Combustion section supply system having fuel and water injection for a rotary machine

A fuel supply system 32 for a rotary machine 10 is disclosed. Various construction details are developed which enable operation of a plurality of fuel injectors 28 in the machine at a low pressure drop with a wide range of fuel and water fuel rates. In one embodiment, an auxiliary water supply system supplies water at a location in close proximity to the fuel injector.

TECHNICAL FIELD 
This invention relates to a fuel supply system for a plurality of fuel 
injectors and more particularly to a system for supplying water and fuel 
to the fuel injectors to reduce emissions over a wide range of flow rates. 
Although this invention was developed in the field of axial flow, rotary 
machines, it has application to other fuel supply systems having a 
plurality of fuel injectors or fuel nozzles. 
BACKGROUND OF THE INVENTION 
An axial flow, gas turbine engine has a compression section, a combustion 
section and a turbine section. An axial flow path for working medium gases 
extends through these sections of the engine. The working medium gases are 
compressed in the compression section. The compressed gases are mixed with 
fuel in the combustion section and burned to add energy to the gases. The 
hot, pressurized gases are expanded through the turbine section where work 
is extracted from the gases. 
Examples of typical fuel supply systems which provide for fuel and water 
mixing and dividing arrangements are shown in U.S. Pat. No. 4,214,435 
entitled "Method For Reducing Nitrous Oxide Emissions Form A Gas Turbine 
Engine" issued to Campbell and U.S. Pat. No. 4,918,925 entitled "Laminar 
Flow Fuel Distribution System" issued to Tingle. 
One device for delivering fuel to the combustion section is a fuel nozzle 
or fuel injector. The fuel injector may have a relative pressure drop in 
comparison to the pressure drop of the fuel supply system which is 
relatively high. In such constructions, maldistribution of the fuel 
supplied to the plurality of fuel injectors is not a concern. 
Maldistribution is small, because the fuel supply system pressure drop is 
small in comparison to the pressure drop of the fuel injector and that 
pressure drop, which is the same for all fuel injectors, remains 
relatively constant between injectors for a given flow rate. 
Another type of fuel nozzle or fuel injector has a very relatively low 
pressure drop in comparison to the pressure drop of the fuel supply 
system. An example of such a fuel injector is shown in U.S. Pat. No. 
4,977,740 entitled "Dual Fuel Injector" issued to Thomas J. Madden, Barry 
C. Schlein, and W. Barry Wagner, which is assigned to the Assignee of this 
Application. This particular fuel injector uses both gaseous and liquid 
fuels and is designed to operate with water injection system for supplying 
water to the burning fuel to reduce the formation of nitrous oxides (NOx). 
Maldistribution problems are a particular concern in such arrangements 
because the fuel injector pressure drop is relatively small and the fuel 
supply system must operate over a wide flow range. For example, water flow 
rates which are up to one and a half (11/2) times the fuel flow rate may 
be required to control emissions. 
Large manifold pipes are necessary to accommodate the highest combined flow 
rates with reasonable pressure losses as dictated by the maximum fuel pump 
output capacity. At low flow rates, such as the engine starting condition, 
the length of time to fill the manifold pipes prior to commencing the 
starting sequences are excessively long. 
Accordingly, scientist and engineers working under the direction of 
Applicants' Assignee have sought to develop a fuel supply system which can 
accommodate a wide range of flow rates and a wide range of water-fuel 
ratios during operative conditions while minimizing maldistribution 
problems. 
DISCLOSURE OF THE INVENTION 
This invention is in part predicated on the recognition that increasing the 
water-fuel ratio as flow rates increase is desirable for emissions but may 
cause the problem of blow out of the combustion chamber if the flow rate 
is suddenly decreased, such as might occur in an emergency situation. This 
occurs because a combustible liquid having a high water-fuel ratio remains 
in the system for a short time even though the flow rate of the 
combustible liquid has been decreased. At low flow rates, the high 
water-fuel ratio may cause blow out of the flame in the combustion 
chamber. Blow outs are to be avoided because of problems associated with 
re-lighting the combustion chamber which already contains fuel from the 
blow out condition. 
According to the present invention, an axial flow rotary machine has a 
combustion section having a plurality of fuel injectors and a fuel supply 
system for the injectors, the fuel supply system including: 
1. an auxiliary mixing system having an auxiliary mixer at each fuel 
injector for supplying fuel and water to the fuel injector; 
2. a main supply system having a main mixer for fuel and water for 
supplying a combustible liquid to the auxiliary mixing system; and, 
3. an auxiliary water supply system in flow communication with the 
auxiliary mixing system which adapts the engine to supply additional 
amounts of water to the injector at preselected operative conditions of 
the machine. 
In accordance with one detailed embodiment of the present invention, the 
auxiliary water supply system includes a shunt conduit extending from a 
point upstream of the main mixer to the auxiliary mixing system to divert 
water from the main supply system via an alternate path at high water and 
fuel flow operative conditions permitting an increased flow of fuel 
through the main supply system. 
In accordance with the present invention, the fuel supply system includes a 
source of gaseous fuel in flow communication with the fuel injector, and 
the method of operating the engine includes flowing water through the main 
supply system at low flow rates and through the auxiliary water supply 
system at higher flow rates. 
According to the present invention, a method of operating an axial flow 
rotary machine includes the steps of supplying a combustible liquid 
comprising fuel and water via a main supply system at low flow operative 
conditions of the engine and, at high flow operative conditions, supplying 
a substantial portion of the water via an auxiliary water supply system 
such that the amount of water mixed with fuel in the main supply system 
will not cause blow out of the combustion chambers during transient 
conditions should the flow rate of liquid fuel and water to the combustion 
section suddenly drop. 
A primary feature of the present invention is an auxiliary mixing system 
having an auxiliary mixer at each fuel injector. In one embodiment, the 
auxiliary mixer is in close proximity to the fuel injector. Another 
feature is a main supply system having a main mixer. The main mixer is in 
flow communication with a source of fuel and a source of water. Still 
another feature of the present invention is the pressure drop 
characteristic of the main supply system and the pressure drop 
characteristic of the auxiliary water supply system. The pressure drop 
characteristics are sized to avoid maldistribution in the main supply 
system at low flow rates and maldistribution in the auxiliary water supply 
system at high flow rates. Still another feature is a device for supplying 
water to the auxiliary supply system under preselected operative 
conditions, such as a regulating valve responsive to back pressure. A 
feature is the pressure characteristic of the valve selected so that once 
the valve opens flow from the source of water will preferentially flow 
through the auxiliary system at much greater rates than through the main 
supply system and may be under some operative conditions, nearly 
nonexistent in the main supply system. In one detailed embodiment, the 
fuel supply system has a flow divider valve for dividing the flow in the 
main supply system. The fuel injector is an air atomizing injector which 
operates at low pressures at low flows and the manifolds leading from the 
fuel divider valve have equal volumes to provide a pressure characteristic 
for the lines which avoids maldistribution at low flow operating 
conditions. In one embodiment, the fuel injector is adapted to receive 
gaseous fuel from a source of supply such as a natural gas line and the 
main supply system supplies water at low flow rates and the auxiliary 
system may be used to provide additional water at high flow rates. 
A primary advantage of the present invention is the ability of the engine 
to go from high operating flow rates with a combustible liquid fuel (such 
as a mixture of hydrocarbons and water) to low operating flow rates 
without blow out of the combustion chamber which avoids the dangers 
associated with a re-light of the combustion chamber after such a blow 
out. Another advantage of the present invention is the reduced emissions 
which results from using water-fuel ratios which differ for different flow 
rates and providing a balanced supply of the combustible liquid to a 
plurality of fuel injectors over a range of flow rates which results from 
employing an auxiliary water supply in conjunction with a main supply 
system. 
The foregoing features and advantages of the present invention will become 
more apparent in light of the following detailed description of the best 
mode for carrying out the invention and in the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 is a side elevation view of an axial flow, rotary machine 10, such 
as a gas turbine engine, having a portion of the engine broken away. The 
engine has a compression section 12, a combustion section 14 and a turbine 
section 16. The turbine section includes a turbine 18 for powering the 
compression section and an associated free turbine 22 for extracting work 
from the engine for other purposes. An annular flowpath 24 for working 
medium gases extends axially through these sections of the engine. 
The combustion section 14 includes a plurality of combustion chambers 26 as 
shown or alternatively might comprise a singular annular combustion 
chamber. The combustion chamber or chambers are provided with a plurality 
of fuel injectors 28. A fuel supply system 32 is in flow communication 
with the fuel injectors. 
The fuel supply system is also in flow communication with a source of 
liquid fuel 34 via liquid fuel conduit 36 and a source of water 38 via a 
water supply conduit 42. These conduits enable the fuel supply system to 
supply a combustible liquid to the fuel injector at a first flow rate at a 
first operative condition of the engine and at a second flow rate at a 
second operative condition of the engine. The fuel supply system is also 
in flow communication with a source of gaseous fuel 44 via a gaseous fuel 
conduit 46. Thus, the fuel flowing to the fuel injector via the fuel 
supply system may be a liquid or a gas. The water flowing to the injector 
may be a liquid or a gas, such as steam. 
Steam might be provided by passing the water through a heat exchanger 48. 
The heat exchanger may be regenerately heated by the hot gases discharged 
from the gas turbine engine. The steam may be mixed with the gaseous fuel 
in conduit 46 or supplied via a separate conduit 52 as shown. 
A control means, such as an electronic fuel control 54, is responsive to 
engine power. The control means establishes the flow rate of fuel and 
water to the fuel supply system 32. The flow rate of water is a 
predetermined function of the fuel flow rate. The fuel flow rate is a 
function of power, water flow rates, exhaust gas temperature, ambient 
temperature, and other parameters. 
FIG. 2 is an enlarged view of a portion of the combustion section 14 of the 
engine shown in FIG. 1. FIG. 2 shows a portion of the combustion chamber 
26, a fuel injector 28 having a low difference in pressure across the fuel 
injector and conduits for liquid fuel and water and for gaseous fuel 46. 
The working medium flow path 24 passes from the compression section 12 into 
the combustion section 14. Each combustion chamber 26 is adapted by one or 
more openings to receive pressurized gases in the form of air from the 
working medium flow path. The fuel injector 28 is disposed in an 
associated opening in the combustion chamber to pass the pressurized gases 
(air) into the combustion chamber and to inject fuel and water into the 
air as the air is discharged into the discharge region of the injector. 
One or more igniters (not shown) extend into the combustion chamber to 
ignite the mixture of fuel and air as the air passes from the discharge 
region of the fuel injector at the start up condition of the engine. 
The fuel supply system 32 is shown in schematic fashion and includes an 
auxiliary mixing system 56 for each fuel injector 28. The auxiliary mixing 
system is in flow communication with a main supply system 58 and an 
auxiliary water supply system 62 via an auxiliary mixer (not shown). 
FIG. 3 is a schematic representation of the fuel supply system 32 for the 
gas turbine engine 10 shown in FIG. 1 and FIG. 2. The source of liquid 
fuel 34 includes a modulator valve 64 and a liquid fuel pump 66 for 
supplying liquid fuel. The source of water 38 includes a water pump 68 and 
modulator valve 72 for supplying water to the fuel supply system. The 
control means 54 is responsive to engine power and is in signal 
communication with the pump and modulator valves via lines 74, 76 to 
supply water as a function of fuel flow rate. 
The auxiliary mixing system 56 for the plurality of fuel injectors 28 
includes an auxiliary mixer 78 at each fuel injector. The auxiliary mixer 
78 is adapted to mix with water a liquid fuel or a combustible liquid 
containing a hydrocarbon fuel and water to form a combustible liquid 
having a higher water-fuel ratio. 
A first conduit 82 extends from the fuel injector 28 to the auxiliary mixer 
78. The first conduit is in flow communication with the auxiliary mixer 
and with the fuel injector at a first point A. The conduit has a hydraulic 
diameter D.sub.h and a length L which is less than fifty (50) times than 
the hydraulic diameter D.sub.h of the conduit. Thus, the volume of the 
conduit falls below a predetermined limit and limits the volume of 
combustible liquid in the first conduit at any time during the operation 
of the engine. This is especially important at high flow rates because the 
water-fuel ratio of the combustible liquid in the first conduit is high 
and may cause a blow out if the flow rate suddenly drops. This avoids a 
blow out by having the volume of each first conduit less than this 
predetermined amount and lessening the amount of time this undesirable 
high water-fuel ratio fluid flows during transient operation, such as from 
the second (high flow rate) operative condition to the first (low flow 
rate) operative condition. 
The main supply system includes a main mixer 84, a second conduit 86, a 
third conduit 88, a fourth conduit 92, a flow divider valve 94, and a 
plurality of fifth conduits 96. The main mixer is adapted by its 
construction to mix liquid fuel and water to form a combustible liquid. 
The second conduit 86 extends from the main mixer to place the main mixer 
84 in flow communication with the source of liquid fuel 34 via the fuel 
supply conduit 36. The third conduit 88 extends from the main mixer to 
place the main mixer in flow communication with the source of water 38 at 
a fourth point D via the water supply conduit 42. The fourth conduit 92 
extends downstream from the main mixer 84. The fourth conduit 92 is 
adapted to place the main mixer 84 in flow communication with the flow 
divider valve 94. The flow divider valve is downstream of the main mixer 
and is in flow communication with the main mixer through the fourth 
conduit at a second point B. 
The plurality of fifth conduits 96 extend at a third point C from the flow 
divider valve. Each fifth conduit extends to an associated auxiliary mixer 
78 of the auxiliary mixing system 56 to place the auxiliary mixer 78 in 
flow communication with the flow divider valve 94. 
The auxiliary water supply system includes a sixth conduit 98, a water 
manifold 102 and a plurality of seventh conduits 104. The sixth conduit, 
water manifold and an associated seventh conduit form a shunt system or 
conduit around the main supply system as shown in FIG. 1 and FIG. 3. 
The sixth conduit 98 is in flow communication with the source of water 38 
at a fourth point D. The sixth conduit includes a regulating valve 106 
downstream of the fourth point D. The regulating valve is in flow 
communication with the source of water and is responsive to back pressure 
such that the regulating valve opens at the second operative condition of 
the engine. Opening the regulating valve permits the flow of water via the 
regulating valve to the water manifold. The pressure flow distribution 
characteristic of the auxiliary water supply system minimizes 
maldistribution at this higher flow rate in the auxiliary water supply 
system. Maldistribution is also avoided in the main supply system through 
the continued use of the flow divider valve. 
The water manifold 102 is in flow communication with the sixth conduit 98 
at a point E downstream of the regulating valve 106. The plurality of 
seventh conduits 104 each extend from the water manifold to an associated 
auxiliary mixer 98 of the auxiliary mixing system 56. 
The volume of the main supply system 58 from the flow divider valve 94 via 
one fifth conduit 96 and the auxiliary mixing system 56 to the fuel 
injector 28 (B-A) is substantially equal to the volume from the flow 
divider valve to the fuel injectors of the other fifth conduits and 
auxiliary systems (such as B-A') to ensure the combustible liquid arrives 
at each fuel injector 28 at approximately the same time during start up of 
the axial flow rotary machine. 
The pressure-flow distribution characteristic of the main supply system 
from the flow divider valve to the fuel injector provides for 
approximately equal flow to each fuel injector for the first flow rate 
during operative conditions of the engine that are less than the second 
flow rate. 
The pressure-flow distribution characteristic of the auxiliary water supply 
system from the regulator valve of the supply system to the fuel injector 
(E-A) provides for approximately equal flow rates from the auxiliary water 
supply system to each fuel injector at the second flow rate to ensure that 
equal amounts of additional water are provided to each fuel injector. 
As shown, the water supply conduit 102, the third conduit 88 and each 
seventh conduit 104 have check valves 108 disposed in said conduit to 
permit flow only toward the fuel injector 28 in the main supply system and 
in the auxiliary supply system. 
FIG. 4 shows in more detail the auxiliary mixer 78 of the auxiliary mixing 
system 56. The auxiliary mixer includes a first chamber 112 in flow 
communication with a screen 115 for mixing the fuel and water or a 
combustible liquid and water. The first chamber is in flow communication 
with the source of fuel 34. A second chamber 114 is in flow communication 
with the water supply system via the auxiliary water supply system 62. The 
second chamber has an orifice 116 at right angles to the first chamber for 
flowing the fuel and water together into the first chamber prior to the 
mixing which takes place in the screened portion of the chamber. 
During operation of one hypothetical gas turbine engine of the type shown 
in FIG. 1, the engine is started at a fuel flow rate for example of 
approximately six hundred (600) pounds per hour of pure fuel. Upon 
ignition, the fuel rate is increased to two thousand (2000) pounds per 
hour with a mixture of approximately seven hundred (700) pounds per hour 
of water being provided via the main supply system 58. At this point, the 
regulating valve 106 to the auxiliary water supply system 62 has not 
opened. The water to fuel ratio is approximately thirty-five hundredths 
(0.35). As the fuel flow rate increases up to a limit of three thousand 
(3000) pounds per hour of fuel, the water flow rate increases and the 
water to fuel ratio may be increased. Below these fuel and water flow 
rates, the fuel supply system only uses the main supply system to deliver 
fuel and water to the fuel injectors. 
At medium power above a fuel flow rate of three thousand (3000) pounds per 
hour, the flow rates are typically in the range of five thousand to six 
thousand (5000-6000) pounds per hour. At this flow rate, the regulator 
valve 106 opens enabling a flow rate of approximately three thousand 
(3000) pounds per hour of water via the auxiliary water supply system 62. 
With this flow rate, good distribution occurs in all manifolds. Some water 
does enter the main supply system because of the pressure balance. As flow 
rates approach twelve thousand (12,000) pounds per hour of fuel, the fuel 
flows entirely through the main supply system with only trace amounts of 
water (if any) in the main supply system 58. The remainder of the water is 
supplied via the auxiliary water supply system 62 where it is mixed with 
fuel in the auxiliary mixing system. The flow rate of the water may be 
increased until the water-fuel ratio is greater than one (1.0) and 
approaches 1.3 at very high powers. 
If there is a snap deceleration for emergency reasons, such as reducing 
power to the power turbine because of reductions in load or to stop the 
generator from over-speeding, the flow rate drops dramatically to a low 
flow rate. For example, the flow rate may drop to a flow rate of seven 
hundred and fifty (750) pounds per hour. Prior to this time, for example, 
we might have had twelve thousand (12,000) pounds per hour of fuel flowing 
and fifteen thousand (15,000) pounds per hour of water. Thus, the flow 
rate through the fuel injectors into the combustion chamber suddenly 
drops. However, combustible liquid in the first conduit 82 of the 
auxiliary mixing system 56 is at a water to fuel ratio which is quite 
high. Were the engine to operate at this high water to fuel ratio for any 
length of time, the flame in the combustion chamber 26 would blow out. The 
first conduit is sized small enough so that this high water to fuel ratio 
is transient, disappearing quickly because at low flow rates only fuel is 
being flowed into the auxiliary mixing system 56 through the main supply 
system 58. Blow outs are avoided. 
If the first conduit had a substantial volume, the high water to fuel ratio 
would not be transient. A blow out of the combustion chamber might occur. 
Such blow outs can cause an explosion when fuel behind the engine ignites 
as re-ignition of the engine takes place. 
In summary, the method of operating the engine enables flowing a 
combustible liquid comprising fuel and water at a fairly low water to fuel 
ratio at low fuel rates. As flow rates are increased, more and more water 
is diverted to the auxiliary water supply system so that the water-fuel 
ratio in the main supply system stays small. However, the water-fuel ratio 
for the overall fuel supply system (that is, as it comes out of the 
auxiliary mixing system) is quite high. During transient operation, a 
small volume of the first conduit avoids the blow out by the high 
water-fuel ratio liquid because of the small amount of such liquid which 
is quickly replaced by the low water-fuel ratio liquid that is being 
supplied via the main supply system with the auxiliary water supply system 
shut down. 
The fuel supply system has particular advantage when operated with gaseous 
fuel as well. At lower gaseous fuel flow rates, water is supplied via the 
main supply system 58 to the fuel injectors 28 to ensure the correct 
amount of water is equally supplied to each injector. The pressure 
distribution characteristic of the main supply system (primarily the fuel 
distribution valve) ensures that equal flow distribution occurs even at 
low flows. As the gaseous fuel flow increases, the amount of water being 
flowed to the fuel injector increases. As the flow of water reaches a 
predetermined level, the regulating valve 106 opens in the sixth conduit 
98 enabling additional water to flow via the water manifold and auxiliary 
mixing system to each fuel injector. In this embodiment, water is flowed 
via both chambers 112, 114 in the auxiliary mixer. 
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 scope of the claimed invention.