Multiple jet burner

A gas burner comprising a housing with a front exit, a back surface, and an outer surface. The housing has a closed back surface at one end and an open exit at the other end. The housing is separated into a fuel-oxygen mixing chamber and a second chamber by a support plate. A multiplicity of jets passing through the support plate such that the fuel-oxygen mixing chamber is in communication with the second chamber through the jets. The fuel-oxygen mixing chamber has an inlet for a first-gas, usually a fuel gas, and an exit. The second chamber has an inlet for a second-gas, usually oxygen. The jets arranged such that each jet centerline is unique with respect to all other jet centerlines and each jet centerline is directed from the support plate to the housing exit. The housing exit contoured such that a substantially constant distance is maintained between the boundary of the exit and a closed path lying in the surface of the exit which is the shortest path circumscribing projections of the jet centerlines onto the surface of the exit. Constructing the burner entirely out of quartz or similar material is indicated. Fuel-oxygen mixing chambers in the shape of a parallelpiped, a frustum of a wedge, and a hollow circular cylinder sector for use in a radial burner are indicated. Recessing the jets with respect to the housing exit is indicated.

BACKGROUND-FIELD OF INVENTION 
This invention relates to burners and more specifically to an improved 
burner to be used in the glass blowing arts or fiber optics field. 
BACKGROUND AND SUMMARY OF THE INVENTION 
The standard lathe ring burner used in the glass blowing industry has been 
of the types marketed by Litton Engineering Laboratories and by Carlisle 
Machine Work. These surface mix burners were constructed from metals such 
as stainless steel, nickel inconel, and other alloys. These prior art 
burners were originally designed to use natural gas and propane as fuels 
and have been used extensively for working the new higher temperature 
boro-silicate glasses. In the 1960's, the semiconductor industry began 
employing silica and dear fused quartz vessels in their integrated circuit 
foundries. Consequently, silica and clear fused quartz became important 
industrial glasses. In order to shape these glasses, extremely high 
working temperatures were required. Litton burners were used with hydrogen 
to obtain these high temperatures. 
The growth of semiconductor technology through successive generations of 
larger silicon wafers and cleaner fabrication environs brought about the 
requirement for larger diameter and purer quartz vessels. Larger gas 
burners were required to work the larger diameter quartz tubing. The glass 
blowing industry responded by increasing the number of metal burners. The 
typical glass shop work horse burner of 1970 was a ring burner with eight 
single jet heads or six seven-jet heads, while that burner grew to one 
with twelve or fourteen seven-jet heads and, even at that size, it was 
difficult to develop the heat densities required to comfortably work the 
larger diameter tubes. Besides the generally poor performance of using 
metal burners, none of the prior art burners addressed the issue of quartz 
tubing contamination. 
It is well known that fabrication of modern integrated circuits requires 
increasingly lower contamination environs as the circuit density increases 
in order to achieve acceptable silicon wafer yield rates. Towards this 
end, the semiconductor industry has employed quartz as vessel material 
because it tends to be nonreactive with the enclosed working gases and 
tends to cause fewer impurities in the silicon wafer. During the shaping 
of quartz tubing into quartz vessels, however, prior art burners exhibit 
metallic burner "spit," metallic particulate contamination, and other 
phenomena which causes contamination of the quartz vessel. The 
semiconductor industry's purity requirements are adversely effected by the 
impurities in the quartz vessel caused by prior art burners. 
It is expected that the present invention will have application in the 
various manufacture processes for preforms used in the manufacture of 
glass fiber optic transmission lines. These processes are well known and 
generally involve deposition of a source material on a fiber optic 
preform. Like the semiconductor fabrication process, there is a need for 
pure environs in the manufacture of such fiber optic preforms. It is 
contemplated that the present invention be used in applying heat energy to 
the source material in order to provide high temperature and high purity 
source material for deposition. More particularly, it is intended that the 
present invention be used in applying heat energy to fiber optic preform 
raw material such that such raw material is substantially molten. Then, 
carrying the molten fiber optic particles through the force of the 
pre-ignition and post-ignition fluid flow from the present invention 
burner to the fiber optic preform. The molten fiber optic particles being 
deposited on a fiber optic preform and solidifying thereto as the 
particles cool. 
Metal burners are at a disadvantage as compared to all-quartz burners when 
operated at the extremely high temperatures and heat densities required 
for working quartz tubing. Metal burners absorb significant amounts of 
heat from the work piece which leads to energy inefficiencies, flame 
instability, contributes to metallic-based and particle-based 
contamination of the work piece, and leads to melting of the metal burner 
itself. Melting concerns limit the economy and shape of metal burner 
designs, and discourage the metallic construction of burners in the 
configuration of the present invention because of the narrow jets and the 
proximity of the jets to the combustion flame and heat reflecting work 
piece. Metal burners also expose a human operator to the discomfort of 
high temperatures. Conversely, all-quartz burners are natural heat 
insulators and do not absorb significant amounts of heat from the work 
piece, thus all-quartz burners are more efficient than metal burners and 
do not tend to melt. Moreover, human operators are able to perform more 
competently, comfortably, and safely when using all-quartz burners because 
they do not conduct large amounts of heat energy from the work piece to 
the operator. Accordingly, all-quartz burners have substantial advantages 
over metal burners. 
An all-quartz burner is constructed entirely from vitreous silica, fused 
silica, fused quartz, quartz glass, or other such material. This ensures 
that all joints are well sealed because joints and structural walls are 
made from the same material and are one-piece. There are no welds, brazes, 
press-fits, or other such fastening joints or sealing joints commonly 
found in metal burners. This reduces contamination from joint material and 
poorer sealing associated with prior art burners. 
A prior art burner typically has independent discharge ports for fuel and 
oxygen which terminate at a face plate. The prior art burner face plate is 
exposed to atmospheric air, thus discouraging significant fuel-oxygen 
mixing before being exposed to atmospheric air and airborne contamination. 
Accordingly, a prior art burner mixes fuel, oxygen, and substantial 
amounts of atmospheric air. This leads to inefficient burning and a 
difficult to control and less clean combustion process. The present 
invention deletes the face plate on the housing exit, thus reducing 
weight, cost, and manufacturing difficulty. Also, deleting the face plate 
in the present invention burner promotes combustion in the absence of 
atmospheric air. 
The front exit of the present invention burner is contoured such that there 
is a gap of approximately constant distance between the burner exit and 
the shortest dosed path which circumscribes a projection of all the jets 
onto the burner exit. For a burner with jets flush with the burner exit, 
this dosed path is approximately the path taken by a rubber band snugly 
expanded around the jets. The approximately constant distance gap promotes 
the development of an envelope of fuel gas which tends to surround the 
combustion flame. Accordingly, the fuel-oxygen mixture jet stream is 
isolated from the atmosphere by a fuel gas envelope. Contouring of the 
fuel-oxygen mixing chamber and proper sizing of the front exit of the 
housing with respect to the fuel-oxygen mixture jet stream permits the 
present invention to be operated in a mode in which an envelope of fuel 
gas extends from the burner exit to the work piece. This effectively 
produces an atmospheric-air-free combustion zone which leads to better 
mixing, more efficient and cleaner burning, improved flame temperature, 
and improved flame heat densities. A gap between the shortest closed path 
which circumscribes the projection of all the jets onto the burner exit 
and the front exit of the housing of between 0.010 and 0.120 inches gives 
good results. 
Prior art burners have failed to design for fuel-gas mixing before exposure 
to atmospheric air, and moreover, have generally failed to move beyond 
circular face burners or cylindrical mixing chambers. As compared to 
cylindrical chamber or circular face prior art burners, new and unexpected 
results have been achieved by fuel-oxygen mixing chambers in the shape of 
approximately rectangular parallelepiped and frustum of a wedge contours. 
Housing exit aspect ratios of approximately 1.0 (square) up to 10.0 
(rectangle) give good results, while aspect ratios of approximately 1.2 to 
5.0 give superior results. 
The present invention also promotes further substantial and predetermined 
mixing of fuel and oxygen by recessing the oxygen jet outlets within the 
fuel-oxygen mixing chamber. Recessing the jet outlets from the housing 
exit approximately 5% to 25% of the length of the fuel-oxygen mixing 
chamber has produced good result. Thus, recessing the jets provides a 
fuel-oxygen mixing chamber which promotes even better mixing of fuel and 
oxygen before exposure to atmospheric air. This results in new and 
unexpected results in view of the prior art because the present invention 
promotes better pre-exit mixing which yields more efficient burning, 
improved flame temperature, and improved flame heat densities. 
Additionally, in some embodiments of the present invention, manufacturing 
of the burner is significantly easier and less costly when recessed jets 
are employed. 
Complex burner contours pro,note optimal pre-ignition mixing, combustion 
control, flame temperature, and heat characteristics. It is generally 
believed that metal burners designed with complex burner contours would 
involve significant potential for burner melting and prohibitively high 
labor costs, manufacturing costs, manufacturing precision, and 
manufacturing reliability. Burners with complex contours constructed from 
quartz glass are constructed more easily, less labor intensively, less 
expensively, and are more resistant to thermal stress than comparable 
metal burners. The present invention contemplates using contours in the 
shape of approximately a parallelepiped, a frustum of a general cone, a 
frustum of a general wedge, and other prismoids for fuel-oxygen mixing 
chambers, as well as a radial burner embodiment using a hollow circular 
cylinder sector for a fuel-oxygen mixing chamber contour. Accordingly, 
such burners constructed from vitreous silica, fused silica, fused quartz, 
quartz glass or other such material can achieve improved burner designs 
which lead to new and improved results by providing improved heat 
densities, combustion control, flame shapes, flame purity, and safety. 
It is the principal object of the invention to provide a burner which is 
free of the mentioned disadvantages of the known burners. More 
particularly, the present invention provides improved heat density, flame 
shape, operator safety, operator comfort, combustion control, increased 
heat transfer, and an ultra-pure flame which significantly reduces 
contamination of the quartz tubing work piece and finished quartz vessel. 
These and other objects are accomplished in accordance with the illustrated 
preferred embodiments of the present invention by providing a gas burner 
comprising a housing with a front exit, a back surface, and an outer 
surface. The housing has a dosed back surface at one end and an open exit 
at the other end. A support plate separates the housing into a fuel-oxygen 
mixing chamber and a second chamber. A multiplicity of jets pass through 
the support plate such that the fuel-oxygen mixing chamber is in 
communication with the second chamber through the jets. There is no face 
plate on the housing exit. The fuel-oxygen mixing chamber has an inlet for 
a first-gas, usually a fuel gas, and an exit. The second chamber has an 
inlet for a second-gas, usually oxygen. The entire burner may be 
constructed from vitreous silica, fused silica, fused quartz, quartz glass 
or other such nonreactive material.

DESCRIPTION-FIG. 1 
FIG. 1 shows a perspective view of a basic version of my burner. The top 
surface of a housing 102 has been removed in order to show a multiplicity 
of jets 112 arranged in a row, in this particular embodiment a 1.times.5 
jet configuration. A fuel-oxygen mixing chamber 100 in the approximate 
shape of a frustum of a right wedge is formed by housing 102 closed on one 
end by a support plate 108 defining the larger wedge section of the 
fuel-oxygen mixing chamber and open at the other end at a front exit 116 
defining the smaller wedge section of the fuel-oxygen mixing chamber. The 
housing exit 116 is rectangular in shape with an aspect ratio of 5.0 and a 
gap of 0.04 inches between the inside boundary of exit 116 and the 
shortest closed path located in the plane of exit 116 which circumscribes 
a projection of the jets onto the exit 116 plane. FIG. 1 shows a focused 
housing 102 where the housing walls slope towards the center of front exit 
116 creating a nozzle effect. A second chamber 120 is formed by housing 
102 closed on one end by support plate 108 and closed on the other end by 
a back surface 106. 
Jets 112 are attached to support plate 108 and recessed from the housing 
exit 116 such that the jets 112 are recessed approximately 15% of the 
distance from support plate 108 to the housing exit 116. Jets 112 extend 
into fuel-oxygen mixing chamber 100 separating the fuel gas from the 
oxidizing gas until termination of jets 112. Accordingly, jets 112 avoid 
premature mixing of fuel and oxidizing gas which improves safety and 
assures improved heat density, flame shape, combustion control, and 
increased heat transfer to the work piece. 
Other configuration are contemplated in which each jet 112 of the plurality 
of jets 112 can be of different lengths and diameters from any or all of 
the other jets 112. FIG. 1 shows focused jets 112 where jets 112 slope 
towards the center of exit 116 approximately paralleling the housing walls 
creating a nozzle effect. Each jet 112 can be aligned normal to the 
support plate 108, focused towards the center of exit 116, focused away 
from the center of exit 116, or some combination of these. 
Second chamber 120 communicates with fuel-oxygen mixing chamber 100 through 
jets 112. A first-gas inlet port 104 is mounted on housing 102 and 
communicates with fuel-oxygen mixing chamber 100. A second-gas inlet port 
124 is mounted on housing 102 and communicates with second chamber 120. 
The second gas, for example oxygen gas, moves from inlet port 124 into 
second chamber 120, through jets 112, mixes with fuel gas in fuel-oxygen 
mixing chamber 100. The first gas, for example hydrogen fuel gas, moves 
from inlet port 104 into fuel-oxygen mixing chamber 100, mixes with oxygen 
gas in fuel-oxygen mixing chamber 100, then the fuel-oxygen mixture moves 
to exit 116 surrounded by a fuel envelope created by the 0.04 inch gap 
between the inside boundary of exit 116 and the shortest closed path 
located in the plane of exit 116 which circumscribes a projection of the 
jets onto the exit 116 plane. 
Although not wishing to be limited to only an all-quartz burner, the entire 
burner can be constructed from vitreous silica, fused silica, fused 
quartz, quartz glass, or other such nonreactive material. Accordingly, an 
all-quartz burner structure is one-piece and all joints are well sealed. 
There are no welds, brazes, press-fits, or other such attachment 
requirements commonly found in metal burners. 
Description-FIGS. 2 to 3 
FIG. 2 shows a front view of a 3.times.3 jet, square face burner. Nine jets 
112 are shown in this embodiment. The number of jets 112 can be varied 
from one to more than several hundred. A square face housing 102 is shown. 
The face, or cross section, of housing 102 can be varied substantial, for 
example the housing cross section may be triangular, rectangular, 
pentagonal, and other polygonal shapes, ellipsoidal, and other closed 
curve shapes, and combination polygonal and closed curve shapes. FIGS. 4-7 
indicate a few specific examples, but other housing cross sections are 
contemplated. Cross sections which vary along a direction from support 
plate 108 towards exit 116, are also indicated. For example, FIG. 1 shows 
a focused, or nozzle, housing 102 while FIG. 4 shows a flared, or 
diffuser, housing 102. FIGS. 1 and 4 depict fuel-oxygen mixing chambers 
100 contoured in the shape of approximate frustums of right wedges. 
However, FIG. 1 shows support plate 108 defining the larger wedge section, 
while FIG. 4 shows support plate 108 defining the smaller wedge section. 
FIG. 3 is a side view of the cross section indicated by the section lines 
3--3 in FIG. 2. Fuel-oxygen mixing chamber 100 is contoured as 
approximately a rectangular parallelepiped. Jets 112 are mounted to 
support plate 108 and arranged approximately parallel to housing 102. Two 
first-gas inlet ports 104 are mounted on housing 102 downstream of support 
plate 108 and provide a first-gas, for example fuel gas, to fuel-oxygen 
mixing chamber 100. Two second-gas inlet ports 124 are mounted on back 
surface 106 of housing 102 and provide a second-gas, for example oxygen 
gas, to second chamber 120. Second chamber 120 passes the second-gas, or 
oxygen, through jets 112 into fuel-oxygen mixing chamber 100 where oxygen 
and fuel gas mix before exiting the burner housing 102 at exit 116. A 
combustion-flame volume 114 extends from exit 116 to an ignition surface 
showing the approximate structure of a combustion flame. A fuel gas 
envelope 110 encloses combustion-flame volume 114. 
Description-FIG. 4 
FIG. 4 shows a top view of a 3 column jet 112 burner with housing top 
removed. Jets 112 are mounted on support plate 108 and are directed away 
from the center of exit 116 creating a flaring, or diffusing, effect. The 
housing 102 walls slope away from center of exit 116 and define a 
fuel-oxygen mixing chamber 100 in the shape of a frustum of a right wedge 
with support plate 108 defining the smaller wedge section. It is 
contemplated that the present invention may be constructed by flaring 
either jets 112 or housing 102 walls along one or more directions. For 
example, a rectangular face burner may only have flaring away from the 
exit center in the direction of the short side of the rectangle, but not 
in direction of the long side of the rectangle. Moreover, it is 
contemplated that flared jets, focused jets, flared housing, and focused 
housing be combined to create burner configurations. 
Description-FIG. 5 
FIG. 5 shows a front view of a 4.times.5&6 jet, rectangular face burner. 
Jets 112 are arranged in 2 rows of 5 columns and 2 rows of 6 columns. 
Adjacent jet rows are offset. Jets 112 are arranged normal to exit 116 
with no flaring or focusing. First-gas inlet port 104 is mounted on 
housing 102 along the short side of the rectangular parallelepiped housing 
102. 
Description-FIGS. 6 to 7 
FIG. 6 shows a top view of a 1.times.19 jet, radial burner with housing top 
removed. FIG. 7 shows a front view indicated by the section lines 7--7 in 
FIG. 6. Second chamber 120 is a hollow right semicircular cylinder formed 
by housing 102, support plate 108, and back surface 106. Fuel-oxygen 
mixing chamber 100 is a hollow right semicircular cylinder formed by 
housing 102, support plate 108, and open at exit 116. Second chamber 120 
and fuel-oxygen mixing chamber 100 are concentric. Second chamber 120 
communicates with fuel-oxygen mixing chamber 100 through jets 112. Jets 
112 are arranged in a radial manner and mounted normal to support plate 
108. FIG. 6 shows three second-gas inlet ports 124 mounted on housing 102 
upstream of support plate 108. FIG. 7 shows three first-gas inlet ports 
104 mounted on housing 102 downstream of support plate 108. The 
second-gas, or oxygen, moves from second-gas inlet ports 124 into second 
chamber 120, through jets 112, and mixes with the first-gas, or fuel gas, 
in fuel-oxygen mixing chamber 100. The second-gas, or fuel gas, moves from 
second-gas inlet ports 104 into fuel-oxygen mixing chamber 100, mixes with 
oxygen gas in fuel-oxygen mixing chamber 100, and then the fuel-oxygen 
mixture moves to exit 116 surrounded by a fuel envelope created by a gap 
of approximately constant distance between the inside boundary of exit 116 
and the shortest closed path located in the semicircular cylindrical 
surface of exit 116 which circumscribes a projection of the centerlines of 
the jets 112 onto the curved surface of exit 116. 
Back surface 106, support plate 108, and exit 116 are shown in the top view 
of FIG. 6 as semicircles, while fuel-oxygen mixing chamber 100 and second 
chamber 120 are shown as hollow right semicircular cylinders. However, 
other combinations of polygons and closed curve shapes and volumes are 
contemplated. For example, fuel-oxygen mixing chamber 100 and second 
chamber 120 could be contoured as hollow circular cylinders sectored at 
angles other than 180 degrees, or as hollow prismoids. Back surface 106, 
support plate 108, and housing 102 could be shaped such that they define a 
wedge-like second chamber 124. 
Operation-FIGS. 1 to 5 
A manner of using the present invention is to connect a high pressure 
oxidizing gas supply, for example oxygen, to first-gas inlet port 104 and 
a high pressure fuel gas supply, for example hydrogen, to second-gas inlet 
port 124. Exit 116 is at atmospheric pressure, a lower pressure than both 
the first-gas and second-gas supplies, thus both the first-gas and 
second-gas proceed towards exit 116. Accordingly, the direction of flow 
from second-gas inlet port 124 and first-gas inlet port 104 to exit 116 is 
the downstream direction and provides a reference direction for the 
present invention. The second-gas moves from inlet port 124 into second 
chamber 120, through jets 112, and mixes with first-gas in fuel-oxygen 
mixing chamber 100. First-gas moves from inlet port 104 into fuel-oxygen 
mixing chamber 100, mixes with second gas in fuel-oxygen mixing chamber 
100, then the first-gas-second-gas mixture moves to exit 116. The 
fuel-oxygen mixture is surrounded by a fuel gas envelope created by the 
gap between the inside boundary of exit 116 and the shortest closed path 
located in the surface of exit 116 which circumscribes a projection of the 
jets onto the surface of exit 116. 
Although the preferred embodiment indicates a fuel gas supply connected to 
first-gas inlet port 104 and an oxidizing gas supply connected to 
second-gas inlet port 124, the invention also contemplates reversing this 
arrangement such that the fuel gas supply is connected to the second-gas 
inlet port 124 and the oxidizing gas supply is connected to the first-gas 
inlet port 104. Such an arrangement yields a flame with diffuse heat 
energy and temperature characteristics. 
The present invention's inherent flame and heat characteristics are 
believed to be determined in part by the length, focus, and diameter of 
jets 112; and the length, shape, and cross section of housing 102; and the 
size and shape of exit 116. A burner's flame may be adjusted within its 
inherent flame and heat characteristic by varying the supply gas pressures 
at first-gas inlet port 104 and second-gas inlet port 124. 
The present invention can be used in the same applications as prior art 
burners; additionally, the present invention is well-suited for lathe 
applications. A lathe mounted work piece can be heated to proper working 
temperatures by placing the burner such that the combustion-flame volume 
114, as shown in FIG. 3, is directed toward the rotating axis of the work 
piece. In using the burner invention as embodied in FIGS. 1 or 5, the 
burner can be positioned such that the rows of jets 112 are aligned 
parallel with the rotating axis of the lathe mounted work piece. Such an 
orientation of burner to work piece increases heat energy delivered to the 
work piece by focusing the combustion flame where is does the most good 
along the work piece. 
Experimentation indicates that new and unexpected heat densities, flame 
temperature, and heat patterns of approximately the same size as the cross 
sectional area, or face, of the housing exit 116 are produced on work 
pieces by using burners of the type indicated in FIGS. 1 or 5. Thus, 
smaller burners are able to provide increased areas of high heat density 
and temperature density. Experimentation indicates that new and unexpected 
efficiencies are obtained in that work pieces can be heated to higher 
temperatures, plus working temperatures are achieved faster than prior art 
burners. In particular, rectangular face burner embodiments of the present 
invention appear to provide approximately 40% more heat energy than prior 
art circular face burners. A single 1.times.7 jet, rectangular face burner 
can heat a standard 50 millimeter quartz tubing work piece to working 
temperatures in a few seconds. 
It is contemplated that the present invention be used in applying heat 
energy in the well known art of deposition of fiber optic raw material 
onto fiber optic preforms. Manufacturing fiber optic preforms requires 
high temperature and energy and molten source material substantially free 
of contamination. More particularly, it is intended that the present 
invention be used in applying heat energy to fiber optic preform raw 
material such that such raw material becomes substantially molten. Then, 
carrying the molten fiber optic particles through the force of the 
pre-ignition and post-ignition fluid flow from the present invention 
burner to the fiber optic preform. The molten fiber optic particles are 
then deposited onto a fiber optic preform and solidifying thereto as the 
particles cool. 
Operation-FIGS. 6 and 7 
The present invention embodied in FIGS. 6 and 7 works under the same basic 
principles as the other embodiments shown in FIGS. 1 to 5. The burner of 
FIGS. 6 and 7, however, is configured to provide heat energy and 
temperature combustion flame in areas of concentration that are different 
from those burners depicted in FIGS. 1 to 5. For example, the burner of 
FIGS. 6 and 7 can be positioned so that the burner collars a lathe mounted 
tubing work piece. In such an application, the radial burner provides 
concentrated heat energy and temperature along a narrow band on the 
rotating work piece. Thus, the work piece is heated to working 
temperatures significantly faster and more efficiently. 
It is contemplated that the radial burner embodiment be constructed with 
radial jets 112 flush with exit 116, rather than recessed, in order to 
promote easier manufacture while still providing improved burner 
characteristics over prior art burners. 
Summary, Ramification, and Scope 
Although the description above contains many specificities, these should 
not be construed as limiting the scope of the invention but as merely 
providing illustrations of some of the presently preferred embodiments of 
this invention. For example, fuel-oxygen mixing chamber 100 could be hour 
glass shaped, a frustum of a general cone, or some combination of prismoid 
and spheroid shapes. Other variations include for example, first-gas inlet 
port 104 and second-gas inlet port 124 could have various cross sections 
and shapes, such as square, round, ellipsoid, other shaped cross sections; 
and second chamber 120 could be prismoid, hemispheroid, conical, bulbed, 
or other such chamber shape. Also, the various burner elements disclosed 
in this application alone tend to provide improved burner performance, 
while when combined with other elements disclosed in this application tend 
to promote synergistic results. For example, a fuel-oxygen mixing chamber 
100 in the shape of a rectangular parallelepiped alone tends to promote 
good burner performance, while when combined with recessed jets 112 that 
burner performance tends to be further improved, and more than might be 
expected from recessing the jets 112 in combination with a cylindrical 
fuel-oxygen mixing chamber 100 in a circular face burner. 
Thus the scope of the invention should be determined by the appended claims 
and their legal equivalents, rather than by the examples given.