Fuel injection assembly for a gas turbine engine

A fuel injection assembly for a combustion chamber of a gas turbine engine is disclosed in which a plurality of premixing chambers are in communication with the combustion chamber and adjacent pairs of the premixing chambers are connected to a single prevapoization chamber by prevaporization conduits. Fuel is injected into the prevaporization chamber via a fuel injector and is mixed with oxidizer passing into the prevaporization chamber such that the fuel/oxidizer mixture has a richness exceeding the stoichiometric ratio. The fuel/oxidizer mixture passes into the prevaporization conduits through a diaphragm opening and, upon entering the premixing chamber, is mixed with additional oxidizer such that the fuel/oxidizer mixture in each premixing chamber has a richness less than the stoichiometric ratio. The premixing chambers are bounded by generally tubular walls, a portion of each adjacent tubular wall forming a protective hood between the fuel injector and the combustion chamber so as to prevent self-ignition of the fuel/oxidizer mixture in the prevaporization chamber. Oxidizer entering the premixing chambers passes through one or more oxidizer swirlers to assure a complete mixing of the fuel and oxidizer prior to its passing into the combustion chamber.

BACKGROUND OF THE INVENTION 
The present invention relates to a fuel injection assembly for a gas 
turbine engine, more particularly such an assembly that minimizes the 
generation of nitrogen oxidizes and eliminates the possibility of 
self-ignition of the fuel/oxidizer mixer before passing into the 
combustion chamber. 
French Patent 1,590,542 discloses a fuel injection assembly for a gas 
turbine engine which comprises a fuel injector injecting fuel into a 
prevaporization chamber and at least two prevaporization conduits 
connected to the chamber and to two intake orifices of different premixing 
chambers which issue into the combustion chamber. The prevaporization 
chamber is fitted with intake orifices for a pressurized prevaporization 
oxidizer and each premixing chamber has an intake device for dilution 
pressurized oxidizer. 
The known fuel injection assemblies have not completely resolved the 
problems of excessive generation of nitrogen oxide (NO.sub.x) and smoke, 
nor have they eliminated the danger of self-ignition of the fuel/oxidizer 
mixture, resulting in poor combustion control. 
SUMMARY OF THE INVENTION 
A fuel injection assembly for a combustion chamber of a gas turbine engine 
is disclosed in which a plurality of premixing chambers are in 
communication with the combustion chamber and adjacent pairs of the 
premixing chambers are connected to a single prevaporization chamber by 
prevaporization conduits. Fuel is injected into the prevaporization 
chamber via a fuel injector and is mixed with oxidizer passing into the 
prevaporization chamber such that the fuel/oxidizer mixture has a richness 
exceeding the stoichiometric ratio. The fuel/oxidizer mixture passes into 
the prevaporization conduits through a diaphragm opening and, upon 
entering the premixing chamber, is mixed with additional oxidizer such 
that the fuel/oxidizer mixture in each premixing chamber has a richness 
less than the stoichiometric ratio. The premixing chambers are bounded by 
generally tubular walls, a portion of each adjacent tubular wall forming a 
protective hood between the fuel injector and the combustion chamber so as 
to prevent self-ignition of the fuel/oxidizer mixture in the 
prevaporization chamber. Oxidizer entering the premixing chambers passes 
through one or more oxidizer swirlers to assure a complete mixing of the 
fuel and oxidizer prior to its passing into the combustion chamber. 
The design according to the present invention eliminates self-ignition of 
the fuel/oxidizer in the prevaporization chamber and insures lean and 
complete combustion of the fuel/oxidizer in the combustion chamber, 
thereby reducing generation of nitrogen oxides and smoke. To achieve these 
goals, the cross-section of the intake orifices for the prevaporization 
oxidizer and the pressure of the prevaporization oxidizer are such that 
the richness of the prevaporized fuel/oxidizer mixture is higher than 
stoichiometric, whereas the intake cross-section for the dilution oxidizer 
and the pressure of the dilution oxidizer are such that the fuel/air 
mixture in each of the premixing chambers has a richness less than 
stoichiometric. 
To further carry out the objects of the invention, the prevaporization 
conduits are connected in parallel to the prevaporization chamber and a 
diaphragm opening is located between the prevaporization conduits and the 
associated prevaporization chamber. A single diaphragm opening is located 
between the pair of prevaporization conduits and the prevaporization 
chamber. 
The fuel injection assembly also comprises a hood protecting and insulating 
the fuel injector from the combustion chamber to prevent self-ignition of 
the fuel/oxidizer mixture in the prevaporization chamber. The protective 
hood has an opening enclosing the prevaporization oxidizer intake orifice 
of the prevapoization chamber and a second opening connected to a source 
of pressurized oxidizer. The opening extends around the prevaporization 
chamber in order to form an annular space through which the oxidizer may 
pass. The portions of the walls of the premixing chambers which form the 
protective hood are perforated with orifices issuing into the premixing 
chambers to permit the passage of dilution oxidizer. 
Dilution oxidizer also passes into each premixing chamber through a helical 
intake swirler which is oriented coaxially with the premixing chamber 
intake through which passes the prevaporized fuel/oxidizer mixture. Each 
premixing chamber may contain a single helical swirler as well as 
additional dilution oxidizer intake orifices through other wall portions 
to provide a sufficient quantity of dilution oxidizer. Alternatively, the 
walls of the premixing chambers may be formed without orifices and a pair 
of coaxial helical swirlers are located coaxially with the premixing 
chamber intake to provide a sufficient quantity of dilution oxidizer. The 
walls of the premixing chambers are generally tubular and may converge in 
a direction toward the exhaust opening of the combustion chamber so as to 
have a generally frusto-conical configuration. 
When utilized in a known dual-head injector, the fuel injection assembly 
according to the present invention may be utilized in either one of the 
dual heads, i.e. either the "low power" head or the "high power" head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As best seen in FIG. 1, the combustion chamber 6 is bounded by an external 
wall 2 which extends in an annular fashion about the axis of symmetry 1, 
an inner wall 3 which also extends about axis 1 in annular fashion, and a 
transverse end wall 4 which interconnects the walls 2 and 3. End wall 4 is 
located generally upstream in relation to the gas flow direction, 
illustrated by arrow F, which passes outwardly through the exhaust opening 
5. Accordingly, the combustion chamber 6 assumes an annular geometry about 
symmetrical axis 1. 
A dual-head combustion chamber is illustrated in FIG. 1 and, in known 
fashion, an annular array of fuel injectors 7 operate during the low power 
operating mode of the engine while the annular array of fuel injectors 8 
are used for full power operation of the engine, such as during aircraft 
take-off. The fuel injectors 7 are separated from the fuel injectors 8 by 
an intermediate separator 9 and each are respectively connected to a fuel 
supply by conduits 10 and 11. A pressurized oxidizer source, symbolically 
denoted by arrow G, feeds pressurized oxidizer to the combustion chamber, 
both to support the combustion of the fuel and to cool the walls of the 
various combustion chamber components exposed to the high combustion 
generated temperatures. Generally speaking, the pressurized oxidizer 
source comprises the gas turbine engine compressor located upstream of the 
combustion chamber and which is driven by the gas turbine. 
A first embodiment of the invention is illustrated in FIGS. 2 and 3. Two 
premixing chambers 12A, 12B are bounded by generally frusto-conical walls 
13A, 13B which extend about axes A13 and A13', respectively, substantially 
parallel to the axis 1. The walls 13A, 13B are affixed to the combustion 
chamber end wall 4 and each converges in a downstream direction, in the 
direction of arrow F toward the exhaust 5 of the combustion chamber. The 
premixing chambers 12A and 12B have openings 14A, 14B which allow 
communication between the interior of the premixing chambers and the 
combustion chamber 6. Annular and generally hemispherical bodies 15A, 15B 
are located in the upstream end apertures 17A, 17B of each of the 
premixing chambers 12A, 12B such that annular intake spaces 18A, 18B are 
formed between the bodies 15A, 15B and the walls 13A, 13B so as to enable 
pressurized oxidizer to the flow into the premixing chambers 12A, 12B from 
space 33 as illustrated by arrow H1. Body 15A is coaxial about axis A13, 
while body 15B is coaxial about axis A13'. 
Prevaporization conduits 19A, 19B are each connected to one of the bodies 
15A, 15B into which they coaxially issue through premixing chamber intake 
orifices 20A, 20B, and to a prevaporization chamber 21. Prevaporization 
chamber 21 is bounded by a cylindrical wall 22 extending about axis A22 
which extends substantially parallel to the axis 1. Helical "swirlers" 
24A, 24B are located between the end of each prevaporization conduit 19A, 
19B which terminates in the openings 20A, 20B and an upstream end opening 
23A, 23B of the corresponding body 15A, 15B. The "swirlers" admit dilution 
oxidizer (indicated by arrows H2) into the premixing chambers 12A, 12B and 
impart a rotation to the dilution oxidizer passing through the swirlers to 
insure a homogenous mixing of the fuel/oxidizer mixture within the 
premixing chambers 12A, 12B. The structure of the swirlers 24A, 24B is 
well known and it is not believed necessary to provide further description 
here. 
A diaphragm opening 25 is formed in the upstream end 26 of the 
prevaporization chamber 21 to enable communication between the interior of 
the prevaporization chamber 21 and the two prevaporization conduits 19A, 
19B. A fuel supply conduit 11 is connected to the fuel injector 27 to 
enable fuel to be injected inside the prevaporization chamber 21 in an 
upstream direction (opposite the direction of arrow F) toward the 
diaphragm opening 25. A protective hood 28 extends between adjacent 
portions of walls 13A, 13B, to insulate and protect the fuel injector 27 
from the combustion chamber 6. The upstream ends of the portions of walls 
13A, 13B which form the protective hood define an opening 29 which 
encloses the downstream end 31 of the wall 22 forming the prevaporization 
chamber 2I so as to define therebetween an annular space 30. Annular space 
30 enables oxidizer to pass into the interior of the protective hood 28, 
as well as into the prevaporization chamber 21, as illustrated by arrows 
H6. 
In the embodiment illustrated in FIGS. 2 and 3, only one swirler 24 is 
associated with each of the intake openings 20. In this embodiment, 
dilution oxidizer is supplemented by orifices 32A, 32B extending through 
bodies 15A, 15B to enable oxidizer from the space 33 to pass into the 
premixing chambers 12A, 12B, as illustrated by arrows H3. The oxidizer 
also is supplemented by orifices 34 formed in those segments of walls 13A, 
13B that define the protective hood 28 enabling oxidizer to pass into the 
premixing chambers 12A, 12B from the; interior 35 of the protective hood 
28, as illustrated by arrows H4. Additional oxidizer enters the, premixing 
chambers 12A, 12B through orifices 36 formed in walls 13A, 13B which are 
located substantially opposite the orifices 34 to enable oxidizer to enter 
the premixing chambers 12A, 12B as illustrated by arrows H5. 
An alternative embodiment is illustrated in FIG. 4 which utilizes a pair of 
coaxial swirlers for each premixing chamber 12A, 12B. As illustrated 
therein, swirlers 24A, 24B are coaxially located within swirlers 124A, 
124B and are located coaxially around the intake openings 20A, 20B of the 
premixing chambers 12A, 12B. In this particular embodiment, the dilution 
oxidizer orifices 32, 34 and 36 of the previous embodiment are eliminated. 
Separating walls 37A, 37B are located between the swirlers 24 and 124 for 
the purpose of initially separating the oxidizer flows H2, H102 entering 
the premixing chambers 12A, 12B through the swirlers. As can be seen, the 
walls 37A, 37B may converge in a direction towards the exhaust opening of 
the combustion chamber. Depending upon the criteria of each particular 
application, the swirlers 24, 124 may rotate the oxidizer in the same 
direction, or in opposite directions, to insure the homogeneity of the 
fuel/oxidizer mixture. The walls of the various elements of the fuel 
injection assembly exposed to heat and to the temperatures in the 
combustion chamber may have small holes 38 extending therethrough so as to 
provide, in known fashion, multiple cooling perforations of the walls. 
The incorporation of a fuel injection assembly according to the present 
invention into a dual-head combustion chamber is illustrated in FIGS. 5-8. 
FIGS. 5 and 6 disclose the use of the fuel injection assembly according to 
the present invention in the radially innermost head of the dual-head 
assembly, while FIGS. 7 and 8 illustrate the fuel injection assembly 
utilized in the radially outermost fuel injector head. In both of these 
embodiments, the fuel injection assemblies of the present invention are 
more compact than the known fuel injectors, since a single fuel injector 
supplies fuel to two intake orifices of the premixing chambers, thereby 
allowing optimal arrangement of the intake orifices and, hence, achieving 
satisfactory homogeneity of the fuel/oxidizer mixture supplied to the 
combustion chamber. 
In both of the embodiments, the protective hood constitutes a screen 
protecting the fuel injector 27 and prevaporization chamber 21 from the 
high temperatures in the combustion chamber 6. This design reduces, or 
eliminates, the hot spots in the fuel injection zone and, thus, reduces or 
eliminates the danger of self-ignition. 
The oxidizer flow, and pressure, entering the prevaporization chamber 21, 
as illustrated by arrow H6, and the fuel injector 27 are in such a ratio 
that the prevaporized fuel/oxidizer mixture in the prevaporization chamber 
21 and in the prevaporization conduits 19A, 19B has a richness higher than 
the stoichiometric ratio. The prevaporized mixture entering the premixing 
chambers 12A, 12B is then agitated by the flow of dilution oxidizer 
passing through the swirlers 24A, 24B (124A, 124B) and by the oxidizer 
passing through orifices 32, 34 and 36 (arrows H2, H3, H4 and H5) and the 
annular spaces 18A, 18B (arrows H1), along with the oxidizer passing 
through the cooling perforations 38, the resulting fuel/oxidizer mixture 
in the premixing chambers 12A, 12B has a richness less than the 
stoichiometric ratio. Accordingly, the initial prevaporization, which is 
entirely separate from the final fuel/oxidizer mixture, allows the 
generation of rich prevaporized fuel/oxidizer mixtures sheltered from 
self-ignition and from flashbacks. The invention also permits a 
high-energy injection of the lean mixture from the, premixing chambers 
12A, 12B into the combustion chamber 6 whereby the formation of smoke and 
nitrogen oxides (NO.sub.x) is reduced or eliminated thereby achieve 
non-polluting combustion. The orientation of the intake openings 20A, 20B 
in the premixing chambers 12A, 12B, for the prevaporized mixture 
facilitates the downstream flow of the fuel/oxidizer mixture. 
The converging shape of the walls 13A, 13B forming the premixing chambers 
12A, 12B accelerates the fuel/oxidizer mixture towards the combustion 
chamber so as to insure the complete combustion of the mixture. 
In the embodiment of FIG. 4, the oxidizer intake by means of the second 
swirlers 124A, 124B replaces the oxidizer intake through the orifices 32, 
34 and 36 in the embodiment of FIGS. 2 and 3. The swirlers 24A, 24B and 
124A, 124B enhance the agitation of the fuel/oxidizer mixture to assure 
its homogeneity, thereby insuring complete combustion within the 
combustion chamber 6. 
Although the invention has been illustrated by having a single fuel 
injector 27 associated with two premixing chambers 12A, 12B, it is within 
the scope of this invention to combine more than two premixing chambers 
with a single fuel injector. 
The foregoing description is provided for illustrative purposes only and 
should not be construed as in any way limiting this invention, the scope 
of which is defined solely by the appended claims.