufficient in size to allow for the flow of sufficient primary air
so as to prevent yellow tipping and soot formation. The slots are
elongated in radially cross-sectional shape, and their widths are
limited to a dimension of 0.13 inches. The width is also limited to
dimensions equal to or greater than 0.09 inches so as to prevent
the formation of soot.
Inventors: |
Zia; Ninev Karl;
(Indianapolis, IN) ; Garloch; Duane D.; (Carmel,
IN) |
Correspondence
Address: |
MARJAMA & BILINSKI LLP
250 SOUTH CLINTON STREET
SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
Carrier Corporation
Farmington
CT
|
Family ID: |
37911396 |
Appl. No.: |
11/245853 |
Filed: |
October 7, 2005 |
Current U.S.
Class: |
431/354 |
Current CPC
Class: |
F23D 14/583
20130101 |
Class at
Publication: |
431/354 |
International
Class: |
F23D 14/62 20060101
F23D014/62 |
Claims
1. A burner insert for placement within an outlet end of an inshot
burner nozzle, said burner insert having an axially elongated
annular body with an axially extending inner flow passage and
further comprising: a plurality of axially extending secondary
openings formed in said insert, said secondary openings being
radially spaced from said inner flow passage and at least some of
said secondary openings being formed as elongated slots in radial
cross-sectional shape.
2. A burner insert as set forth in claim 1 wherein said elongated
slots have a uniform width which is equal to or less than 0.13
inches.
3. A burner insert as set forth in claim 2 wherein said slot width
is equal to or greater than 0.09 inches.
4. A burner insert as set forth in claim 1 wherein said secondary
openings are generally V-shaped in radial cross-sectional
shape.
5. A burner insert as set forth in claim 4 wherein said V-shaped
openings having their apex extending towards said inner flow
passage.
6. A burner insert as set forth in claim 4 wherein said secondary
openings have a relationship as follows: b 14N.apprxeq.126.56-0
wherein N=the number of V-shaped openings and .theta.=1/2 the
included angle of the V-shaped opening.
7. A burner insert as set forth in claim 1 include a plurality of
openings having a circular radial cross sectional shape.
8. A burner insert as set forth in claim 1 wherein the space
between said secondary openings is no less than 0.045 inches.
9. A method of preventing flashback in a flame retainer of an
inshot burner nozzle for use with propane comprising the steps of:
providing an insert having an axially elongated annular body with
an axially extending inner flow passage; providing a plurality of
axially extending openings in said insert, said secondary openings
being radially spaced from said inner flow passage and at least
some of said secondary passages being formed as elongated slots in
radial cross sectional shape.
10. A method as set forth in claim 9 and including the further step
of limiting the width of said secondary passages to be equal to or
less than 0.13 inches.
11. A method as set forth in claim 10 and including the further
step of forming the secondary passages such that the width of the
slots is uniform and is equal to or greater than 0.09 inches.
12. A method as set forth in claim 9 wherein said at least some of
said secondary openings are generally V-shaped in radial cross
sectional shape.
13. A method as set forth in claim 9 wherein said plurality of
secondary openings are formed such that the thickness of the walls
therebetween is no less than 0.045 inches.
Description
TECHNICAL FIELD
[0001] This invention relates generally to residential furnaces
and, more particularly, to inshot burners with flame retainers.
BACKGROUND OF THE INVENTION
[0002] Gas fired appliances, such as residential and light
commercial heating furnaces, often use a particular type of gas
burner commonly referred to as an inshot burner. In this type of
burner, fuel gas under pressure passes through a central port
disposed at the inlet of a venturi burner nozzle. Atmospheric air
is drawn into the burner nozzle and mixes with the fuel gas as it
passes through the burner nozzle. In some constructions, a burner
head insert, also referred to as a flame retention insert, made of
compressed sintered or powdered metal is mounted in the outlet end
of the tube. In operation, as gas is injected into the inlet end of
the nozzle, it entrains air into the nozzle. This primary air/gas
mix flows through the nozzle to the burner head insert. The primary
air/gas mix passes through outlet openings defined by the insert
and burns as it exits the insert forming a flame projecting
downstream from the burner head insert. Secondary air flows around
the outside of the venturi tube and is entrained in the burning
mixture downstream of the insert in order to provide additional air
to complete the combustion process.
[0003] Some of the problems associated with conventional inshot
burner designs are improper ignition, flame instability, noise and
nitrogen oxides formation. Ignition problems can arise when the
ignition location is critical. The velocity of the primary air/gas
flow from the insert can be greater than the flame speed. Under
this condition, the flame lifts off from the burner insert, i.e.
the flame begins to burn at a location spaced from the outer face
of the flame retention insert. Flame liftoff is a major cause of
the noise associated with the operation of inshot burner nozzles.
If the velocity of the air/gas mixture is too slow when compared to
the flame speed, flashback can occur. Flashback is the burning of
the gas within the burner nozzle itself. This condition can cause
overheating and deterioration of the nozzle.
[0004] Flame retention or burner head inserts have been designed in
an attempt to achieve better flame stability and reduction of
noise. U.S. Pat. No. 6,036,481 provides a burner head insert having
an inner flow passage and a plurality of second flow passages with
tapered splines therebetween. U.S. Pat. No. 5,186,620 provides a
central passage, secondary openings of smaller diameters arranged
circularly around the central insert and a plurality of peripheral
openings with stepped notches. While such designs are helpful in
addressing the problems discussed hereinabove, they do not
adequately address the problem of flashback and the propensity for
producing soot, particularly when using propane rather than natural
gas as the fuel. That is, the applicants have found that flashback
of flame to the outer perimeter flow passages in a burner insert
can be substantially reduced or prevented if certain dimensional
limitations are placed on the passages. However, when dealing with
other design limitations on the overall size of the burner, simply
downsizing the perimeter passages results in insufficient primary
air for combustion. That is, as the size of the passages is reduced
to prevent flashback, there is a tendency to cause a yellowing of
the flame tip which, in turn, tends to cause the formation of soot.
Further, attempting to increase the number of the passages
eventually reaches the minimum limit of wall thickness (i.e. the
recognized industry standard of 0.045-0.060 inches) for powdered
metal parts, which is the most viable and economical method of
producing flame retainers.
DISCLOSURE OF THE INVENTION
[0005] The applicants have found that if the perimeter flow
passages are formed having at least one dimension which is
approximately 0.13 inches or less, a flamelet which might otherwise
propagate upstream through that channel can be quenched and halted
by the proximity of the channel wall. In order to obtain the
necessary flow of air through the passages to prevent sooting,
while maintaining the minimum limit of wall thickness, the passages
are preferably formed having a radial cross sectional shape that is
elongated in form, essentially by tying multiple holes together to
form slots to increase the flow area while preserving the wall
thickness between passages and also maintaining a criteria of
having a passage dimension (i.e. slot width) no greater than the
0.13 inches.
[0006] In accordance with one embodiment of the invention, the
passages are V-shaped in radial cross section. This is accomplished
in one way by having a plurality of circular openings at one radius
and a second plurality of openings at a greater radius, and
removing the material between the outer openings and inner opening
to provide a V-shape with the apex toward the center.
[0007] Another embodiment of the present invention is to provide
passages having radial cross sections that are elongated in shape
with their elongations being disposed radially. This, again, is
accomplished by having a plurality of openings formed at a smaller
radius and a plurality of openings at a greater radius, and
removing material therebetween to provide elongated slots that are
radially disposed.
[0008] According to another embodiment of the invention, the
passages are formed such that in radial cross section, they are
annular in form and are circumferentially equally spaced around a
central opening. The restricted radial width prevents flashback,
while the circumferential length is sufficient to prevent
sooting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A and 1B are illustrations of a flame retainer device
in accordance with the prior art.
[0010] FIG. 2 is a modified version of a flame retainer.
[0011] FIG. 3 is a further modified flame retainer.
[0012] FIG. 4A is a flame retainer in accordance with a preferred
embodiment of the invention.
[0013] FIG. 4B is an alternative embodiment thereof.
[0014] FIG. 4C is another alternative embodiment thereof.
[0015] FIG. 5 is a graphic illustration of the relationship between
slot width and tendencies to form soot or allow flashback.
[0016] FIG. 6 is an alternative embodiment of the invention.
[0017] FIG. 7 is a further alternative embodiment thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Referring now to FIGS. 1A and 1B, there is shown a flame
retainer structure in accordance with the prior art. The flamer
retainer, shown generally at 11 comprises a cylinder 12 having an
outer surface 13 and a central passage 14 extending therethrough. A
plurality of secondary openings 16 of smaller diameter are arranged
circularly around the central passage 14.
[0019] While the size of the central passageway 14 is somewhat
decided by other considerations, the designers have taken some
liberty with the size of the secondary openings 16 to bring about
desired results. Generally, the size of the secondary openings 16
has been chosen to bring about the desired performance
characteristics. While the number and particular location of the
secondary openings has been varied to bring about particular
results, the secondary openings have generally been circular in
form with their axes aligned with the axes of the central passage
14.
[0020] The applicants have found that the use of propane, as
opposed to natural gas, presents problems because of propane flame
characteristics. In particular, in order to prevent the formation
of soot, the secondary openings must be sufficient in number and
size to allow for the free flow of the primary air/gas mixture
therethrough. However, it has also been found that as the size of
the secondary openings 16 reaches a certain level, flashback is
likely to occur.
[0021] Shown in FIG. 2 is a modified version of the flame retainer
which includes a central passage 14 and a plurality of secondary
openings 17. The secondary openings 17 comprise a first set of
secondary openings 18 with their centers being located on a
radially inward circle 19 as shown in FIG. 2, and a second set of
secondary openings 20 having their centers being located on a
radially outer circle 21. The diameters of the first and second
sets, 18 and 20, respectively, are identical, and, when tested it
was found that flashback did occur. While the number of secondary
openings 17 has been increased over the prior art design of FIGS.
1A and 1B, it was found that there was still not sufficient primary
airflow therethrough to prevent the formation of soot. Further, to
increase the number of secondary openings 17 in order to overcome
the problem was not possible because of the need to maintain a
certain wall thickness between the secondary passages 17 in
accordance with industry standards.
[0022] Referring now to FIG. 3, in order to address the problems of
flashback and insufficient primary air, the flame retainer was
formed with secondary openings 22 that were smaller in size and
greater in number. That is, the 24 secondary openings 22 were
formed having a diameter of about 0.10 inch and were densely
situated such that the number of openings was maximized while still
maintaining the desired wall thickness. The total area of the
secondary openings 22 was found to be 0.188 square inches. When the
flash retainer was tested, it was determined that the design was
adequate for the prevention of flashback, but there was
insufficient primary air such that a yellowing of the flame tip
occurs.
[0023] In an effort to increase the flow of primary air to prevent
the flame yellow tipping, while at the same time restricting the
dimensions of the secondary openings, the openings of the flame
retainer of FIG. 3 were interconnected by removing material between
an opening located in the radially inner set of openings and the
adjacent radially outer openings to thereby form a plurality of
V-shaped secondary openings 23 as shown in FIG. 4A. That is, the
five V-shaped secondary openings 23 retained the dimension d.sub.1
of about 0.10 inches throughout its length, but the elongated shape
increased the total area of the secondary openings 23 to about
0.322 square inches, thereby allowing for increased flow of primary
air as compared with the FIG. 3 embodiment. When tested, this
modified design was found to be acceptable in respect to the
prevention of flashback and also with respect to the non-formation
of soot. That is, the increased flow of primary air eliminated the
flame yellow tipping that had occurred in the FIG. 3
embodiment.
[0024] A slight variation of the FIG. 4A embodiment is shown in
FIG. 4B where, again, there are five V-shaped secondary openings 26
and five radially inner openings 27 as shown. Whereas the radially
inner openings 27 are substantially identical to the radially inner
openings 24 of the FIG. 4A embodiment, the V-shaped secondary
openings 26 are somewhat shorter in overall length and somewhat
wider than the secondary openings 23 of the FIG. 4A embodiment.
Also, the ends of the V-shaped slots of the secondary openings 26
are flat as compared with the rounded ends of the slots in the
secondary openings 23 of the FIG. 4A embodiment. It should be kept
in mind, however, that although the width d.sub.2 of the slots 26
is slightly increased from that dimension d.sub.1 of the FIG. 4A
embodiment, that dimension is limited by the need to prevent
flashback as will be further discussed hereinafter.
[0025] When tested, the FIG. 4B embodiment was found to perform
satisfactorily in preventing flashback while at the same time
preventing the occurrence of yellowing at the flame ends. The total
area of the secondary openings 26 and 27 was found to be about
0.334 square inches.
[0026] FIG. 4C illustrates yet another variation of a V-shaped
secondary opening 28 wherein the number of V-shaped secondary
openings 28 has been reduced to four, their angles widened, and the
number of radially inner openings 29 has been reduced to four. Here
the total area of the secondary openings 28 and 29 was found to be
around 0.333 square inches. The design was tested and was found to
be satisfactory in respect to the prevention of flashback and
yellow tipping. The length of the secondary openings 28 are
increased over the length of the V-shaped slots 26 of the FIG. 4b
embodiment, and the dimension d.sub.3 is, again, limited in order
to prevent the flashback occurrences.
[0027] Considering the dimensions d.sub.1, d.sub.2 and d.sub.3 of
the FIGS. 4A, 4B and 4C embodiments, respectively in greater
detail, there is shown in FIG. 5 a relationship which exists
between the width of the slots for the secondary openings and the
occurrence of flashback. Briefly stated, if the slot width is
maintained at a dimension no greater than 0.13 inches, flashback
will not occur. When that dimension is increased beyond the 0.13
inches, flashback is likely to occur and will increase with an
increase in that dimension. On the other hand, if the slot width is
decreased too far, sooting is more likely to occur. That is, if the
dimension is reduced below 0.09 inches, then sooting is likely to
occur.
[0028] In each of the 4A, 4B and 4C embodiments, it will be
recognized that the secondary openings 23, 26 and 28 are all
V-shaped, with an included angle that points toward the central
passage 14. In an analysis of these different designs, the
applicants have recognized a relationship as follows:
14N.apprxeq.126.56-0
[0029] where N=the number of V-shaped patterns in the flame
retainer
[0030] .theta.=1/2 of the included angle of the V-shaped opening in
degrees
[0031] Applying the above formula to the FIGS. 4A, 4B and 4C
embodiment we obtain: TABLE-US-00001 14(5) .apprxeq. 126.56 - 59
.apprxeq. 67.56 14(5) .apprxeq. 126.56 - 56 .apprxeq. 70.56 14(4)
.apprxeq. 126.56 - 71 .apprxeq. 56.56
[0032] In addition to V-shaped patterns for secondary openings, the
applicants have found that other shapes of elongated slots may also
be employed to obtain the results contemplated by the present
invention. For example, in the FIG. 6 embodiment, there are 12
secondary openings 32 which are formed as elongated slots aligned
with their long axes in a radial direction with the width d.sub.4
being restricted as discussed hereinabove. The FIG. 6 embodiment
was found to have a total open area for the combined secondary
opening 32 of 0.380 square inches, and was found to perform
satisfactorily both with respect to the prevention of flashback and
the prevention of soot.
[0033] The FIG. 7 embodiment is yet another possible embodiment and
is similar to the FIGS. 4A and 4B embodiments except that, rather
than the V-shaped secondary openings, the secondary openings are
curvilinear in form with their long dimension being along the
periphery and having a width d.sub.5 that is in compliance with the
requirements as discussed hereinabove. Further, there are five
radially inner openings 33 as shown. The combined open area of the
slots 32 and the openings 33 was about 0.364 inches. In addition to
the diameter of the slots 32, the diameter of the openings 33 is
also limited to prevent flashback as discussed hereinabove.
[0034] While the present invention has been particularly shown and
described with reference to a preferred embodiment and modified
embodiments as illustrated in the drawings, it will be understood
that one skilled in the art may make various changes in detail
without departing from the spirit and scope of the invention as
defined by the claims.
* * * * *