Fuel distribution valve for a combustion chamber

A fuel distribution valve 16 for a gas turbine engine is disclosed. Various construction details are developed which improve the ability of the combustion chamber 12 to avoid blowouts of the combustion chamber. In one particular embodiment, the fuel distribution valve has ports 38 for controlling the fuel flow to fuel nozzles 14 in the combustion chamber. The ports provide equal flow area at high engine power, high aircraft Mach number (greater than 0.8M) operation while providing unequal flow areas at certain preselected low power operative conditions of the engine which follow the high power operative condition.

TECHNICAL FIELD 
This invention relates to axial flow rotary machines which have an annular 
combustion chamber, a plurality of fuel nozzles disposed in the annular 
combustion chamber and a fuel distribution valve for distributing fuel to 
the nozzles. This invention has application to other fields in which 
combustion chambers having multiple fuel nozzles are employed. 
BACKGROUND ART 
One example of an axial flow rotary machine using an annular combustion 
chamber is a gas turbine engine for powering an aircraft. A flow path for 
working medium gases, typically air, extends axially through a compression 
section, a combustion section and a turbine section. The combustion 
section includes a combustion chamber. A plurality of nozzles are disposed 
in the combustion chamber for spraying fuel into the working medium flow 
path. The fuel is ignited and burned with oxygen in the working medium 
gases to add energy to the working medium gases. 
The fuel system typically includes a source of pressurized fuel, such as 
fuel supplied from a fuel tank via a fuel control. The fuel control is 
responsive to power settings of the engine to vary the flow rate of fuel 
to the engine. A fuel distribution valve receives fuel from the fuel 
control and distributes the fuel via manifolds to the fuel nozzles in the 
combustion chamber. One example of such a fuel distribution valve is the 
fuel distribution valve used in the PW-4000 engine manufactured by the 
Pratt and Whitney Group, an operating unit of the Assignee of this 
invention. The fuel distribution valve for the PW-4000 engine includes a 
casing having a plurality of ports extending through the casing and a 
piston movable with respect to the ports for uncovering more or less area 
of the port in response to the flow rate of fuel. 
Each port has the same amount of flow area for a given location of the 
piston to distribute an equal amount of fuel to the fuel nozzles in the 
combustion chamber. This provides uniform combustion within the combustion 
chamber and avoids localized high temperature regions in the chamber. 
These high temperature regions could cause overheating of components of 
the engine such as the turbine, which are downstream of the combustion 
chamber. 
One of the problems encountered during operation of a gas turbine engine is 
that, at low fuel flow, the burning gases in the combustion chamber may 
blow out either as a result of high velocities of the working medium gases 
(primarily air) in the annular combustion chamber, low pressures or 
temperatures in the combustion chamber, a lean fuel/air ratio or 
combinations of these conditions which are aggravated by transient 
operation of the engine. As will be realized, a blowout of the combustion 
chamber will result in a loss of power from the engine and is a condition 
to be avoided. 
Accordingly, scientists and engineers working under the direction of 
Applicants' Assignee have sought to improve the ability of the fuel supply 
system to resist a blowout of the combustion chamber during operative 
conditions of the engine. 
DISCLOSURE OF INVENTION 
This invention is in part predicated on the recognition that as the gas 
turbine engine is decelerated from a higher power condition, such as 
cruise power, to a lower power condition, such as an idle descent power, a 
momentary underfueling of the combustion chamber may take place. The 
underfueling of the combustion chamber occurs because the fuel flow to the 
combustion chamber decreases at a faster rate than the airflow through the 
combustion chamber. The condition is aggravated by reduced pressures in 
the combustion chamber. Thus, the transient mismatch in fuel and air flow 
rates may result in a fuel/air ratio in the combustion chamber that is too 
lean to support combustion. 
According to the present invention, a fuel distribution valve for providing 
fuel to a plurality of fuel nozzles in a combustion chamber includes a 
plurality of ports uncovered by a piston, at least one of the ports having 
a larger flow area than the remainder of the ports to provide a fuel rich 
region of the combustion chamber which acts as a pilot light to the 
combustion chamber. 
In accordance with one particular embodiment of the present invention, the 
flow areas of the ports are equal at operative powers of the engine at 
which blowout is not considered a problem, such as sea level takeoff or 
other higher power operative conditions of the engine. 
A method of operating the engine includes the steps of flowing fuel through 
a fuel distribution valve having ports sized such that at least one port 
provides increased flow in comparison to the fuel flow through the 
remaining ports to provide a fuel rich region of the combustion chamber at 
low power operative conditions of the engine. 
A primary feature of the present invention is a fuel distribution valve 
having an inlet passage and a plurality of outlet passages. The valve 
includes a wall having a plurality of ports. Each port places the inlet 
passage in flow communication with an associated outlet passage. A piston 
is slidable with respect to the wall to uncover each port from one end of 
the port to the piston to vary the flow area of the port. The plurality of 
ports includes at least one port which has an increased flow area in 
comparison to the flow area of other ports at the same piston position. In 
accordance with one embodiment of the present invention, the port having 
an increased flow area at the first piston position has a reduced flow 
area between the first piston position and a second piston position such 
that the total flow area of the first port is equal to the flow area of 
the remaining ports. 
A primary advantage of the present invention is the ability of the 
combustion chamber to sustain combustion under operative conditions of the 
engine which may cause blowout of the combustion chamber. This results 
from having two different local fuel/air ratios in the combustion chamber 
with the fuel rich region providing pilot light to the fuel lean regions 
of the combustion chamber. Another advantage of one embodiment of the 
present invention is the efficiency of the engine which results from 
equalizing the flow areas of all ports at high power operative conditions 
of the engine while providing acceptably lean fuel/air ratios at low power 
operation. Still another advantage is the ability to provide local 
fuel/air ratios which may be tailored over the production life of a series 
of engines by simply changing the port configuration in the fuel 
distribution nozzle. 
The foregoing features and advantages of the present invention will become 
more apparent in light of the following detailed description of the best 
mode of carrying out the invention and the accompanying drawing.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 is a view of a portion of the combustion section 10 of a gas turbine 
engine embodiment of the present invention. The view is partly in 
schematic showing a combustion chamber 12 for a gas turbine engine and a 
plurality of fuel nozzles 14 disposed in the combustion chamber. 
As shown in a cross-sectional view which is partly broken away, the 
combustion section 10 of the engine also includes a fuel distribution 
valve 16. The fuel distribution valve includes a housing 18 having a 
chamber 22 disposed about an axis R and an inlet passage 24. The inlet 
passage is connected via a fuel supply line 26 to a fuel control (not 
shown). 
The housing 18 has a plurality of outlet passages, as represented by the 
passages 28a, 28b, which are in flow communication via the chamber 22 with 
the inlet passage 24. Each outlet passage is connected via a manifold, as 
represented by the manifold 32, to a pair of fuel nozzles 14. 
The fuel distribution valve 16 includes a cylindrical casing or sleeve 34 
disposed in the chamber 22 of the housing. The cylindrical sleeve extends 
about the axis R of the housing. The cylindrical sleeve has a wall 36 
having a plurality of ports 38 extending through the wall. The sleeve has 
an inlet passage 42 in flow communication with the inlet passage 24 of the 
housing. Each port places an associated outlet passage 28 in the housing 
in flow communication with the inlet passage. 
The fuel distribution valve includes a piston 44 disposed in the sleeve. 
The piston is slidable in a direction, such as the axial direction, with 
respect to the sleeve wall 36 and to the ports 38. The piston has a 
circumferentially extending wall 46 and an end 48 which bound a chamber 52 
on the interior of the piston. The end has a first reaction face 54 which 
adapts the piston to receive a pressure force from pressurized fuel on the 
interior of the sleeve in the inlet passage. 
The piston 44 has a second or opposing reaction face 56 which bounds the 
chamber 52 in the piston. A path 58 for fuel extends from the outlet 
passage 28 to the piston chamber 52 to provide a reference pressure to the 
chamber. The path extends from the outlet passage to a circumferential 
drain hole 62 in the sleeve. The drain hole is connected via an axial slot 
64 in the sleeve to a hole 66 in the piston which extends to the chamber 
within the piston. A spring 68 is also disposed between the second 
reaction face and the housing to exert a spring force on the piston. 
A seal groove 72 and a seal 74 extend circumferentially about ports 38 
which do not supply the reference pressure fuel to the piston chamber. The 
seal extends between the sleeve 34 and the housing 18 to block fluid 
communication between the ports. The seal also channels flow to drain 
holes 62 adjacent to five of the ports. 
As shown by the broken line in FIG. 1, the piston 44 has a first position 
P.sub.1 with respect to the wall 36 of the sleeve at which the wall 46 of 
the piston entirely covers the ports 38, interrupting flow from the inlet 
42 of the sleeve through the ports to the outlet chambers 28. In the 
closed position, a drain groove 76, which extends circumferentially in the 
wall of the piston, is aligned with drain holes 62 at all but two of the 
ports. The drain holes in the sleeve allow the manifolds 32 at engine 
shutdown to drain from the top manifolds to the bottom manifolds via a 
corresponding hole 78 in the walls of the piston and the chamber. Two of 
the ports do not have associated drain holes so that the manifolds remain 
full of fuel to provide a sequential lighting of the combustion chamber as 
the other manifolds fill during ignition. 
As shown in FIG. 1 in full, the piston 44 has a second position P.sub.2 
with respect to the wall 36 of the sleeve 34 at which a plurality of the 
ports 38 are uncovered to the maximum extent of uncoverage in the axial 
direction, that is, the direction of relative movement between the piston 
and the sleeve. The ports could extend beyond the piston and be blocked by 
the piston at position P.sub.2. Thus, the maximum extent of uncoverage 
would be less than the full length of the port. A retrofitted piston 44 or 
spring 68 would then alter the position of the piston, permitting 
increased flow area through the port without changing the sleeve. 
As will be realized, in alternate constructions the piston 44 might be 
fixed and the sleeve 34 slidable with respect to the piston or the piston 
might be disposed circumferentially about the sleeve. 
FIG. 2 is a cross-sectional view of the sleeve 34 shown in FIG. 1 showing 
the relationship of the drain holes 62 through the sleeve to the ports 38 
in the sleeve. An opening 80 extends from each port to the associated 
outlet passage. The seal groove 72 extends circumferentially about the 
exterior of the sleeve and, as shown in FIG. 3, extends axially along the 
sleeve. 
FIG. 3 is a cross-sectional view taken along the line 3--3 of FIG. 2 
showing the ports 38 and the associated opening 80 through the sleeve 36 
which places the ports in flow communication with the outlet passage 28. 
As mentioned, the seal groove 72 for receiving the seal 74 extends about 
all but one of the ports to block fluid communication between the ports. 
The remaining port has no seal and provides the flow via the path 58 to 
the interior chamber 52 of the piston to provide the reference pressure to 
the piston. 
FIG. 4 is a developed view of the sleeve 36 shown in FIG. 3 showing the 
relationship of the seal to the ports 38 and drain holes 62 and the 
relationship of the ports to each other. The plurality of ports includes 
at least one first port 38a. The remainder of the plurality of ports forms 
a group of second ports 38b. Each second port has a substantially 
rectangular shape having a length L.sub.r and a width W.sub.r. Each first 
port has a width which varies over the length of the port as is shown in 
FIG. 5. 
FIG. 5 is a partly schematic enlarged view of the first port 38a. The first 
port is superimposed over one of the second ports 38b which is shown by 
dotted lines. Both the first and second ports have an overall length 
L.sub.r. The second port has a width W.sub.r which is unvarying over the 
length of the port. 
The first port 38a has a width W.sub.1 over a first length L.sub.1 which is 
greater than the width W.sub.r. As a result, the first port has a greater 
flow area with the piston at the third position (shown by the phantom line 
marked P.sub.3). The first port has a width W.sub.2 which is smaller than 
the width W.sub.r over a second length L.sub.2 such that the area of the 
first port over the length L.sub.1 and L.sub.2 is approximately equal to 
the area of the second port over the length L.sub.1 and L.sub.2. As shown, 
the areas of port 38b are rectangular but they could be of other shapes. 
The areas are approximately equal if the flow through the first port and 
the second port (with the piston at position P.sub.4 where it uncovers the 
lengths L.sub.1 and L.sub.2) are within one percent of the average total 
flow through the ports at the maximum flow condition. As a result, with 
the piston at position P.sub.4, the flow through the first port and the 
flow through the second port should be equal and the flow should be equal 
for any piston position between position P.sub.4 and position P.sub.2. 
During operation of the gas turbine engine, the pressure and volume of the 
flow of fuel to the fuel distribution valve 16 at a high powered 
condition, such as occurs at certain cruise conditions and sea level 
takeoff, forces the piston to position P.sub.2. At position P.sub.2, the 
ports are uncovered to their maximum extent to allow equal fuel flow to 
all fuel nozzles 14 of the engine. As fuel flow is decreased to a lower, 
preselected level, the pressure acting on the face 54 of the piston 
decreases causing the piston 44 to move to position P.sub.4 at which the 
fuel flow is still equal by reason of the equalized areas of the first 
port 38a and the second ports 38b. As the piston moves into the idle power 
region, such as might occur during descent of the aircraft from cruise 
altitude, the piston moves to position P.sub.3 at which fuel flow through 
the first port is greater than fuel flow to each of the second ports. 
As shown in FIG. 7, the fuel flow through this port is approximately 
fourteen (14) percent of the average total fuel flow through the port in 
comparison to the fuel flow through each of the remaining ports which is 
approximately ten (10) percent of the average total fuel flow through the 
ports. This causes the region of the combustion chamber near the fuel 
nozzles supplied by the first port to run at a much richer local fuel/air 
ratio than the regions of the nozzle supplied by the second ports which 
run at a leaner fuel/air ratio. This results in two different local 
fuel/air ratios with each of the fuel/air ratios interacting on the 
transient velocities, pressures, temperatures, and other conditions of the 
combustion chamber. The richer fuel/air ratio region provides a pilot 
light to maintain combustion in the combustion chamber and avoid blowouts 
should a blowout occur in the other regions of the combustion chamber by 
reason of the fuel/air ratio being too lean. The flight regime where the 
combustion chamber is most vulnerable to blowouts is generally where the 
aircraft is in a decelerating operative condition from high Mach number, 
low altitude operation. Thus, the ability of the fuel system to avoid a 
blowout in the burner is enhanced during unusual transient conditions 
while still permitting the fuel system to operate in an economically and 
environmentally sound manner. 
As the piston moves from position P.sub.3 to P.sub.4, the port is 
configured to protect the turbine against high temperature associated with 
local maximum fuel/air ratios as the enriched fuel/air ratio is phased out 
with increased power of the aircraft. 
As will be realized, it is a relatively simple matter to adjust the 
fuel/air ratios of the regions of a combustion chamber in a single engine 
by changing the sleeve of the fuel distributor valve to retrofit a 
customized port configuration over the life of the engine. For example, as 
different engines are produced in a model of a particular engine series 
and changes are made to the newer model engines in the series, it is 
relatively easy in these different engines to tailor the flow of fuel to 
different regions of the combustion chamber to accommodate minor design 
and performance changes in the engines. 
Although the invention has been shown and described with respect to detail 
embodiments thereof, it should be understood by those skilled in the art 
that various changes in form and detail thereof, may be made without 
departing from the spirit and the scope of the claimed invention.