Note: Descriptions are shown in the official language in which they were submitted.
I J 7~8~ ~
GAS TURBINE FUEL SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fuel systems for use in
gas turbine engines.
2. Summary of the Prior Art
In order to operate efficiently, gas turbine engines
must be run at very high temperatures. AS one would
expect, these temperatures get particularly high in a
combustor section of the engine where engine fuel is
burned. High combustor temperatures are necessary in
order to fully ignite the fuel and, additionally, to
derive the maximum amount of energy available from the
burning fuel. As the fuel is ignited, it combines with
high pressure air to form high-temperature, high-
pressure combustion gases. These gases are utili~ed
downstream of the combustor by a turbine section where
the kinetic energy of the gases is transformed into
useful mechanical energy. Under basic thermodynamic
principals, increasing the temperature and pressure of
the combustion gases increases the amount of mechanical
energy produced.
Because of the necessarily high combustor temperatures,
an engine fuel system must be provided that is capable of
safely and reliably supplying a continuous flow of fuel
to the combustor during high temperature engine operation.
Typically, in the present state of engine development,
~ ~ 7~
-- 2
fuel systems are subjected to temperatures in excess of
800F (426.67C~. The Federal Aviation Authority (FAA)
requires that commercial engine fuel systems undergo a
flame endurance test to show that a particular engine's
fuel system is capable of safe operation in this harsh
- environment. At least one aircraft engine manufacture,
namely the assignee of the subject invention, additionally
requires that the fuel system must be capable of carrying
any fuel leakage overboard in the event a fitting or a
10 line in a primary flowpath should fail.
:. SUMMARY OF T~IE INVENTION
_ _ _
It is, therefore, an object of the present invention
to provide a fuel-supply system that is capable of safe
operation in the high-temperature environment surrounding
15 a gas turbine engine combustor.
It is another object of the present invention to
provide a gas turbine fuel-supply system that features
a primary and a secondary fuel flowpath for the purpose
-i of carrying any leakage fuel overboard in the event of
20 a failure in a part of the primary fuel flowpath.
It is another object of the present invention to
provide a gas turbine fuel-supply system of a simply,
functional construction with a minimum of parts that
might cause problems in the high temperature environment
25 of the region surrounding the engine combustor.
These and other objects are accomplished by the
present invention that features a unique fuel manifold
circumventing a combustor section of a gas turbine engine.
The fuel manifold comprises a plurality of manifold
30 segments that interconnect a plurality of fuel injector
base sections to form an integral fuel manifold assembly.
The mainfold construction provides a primary fuel flow-
path enclosed within a plurality of walls. In one
embodiment the primary flowpath is formed within an
35 inner flexible tubular wall and is surrounded by a
~ 3 7~8~'1
-- 3 --
- secondary fuel flowpath within a concentric/ outer
tubular wall. This double-walled feature thereby provides
flame and thermal protection to the primary fuel flow-
path and, additionally, provides a means of collecting
any possible leakage fuel for the purpose of carrying
it overboard.
To accommodate thermal expansion and contraction,
the manifold segment outer walls have telescoping
sleeves. The sleeves slide in a telescoping fashion
during temperature variations. The manifold segment
inner walls slideably interconnect with machined passages
through base sections of the injectors. The slideable
interconnection accommodates thermal effects and
any tolerance stackup with a male-female interaction.
When fully assembled these parts connect together
to form an integral double-walled fuel manifold assembly.
DESCRIPTION OF THE DRAWINGS
_ _ _
The present invention will become more clearly
understood by reference to the appended specification in
conjunction with the drawings wherein:
FIGURE 1 depicts a cross-sectional view of a typical
gas turbine engine;
FIGURE 2 depicts a perspective view of a prior art
fuel-supply system;
FIGURE 3 depicts a perspective view of a partially
disassembled fuel-supply system in one embodiment of the
present invention;
FIGURE 4 depicts a cross-sectional view of a fuel
manifold segment that forms a part of the present invention;
FIGURE 5 depicts a view, partly in cross-section and
partly broken away, of a fuel injector that forms a part
of the present invention;
FIGURE 6 depicts a cross-sectional view of a fuel-
supply tube and a portion of a fuel manifold segment of
the present invention~
11 J 7û84-~1
-- 4
Referring now to FIGURE 1, a typical gas turbine
engine 10 is illustrated in a manner that shows where
basic engine components are located in relation to each
other. Starting at an upstream end of the engine 10,
outside air flows into the engine at an engine intake
12. This air i5 initially compressed and accelerated
by an engine fan 14. The air then enters a compressor
section 16 where the air is further compressed to the
point where it can fully support the combustive process.
Combustion actually occurs in a combustor 18. The
compressed air is derived from the compressor 16, mixed
with fuel and directed into the combustor 18 by a fuel
injector 20. The air-fuel mixture is continuously
ignited and burned inside the combustor 18 to form high-
pressure, high-temperature combustion gases that provide
a source of energy to the engine 10.
- In order to make use of that source of energy, the
combustion gases are directed at a high velocity into
a turbine section 22 where the gases drive a rotatable
turbine rotor 24. The turbine rotor 24, in turn, provides
power to a turbine shaft 25 which can then be utilized
to direct mechanical energy to whatever end use is
desired. Ultimately the shaft 25 might be used to power
an airplane propeller, a helicopter blade, a fan providing
forward thrust, or for any of a number of other useful
purposes.
One of the problems inherent in the operation of a
gas turbine engine is the effect of high temperatures
that are developed in the region of combustion. These
high temperatures put a tremendous thermal strain on
engine components which must structurally accommodate
the effects of thermal expansion and contraction. Even
more importantly, safety hazards caused by high
temperatures must be fully considered by the engine
designers. Fuel leakage considerations become important
in the area surrounding the combustor 18 where the fuel
~ ~ 7~
- 5 -
must be directed by a fuel system 26 in a safe and
reliable manner. In a typical gas turbine engine, the
fuel system 26 must be capable of withstanding temperatures
in excess of 800F (426.67C) that commonly exist around
a combustor outer casing 28.
Referring now to Figure 2, a prior art fuel-supply
system 30 is shown that might be used on an engine such
as that shown in Figure 1. This system is comprised of
a fuel-supply tube 32 and a fuel manifold 34. Typically,
the manifold 34 is extended around the engine's
combustor outer casing to supply fuel to a plurality
of fuel injectors 20. The injectors then direct the
fuel into the combustor for supporting the combustion
process.
Referring now to Figure 3, a fuel system that
comprises one embodiment of the present invention is
shown in a partially disassembled form.
Again this fuel system 26 might be used on a typical
gas turbine engine such as that shown in Figure 1. The
system 26 includes a fuel-supply tube 32 that supplies
fuel to a fuel manifold 34. The mainfold 34 circumvents
combustor outer casing (not shown in Figure 3) and
supplies fuel to each of a plurality of fuel injectors
20.
A unique feature of the applicants' fuel system is
that the manifold 34 is comprised of a construction
that provides a plurality of walls enclosing a primary
fuel flowpath. This is made possible by using double-
walled manifold segments 36 that interconnect the fuel
injectors 20 that are machined with dual fuel flowpaths
to form an integral double-walled fuel manifold
assembly. With this form of construction, the manifold
provides a primary fuel flowpath inside an inner wall
38 in the form of a hose and a secondary fuel flowpath
between the inner wall 38 and an outer wall 40. In
Figure 3, an inner wall 38 and outer wall 40 of one complete
`~ ~ 1 7Q8~
-- 6 --
manifold segment are shown next to the partially dis-
assembled fuel manifold 34.
The second flowpath is provided for directing any
leakage fuel that escapes the primary flowpath to the
fuel supply tube 32 from which the fuel leakage is
drained overboard of the engine. The outer wall 40
also provides a thermal insulator and fire shield for
the protection of the primary flowpath. In alternate
embodiments, additional fuel flowpaths might be provided.
Referring now to Figure 4, a complete manifold
segment 36 and a base section 42 of an injector 20
are shown. In this Figure, the double-walled form of
construction of the manifold can be readily appreciated.
In the embodiment shown, the outer wall 40 is comprised
of two or more telescoping sleeves 44 and 48. Where the
sleeves are concentric, a groove 46 is formed in an inner
sleeve 48 and an O-ring 50 is inserted in the groove to
provide a slideable interconnection between the inner
sleeve and an outer sleeve 44 in a manner that seals
where the sleeves overlap. This slideable interconnection
between the sleeves permits the segment 36 to expand and
contract with a telescoping action. The assembly thereby
inherently accommodates physical displacement at the
assembly interconnections. The sleeves are also sealed with
O-rings 50 provided in detents 51 at the connections with
the injector bases 42 as a means of mechanical attachment
and fluid sealing.
In one embodiment of the invention, the inner wall 38
is a part of polytetrafluoroethy~ene (sold under the trade
mark TEFLON) hose assembly 52. As an additicnal barrier, the
hose assembly 52 can be encased in a firesleeve 53. At one
end of the hose assemb~y 52, a fluid mechanical connector 54
is used to connect the assembly 52 to the injector base 42.
At the other end, the assembly 52 is inserted into the fuel in-
jector base ~ fo~m a male-female interconnection with a double
O-ring seal 56. The male-female interconnection permits
f~
1~7~8~1
-- 7
the hose assembly 52 to slide within the injector base
to accommodate thermal growth and mechanical tolerances.
Referring now to Figure 5, a fuel injector 20 is
shown in one embodiment that is utilized in the present
invention. As in the case of the double-walled manifold
segments 36, the injector base 42 is provided with
both a primary and a secondary fuel flowpath. The
primary path is an inner passage 58 through the base 42,
with openings at either end that are in flow com-
munication with the primary flowpath of the adjoiningsegments 36. The secondary fuel flowpath is an outer
passage 60 that is in flow communication with the
secondary flowpath in each adjoining segment. With
this unique interconnection between the segments 36
and the injectors 20, the fuel manifold assembly is
provided with a double-walled construction that includes
complete primary and secondary fuel flowpaths.
Inside the injector, a fuel flow passage 62 is
extended through a full length of the injector body
to an injector spray tip 64. The fuel is sprayed out
of the injector tip 64 into the engine combustor to
supply the combustion process.
Referring now to Figure 6, a portion of the fuel-
supply tube 32 is shown where it intersects a manifold
segment 36. Again, as in the case of the fuel manifold,
a double-walled construction is used to provide a
primary and secondary fuel flowpath. The primary flow-
path 66 of the supply tube 32 is in direct flow com-
munication with the primary flowpath of the injector
base 42, and similarly, the secondary flowpath 68 of the
supply tube is in direct flow communication with the
secondary flowpath of the injector base 42. This permits
leakage fuel to be drained away from the fuel manifold
through a drain fitting 69.
It will become obvious to one skilled in the art
1~7~8~
-- 8 ~
that several changes and variations can be made to the
above-described invention without departing from the
broad inventive concepts thereof. It is intended that
the appended claims cover these and all other variations
in the present invention's broader inventive concepts.
