Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLOW MODIFYING DEVICE
1. Field of the Invention
This invention relates to flow modifying devices
and particularly to a new and improved fluid flow
modifying device in which the amount and direction of
discharge of the fluid from the device can be varied.
2. Description of the Prior Art
Many combustion chambers within gas turbine
engines employ flow modifying devices, such as swirlers t
to mix fuel and air and to aid in distributing the
resultant mixture within the combustion chamber. The
swirlers impart a swirling motion to the air. The
swirling air increases the tendency of the fuel to
atomize, causing better mixing and thus more efficient
burning of th~ mixture in the combustion chamber.
However, many currently used swirlers have a
fixed geOmetEy~ That is, the amount and the direction
oE dischar~e, or swirl an~le, of air from the swirler
i5 relatively constant, regardless of the amount of
fuel which is injected into the combustion chamber.
For reasons of reducing objectionable gaseous
emissions and improving combustor efficiency, it is
desirable to be able to vary the amount of air which
mixes with the fuel and to vary the swirl angle of the
air as it leaves thè swirler. For example, when the
engine is running at idle, it is preferable that there
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be a rich fuel-air mixture, that is, a high fuel to air
ratio, in the primary com~ustion zone and tha-t the
residence time of thè mixture within the primary zone
be relatively long. The primary combustion zone
comprises approximately the upstream third of the
combustion chamber. Such a rich mixture reduces CO and
HC emission levels at idle, and also enhances altitude
relight capability. Correspondingly, with low airflow
through'the combustor r as would occur with a rich
mixture at idle, a higher swirl angle is needed to
atomize the fuel prop'erly.
On the other hand r at high power operating
conditions, it is preferable to have a lean fuel-air
mixture, that is, a low fuel to air ratio, and to have
a lower swirl angle in order to distribute the mixture
more uniformly throughout the combustion chamber. This
results in reduced NOx and visihle smoke emissions.
Furthermore, with a lean mixture at higher power
conditions, less o~ a s~irl angle is required to properly
atomize the fuel.
One approach which hàs been employed to vary the
uel-air ratio is a two-stage, or double-annular,
co~bustion sy~te~. In such a system, a pilot dome
prod~lces a rich mixture for operation at idle engine
conditions, while a second dome or mixing chute a5se~bly
provides lean mixtures at hig~er power conditions.
~lthou~h SUC}l ~o-stage combustion systems are preferable
to combustors employin~ single, fixed yeometry swirlers,
they can be complex and expensive to fabricate,' and can
add a significant amount of weight to the engine.
Anothèr approach'to varying the fuel-air ratio
has heen the use of a shutter assembly for op~ning and
closin~ air SCOOp5, the openings of which are normal to
the flow'of compres'sed air from the compressor~ Such
shutter assemblies, however, often have no positions
æ~
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intermedia.te the open and closed positions~ Furthermore,
while they may vary the'amount of air entering the
com~ustion chamber, they fail to provide a corresponding
variation in the swirl angle of the air. Another
drawback of shutter ass'emblies in which the openings of
the scoops are disposed normal to the air flowing from
the compressor is that the compressed air exerts heaYY
5tresses directly against the elements of the shutter
assembly. In order to avoid leakage and prevent damage,
the elements must be fabricated so as to withstand such
stresses, which'can in turn result in increased cost and
wei~ht~ '
In view of the a'bove problem, it is therefore an
object of the present invention to provide a Elow
modifying device, particularly adaptable to a combustion
ch.amberl which can vary the amount of air discharged from
it, and therefore the fuel-air ratio, to improve
combustor efficiency and reduce undesirable gaseous
emissions.
20. Another object of the present invention is to
provide a flow modifying device in which the direction
of dischar~e, or swirl angler of the air can ~e varied
in relation to the amount of air which is dischar~ecl
Erom the device in orde.r to improve fuel-air mixing and
distribution.
Yet another object of the present invention is to
provide a ~low mod`ifyin~ device which is relatively
simple and inexpensive~ '
Still another ob'ject of the present invention is
3~ to provide a flo~ ~odifyin~ device having eIements
arranged so that, when' the device is employed i~ a
combu:stion chamber located in the path of a flow of'
compres~sed air, the elements of the device are
substanbially protected fr~m stres's-es exerted by the :
compressed air.
~æo~æ3
13DV-8412
SUMM~RY.OF THE INVENTION
A swirler for a gas turbine engine combustor is
disclosed~ for simultaneousl~ contr-olling combustor flow
rate, swirl angler res'idence time'and fuel-air ratio to
provide three regimes of'operation. A first regime is
provided in which.'fuel-air ratio i5 less than
stoichiometric, NOx is produced at one level t and
combustor flow rate is high. In the second regime,
fuel-air ratio is nearly stoichiometric, NOx production
0 i5 less than that of the first reyimel and combustor flow
rate i5 low. In a third re~imer used for example at
lightoff, fuel-air ratio is greater than stoichiometric
and th.e combustor flow rate is less than in either of the
other regimes~
.. .. .. .. .. .. . .. .. .. .. .. .
B~IEF DESCRIPTION OF ~HE DRAWINGS
This invention ~ill be better understood from the
following description taken in con~unction with the
accompan~ing draw.ing r wherein:
FIGURE 1 is a fragmentary cross-sectional view
of a combustion c~mber and a swirler incorporating
eatures of the present invention.
FIGURE 2 is a cross-sectional view of a swirler
taken along linas 2-2 of Figure 1.
FIGURES 3 through 5 are fragmentary cross~-sectional
views of the swirler taken along lines 3-3 of Figure 2 and
showing different relative positions of the plate and vane
assembly.
FIGUR~ 6 is a schèmatic view of a gas turbine
engine combustor.
FIGURE 7 is a plot of combustor inlet .~emperature
as a function of compres'sor pressure ratioO
FIGURE 8 is a plot of NOx production as a function
of fu~l-air ratio.
FIGURES 9,,10,. and ll are'plots of emissions versus
combu~tor'inlet temperature.
8~
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to a co~sideration of the drawing,
and in particular to Figure 1, there is shown the
upstream portion of a combustion chamber lcombus~or~ 20
in a gas turbine engine. A mixture of air and fuel
enters and is burned within the combustion chamber 20.
The energy of the resulting exhaust gases is extrac-ted
to perform work~ such as to rota~e'a ~urbine tnot shown).
The fuel for combustion is introduced from the
pressurized fuel nozzle 21. As the fuel exits the fuel
nozzIe 21, it is mixed with air in the swirler 22 and
the resulting mixture enters the combustion chamber 20
to be burned. The swirler-22 impar~s a swirling motion
to the air flowing through it and ~us to the fuel
emitted ~rom the fuel nozzle 21 which mixes with the
air causing atomization of the fuel' and thereby promoting
better mixing.
As shown in Figure 6, incoming air enters a
plenum 22B~ The air can exit the plenum only at ~hree
locations: through the swirler 22 of the present
invention, through yenturis 38 (which can provide a
swirling up5tream in the opposite direction to that
provided by the present invention~, or through dilu-tion
holes 22D. Thus, an increase in airflow through one exi-t
location must result in a decrease in airflow through one
of t.he others. The present invention allocates airflow
a~ong these three exits in a manner which will become
clear in the followin~ discussion.
The present invention comprises a flow modiying
3G device, such as the swirler 22, which receives at least
a porti~n of its fluid from a generally radial direction
and discharges that `fluid in a generally axial direction
and which can vary the amount and direction of the
. . .
dischàrge'of thè ~luid, such as air, flowing through it.
By "ràdial" it is meant in a direction generally
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perpendicular to the swirler longitudinal axis, the axis
bein~ depicted by the dashed line 27. By "axial" it is
meant in a direction gen~rall~ parallel to the swirler
longitudinal axis ~1. A radially displaced axis 27a is
shown in Figure 1 and in end vie~ in Figure 2. The
radially displaced axis 27a is parallel to the
longitudinal axis 27 and serves a reference function
which ~7ill be described later more fully.
In a particular embodiment of the invention, a
first element, as can be seen in Figures 1 and 2,
comprises an annular, radially aligned plate 23 and a
plurality of axially ex~ending channels 24. Preferably,
and as can be seen in Figure 3, the portions 23a o~ the
plate 23 circumerentially adjacent each of the openings
24 include at least one radially extending surface 25a
or 25b which lies in a plane angled from the longitudinal
axis 27:of the swirler 22. These portions 23a are termed
vanes. As will be seen later, in certain relative
positions of the first and second elements, the surfaces
2~ 25a and 25b establish the sw.irl angle imparted to the
air as it exits the swirler 22. Thus, the angle which
the suraces 25a and 25b make with the displaced axis 27a
is determined by the degree of swirl desired. As can be
seen in Figure 3, the preferred cross-sectional shapes oE
~S the portions of the plate 23 circum~erentially adjacent
each channel 24 is that of a hexagon, tl~at is, -three sets
o~ paxallel and opposite radially extending suraces, 25a
and 25b, 26a and 26bl and 28a and 28b~
As can be seen in Figures 1 and 2, the second
ele~ent .is substantially annular and comprises a Yane
assembly 29 including a plurality of radially exten~ing
vanes.30 ~hich are interconnected at the radially inner
and outer~ ends to annular memb-ers 31 and 32 respectivelyr
Thè vanes:3a.are so disposed .that:an axially extending
chànn;el:33 is defined between: each pair of vanes.
~%01!~!~23
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As can best be seen in Figure 3~ the radially
extendin~ surfaces 34 and 35 define the channels 33 and
the angle which these ~urfaces make with the displaced
axis 21a of the swirler determines' at least partially
the swirl angle imparted: to the air as it exits the
swirler 22. This angle should thus be predetermined
according to ~he degree of swirl desiredO For reasons
to be explained hereinafter, the distance between the
surfaces 34 and 35 o adjacent vanes 30 is substantially
the same'as the width o~ the surface 28a of the plate 23,
and the suxfaces 34 and 35 of the vanes 30 are parallel
to the surfaces 26a and 26h of the plate 23~
AS can be seen in Figure 1, the swirler 22
includes a hollow hub 36 which is generally annular.
The'upstream portion of ~he hub 36 extends generally
radially, lying in a plane perpendicular to the swirler
longitudinal axis 27~ The hub 36 is curved such that
the downstr.eam portion, which is disposed radially
i.nward of the plate 23 and the vane assembly 29, and
which hub can be integral or attached with the plate 23,
extends generally axially. The vane assembly 29 and the
upstream portion of the hub 36 define an annular
radially ~acing air inlet 37 through which a portion oE
the air for combustion enters the swirler.
~5 The fact that the air enters the variable portion
o~ the swirler 22, that is r the vane assembly 29 and
plate 23`portion, from a radial direction xather than
axially is advantayeous because the vane assembIy and
plate are thereby pro.tected by the upstream portion o~
the hùk 36 from the stresses` which`would be exerted by
a direct flow of compressed air against ~hem. 'The
upstream portion of the hub 36 can include as inteyral
or attachèd with:it a radially aligned annular disc 39
Fuel ior combustion exits. the`fuel' nozzIe 21~ which
extends through a gap in the'annular disc 39 o~ the
12~ 3
13DV-8~12
_ ~ _
upstream portion of the hub 36, and ~lows through the
hollow interior of the hub 36 prior to entering the
combustian chamber. The swirler can also include a
plurality o~ fluid duots, such as the Yenturis 38~ in
the annular disc 33 o* the upstream portion of the hub
36r through which air enters from a generally axial
direction and mixes with fuel~ Thus, with this
arrangement, initial mixing of air and fuel occurs in
the interior of the hub 36 as air from the venturis 38
.lO mixes with fuel from the fuel nozzle 21. As this
mixture then exits the hub 36, it is further mixed with
air from the radial air inlets 37 after it flows through
the vane assembly 29 and the plate 23. It is the amount
. of the direction of dischar~e of the second source of
air, that is, the air entering the swirler radially and
flowing through the vane assembly 2~ and plate 23, which
the present invention can vary.
Varying of the amount and direction of dischaxge,
or swirl angle, of air from the swirler 22, is
acco~plished by positioning, preferably rotatably, the
second element, such as the vane assembly 29, relative
to the first element, such as the plate 23. The vane
asse~bly 29 is rotatably mounted on the swirler hub 36.
Means Eor positioning ~he second element preferably
~5 compri.se at least on.e actuatable drive arm 40 connected
to the seconcl element, as can be seen in Figure 1 and 2
The radially outer portion of the drive arm 40 is
connected to means which impart motion to the drive arm.
For example, the dri~e arm 40.can be connected to a
unison ring 41 through a spherical bearing 42. The
unison ring 41 can be connected with other dri~e arms 4Q
associated with other swirlers in the combustion section
of the engine such that all o~ the drive arms will be
moved together~
The radially inner end ;of the dri~e arm ~O.is
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. g _
preferably connected to the vane assembly 29 through a
hinge 43~ The use of a hinge 43 permits the vane
assembly 29 to be rotated even when there is an axial
dimensional mismatGh between the vane assembly 29 and
the unison ring 41. As sho~n in Figure 2, the hinge 43
can include shims 44 to permit presetting of the
circumferential position of the drive arm 40 to thereby
synchronize the position of that drive arm with other
drive arms which might be connected with the unison
ring 41.
The swirler 22 is connected wit~ the upstream end
of the combustion chamber 20 by an appropriate means,
su~h as by welding or ~olting flanges 45, extending from
the plate 23, to a lin~r 47 of the combustion chamber.
Likewise, the unison ring 41 can be supported ~y any
suitable means, such as by a roller bearing 48 and
support bracket 46. This embodiment of the 10w
modifying operates as follows:-
Figure 3 shows the swirler in its open position.
The vane assembly 29 is positioned such that the surfaces34 and 35 of -the vanes 3~ are aligned with the surfaces
26a and 26b respectively of ~he plate 23. Thus, the
channels 33 of the vane assembly 29 are aligned with the
channels 24 of the plate 23 such that the maximum amoun-t
~5 o~ air passes through them~ The direction that the air
will Elow as it is discharged from the slots 33 and
openings 24, ~hat is, its swirl angle~ is determined by
~he an~le that the surEaces 34 r 35, 26a~ and 26br which
ar~ preexably parallelr make with the displaced axi~ 27a.
Figure 4 shows the ~ane as~em~ly 29 after it has
been rotatably positioned to an intermediate position.
Part of the air flow`ing through each of the channels 33
of the vane assembly 29 impinges upon and is turned by a
surface 25b of the plate 23. `This part of the air causes
the`xemainder of th~e air flowing through the channel 33
23
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to also be turned and flow across the adjacent
surface 25a~
Figure 5 shows. the vane assem~Iy 29 af.ter it has
been rotatably positioned to the' closed position. The
surfaces 2ga of the pl.ate 23'block the channels 33 such
that suhstantially no air can flow through the channels
33 or channels 24. When the vane assembly 29 is in the
closed position, the.only air entering the combustion
chamber 20 through the swirler 22 would be tha~ flowing
from the venturis 38 through the int~rior of the swirler
hub 36, a~ can be seen in Figure lr or through the
dilution holes 22D in Figure 6.
Accordingly, an in~ention has ~een described in
which a register plate valve for throttling axially
flowing air is incorpôrated into a combustor in a gas
turbine engine. The'second pla~e 29 of the valv~ as
shown in Figures 3-5 includes a plurality of vanes 30
which are positioned in a radial array as shown in
Figure 2. The vanes 30 resemble parallelograms in cross
sections as shown in Figure 3. The distance 75 between
adjacent faces 34 and 35 at a given r'adius such as radius
78 in Figure ~ does not change in the downstream
direction~ That is, distance 75a in Figure 3 equals
downstream distance 75br so that the width of the channel
~5 33'does not change in the downstream directi.on. Faces
34 and 35 make a first swirl angle 80 with the radially
d'isplaced longitudinal axis 27a~ This angle 80 i5
preferabIy within the approximate range of lS to 30
degxees.
The first plate 23'contains a radial array of
vanes ~3A as shown in Figure 2 which'are hex'agonal in
cross section as shown in Figures 3-5. Opposite faces
of the hexagonal cross sectionæ~ are parallel. (That is,
faces 25a an~ b are parallel`.,:faces 2Ga and b are
parallel'r and faces 2ga and b 'are parallel). Faces 26a
~2~ 2~
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and 26b define an angle with the displaced axis 27a
which is the same as angle 80~ Thus, when the first and
second plates 23 and 29 are positioned as shown in
~igure 3, the ~aces 26b and 35 are aligned along line 83
and faces 26a and 34 are aligned along line 85 (that is,
the respectlve Eaces are colinear ~i~h thb corresponding
lines 83 or 85.) In such a caset a continuous channel
including channel s-ubparts 24 and 33 is defined by these
faces. The air flowing through the channel is imparted
a swirl angle determined by anyle 80. A gap 88 is sho~n
between ~he two plates 23 an~ 29, but this is
illustrative only. The gap is actually of the order of
one thousandth inch and no 'appreciable airflow travels
alon~ the gap in the directions-of arrows 90. The
register plate throttle is preferably dimensioned so
that approxima~ely fifteen per'cent of the air entering
the combustor does so through`t'nis throttle, as
positioned in Figure 3. The remainder enters through
venturis 38 and dilution holes 22d of Figure 6.
~he operating regime shown in Figure 3 and just
described is used during takeoff and cruise conditions
of aircraft flight. The regime used for idle conditions
is shown in Figure 4. In Figure 4I the first plate ~3
has been rotated so that the vanes ~3a partial].y obstruct
~S the channels 33'of tl~e second plate 29. In such a case,
the swirl angle of the air is dominated by the angle 95
which faces ~5a and b make with the displaced axi5 27a.
Faces ~Sa ~nd b define a ~low channel and are parallel
in cross section~ The angle 95 is preferably within the
approximate range of 50 to 7Q de~rees.
Under the conditions o~`Figure 4, a large swirl
angle 95 is imparted to the'air and consequently a
larger residence time'of the air in the combustor is
imparted' as` comparea with the residence time of Figure 3.
This larger residen'ce time'pr'omotes fuller combustion
8~i2~
13DV-8412
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of fuel at idle~ The thro-ttle valve is preferably
dimensioned so that, at idle, under the conditions of -
Figure 4, about five percent of the combustor airflow
is supplied by the register plate throttle and the
remainder is supplied by venturis 38 and dilu-~ion holes
22d in Figure 6.
The operating regime of Figure 5 is used during
engine ignition (i.e., '~lighto f")~ The register plate
throttle closes off all airflow to provide a very rich
fuel mixture.
Some important aspects of the present invention
are now discussed with reference to Figures 6, 7, and 8.
Figure 7 is a plot o combustor inlet temperature as a
function of enyine'ccmpressor ratio~ NOx production is
a function of this temperature. The three operating
conditions corresponding to Figures 3 and 4 are indicated
in Figure 7 of Figures 3'and 4 being abbreviated as
"F3" and "F4".
Figure 8 is a plot of NOx production as a
~unction of combustor fuel-air ratio. NOx production
peaks at the'stoichoimetric ratio, which is
approximately .067 by weight. The stoichoimetric ratio
is that at which the air present contains exactly t~e
amount of oxygen needed to completely burn fuel in-to
carbon dioxide and water vapor, One explanakion Eor
this peak at the s-toichoimetric ratio is that the
combustor temperature tends to be highest at this ratio
and consequently,,since NOx production is t~mperature-
sensitive, NOx production i5 also highest.
In considexing Figure 7 anA 8 to~ether,,one sees
that,,under the regime'o~ ~igure 3'(~akeoff or cruise~
combustor inlet temperature is ~uch higher ~han at idle,
and so NOx production tends to be'similarly higher for
this-reason'. Hawevèrl as discu~sed in connec-tion with
Figure'3, use`of'the regime o` Figure 3'results in a
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high airflow rater low .residence time, and lean fuel-air
ratios within the combustor as shown by point 98a in
Figure 8. Consequently, despite the higher combustor
inlet temperature, the lowered residence time subjects
atmospheric nitrogen to hi.gh temperatures for a short
time, thus promoting lessened N5x production. Also, as
illustrated in Figure 8, the lean ~uel-air ratio results
in a low NOx production rate. Calculations made in
conjunction with`exper`imental e~idence indicates that
1~ the regime of Fiyure 3 results in NOx production of about
15 to 20 pounds per thousand pounds of fuel, compared to
40 to 50 lbs/1000 lbs~ fuel for con~entional combustion
systems.
During idler using the regime of Figure ~,
several factors affect NOx production~ (At idler fuel
control means kno~n in the art reduces fuel suppliea to
the combustGrs.) The lowered combustor inlet temperature,
as shown in Figure 7 r tends to reduce NOx production.
~Iowever, t~e engine`at idle is preferably run at a
fuel-air ratio whi`ch is at or near stoichiometric, as
shown by point 98 in Figure 8. This tends to increase
NOx production. Further, the increased swirl angle of
F.igure 4 tends to increase residence time in the
combustor as does the reduced air~low under idle
~5 condi.tions~ Both of these factors tend to increase NOx
production, in exposing atmospheric nitrogen to high
combustor temperatu.res for longer times. However~
calculation a~d experiment indicate that the use of the
~egime`in Figure ~ results in reduced NOx production of
about three to ~our pounds NOx per thousand pounds of
fuel. The lowe`red combustor inlet` temperature o~ the
idle c~nditions of Figure 4 is thus, in a sense,; the`
dominating factor in NOx pxoductiont despite the upward
influence on NOx productlon~iof:low flow rater high swirl
angle, stoic~iiometric ratio, and incr`eased residence
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13D~-~412
-- 1~ --
time, all of which are associated with the regime of
Figure 4.
In addition, the stoichiometric fuel-air ratio,
the hi~h'swirl an~le and the increased residence time
S of Figure 4 serve to promote-more co~plete combustion,
thereby reducing carbon monoxide (Co) and hydrocarbon
(HC) production.
Some of these performance characteristics of
the present invention are further illustrated in
Figures 9-11. Figure 9 is a plot of carbon monoxide
(CO) produced versus combustor inlet temperature tT3),
Figure 10 is a plot of hydrocar~on emissio~s (HC~
versus combustor'inlet temperature and Figure 11 is a
plot of NOx emissions versus combustor inlet
temperature. In all three plots, thé gas quantity on
the vertical axis (CO, HC, or NOx) has units of pounds
of the gas produced per t~ousand pounds of fuel burned.
In the three plots, the per~ormance of the present
invention, based on computations taken from experimental
evidence, is lab~led~l'invention," while thè performance
of a typical prior art combustor is labeled "prior art."
The three plots are considered self-explanatory.
One of the principal merits of the present
invention lies in the pro~ision of three selectable
~5 positions of the register plate throttle. These are
s~own in Figures 3-5. These three positions provide two
separate s~irl an~les and ~hxee separate aperture settings
determined by the degree o~ obstruction of the channel 33
by the vane~ 23 of the plate 23.' Thus, the airflow rate
(in pounds per second) is simultaneously controllabIe
with~the s~irl angle. Further, the register plate
throttle'ser~es` to shift airflow from the'combustor dome
to the dilution holes without the use o~ other components
of ~ariable ~eometry.
In the prefer'red-embodIment, operation'of the
23
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register plate throttle is restricted to one of the
three regimes shown in ~igures 3~5, and no others.
For example, a regime intermediate those of Figures
3 and 4 is not contemplated. Therefore, once designed r
the combustor is configured to operate in either a
first regime having a first airflow and first swirl
angle, in a second regime ha~ing a second airflow ~nd
second swirl angle, or a third regime having zero
airflow and no swirl angle~
It is to be understood that this invention is
not limited to the particular embod.iment disclosed,
and it is intended to cover all modifications coming
within the true spirit and scope of this invention
as claimed.
