Turbine engine with combustor premix system

A turbine engine having a combustor premix system for mixing fuel and air to provide increased efficiency by reducing temperature peaks in the combustor. The system includes a primary mixing chamber for mixing compressed air and atomized fuel and a secondary mixing chamber located between the primary mixing chamber and the combustor for mixing additional compressed air to the fuel-air mixture. The secondary mixing chamber comprises a plurality of tubes with air metering ports in the walls thereof and a control assembly to vary the air flow to the ports for off design engine operating conditions, and optimizes fuel-air mixtures for the combustor at all engine operating speeds improving fuel economy and exhaust pollution control. The primary mixing chamber is located adjacent to and between the compressor for the air and the combustor so that the fuel-air mixture flowing therethrough tends to cool the compressor and the chamber itself shields the compressor from radiant heat from the combustor.

FIELD OF THE INVENTION 
The invention relates to a premix system for mixing fuel and air before 
entering the combustor of a turbine engine. The system includes a primary 
mixing chamber and a secondary mixing chamber, the latter comprising a 
plurality of tubes exiting into the combustor with each tube having a 
plurality of metering ports in the sides to allow compressed air to flow 
into the tubes. The primary mixing chamber is located adjacent to and 
between the air compressor and the combustor to shield the compressor. 
BACKGROUND OF THE INVENTION 
In a typical turbine engine, air is compressed, then mixed with a fuel, and 
the resulting mixture is ignited in a combustor so that the expanding 
gases of combustion can rapidly move across and thus rotate turbine 
blades. The fuel can be liquid or gaseous and the turbine can be an axial 
flow or a radial in-flow type. Such turbine engines can be used for 
industrial power or moving an airplane or ground vehicle. Variable or 
fixed turbine vanes direct the expanding gases from the combustor to the 
rotatable turbine blades. 
While various types of turbine engine designs have been used in the prior 
art, there are numerous disadvantages and great need for improvement. 
Thus, many of the prior art turbine engines have combustors that 
experience temperature peaks, also known as hot spots, which reduce the 
fuel efficiency of the engine by requiring additional cooling air for 
cooling of the turbine vanes. This is usually a result of the nozzle 
design which sprays a fuel and air mixture into the combustor for 
ignition. In addition, many of these prior art turbine engines operate at 
very high temperatures, requiring high strength and high 
temperature-resistant alloys which are very expensive. Moreover, many of 
these turbine engines require a very long combustor which increases the 
materials and costs for the engine. Finally, many of these prior art 
turbine engines require (but do not optimize) the variation of the mixing 
of fuel and air depending upon the power requirements of the engine which 
differ during off design engine operation at low power, high power, and 
starting. 
Examples of such prior art turbine engines are disclosed in the following 
U.S. Pat. Nos. 2,471,892 issued to Price; 2,946,185 issued to Bayer; 
4,005,572 issued to Giffhorn; 4,100,733 issued to Striebel et al; and 
4,195,476 issued to Wood. 
SUMMARY OF THE INVENTION 
Accordingly, a primary object of the present invention is to provide a 
turbine engine with improved fuel efficiency throughout the engine 
operating range and a homogenous flame front in the combustor to limit the 
amount of air required to cool the turbine vanes and to reduce temperature 
peaks in the combustor. 
Another object of the present invention is to provide a turbine engine with 
a combustor premix system eliminating the use of inefficient nozzles. 
Another object of the present invention is to provide a turbine engine with 
a shielding assembly between the combustor and the compressor so that 
lower strength and lower temperature-resistant alloys can be utilized 
within the aft compressor section. 
Another object of the present invention is to provide an external primary 
mixing chamber for fuel and air adjacent to or incorporated into the 
combustor which utilizes the heat therefrom to vaporize the fuel and a 
secondary mixing chamber adjacent the combustor, all resulting in a 
shorter combustor in the turbine engine. 
A further object of the present invention is to provide a combustor premix 
system which is capable of mixing optimized vaporized fuel and air through 
high and low power requirements of the turbine engine and also during 
starting thereof. 
The foregoing objects are basically attained by providing in a turbine 
engine including a housing having rotatable turbine blades supported 
therein and a combustion chamber communicating with the turbine blades, 
the improvement which comprises a primary mixing chamber located in the 
housing for mixing compressed air and atomized fuel; a mechanism for 
introducing compressed air into the primary mixing chamber; a mechanism 
for introducing atomized fuel into the primary mixing chamber; a secondary 
mixing chamber, located in the housing between the primary mixing chamber 
and the combustion chamber, for receiving the compressed air and atomized 
fuel from the primary mixing chamber, the secondary mixing chamber 
comprising a plurality of tubes for conducting the fuel-air mixture into 
the combustion chamber; and a mechanism for introducing additional 
compressed air into the secondary mixing chamber to mix with the fuel-air 
mixture therein, this mechanism for introducing additional compressed air 
comprising a plurality of ports in the walls of each of the tubes. This 
mechanism also includes a metering plate to control air supply to the 
tubes for off-design operating conditions. 
By utilizing the secondary mixing chamber, inefficient nozzles are 
eliminated from the combustor and the fuel and air are continuously mixed 
in an efficient manner to reduce hot spots in the combustor by providing a 
homogenous flame front. In addition, this results in a smaller volume of 
cooling air passing across the turbine vanes and enhances the potential 
energy of the engine by increasing the working mainstream mass airflow. 
Moreover, the secondary mixing chamber can be utilized during all of the 
power requirements of the turbine. 
In addition, a shielding assembly is interposed between the compressor and 
the combustor to reduce the need for high strength and high temperature 
resistant alloys in construction of the compressor, this assembly being 
formed by the primary mixing chamber. 
Other objects, advantages and salient features of the present invention 
will become apparent from the following detailed description, which, taken 
in conjunction with the annexed drawings, discloses a preferred embodiment 
of the present invention.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. 1-4, the turbine engine 10 in accordance with the 
present invention comprises a housing 12 having an air inlet 14 and an 
exhaust 15, a shaft 17 rotatably mounted inside the housing 12 and having 
a compressor with compressor blades 18 and turbine blades 19 thereon, a 
combustor 20 located inside the housing and communicating with the turbine 
blades 19, a primary mixing chamber 22 located inside the housing, and a 
secondary mixing chamber 24 located between the primary mixing chamber and 
the combustor. 
The basic purpose of the invention is to provide an efficient mixing of air 
and fuel to be burned in the combustor 20. This is generally accomplished 
by having atomized fuel introduced into the primary mixing chamber 22 
together with compressed air from the compressor blades 18 and diffuser 36 
and conducting this mixture to the secondary mixing chamber 24 where 
additional compressed air is added to the mixture, and this resultant 
mixture is introduced into the combustor 20 where it is ignited by ignitor 
26. The secondary mixing chamber 24 replaces conventional nozzles and 
includes a plurality of cylindrical tubes 28 having a plurality of 
cylindrical air metering ports 30 extending transversely through the walls 
of each tube. The fuel-air mixture from the primary mixing chamber flows 
through the tubes 28, and additional compressed air from the compressor 
blades is mixed with the mixture in the tubes via the metering ports 30, 
as more clearly seen in FIG. 3. 
THE HOUSING 
As best seen in FIG. 1, the housing 12 has the air inlet 14 defined in its 
forward end by means of an annular cowling 32 and at its aft end has the 
exhaust 15 defined by an annular external exhaust tube 34 and an internal 
annular wall 35. Tube 34 and wall 35 define an annular exhaust passageway 
for the ignited and burned fuel to exit the engine. 
An annular diffuser 36 is formed aft of the annular cowling 32 and includes 
a front annular wall 38 formed as part of the cowling 32 and an annular 
rear wall 39 spaced from the front wall to define a flow path of air from 
the compressor blades 18, this flow path being interrupted by a plurality 
of diffuser blades 40 and 41. Diffuser blades 41 are radially oriented and 
adjacent the exhaust tip of the compressor blades while diffuser blades 40 
are horizontally oriented and adjacent the wall of housing 12. 
THE SHAFT 
The shaft 17 is rotatably mounted in a conventional manner inside the 
housing 12 with the compressor blades 18 at the forward end and the 
turbine blades 19 at the aft end. The shaft has a flow cavity 43 defined 
therein which is connected to a fuel line 44 which is in turn connected to 
a fuel supply. Flow cavity 43 extends longitudinally of the shaft for a 
certain distance and then extends radially ending in a plurality of fuel 
ports 45 to deliver atomized fuel into the primary mixing chamber 22 by 
means of rotation of the shaft. The fuel can be supplied at low pressures 
of approximately 5 to 15 psi from the fuel line 44. 
A pair of air buffer seals 48 and 49 in the form of annular flanges 
extending rearwardly of the housing are formed on the shaft 17 which mate 
with similar annular buffer seal flanges 51 and 52 formed on the forward 
side of the primary mixing chamber 22. 
THE COMBUSTOR 
The combustor 20 located inside the housing 12 is annular and is defined on 
its forward and inboard sides by means of a curved annular wall 54, on its 
outboard side by the annular secondary mixing chamber 24, and on its aft 
side by means of a curved annular wall 55 and turbine exit nozzle vanes 57 
formed in an annular array. These nozzle vanes can be formed integrally on 
their outboard surfaces with an annular curved wall 58 and on their 
inboard surfaces with a curved annular wall 59. As seen in FIG. 2, wall 58 
has slots 60 formed therein and extending into each of the vanes 57 to 
provide cooling air thereto. 
The conventional ignitor 26 extends through the outer housing 12 and into 
the combustor 20 through a suitable aperture in wall 55. 
As best seen in FIG. 2, a plurality of dilution orifices 62 are formed in 
walls 54 and 55 defining the combustor 20 to allow additional compressed 
air to enter the combustor in a conventional manner. Additional cooling 
orifices 63 are similarly provided in these walls. 
Thus, the walls 54 and 55 together with exhaust nozzle vanes 57 and the 
secondary mixing chamber 24 define a combustion chamber for igniting and 
burning a fuel-air mixture in the combustor 20. 
THE PRIMARY MIXING CHAMBER 
The primary mixing chamber comprises a forward curved annular wall 65 and a 
corresponding rear curved annular wall 66, both of which extend generally 
radially of the engine. As seen in FIG. 1, wall 66 is curved at its 
largest radial position towards the aft end of the housing into contact 
with the secondary mixing chamber 24. The forward wall 65 is also curved 
at its largest radial position and extends rearwardly into contact with 
the forward end of the secondary mixing chamber 24, these walls 65 and 66 
thereby forming a radially and axially extending flow passage beginning 
adjacent the fuel ports 45 on shaft 17 and extending to and communicating 
with the secondary mixing chamber 24. 
Wall 65 has a forwardly and radially extending flange 67 on its forward 
side in contact with wall 39 of the diffuser 36 as a support. 
On the forward edge of wall 65 are the pair of buffer seal flanges 51 and 
52 which mate with air buffer seals 48 and 49 on shaft 17. 
As seen in FIGS. 1 and 2, the forward and rear walls 65 and 66 of the 
primary mixing chamber are separated and their inboard edges are located 
adjacent the plurality of fuel ports 45 so that fuel exiting thereby can 
enter the primary mixing chamber. 
Radially outward of the shaft 17 are a plurality of transfer tubes 68 which 
extend between walls 65 and 66 of the primary mixing chamber and are 
coaxial with a plurality of corresponding air ports 69 and 70 located 
respectively in walls 65 and 66. 
Extending in the aft direction from the innermost edge of wall 66 is an 
annular air buffer seal 71 lying adjacent shaft 17 with a plurality of air 
ports 72 formed therein, the longitudinal axes of these ports extending in 
the radial direction of the engine. 
As seen in FIG. 2, walls 65 and 66 have a series of U-shaped radial slots 
73 formed in their outer peripheries with U-shaped webs 74 interconnecting 
the walls in the peripheries of the slots. These slots form flow-through 
passageways for compressed air exiting the diffuser 36. 
The primary mixing chamber 22 is located closely adjacent to and between 
the compressor 18 and the combustor 20 so that the heat from the combustor 
vaporizes the fuel-air mixture therein and so that the fuel-air mixture, 
moving through the primary mixing chamber, tends to cool the compressor 
aft section. In addition, the primary mixing chamber shields the 
compressor aft section from radiant heat from the combustor. To increase 
vaporization, wall 66 could be eliminated, which would also cool the 
combustor and reduce the amount of cooling air to cool the combustor. 
THE HEAT SHIELD 
A convex-concave annular heat shield 75 extends radially outward from 
flange 71 in between wall 66 of the primary mixing chamber and wall 54 of 
combustor 20. This heat shield 75 is rigidly coupled at its aft end to a 
curved annular support wall 77 which is also coupled at its outboard side 
to wall 54 and at its aft side to wall 59. 
The heat shield 75 does not extend radially outward to the fullest extent 
of walls 66 and 54 but instead ends before these walls. Thus, fuel flowing 
radially outwardly in the primary mixing chamber 22 will be vaporized by 
the radiant heat from wall 54 of the combustor as that fuel passes 
radially outwardly past the radial extent of the heat shield 75. 
THE SECONDARY MIXING CHAMBER 
As seen in FIGS. 1-4, the secondary mixing chamber 24 is basically 
comprised of four annular walls 79, 80, 81 and 82 which are spaced apart 
and are concentric, with wall 79 being at the largest radial distance from 
shaft 17. Radially extending through walls 80-82 are a plurality of the 
cylindrical tubes 28 which are open at their ends so that the fuel-air 
mixture flowing from the primary mixing chamber can pass therethrough into 
the interior of combustor 20. While shown integral with walls 80-82, tubes 
28 could be threaded at their outward ends and threadedly received in 
threaded bores in wall 80 with the remainder of the tubes fitting with 
clearance in bores in walls 81 and 82. This would make the tubes easily 
removable for maintenance and increase cooling air flow through the 
clearance. 
In addition, each of these tubes 28 has a plurality of air metering ports 
30 in the walls thereof, these ports being substantially cylindrical and 
having their longitudinal axes perpendicular to the longitudinal axis of 
each tube 28. 
As best seen in FIG. 2, an aft wall 83 in the form of an annular ring 
couples walls 79 and 81 together. A forward annular wall 84 couples walls 
80 and 81 together. 
As seen in FIGS. 2 and 4, wall 83 has a plurality of orifices 86 for 
compressed air to enter into the inside of the secondary mixing chamber, 
which orifices can be aligned with orifices 87 in an annular metering 
plate 88 which can be selectively moved relative to orifices 86 to control 
and meter the amount and rate of compressed air entering the secondary 
mixing chamber, at off-design engine operating conditions. 
Wall 65 in the primary mixing chamber contacts wall 79 in the secondary 
mixing chamber and wall 66 similarly contacts wall 80. 
Between walls 79 and 80 in the area of the slots 74 in the primary mixing 
chamber are a plurality of plates 89 closing off the forward side of the 
secondary mixing chamber. 
OPERATION 
In operation of the turbine engine 10 in accordance with the present 
invention, air and fuel are first delivered to the primary mixing chamber, 
then to the secondary mixing chamber where additional air is added and 
then this resultant mixture is ignited in the combustor and expands 
through nozzle vanes 57 past turbine blades 19 and out via exhaust 15. 
The air forming the mixture (illustrated by simple arrows in the drawings) 
enters the engine via air inlet 14, is compressed by rotating compressor 
blades 18 and then passes through the diffuser 36. From there, the air 
proceeds aft of the combustor and into the combustor via dilution orifices 
62 and cooling orifices 63 and also into the secondary mixing chamber via 
orifices 87 in the metering plate and 86 in the chamber itself. In 
addition, compressed air flows from the diffuser through the various slots 
73 in the primary mixing chamber into the space between the primary mixing 
chamber and the combustor. The air therein also flows through buffer air 
ports 72 in flange 71 and then into the primary mixing chamber. Similarly, 
air flows from the area between the primary mixing chamber and the 
combustor via transfer tubes 68 in the primary mixing chamber and then 
into the primary mixing chamber itself. 
At the same time, the shaft rotates and has fuel delivered therethrough via 
fuel line 44 and flow cavity 43 so that it is expelled under centrifugal 
force via fuel ports 45 into the primary mixing chamber 22. This rotation 
of the shaft and slinging of the fuel also results in atomization of the 
fuel. The fuel is illustrated by a plurality of X's in the drawings. 
The fuel which is now atomized and the compressed air located in the 
primary mixing chamber 22 are mixed and flow radially outwardly of the 
primary mixing chamber past the heat shield 75. The mixed fuel and air is 
illustrated by arrows with X's at the tail ends in the drawings. At this 
point, the heat from the combustor will vaporize the fuel in the rich, 
non-autoignitable air-fuel mixture. This mixture then flows radially and 
then rearwardly into the tubes 28 of the secondary mixing chamber 24. 
While inside these tubes, the vaporized fuel-compressed air mixture has 
additional compressed air added thereto via air metering ports 30, this 
compressed air entering the secondary mixing chamber via the variable 
combination of orifices 86 therein and orifices 87 in the metering plate 
88. 
The resultant mixture of compressed air and vaporized fuel then exits from 
the secondary mixing chamber 24 and is ignited via ignitor 26 in the 
combustor 20. Additional compressed air is mixed with the fuel in the 
combustor via dilution orifices 62 and cooling orifices 63. The radial 
flame profile can be defined through conventional cooling air methods. 
The expanding ignited fuel flows radially inwardly and then axially 
rearwardly past the nozzle vanes 57 and across turbine blades 19, 
resulting in rotation of these blades and therefore of the shaft 17. The 
exhaust gases which pass by the blades then exit the engine via exhaust 
15. 
Thus, the secondary mixing chamber 24 takes the place of conventional 
nozzles in a combustor and provides combustion with a minimum of 
temperature peaks in the combustor. 
While a radial in-flow combustor is illustrated, the present invention can 
be utilized with various different types of combustors including can 
types, can annular types, scroll types, reverse flow annular types and 
axial types. Moreover, the present invention can be utilized with radial 
in-flow and axial flow turbine engines utilizing liquid or gaseous fuel 
injecting fuel into the primary mixing chamber by conventional fuel 
nozzles, radial slingers or injectors. These engines can be of the 
turbofan, turbojet or turboprop type for aircraft, can be stationary 
engines used in industrial facilities or can be used in ground vehicles. 
EMBODIMENT OF FIG. 5 
As seen in FIG. 5, a modified secondary mixing chamber is shown where the 
tubes 98 therein are the same as that shown in FIG. 3; however, the air 
metering ports 99 are different in that the longitudinal axes thereof are 
at an acute angle of, for example, about 45.degree. to the longitudinal 
axis of the tube. 
While various advantageous embodiments have been utilized to illustrate the 
present invention, it will be understood by those skilled in the art that 
various changes and modifications can be made therein without departing 
from the scope of the invention as defined in the appended claims.