Note: Descriptions are shown in the official language in which they were submitted.
UUl~ L) OL~ '1'111~ 11 V 1!~ \I'l'lUN
Field of the Invention:
.... _ _ . . . _ _ _
This invention relates ~o combustion chambers for
gas turbine engines and more particularly to cy~indrical com~
bustion chambers having seconda~y air inlet tubes pro~ecting
. thereinto to deliver combustion air to the combustion ~one.
Description of the Prior Art:
Reference is made to U.S. Patents 3,134,229
4,05~,02~; and 3,~72,664 to show various con~igurations
of secondary air inlet tubes to gas turbine combustion ,.
chambers and generally referred to as air scoops~ In
the first two pa~ents, the air scoops extend into the com-
bustion chamber and, by design, deliver air in a pattern
having a major upstream component for increased penetration
and mixing of the air with the fuelO However, as subse-
quently discussed, it has been found that this, in fact,
causes upstream recirculation of the fuel, forming fuel rich
pockets that produce smoke and hot spots on certain of the
combustion parts causing premature burn-out of such parts.
The remaining patent shows an air scoop having a
downstream slanted direction; however, the scoop does not
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47,705
significantly extend into the combustion chamber for pene-
tration of the airg and also the swirl imparted to the
secondary air by the swirling apparatus within the scoops
may well induce an upstream flow similar to that deseribed
in the above patents.
SUMMARY OF THE IN~ENTION
-
This invention provides a gas turbine combustion
ehamber wherein at least the first row of secondary eombus-
tion air inlet seoops of a eombustion ehamber are slanted
downstream to minimize the upstream flow of air entering the
eombustor therethrough and to, in turn, reduee the reeireu-
lation of fuel intercepted and entrapped in the upstream air
flow which would otherwise form fuel rich pockets causing
smoke and early failure or burn-out of parts.
BRIEF DESCRIPTION OF THE DRQWINGS
Figure l is a schematic view of a prior art com-
bustion chamber with radially extending secondary air scoops;
and,
Figure 2 is a view similar to Figure l showing the
chamber and air scoops of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure l, a stepped cylindrical com-
bustion chamber 12 is shown having a fuel nozzle 11 at the
head end. The primary combustion air enters at the head end
through an air entry collar member 13. The primary air is
divided upon entry, with a portion thereof flowing to adja-
cent the face of the fuel nozzle for mixture with the fuel
to provide the fuel rich easily ignited mixture, and another
portion flowing along the inner face of the combustiorl dome
15 as guided by an annular baffle 14 to maintain a flow of
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L~7, 705
cooling air along the wa]l of the combustor.
Secondary combustion air is injecked through a
first annular row of air scoops 16 which extend into the
combustion chamber to generally adJacent the primary com-
bustion zone to provide penetration of secondary air into
the rich air/fuel mixture to provide sufficient air to
completely burn the fuel. A second downstream annular row
of air scoops is also shown having less penetration. How-
ever, it has been found that the primary radial direction of
entry of the secondary air through the first row of scoops
causes, in addition to the primarily downstream direction 19
of air flow, an induced air flow having an upstream compon-
ent 18. This upstream flowing air intercepts and entraps a
portion of the atomized fuel injected by the nozzle and
redirects such fuel to generally ad~acent the baffle 14 and
dome 15. This volume adJacent these members thus tends to
become excessively rich in fuel, causing incomplete com-
bustion producing smoke. In addition, combustion of such
fuel in this region adjacent the baffle tends to overheat
the baffle causing hot spots therein resulting in premature
failure.
Also, the kinetic energy of the upstream flowing
air is such that it will penetrate the cooling air flow
along the wall of the dome 15 and diminish the cooling
effects thereof to cause excessive heating in this area,
again ultimately resulting in failure of the part.
Referring to Figure 2, the present invention is
seen to comprise essentially the same cylindrical combustion
chamber structure of ~igure 1 including a combustor 22
having a fuel injecting nozzle 21 in its upstream head end
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1,7,705
and an air inlet collar 23 supplying primary air to the fuel
and a layer of cooling air along the wall of the dome 25 as
guided by an annular baffle 24.
However, as is further seen in this configuration,
the first annular row of secondary air inlet scoops 26 pro-
e~2l
jects into the combustion ~r~~~ ~h~ to adjacent the primary
combustion zone with each scoop slanted in a direction such
that the secondary air is directed slightly downstream.
Thus, with scoop structure and direction of entry according
to the present invention, only a small portion of the enter-
ing secondary air has an upstream direction thereby minimiz-
ing the amount of air which entraps the atomized fuel and
carries it to the upstream end, thereby reducing the amount
of smoke produced by such unburned fuel over the normal
prior art arrangement. ~urther, the reduced upstream air
flow has a reduced kinetic energy so that it cannot as
readily penetrate the layer of cooling air flowing across
the dome surface and thereby overheating of this part is
substantially eliminated.
Thus, with such obliquely slanted first row secon-
dary air inlet tubesl the smoke emissions are decreased and
the life of the upstream parts of the gas turbine combustion
chamber is extended.
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